Managing Tomato Diseases, Disorders, and Pests

Tomatoes are the most popular vegetable crop to grow in the home garden.  Many diseases, disorders, and insect pests can affect tomatoes during the growing season. 

Learn more about managing the common problems found with tomatoes in the home garden.


Disease Management Strategy  |  Diseases  |  Physiological Disorders  |  Insect & Animal Pests  |  More Information


Disease Management Strategy

For many home gardeners, diseases and disorders are the most common problems.  There are several steps that the gardener can take to reduce problems before they even start, regardless of the disease or disorder.

To manage diseases and disorders, a combination of cultural tactics is needed.

  • Select varieties with disease resistance.  A partial list of disease-resistant cultivars can be found from Cornell University: Disease Resistant Tomato Varieties
  • Water and fertilize to maintain plants in a vigorous condition.  Healthy plants are more able to deal with disease pressures.
  • Avoid fluctuations of too much and too little water.  Inconsistent watering stresses plants, making them more vulnerable to disease, and many physiological disorders are exacerbated by inconsistent watering.
  • Keep foliage dry.  This is accomplished by:
    • Planting disease-free transplants far enough apart that the plants will not be crowded after fully grown.  This allows the foliage to dry rapidly. 
    • Watering at the base of the plants and in the morning rather than the evening, to minimize the time the leaves are wet.
    • Avoid working with plants when foliage is wet, causing the spread of disease-causing microorganisms (also known as pathogens).
  • Eradicate weeds. Some weeds can serve as an alternate host for diseases, and removing weeds can help improve light penetration and airflow, allowing foliage to dry quickly.
  • Utilize mulch to reduce soil splashing.  This reduces the likelihood of diseases present in the soil from splashing onto the leaves.  It has the added benefit of reducing weeds.  Mulch of any type could potentially be used, but grass clippings, shredded leaves, and straw are great options.
  • Stake or trellis plants to reduce contact with the soil.  Remove as much plant debris as possible in the fall. This helps reduce the overwintering of tomato pathogens.
  • Practice good crop rotation so that tomatoes (and closely related crops like potatoes, peppers, and eggplant) are grown in the same ground only every three or four years. 
  • Accurately identify the problem. You can only treat it appropriately if you know what the problem is.
  • Using fungicides appropriately.  Fungicides may be used to protect new plant tissue and prevent pathogen infection and spread. Fungicide applications should always be used in combination with other management tactics. Remember always to read and follow pesticide labels.

Diseases


Septoria Blight  |  Early Blight  |  Late Blight  |  Anthracnose  |  White Mold  |  Vascular Wilts  |  Bacterial Spot  |  Bacterial Speck  |  Bacterial Canker  |  Viruses


tomato leaf with brown spots and yellow around the spots, symptoms of septoria leaf spot
Leaf spots caused by Septoria lycopersici. (Nancy Gregory, University of Delaware, Bugwood.org)

Septoria Leaf Spot and Blight

Septoria leaf spot, caused by the fungus Septoria lycopersici, is the most common foliar disease of tomatoes in Iowa. It first appears as small, water-soaked spots that soon become circular spots about 1/8 inch in diameter. The lesions gradually develop grayish-white centers with dark edges. When conditions are favorable, fungal fruiting bodies appear as tiny black specks in the centers of the spots. 

microscopic view of a spot with spores exuding from fruiting structure
Cirrhi (ribbon-like mass of spores) exuded from fungal fruiting structure. (Elizabeth Bush, Virginia Polytechnic Institute and State University, Bugwood.org)

Spores are spread to new leaves by splashing rain or overhead watering. Heavily infected leaves turn yellow, wither, and eventually fall off. Lower leaves are infected first, and the disease progresses upward the plant. Defoliation can be severe, especially after periods of prolonged warm, wet weather. Infection can occur at any stage of plant development but appears most frequently after plants have begun to set fruit. The fungus survives the winter in tomato debris. 

