Table of Contents
Tomato Rot Definition
Tomato rot is a broad term used to describe the visible effects that certain mainly fungal diseases have on the plant parts and fruit berries of the Solanum lycopersicum plant otherwise known as the tomato plant.
The effect those tomato rot-causing diseases have on the plant and its fruits that are being referred to is the sickly-look, the decay, and appearance of tomato rot on the tomato plant and especially the tomato fruit.
Tomato rot typically makes the plant and fruit get progressively more and more decayed with dark spots and patches. Weakened and shriveled plant parts and fruits are further evidence of tomato rot.
Tomato Rot Identification
Tomato rot is easily identifiable by closely inspecting the plants and fruits due to their bright coloring. The stem and foliage of the tomato plants are typically deep or bright green. The fruits are usually a rich bright red.
This type of bright and distinct colors with a lack of blemishes and dark markings on healthy tomato plants makes it easy to notice any changes.
The development of tomato rot on cultivated plants will generally manifest the following symptoms:
- Dark patches on parts of the plant and fruits.
- Dark spots on parts of the plant and fruits.
- Wilting leaves stems, and branches.
- Dying and drying up of leaves, stems, or branches.
- Yellowing of leaves and plant parts.
- Browning of leaves.
- The appearance of dark markings and concentric circles on the leaves and fruit.
- Loss of turgidity (firmness) of the fruit
- Decaying of the fruit.
- Presence of mold on the leaves.
- Sporulation on the fruit and leaves.
- The appearance of lesions on the leaves and fruit.
- The development or appearance of scabs and hardened patches on the leaves and fruit.
- Withering, shriveling, and sooty mold present on the petal end of infected fruit.
- Defoliation of the plant.
- Cracking of the fruit.
- Evidence of sunscalding likely due to defoliation.
While some of these symptoms may start small and not be very noticeable before they spread, they lead to clearly visible tomato rot over time.
Causes of Tomato Rot
Several tomato diseases can adversely affect the plant, its parts, the fruit, or all its components. Not all of these numerous diseases directly lead to tomato rot.
Many of these diseases are soil-borne fungal diseases that infect and obtain nourishment from the nutrient-rich tissues of the host plant. They reproduce by generating small spores (microscopic reproductive cells carrying genetic data capable of developing into a new individual of the parent species without fusion or interaction with another reproductive cell). These spores are carried to new host plants by either wind, water, or animal movements.
Types of Tomato Rot Diseases
- Blossom end tomato rot
- Damping-off
- Tomato blight – such as Septoria leaf spot, Early blight, Late blight, and Southern blight.
- Fusarium disease – Fusarium crown and root rot, Fusarium root rot, and Fusarium wilt
- Powdery mildew
- Anthracnose fruit rot
- Tomato wilt
- Verticillium wilt
- Buckeye fruit and root rot
- Leaf mold
- Cercospora leaf mold
- Grey leaf spot
- White mold
- Alternaria stem canker
- Corky root rot
- Didymella stem rot
The above are some of the main types of diseases that directly result in tomato rot.
Blossom end Tomato Rot
This type of tomato rot is often mistakenly called “Tomato Bottom Rot” by farmers or gardeners that don’t understand the disease; or by those seeing it for the first time.
Blossom end rot of tomatoes is perhaps the most popular of the known conditions that cause the decay of the tomato plant and fruits. It is prone to occur with the first set of plants cultivated after a relatively long dry period and affects maturing fruits.
This condition can be identified by the water-soaked area around the bottom of the tomato berry. The tissues in the area become broken down and have a sunken and deflated appearance.
The outer skin shrivels significantly and developed a leathery texture that seems detached from the soft tissue inside that has also shrunk. The outer skin or epicarp also develops a dark color usually brown, or black around the bottom or blossom end of the berry.
Causes of Blossom End Tomato Rot
Calcium Deficiency
Blossom end rot is caused primarily due to a deficiency of calcium in the tissue of the tomato. Calcium is fed to the plant and berry through absorption by the roots and distribution by the xylem and phloem vessels.
Calcium deficiency in the tomato compromises the membrane integrity, rigidity of the cell wall, and maintenance of cell to cell contact.
Common causes of calcium deficiency that can lead to tomato rot
Insufficient Calcium in the Soil
Calcium is essential for the healthy development of tomato plant parts and fruit. Insufficient calcium in the soil can cause a deficiency in the whole plant. Some soil types are already lacking in some soil nutrients either due to soil type, leaching, or over-cultivation.
Hindered Distribution of Calcium Within the Plant
Additionally, there are also instances where there is sufficient calcium in the soil and even in the stems and leaves but not enough being transported to the developing fruit. This situation can also lead to blossom-end tomato rot.
This may be caused by damaged xylem or phloem vessels, cold brittle-causing climatic conditions, heat stress from high temperatures.
Root damage is another cause of hindered calcium absorption and distribution in tomato plants. Root damage can be caused by a range of factors like trauma to the roots from weeding, damage from root-attacking aphid infestation, constriction of roots by weeds and other plants in close proximity, etc.
Insufficient or Inconsistent Water in the Soil
Inconsistent soil moisture and water supply throughout the growing season are the main problems associated with calcium deficiency in the tomato plant.
This is because calcium can only be absorbed by the plant through the roots when it’s in the form of a liquid solution. When there is a rapid early growth of the tomato fruit, the plant may not be able to absorb and distribute calcium with corresponding rapidity.
A period of a partial or total drought where there is low or inconsistent water content in the soil but the fruit continues to develop may also lead to a calcium deficiency. The fruits that are getting lower than average moisture are prone to calcium deficiencies.
Too Much Water
Too much water (waterlogged) content from lack of suitable drainage, too much irrigation, cultivation at the peak of the rains, or cultivation in over-saturated/ marshy soil can also lead to non-absorption of calcium and other nutrients.
Damping Off
Several soil-borne fungal pathogens are known for seriously damaging tomato seedlings by infecting them with diseases like wilt, root rot, and damping off.
Damping-off, which is one of the biggest threats to the health and survival of tomato seedlings, is a mainly Pythium (a genus of destructive root parasitic fungi [family Pythiaceae] that have filamentous sporangia, smooth-walled spherical oogonia, and stalked antheridia including forms like {P. debaryanum} that causes diseases like damping off)-induced root rot disease.
When the fungus infects and kills newly emerged or emerging seedlings it is termed damping-off. This is a common disease in agriculture that can cause extensive damage to nurseries or young plants in the fields.
Damping-off is caused by a number of fungi including; Pythium species spp, Rhizoctonia spp, Phytophthora spp, and Fusarium spp.
The soil-dwelling pathogen Pythium is most frequently responsible for cases of damping-off that occur.
Pythium spp is not specific in its preferred host range but to be rather generalistic having a wide and random infection range of hosts.
Due to this fact, Pythium spp is more damaging to the root rot it causes as it is an efficient saprotroph (or saprophytes organisms that feed on dead organic matter called detritus at a microscopic level) that can survive and sustain itself for prolonged periods on decaying plant matter.
Certain environmental conditions are favorable for the growth and sustenance of the Pythium pathogen. There are high humidity levels, soil moisture, temperature, nitrogen content in the soil, poor soil aeration, and seeds that were sown too closely. These are conditions that promote the spread of Pythium spp.
Damping-off of tomato seedlings occurs in one of two basic stages of their development.
- The pre-emergence phase
- The post-emergence phase
The Pre-emergence phase
In the pre-emergence phase of the damping-off, the germinated tomato seedlings are killed before they can reach the soil surface.
The young radical and plumule are first infected and their development stopped before being killed off as the tender seedling is starved of nutrients while being victim to parasitism. These conditions lead to the complete rotting of the entire seedling.
The Post-emergence Phase
The post-emergence phase of damping-off affects young plant seedlings that have already emerged from the ground. They are attacked and infected making the juvenile plant tissues soft, soaked, and saturated with water at the soil surface level.
The weakened seedling soon succumbs and falls over.
Tomato Blight
Blight is a plant disease that is caused by certain fungi which may be either mildews, rusts, or smuts. It typically causes partial or total chlorosis (physiological plant condition where the plant is unable to produce sufficient chlorophyll due to either an iron deficiency in lime-rich soils, lack of light, or disease).
Blights also cause some or all of the following symptoms; browning, spotting, yellowing, and withering. The death of plant tissues such as leaves, branches, twigs, or floral parts.
Diseases that exhibit similar symptoms are grouped as blights. There are several of these diseases but the focus here is on those that cause tomato rot.
There are four basic tomato blight diseases out of which three are well known and have some similarities that can lead to some confusion if certain factors are not carefully observed.
Septoria Blight/Leaf Spot
Septoria leaf spot or septoria blight is a soil-borne fungal tomato blight disease that affects mainly the stems and leaves of the tomato plant but rarely known to affect the fruit or other parts of the plant.
It is one of the most common foliar diseases of tomatoes and is often easily confused with early blight because of the same areas of attack (leaves and stems) and very similar symptoms and effects of infestation (patchy chlorosis).
Septoria blight is caused by the fungus septoria lycopersici and starts as small water spots on the leaves and stems that may initially not look like big problems. They however rapidly grow to distinct circular-shaped lesions (small injuries where the surface of the skin is broken or bruised) about one-eighth of an inch in diameter.
The lesions gradually develop centers with a whitish-gray hue surrounded by darker edges. This coloring configuration of a whitish-gray center is perhaps the most distinctive visual evidence of septoria blight.
When conditions become favorable for the disease, tiny black specks appear in the middle of the lesion. These the disease spores which are the fungal fruiting bodies ready to carry the individual reproductive units to other plants.
The spore dispersal to nearby potential host plants is achieved by splashing rain. Since septoria blight is soil-borne the infection begins from the lower leaves and rapidly works its way up especially if the weather is wet and humid.
Defoliation is usually severe when there is sustained warm and wet weather and heavily infected leaves increasingly turn yellow or brownish, wither, and eventually fall off which can sometimes happen to all the leaves on a plant.
Infections can occur at any stage in the tomato plant’s development but will usually happen around the time the plant is forming its fruit. The loss of leaves also begins from the lower leaves and gradually works its way upwards
After defoliation of a plant occurs, it is left weakened and vulnerable to hazards like damage from wind, other organisms, and crucially, damage from exposure to the sun which can cause sun scalding.
Early Blight of Tomato
Early blight, Alternaria leaf spot, or target spot as it is sometimes referred to, is often mixed up with septoria leaf spot due to the notable amount of similarities between the two.
Early blight of the tomato plant is caused by a fungus called Alternaria solani and sometimes another related pathogen called Alternaria tomatophila. It is one of the commonly found widespread tomato diseases.
It is fundamentally a leaf spot and foliage blight but can sometimes cause black spots around the ends of the stems and on the shoulders of mature fruits late in Autumn.
Symptoms of early blight start with small brownish or dark spots that appear on the surface of the lowest leaves of the plant which can range in size from a tiny, barely visible dot to about half an inch in diameter.
When the weather conditions become favorable for the disease, a temperature range of about 25°C to 30°C with high humidity. The spots that appeared on the leaves begin to enlarge into lesions with visible concentric ring patterns that are formed from daily growth phases and spore generation. The concentric circle patterns aid in identifying early blight.
There is usually a small yellowish area around the lesions that initially appears to be returning to the plant’s natural green hue but the lesions soon become larger and irregular with a worsening infestation that leads to the leaf turning yellow and dying.
The symptoms of early blight generally begin to manifest around the middle of the season after several fruits have already formed but progressively worsen with time and under conditions where the plant is stressed from issues like high soil temperature, dry weather, or other trauma.
The damage from early blight is progressive and in stages. This is why the foliage just above the ravaged level will usually not be seriously affected till the leaves on the affected area below are all damaged or dead.
At which stage the disease moves up to the next level of foliage and systematically destroys that as well. Some spots can also sometimes appear on the main stem and cause partial girdling (or ring barking is the complete horizontal removal of strips of the bark consisting of cork, cambium, or phellogen, phloem cambium, and sometimes reaching the xylem from around the entire circumference of either the trunk or branch of a plant) causing further damage to the areas above.
The defoliation that results from early blight causes sunscalding to the fruits and can cause freckle fruit a plant disease that causes spots all over the fruits and leaves caused by a related fungus called Alternaria tenuis.
Ripe fruits can sometimes be infected by the early blight around the point of attachment to the stem and may exhibit similar concentric circles to those that appear on the lower foliage.
The Alternaria solani fungal organisms can survive for up to a year in diseased vines and infect new plants with spores when the conditions are suitable.