Management of this disease should start with cultural tactics, in particular those disease management strategies described above. Some cultivars have some notable resistance to Septoria and may be denoted with a "S" after the cultivar name.  Chemical options are available as well.  More information on the control of this disease can be found in these articles: How Can I Prevent Blight on my Tomatoes? and Septoria Leaf Spot.

Early Blight (Alternaria solani)

Early blight, caused by the fungus Alternaria solani, is also known as Alternaria leaf spot or target spot. It is a common disease in Iowa gardens and may attack plants alongside Septoria leaf spot.

leaves showing symptoms of early blight
Foliar symptoms of early blight on tomato (Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org)

Brown to black spots, 1⁄4 to 1⁄2 inch in diameter with dark edges, appear on lower leaves first. Spots frequently merge, forming irregular blotches. Dark, concentric rings often appear in leaf spots, resulting in the “target” appearance. Leaves turn yellow, dry up, and prematurely drop when only a few spots are present. The fungus occasionally attacks fruit, causing large, sunken areas with concentric rings and a black, velvety appearance. Warm, wet weather favors the rapid spread of early blight. 

early blight decimating a stand of tomato plants
Early blight decimating a stand of tomato plants. (Edward Sikora, Auburn University, Bugwood.org)

Management of this disease starts with cultural tactics, in particular those disease management strategies described above.  Crop rotation is important, especially since potatoes can also serve as a host for this disease.  Harvest all ripe fruit at every picking to avoid infecting other fruit. Resistant cultivars of tomatoes provide partial resistance to early blight.  These cultivars may be denoted with an "A" or "ASC" after the cultivar name. Chemical options are available as well.  More information on control of this disease can be found in this article: How Can I Prevent Blight on my Tomatoes?

 

Late Blight (Phytophthora infestans)

plants look like they are melting, a symptom of late blight
Plants look like they are melting, a symptom of late blight. (Edward Sikora, Auburn University, Bugwood.org)

Late blight, caused by the watermold Phytophthora infestans, rarely occurs in Iowa but can devastate tomato plantings during cool, rainy weather. Late blight may infect young (upper) or old (lower) leaves. It first appears as water-soaked areas that enlarge rapidly, forming irregular,
greenish-black blotches, giving the plant a frost-damaged appearance. The undersides of the leaves often show a downy white growth in moist weather.

fuzzy growth on the underside of leaves is evidence of the pathogen itself
Fuzzy growth on the underside of the leaves is manifestation of the pathogen. You will not see this fuzziness on the topside of leaves. (Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org)

Infection of green or ripe fruit produces large, irregularly shaped brown blotches. Infected fruit rapidly deteriorates into foul-smelling masses. Late blight usually appears in mid or late August during persistent cool, wet weather or when cool night temperatures cause frequent heavy dews.

 

Management of this disease starts with cultural tactics, in particular those disease management strategies described above.  Crop rotation is important, especially since potatoes can also serve as a host for this disease.  More information on control of this disease can be found in this article: How Can I Prevent Blight on my Tomatoes?.

 

Anthracnose Fruit Rot

Anthracnose, caused by the fungus Colletotrichum coccodes and C. acutatum, is probably the most common fruit-attacking disease of tomato in Iowa. Symptoms first become visible on ripe or ripening fruit as small, sunken, circular spots in the skin. As these spots expand, they develop dark centers or 

salmon-pink sporulation of anthracnose fruit rot on tomato
Cream/salmon-colored sporulation of anthracnose fruit rot on tomato. (Nancy Gregory, University of Delaware, Bugwood.org)

concentric rings of dark specks, which are the spore-producing bodies of the fungus. In moist weather, these bodies exude large numbers of spores, leaving diseased areas a cream to salmon-pink color. By this stage, decay has penetrated deeply into the tomato flesh. Spotted fruits may rot completely because of an attack by secondary fungi through anthracnose spots. 

early symptoms of anthracnose fruit rot
Early symptoms of anthracnose fruit rot. (Clemson University - USDA Cooperative Extension Slide Series , Bugwood.org)

Anthracnose appears most commonly on ripe or overripe fruits. The fungus survives the winter on diseased tomato vines, in the soil, and in seeds. Spores are spread mainly by rain splash. Warm, wet weather causes the disease to spread and symptoms to develop. While insects or other wounds facilitate infection, tomatoes can also become infected in the absence of wounds. 