New leaf spots contain numerous spores that are dispersed to nearby plants from overhead methods of irrigation in addition to dispersal from raindrop impact.
Reproduction of the Alternaria solani is rapid when the conditions are favorable and may achieve several cycles before the weather becomes unsuitable for their spread.
The fungus and its spores are so viable that the pathogen can be carried under the seed coating and become active when suitable conditions are present.
Septoria Leaf Spot vs Early Blight in Tomatoes
Early blight (Alternaria solani)and Septoria leaf spot (Septoria lycopersici) are two tomato rot diseases that are very similar.
The effects these two pathogens cause are alike and can be seen in the manifestation of symptoms, mode of infection, generation of spores, and mode of dispersal that they often get confused for one another.
They both start from the lower leaves and progress upward. They both cause chlorosis, produce spores and multiply in moist conditions and cause the wilting, dying of some or all the leaves (defoliation) leading to sunscalding, (burn or heat damage from direct exposure to the suns radiation) and in severe cases death of the plant as well.
Differences between Septoria Leaf Spot vs Early Blight
- Alternaria’s concentric-ringed lesions start from the lower leaves but can affect the berry as well. In contrast, Septoria’s lesions are initially smaller brown spots that only become enlargened later in the development of the disease
- Advanced leaf lesions of Septoria contain dark-colored specks that are actually fruiting spores clustered within the lesion. Alternaria on the other hand has spots that are more spread out and have distinct concentric rings and an absence of specks inside.
- Early blight (Alternaria) can affect the immature green or red tomato berries through the calyx or stem attachment. In contrast, Septoria only affects the stem and leaves.
- In Septoria blight, the center of the lesion is whitish or greyish, whereas with Alternaria blight the center of the lesion is dark brown or blackish in hue.
Late Blight
Late blight is caused by what was considered a fungal pathogen called Phytophthora infestans that emerges from mid to late August. This belief persisted for about two hundred years as there were significant similarities to other known fungi that attack tomatoes like early blight and septoria blight.
After comprehensive research however, the late blight pathogen was redesignated as an oomycete (a type of water mold) It is a disease that thrives in wet weather with warm days and cool nights.
This pathogen was responsible for the Irish potato famine that destroyed potato produce successively for over four years from 1845 to 1849 affecting Irish and American history.
The fungus has been observed to favor temperatures below 30°C to thrive and mostly survive in potato seed tubers that have been exposed to spores of the disease or infected tomato transplants.
Dead parts of both potato and tomato can also possibly carry the pathogen in a dormant state until conditions become favorable.
The symptoms begin with indefinite water-soaked dark spots and discolorations on the leaves and soon manifest into the pale green to brownish lesions that can cover the whole surface of the leaf.
Lesions on the abaxial (underside of a leaf) surface of the leaf may be covered with a greyish or whitish moldy growth during wet weather. Subsequently, the infestation worsens, and the disease progresses consuming the leaves till they become more dehydrated, turn yellow then brown before curling up, shriveling, and dying.
Late blight is sometimes mixed up with powdery mildew due to some similarities in the effects on the foliage especially the whitish moldy growth they both induce.
Southern Blight
Southern blight is a tomato rot disease caused by a soil-borne fungus called Sclerotium rolfsii. It is reportedly very difficult to eradicate and infects the lower parts of the tomato stem near the surface of the soil.
The disease is referred to as southern blight because of its low survival rate in environments with prevailing low temperatures and especially frozen soil which are more typical for northern regions.
It, therefore, thrives in areas with warm to hot climates with temperatures ranging between 29°C to 35°C with high humidity and soil moisture.
Southern blight starts with the entire plant beginning to wilt rapidly and losing its usual bright color and leaves shriveling. Then a moisture-laden lesion develops on the lower stem near the soil surface.
This lesion expands within a relatively short time and turns brown as the wound expands eating its way around the stem till it completely girdles the circumference of the stem.
Whitish fungal strands (mycelia/hyphae) are generated around the infected stem and traces can also be found on the soil surrounding the affected plant.
Fusarium
Fusarium is a large cosmopolitan genus of filamentous fungi that are part of a group often referred to as hyphomycetes that are widely distributed in soil generally and are associated with plants.
Most species of this group are harmless saprobes and relatively abundantly distributed in the microbial organisms in the soil. There are however several members of this group that are very destructive to tomatoes, potatoes, and many other important crops.
Fusarium Crown and Root Rot
Fusarium crown and foot rot (FCRR) disease is caused by a pathogen called Fusarium oxysporum sp. radicis lycopersici (FORL) and is among the most destructive soil-borne plant diseases.
It was first reported in Japan in 1974 and was subsequently found in several other countries. FCRR seems to have become more common through greenhouse production although it now occurs in the field as well.
The disease causes very drastic reductions in tomato production worldwide.
Symptoms of fusarium crown and root rot are wide-ranging but relatively similar to other fungal disease symptoms.
The fusarium pathogen oxysporum sp. radicis lycopersici enters the vulnerable plants through wounds and natural openings such as gaps for emerging roots.
Early symptoms in tomato seedlings include stunted development, yellowing, and the premature abscission of the cotyledon and lower leaves. A large brown lesion forms girdling the hypocotyls. Root rot, wilting, and death generally follow.
Fusarium Root Rot
Fusarium root rot is caused by the fungus Fusarium solani f. sp. phaseoli. It is mostly found in soils where dry beans were previously cultivated. Most plants grown in such contaminated soil are likely to be affected by this pathogen to some degree during their development.
Fusarium root rot severity depends on some key factors like; cropping history, moisture and temperature stress, soil compaction, and plant spacing. Soil compaction and early planting in cool moist soil promote the spread of the disease.
It is generally spread between fields by the movements of contaminated soil by winds and animal activity, rainwater and irrigation run-offs, and even on farmyard equipment.
The pathogen first becomes apparent during the blossoming stage of the plant’s development and symptoms include reddish or brownish lesions that appear as streaks or split on the hypocotyl and primary root a few weeks after germination.
These lesions progressively increase in size and may sometimes merge taking a deeper brown hue. Infected plants have stunted development and yellowing leaves but do not always die from the infection.
Fusarium Wilt
Fusarium wilt is a plant disease caused by one of the fungi pathogens from the Fusarium genus named Fusarium oxysporum. It is similar and can be confused with Verticillium wilt and affects crops like tomatoes, eggplants, and pepper but can survive on weeds like mallow, crabgrass, and pigweed.
The pathogen can also survive in the soil for prolonged periods without a host. Some of the spread is linked to fungi associated with waste from tomatoes. Root rot nematode infection renders some Fusarium wilt-resistant varieties of plants vulnerable to the fungus because of physiological changes in the root.
Symptoms of fusarium wilt infestation include; at the onset infected plants appearing wilted during the heat of the day and then seemingly recovering at night when temperatures drop.
An increasing number of leaflets turning yellow on one side of the plant. Many of the leaves exhibit downward curling. Eventually, the entire plant turns a sickly yellow hue. Discoloration of vascular tissues beneath the epidermis has a dark red and brown hue.
The disease thrives in warmer weather and is more severe in acidic warm soil with an approximate ideal soil temperature of 80°F. Atmospheric temperature conditions that favor fusarium wilt development stands roughly (27 to 28°C) dry weather and acidic soil (pH 5 to 5.6)
Fast developing healthy tomato plants that were exposed to fertilization with some amounts of ammonium nitrate are particularly susceptible to the disease.
Powdery Mildew
Powdery mildew of the tomato plant is a soil-borne fungal plant disease that is associated with Leveilulla taurica, Oidium neolycopersici, and Oidium lycopersici. The incidence of these pathogens is as follows: Leveilulla taurica and Oidium neolycopersici has a worldwide distribution while Oidium lycopersici is found in Australia and California (U.S.A.).
Leveilulla Taurica
In contrast to many of the other soil-borne fungal diseases, powdery mildew symptoms begin mostly from the upper parts of the plant foliage and appear as light green to bright yellow spots on the upper leaf surfaces.
Pale-colored powdery fungal sporulations eventually form on the lower leaf surfaces. Then when conditions are favorable masses of white powdery conidia (asexually produced spores of fungi that are borne externally ) are generated on both leaf surfaces.
As the disease progresses the spots become clearer as lesions and eventually become necrotic (death of cells in a living tissue caused by external factors such as infection, trauma, or toxins).
At this point, depending on the severity of the infestation the foliage may all fall off completely exposing any fruits and plant parts to sunscalding. Or the entire plant may die.
Oidium neolycopersici and Oidium lycopersici
Small circular areas of whitish fungal growth with sporulation initially appear early in the infection. This occurs on the upper leaves of the plant.
As the lesions which are now producing spores enlarge, the underlying leaf tissues begin to turn yellow and more dehydrated and curled up till they turn brown and shrivel up dead.
In cases of severe infection, masses of powdery conidia can be observed completely covering the entire leaf surfaces including petioles and calyces though the fruit may sometimes remain uninfected.
Anthracnose
Anthracnose tomato rot disease is another soil-borne disease that is carried by several species of fungi from the genus Colletotrichum which include; C. coccodes, C. dematium, and C. gloeosporioides.
C. coccodes has been recorded on over thirty-five different hosts that themselves lineate from thirteen parent families that primarily include Leguminosae, Solanaceae, and curcubitaceae.
Anthracnose tomato rot disease affects both the developing green tomato berry and the ripe red berry but is only clearly visible on the red fruit.
Green tomato infection will usually go unnoticed but if detected, its latency can be surmounted by subjecting the tomato to a period of low-temperature storage.
Symptoms of anthracnose on ripe fruits start with circular slightly sunken lesions with dark centers that look saturated with trapped water.
A semi-soft decay soon takes hold as the disease spreads and the lesions expand and create concentric rings of dark specks. The rings consist of numerous tiny spore-producing materials of the fungus (microsclerotia and acervuli) till they merge and form large areas of rotten fruit.
As with the other soil-borne fungal diseases, anthracnose disperses its spores during moist or wet weather.
Tomato Wilt
Tomato wilt is a loosely used term to describe diseased tomato plants and fruit that are showing signs of wilting. There are two main mutually similar tomato rot diseases that are generally responsible when the term is used.
The more likely disease that is sometimes interchangeably termed tomato wilt is Fusarium wilt outlined above. The second which is very similar to Fusarium wilt is Verticillium wilt outlined below.
Verticillium Wilt
Verticillium wilt is associated with two species of verticillium namely Verticillium albo-atrum and Verticillium dahlia. Collectively they have a host range of roughly two hundred species of plants.
The disease is soil-borne and favors cold weather and can remain dormant but alive in the soil for some years. Infection happens when the pathogen enters the plant through wounds that may be caused by a new secondary root formation and nematode feeding.
Infected plants also have a v-shaped lesion at the edge of some leaves. Verticillium wilt causes uniform yellowing of the lower foliage, unlike Fusarium that causes partial yellowing of foliage.
As the infection progresses the lower leaves turn yellow, wilt, and die dropping off until only a few leaves that are higher up on the plant remain. The plant does not typically die but is seriously stunted and does not produce healthy fruit.
Symptoms of Verticillium are notably similar to that of Fusarium with internal brown streaking of vascular systems in their stems close to the soil surface. However, the vascular streaking caused by Verticillium is usually a lighter shade of brown and does not extend as far up the stem as Fusarium does.
Buckeye Fruit and Root Rot
Buckeye fruit and root rot are caused by Phytophthora nicotianae. VA. parasitica, Phytophthora capsici, and Phytophthora drechsleri.
Members of Phytophthora have a notably wide range of hosts they infect and can survive without living hosts in the soil and dead plant material for up to two years. It can be spread through overhead irrigation, rain, farm equipment, and even on farmer’s boots.
Initial infection is promoted by moderate temperatures (20°C) and soil moisture levels. All parts of the tomato plant and berries can be affected by the Phytophthora species that cause buckeye fruit and root rot.
They can cause a range of different types of rot that other pathogens may cause individually such as; damping-off, foliar blight, fruit rot, and root and crown rot.
Symptoms include; large brownish water-saturated flaccid lesions on secondary roots and parts of the exposed tap root. With progression, the smaller roots may fall off and decompose.
Infected leaves first develop randomly shaped watery lesions that soon rupture and dry up. Dark green water-soaked stem lesions are usually close to the soil and eventually become dry and brown and will typically girdle the stem when they expand. This can cause the pith tissues to wither and collapse.
On the fruit, grayish-brown water-soaked lesions start developing and soon begin to expand quickly forming concentric rings that look like a buckeye nut, which is where the name is derived from.
Leaf Mold of Tomato
Leaf mold disease of the tomato plant is another fungal infection that is caused by a pathogen called Passalora fulva that was previously called Fulvia fulva or Cladosporium fulvum. It is only known to be pathogenic (spreading disease)on the tomato plant.
Leaf mold is not usually a problem for field-grown crops, especially in northern climatic regions. The higher relative humidity in greenhouses, high tunnels, and other containment cultivation structures make them suitable for the disease to thrive in those environments.
Foliage is usually the only part of the plant that is affected but is enough to completely compromise the productivity of the plant in severe infections as the disease progresses and the plant loses more foliage.
The mold covering the leaves also interferes with the plant’s ability to undertake photosynthesis. In severe cases, blossoms and fruit are also affected. Optimal growth will usually at a relative humidity above eighty-five percent.
The optimal temperature for the growth of leaf mold is roughly between 71°F to 75°F, however, the disease has been shown to also occur at temperatures as low as 50°F and as high as 90°F.
Symptoms include: The older leaves are infected first.
The presence of pale greenish-yellow patches usually about one-fourth of an inch are formed on the upper side of the leaf with no defined margins.
Velvet-like pale green to brown mold forms on the lower surface of the leaf below the leaf spot.
Patches or leaf spots grow together and will usually brown around the same time.
Leaves become infected, shrivel, and die but will often remain attached to the plant.
Infected blossoms quickly turn black and eventually fall off.
Fruit infections begin as a darkened random area on the fruit’s stem end and progressively become sunken and leathery.
Cercospora Leaf Mold
Cercospora leaf mold or Cercospora leaf spot is a fungal plant disease caused by a pathogen called Pseudocercospora fuligena.
The disease starts as small indistinct yellow patches on the tomato leaf with no margins. Progressively brown spots begin to appear within the yellow patches.
Subsequently, the patches expand into large necrotic (area of dying tissue with granular particles of undigested dead cells) lesions with blighting. As with several other soil-borne fungal diseases, Cercospora leaf mold thrives in warm wet weather conditions.
It can cause serious defoliation of the plant and in ideal high humidity conditions can mass-produce reproductive spores that can be disseminated by rain, overhead irrigation, or human and animal movements.
Grey Leaf Spot
Grey leaf spot fungal disease of the tomato plant is a common fungal disease that can affect the crop at any stage of its development. Although it is not known to affect the fruit directly, its unchecked damaging effect on the foliage of the plant can greatly compromise its productivity of fruit.
This tomato plant disease is caused by a pathogen called Stemphylium solani that causes grey or brown lesions in a yellow halo on the leaves that become glazed and ruptured or cracked. As the disease progresses, holes develop in the lesions which can expand to up to 3.1 mm across.
Younger stems and petioles may also develop spots and infected leaves eventually fall off exposing any existing fruits to possible sunscald.
Southern cultivated tomatoes have the most prevalence as the disease favors wet or moist, warm conditions especially when moisture on leaves does not dry before the evening dew sets in.
Grey leaf spot overwinters in plant debris of not only tomatoes but other dead fallen nightshade plant parts and can be spread by splashing water from rain or irrigation and also by wind dispersal.
White Mold
White mold also called timber rot is a fungal disease that affects tomatoes and is caused by the pathogen called Sclerotinia sclerotiorum that has a wide host range infecting up to one hundred and seventy different species.
These hosts include such important crops as beans, cabbage, lettuce, and pepper.
The disease is sometimes referred to as timber rot and primarily affects the flowers and succulent tissues of the tomato plant. The spores undergo a saprophytic (feeding on the dead matter) growth phase on senescent (old and declining in function) flowers before they restart their infection cycle.
Early infection of the pathogen will typically be on the plant tissues of the plant around the areas closest to the soil.
Symptoms of white mold include:
- Water-saturated lesions are formed on the flowers parts and the stem joints where senescent flower petals have dropped. These lesions usually have a faded-looking or deep brown color.
- Discolored areas and watery soft-rotting patches form on some of the stems and leaf axils. Additionally wet, fluffy-textured white mold is generated both inside and outside the plant tissue.
- Girdling occurs when the areas of soft watery rot that formed on the stems dry out and flaking off as they have become brittle.
- The entire plant may also wilt and die if the disease attacks the base of the stem. Tissue decay causes the formation of hard dark-colored oddly-shaped structures termed sclerotia within and outside the decaying tissues.
- Stems can be hollowed out into a dry flaky shell by the action of the fungus. Sclerotinia sclerotiorum can survive in the soil as the hardened dry black sclerotia for up to five years or more.
White mold however requires a conditioning stage of low temperatures before they are biologically able to germinate to form cup-shaped spore-bearing structures called apothecia. These pale yellowish-brown apothecia structures are subsequently formed just above the surface of the soil where they produce ascospores that are easily spread by moving water, wind, plant debris, farmworkers, or equipment.
The pathogen fares best in temperatures that range from 59 degrees Fahrenheit to 70 degrees Fahrenheit. Seventy-two hours of continuous high humidity and wetness promotes spore infection.
Alternaria Stem Canker
Alternaria stem canker is a fungal disease caused by Alternaria alternate (f. sp. lycopersici). This particular plant disease is primarily found in the United States. It attacks all parts of the plant that are above the ground or soil level however, the stem of the host plants is mainly affected.
Symptoms may manifest on all parts of the plant that are above the ground. Dark brown canker sores or lesions with concentric rings are formed on the plant stems. These are usually sites that had previous injuries that may have become infection points for the pathogen.
The cankers sometimes enlarge to the point that they girdle the host plant which will often completely cut off its supply of nutrients and lead to the host plant’s death.
The development of a brown dry rot follows and dark brown streaks open up that can extend into the pith above and below the cankers.
A toxin produced by the fungus growing in the stem canker extends into the upper parts of the host plant where it causes further damage by killing the interveinal leaf tissue.
Curling of leaf margins and eventual death of the leaf soon happens and is repeated on most or all of the plant’s foliage.
Fruit infestation begins as small grey specks on the fruits get progressively larger until they become darker, saturated, and sunken. The concentric rings also increase in size and incidence.
Symptoms are not always apparent on mature green fruit but can develop rapidly when the conditions permit.
Alternaria stem canker spores or conidia (a species of asexually reproductive fungal spore) survive in soil and dead plant matter for up to a year. The typical methods of spread that many fungi undertake to disperse and distribute their spores also generally apply to this pathogen as well.
These methods of dispersal include wind, flowing run-off water from rain, splashing water from rain or overhead irrigation systems, human and animal movements when the spores are contained in dirt-smeared or stuck to surfaces on their bodies.
Movements of operated and autonomous equipment also potentially carry and spread the pathogen’s conidia.
Stem wounds that occur from pruning or other trauma are hotspots for a potential infection that make it easier for the pathogen to get through the plant’s protective outer cell wall. Despite this fact, the disease has been known to also infect apparently uninjured plants.
Corky Root Rot
Corky root rot is a soil-borne fungal plant disease that is caused by the pathogen called Pyrenochaeta lycopersici.
The fungus has been recorded as surviving for prolonged periods as microsclerotia (small hard dark dormant bodies of certain fungi consisting of a mass of hyphal [long multiple-branching filamentous structure of a fungus, oomycete, or actinobacterium] threads capable of remaining dormant for long periods).
Corky root thrives in cool conditions with the most conducive temperature for the development, strengthening, and spread of the pathogen being between 60°F to 68°F (15.5 to 20°C).
It does not typically kill the host plant but drastically reduces the yield that in some instances can be as low as zero.
Symptoms of corky root tomato rot include:
Infected roots clearly have a soft-wood (corky) look and texture with an extensive amount of brownish lesions sometimes forming bands of damaged areas.
The roots develop lengthwise cracking of the cortex while the tips of the older infected roots are severed from the rest. The feebler, smaller feeder roots completely decompose.
Branches of mature plants sometimes die off slowly from the tips and spread inwards.
Didymella Stem Rot
Didymella stem rot is a soil-borne fungal disease that is caused by the pathogen Didymella lycopersici. Its anamorph (an asexual reproductive stage that is usually in mold form) form is called Phoma lycopersici.
It can be found in countries like New Zealand, Denmark, Romania, Morocco, Russia, and the United Kingdom.
The infection typically occurs above the soil especially on the stem but can also affect the foliage.
The symptoms of infestation by this pathogen include:
- Dark brown sunken lesions form around the bottom of the stem and soon aggressively expand and spreads girdling the whole stem. The older leaves rapidly become wilted and turn yellowish.
- Many small black specks called pycnidia that are the fruiting vessels of the fungus are frequently generated in the dark lesions near the base of the stem. Fungal spores from the pycnidia are sometimes spread to the stems, fruit, and leaves by splashing water worsening the level of infestation. Fruits typically get infected at the calyx where it begins as a saturated pale spot and progresses to black shriveled lesions with concentric rings. Leaf infections start as small dark spots and progressively get worse rupturing into brown lesions with concentric rings. Pycnidia may sometimes develop in the middle of these lesions and the leaf can end up with a shot-hole appearance or die.
The conditions that are favorable for the spread and thriving of the Didymella stem rot disease are consistent with similar fungi that favor moist weather and can survive in soil and organic debris.
Didymella can survive in different conditions but ideal temperatures would be 20°C (60°F) with accompanying wet weather.
Treatment and Prevention of Common Tomato Rot Diseases
The advantage of having a problem with several similar diseases is that some of the solutions will be common to many of them. Such as the various blights that cause tomato rot.
Early Blight
There are two ways of dealing with the problem of diseases which are prevention where possible and treatment when the infection has already occurred. There are now several disease-resistant tomato cultivars available that can drastically turn the tide of mass infection in terms of prevention.
Treatment
Fungicides and organic remedies are the two proven ways of effectively tackling tomato rot to some manageable degree for instances of a not-so-advanced and serious infection.
Then it is possible to bring the disease strength to its barest minimum or eradicate it with timely intervention. Fungicides should be applied at a specific time that has been proven effective in subduing the pathogen.
It is also important to alternate between types of chemical fungicides to avoid the pathogen from developing any sort of immunity or insensitivity from the constituent compounds from the pathogens overexposure to the same fungicide.
Use of Fungicides
The table below shows some of the common but effective fungicides that can be used to control early blight. Some of these fungicides are also efficacious against similar fungal diseases.
Active ingredient |
Product name |
Chemical family |
Remarks |
Penthiopyrad |
Fontelis |
7 |
Very good |
Boscalid |
Endura, Lance WDG |
7 |
Very good |
Pyraclostrobin |
Cabrio |
11 |
Very good but insensitivity is increasing |
Fenamidon |
Reason |
11 |
Very good but insensitivity rising |
Azoxystrobin |
Quadris |
11 |
Very good but insensitivity is becoming common |
Cymoxanil and Famoxadon |
Tanos |
27 and 11 |
Good but insensitivity is becoming common |
Fluxapyroxad and Pyraclostrobin |
Priaxor |
7 and 11 respectively |
Good but resistance is getting common |
Pyrimethanil |
Scala |
9 |
Good |
Difenoconazole and Cyprodinil |
Inspire Super |
3 and 9 |
Good |
Mancozeb |
Dithane, Manzate, and Penncozeb |
M |
Good |
Mancozeb and Zoxamite |
Gavel |
M and 22 |
Good |
Difenoconazole and Mandipropamid |
Revus Top |
3 and 40 |
Good |
Cyprodinil and Fludioxonil |
Switch |
9 and 12 |
Good |
Chlorothalonil |
Bravo, Echo, and Equus |
M |
Fair |
Copper (copper hydroxide, copper oxychloride, etc.) |
Koside 2000 Champ Formula 2, Nu Cop 50 DF, C-O-C-S WDG |
M |
Fair.
Copper products that were listed by OMRI (Organic Materials Review Institute) are among the most suitable options for organic production. |
Organic Treatment of early blight
- Neem oil spray on affected areas.
- A solution of baking powder vegetable oil and mild soap.
- Prune (with disinfected garden shears) or stake plants to improve air circulation and reduce fungal presence.
- Use of organic copper fungicide spray.
- Use of Serenade biological fungicide.
- Bio-fungicide: A strain of the bacterium Bacillus subtilis is one of the microbes that are commonly used in the biological control of plant diseases. This strain is also called CEASE Biological Fungicide, is also effective against early blight.
Prevention of early blight
Prevention is always the best way to avoid an expensive battle against fungal pathogens. Methods and location of cultivation and the quality of seeds or seedlings play an important role in the health of crops.
A few of the cultivars with early blight resistance are listed below:
- Iron Lady
- Mountain Supreme
- Mountain Magic
- Defiant PhR
- Jasper
- Juliet
- Verona
Cultural Control of early blight
- Use of only seeds that have been confirmed to be pathogen-free.
- Use only seeds that come from healthy plants.
- Practice informed crop rotation.
- Control of susceptible plants like some of the nightshades.
- Proper fertilization should be carried out with care taken not to over-fertilize.
- Avoid working around plants when conditions are wet.
- Drip irrigation should always be used instead of overhead systems to keep the foliage dry.
- Plants should be staked to help increase airflow and reduce direct contact with the soil.
- Trellises are also helpful in keeping the plant parts off the ground.
- Application of mulch to reduce humidity and plant parts making contact with the soil.
- Plant debris should be removed in the fall.
- The garden or farm should be thoroughly planned before starting to locate crops appropriately.
- Removal and correct disposal of infected plants.
- Frequent inspection of plants for early detection of disease.
- Plant potatoes and other nightshades like peppers away from tomato plants.
Blossom End Rot of Tomatoes
Blossom end rot is one of the few tomato rot diseases that is not caused by fungi. In fact, this particular rot is not a disease but a wasting condition that is caused by a deficiency of a mineral nutrient and not the presence of a pathogen, nor a pest.
Due to this, it is not possible to treat and remedy it using an externally applied substance.
It is, therefore, easier and more effective to undertake preventive measures before cultivation than to try to treat the condition after the crop has already developed.
Treatment
There are limited options in treating blossom end rot but the measures that stand a chance of making a positive impact are:
- Conducting a soil test to determine if there is a calcium deficiency in the soil.
- Apply commercially available dissolved lime pellets solutions, or dissolved lime powder to the soil if calcium deficiency is confirmed.
- Water more deeply and less frequently and remove affected fruit.
- Water in the mornings so that the foliage and fruits are dry before nightfall.
- Plants should not endure long periods without water.
- Overfertilization should be avoided.
- Ammonia-based nitrogen fertilizer can hinder the tomato plant’s ability to absorb calcium and should be avoided.
Prevention of Blossom end rot of tomatoes
Prevention of any disease or unhealthy condition is always more effective and far-reaching than attempted cures. This is especially true in the case of blossom end rot.
Preventive measures sometimes may include a few of those that are also applied to treat diseases and conditions that are already in progress. General preventive measures include:
- Soil test to confirm the suitability of the soil.
- Introduction of the necessary nutrients and minerals that have been found to be deficient in the soil (fertilization)
- Consistent, well-drained irrigation.
- Avoidance of overhead irrigation and usage of direct drip or soaker hose systems.
- Proper crop rotation.
- Insurance of a soil pH as close to 6.5 as possible.
- Early and proper mulching.
- Care should be taken not to over-fertilize the soil.
- Care should be taken not to injure the plant roots either when weeding or tilling and digging near plants. Damaged roots can hinder calcium absorption.
- Avoidance of wrongly applied fertilizer that can lead to fertilizer burn.
- Using fertilizers that are low in nitrogen but high in superphosphate.
- Avoidance of heavy cultivation near tomato crops.
- Non-application of fungicides and pesticides as they will have no effect on blossom end rot.
Fusarium Root Rot
Although most fungal plant diseases have similar biological attributes and therefore similar or common management measures between them, there are instances of optional applications being needed.
Biological Control
The pathogens Fusarium, Rhizoctonia, and Pythium spp. are protected from tomato and other crop roots by Deny (Burkholderia cepacia) which is a registered countermeasure. Although the T22 Planter box (Trichoderma harzianum strain KRL-AG2) is registered, it cannot be used in cold or alkaline soils. The efficacy of these biological control agents in the high plains is not conclusive. The addition of some organic components to the soil may reduce the incidence or spread of the Fusarium root rot pathogen by improving soil tilth and moisture retention
Cultural Control
Planting of seeds should be first be carried out on well-prepared beds in warm soil and the seeds should be of the best quality as certain varieties are more resistant to the Fusarium pathogen.
A minimum of a three-year crop rotation should be observed with the cultivation of non-host plants (e.g. small grains and corn) in the selected area before reintroducing tomato plants there.
Chiseling (sub-soiling) 10 to 20 inches deep between dry bean rows promotes root penetration and improves the tolerance of plants to types of root rot. Care should be taken to avoid injury to the roots.
Irrigation should be executed with attention to avoiding wet foliage especially late in the day and lack of sufficient oxygen reaching the roots due to waterlogging. Plant spacing is important.
Chemical Control
The table below depicts the product list for the chemical control of Fusarium root rot.
| Pesticide | Rate per 100lb seed | Application frequency (days) | Remark |
| Captan | |||
| Captan 75 | 6-9 oz | Seed treatment | Broad-spectrum, but weak against Pythium spp |
| Captan 30-DD | 1.33-2.33 fl oz | Seed treatment | Broad-spectrum, but weak against Pythium spp |
| Captan 400 | 1.5-3.0 fl oz | Seed treatment | Broad-spectrum, but weak against Pythium spp |
| Captan 400-C | 1.5-3.0 fl oz | Seed treatment | Broad-spectrum, but weak against Pythium spp |
| Fludioxonil | |||
| Maxim 4FS | 0.08-0.16 fl oz | Seed treatment | Suppression of Fusarium and Rhizoctonia spp. |
| Thiophanate-methyl | |||
| Topsin M WSB | 20-40 fl oz | Seed furrow treatment | |
| Thiram | |||
| 42-S Thiram | 4.5 fl oz | Seed treatment | Broad-spectrum |
| Thiram 50WP | 4.5 oz | Seed treatment | Broad-spectrum |
General Control Measures For Fungal Diseases of Tomato
As mentioned above, there are cultural methods for preventing and controlling the presence and spread of fungal diseases on the tomato plant and fruit. These methods generally apply to more than one disease in a common group.
Outlined below are some of the control methods of fungal diseases that apply to some pathogens that attack tomato plants.
- Removal of plant debris of not only tomato, but other plants as well to eliminate overwintering spores that await suitable conditions for reactivation.
- Effective sanitation should be carried out before cultivation with all the refuse removed or buried.
- Rotating crops to eliminate repeated cultivation where similar crops that were previously planted could potentially have spores in their debris or passed into the soil.
- Altering or enhancing the microclimate around the tomato plant to reduce humidity in which fungal diseases thrive also helps prevent fungal infections. Staking or the use of a trellis goes a long way in maintaining sufficient circulation to ward off humid conditions.
- Removal or moving the area of cultivation from any elements that cause shading or obstruction of an abundance of sunlight like a large structure or plants/trees.
- Morning irrigation to allow adequate time for the foliage to dry before the evening.
- Usage of a soaker-hose irrigation system will reduce the incidence of wet foliage that can promote fungal development.
- Applying about 6 inches of mulch is helpful in keeping the plant parts away from the soil making it more difficult for the soil-borne pathogens to have access to the plant. It also helps to control weeds and retain moisture.
- Suitable preventive fungicides can also be applied to the area to be cultivated to pre-emptively eliminate potential fungal threats.
Integrated Management
Integrated management systems are organized and centralized corrective measures that have been developed for overcoming specific challenges after thorough research. Here, the integrated management system for certain plant diseases is outlined.
The table below shows:
The Integrated Management of Major Fungal Diseases of Tomatoes
| Soil-borne diseases | Disease | Cultural Practice | Chemical Practice |
| Damping-off | Seed treatment with fungal culture Trichoderma viride (4g/kg of seed) or Thiram (3g/kg of seed) The only effective preventive measure in controlling pre-emergence damping off | Soak with copper oxychloride 0.2% or Bordeaux mixture 1% . Spray 0.2% Metalaxyl. In cloudy weather. | |
| Fusarium wilt | Spot drench with Carbendazim (0.1%) Crop rotation with non-host crops like cereals. | ||
| Verticillium wilt | Rotation to non-susceptible crops like small grains and maize help. | Spot drench with Carbendazim (0.1%) or Benomyl (0.05%) | |
| Foliar Pathogens | Powdery mildew | Dinocap 48% EC (0.1%) or Propiconazol 25% EC (0.15%) or Tradimefon 25% WP 0.15% for effective control. | |
| Late blight | Overhead irrigation should be avoided | Sparinmg with mancozeb (0.2%) or captafol 0.2% or Metalaxyl 0.2% or copper oxychloride 0.2% or Tridemorph 80% EC 1.5ml/L | |
| Early blight | Spray using Mancozeb 0.2% for effective deterrent | ||
| Southern blight | Strict adherence to crop rotation is an effective deterrent against Sclerotium rolfsii. Additionally, tomato plants should not be planted in an area that other host plants were recently harvested. | Fluxapyroxad+pyracostrobin significantly reduced the presence of southern blight | |
| Septoria leaf spot | Seeds should be treated with Thiram or Dithane M-45 (2kg/seed) for the seed-borne infection. For post-germination, Mancozeb 0.2% should be sprayed on the crops for effective intervention. | ||
| Anthracnose | Protect against rain or irrigation splashing. Fertilize the soil with organic mulch. Ensure ideal drainage is available. | Chlorothalonil 75% WP 0.2% or Benoyml 50% WP 0.1% or Thiopenate methyl 70% WP 0.2% |
| Fruit rot | Buckeye fruit rot | Metalaxyl+Mancozeb 0.25% or Cymoxinal+Mancozeb 0.25% spray for effective disease control. |
Soil Solarization
Many pathogenic organisms and spores remain in a dormant but viable state in the soil. Some of these organisms overwinter in the soil.
A host of others may stay longer in the soil waiting for suitable environmental conditions that activate and enable them to attack certain hosts to thrive and reproduce.
In terms of agriculture involving the cultivation of the ground, the soil seems to have the highest concentration of plant pathogens of any medium. Consequently, most plant diseases and a large number of plant pests come from the soil.
Soil solarization (also sometimes called plasticulture) is an eco-friendly, non-chemical method of disinfestation of soil-borne plant pathogens and pests using high temperatures from the sun’s radiation onto plastic-covered rows of soil.
Soil solarization was first developed for soil-borne disease control in California (U.S.) and Israel in the 1970s. It can be further defined as heating the soil with solar energy to initiate both physical and biological processes that result in the control or elimination of soil-borne pathogens and pests.
Solar radiation heats up the soil with the aid of plastic row covers to temperature ranges that are lethal to pathogenic organisms. The plastic row covers must be the transparent kind and will need to be kept in place over moistened soil for a period with abundant sunshine for between two to eight weeks.
Effects of Soil Solarization on Mesophilic Organisms
Temperatures between 40° Celcius and 60° Celcius will kill most soil-borne pests and plant pathogens as they are mostly mesophilic (microorganisms that sustain themselves and grow best in moderate temperatures that are neither too cold nor too hot with an optimal growth temperature range of between 20°C and 45°C [68°F to 113°F])
This high temperature causes death by disfunction or rupture of membranes, increased irregular respiration, and overheating. Prolonged sub-lethal temperature exposure can effectively control the disease by hindering the ability of propagules to germinate.
Thermal dose needed for Soil Solarization
This increases the susceptibility of the pathogen to biological control organisms and drastically reducing the pathogen or pest’s capacity to infect or damage the host. The effect of the high temperature largely depends on the thermal dose applied which is a product of the temperature and time of exposure.
Grafting
Grafting is another plant modification method that can be employed to effectively control or eliminate several plant diseases and pests including many tomato rot diseases like Fusarium crown and rot among others.
Grafting Definition
Grafting in agriculture or botany is the action of placing a portion of one plant that has been surgically removed at a given spot (bud or scion) into or onto the stem, branch, or root of another (stock) that has been carefully cut exposing parts of the inner cell tissue that can potentially be joined with other tissues in such a way that the different components unite or merge without rejection and continue to develop and grow. The rooted part is called the stock and the added part the scion.
This technique was initially thought to be too expensive to be sustained on a commercial level but is now widely used in different regions.
Generally, tomato plant density per hectare is approximately eighteen thousand individuals in the absence of grafting. However, with the usage of the grafting method about nine thousand plants can give the same yield as eighteen thousand ungrafted plants would supply doubling the derived utility from half the resources.
Benefits of Grafting
There are some benefits that can be derived from using the grafting method to control soil-borne pests and diseases. Most of them are as follows:
- Control and elimination of many soil-borne pathogens.
- Promotion of steady growth of the plant.
- Increased yield of crops.
- Increased plant tolerance for low temperatures.
- Extension of the plant growth period.
- Improved fruit quality.
- Removal of problematic or diseased plant parts.
Tomato rot is a serious disease that affects the yield of tomatoes and should be taken seriously and treated as early as possible to prevent further spread.