 

Management of anthracnose starts with cultural tactics, particularly those disease management strategies described above. Harvest fruit regularly, picking all ripe fruit at each harvest and disposing of infected fruit.

 

White Mold (Timber Rot)

bleached lower portion of stem with black fungal survival structures
Infection started at the base of the stem and can girdle the stem. Black structures are sclerotia, survival structures of the fungus. (Rebecca A. Melanson, Mississippi State University Extension, Bugwood.org)

White mold is a fungal disease that can infect more than a hundred different plant species, including field crops, garden vegetables, herbaceous ornamental plants, and a number of common weeds.

White mold, caused by species of the fungus Sclerotinia, is a serious disease that often results in death of plants. Infection by the fungus is favored by cool, moist conditions. Diseased tissue initially shows a water-soaked appearance. White mold can be seen on the infected plant tissue when conditions are humid, and is usually most evident on stem parts. Small black sclerotia, about the size of sunflower seeds, can be seen on or in the diseased tissue, often embedded in the cottony, white fungal strands of the fungus. The dying tissue tends to show a bleached, dried appearance.

infection starting mid-stem progresses in both directions
Characteristic stem bleaching cause by white mold (i.e. timber rot). (Don Ferrin, Louisiana State University Agricultural Center, Bugwood.org)

Sclerotia are the tough survival structures of the fungus, making it a challenge to control the disease. Because the white mold fungus produces survival structures and can infect so many plant species, rotation is often of limited usefulness. Since infection is favored by abundant moisture, practices that improve air circulation, such as wide spacing at planting, staking of plants, and preventing water splash on leaves and stems can help reduce conditions favorable for disease development. Resistant varieties are available with some plants, but not currently with tomato. Fungicides are labeled to help control the disease in certain crops, but are not usually practical for use in the home garden. Sanitation, the careful removal of infected plants, is the most important management practice for home gardeners. Since sclerotia can survive in the soil for several years, removal of infested soil may be feasible only if the area affected is small. Many weeds are susceptible to white mold, so control of weeds in and around the garden is helpful in managing the disease.

Vascular Wilts

The initial symptoms of vascular wilts are wilting of the plant foliage during the heat of the day. Affected plants often recover in the evening or overnight. However, the wilting gradually worsens and many plants eventually die.  

Vascular wilts in tomatoes are caused by two primary types of fungus, Fusarium (Fusarium oxysporum f. sp. lycopersici) and Verticillium (Verticillium alboatrum and Verticillium dahliae).  These soil-borne fungi invade tomato plants through injured roots. The fungi spread into the stem's water-conducting tissue (xylem) and block water flow to the foliage. The foliage of affected plants turns yellow from the base of the stem upwards, then wilts and dies. 

With Fusarium wilt, initially, only one side of a leaf midrib, one branch, or one side of a plant may be affected, but eventually, the entire plant succumbs. Affected plants die early and produce few, if any, fruit. With Verticillium wilt, symptoms do not progress along one side of a leaflet, branch, or plant. Infected plants may survive through the growing season but are stunted, and yield is reduced. 

For both pathogens, a cut through the lower stem of a dead plant often reveals a brownish discoloration of the vascular tissue.  Plants are susceptible at all stages of development, but symptoms are most obvious at or soon after flowering.  Because symptoms can be so similar, a lab test is recommended to determine whether the problem is Fusarium or Verticillium.  

Nothing can be done for plants that have Verticillium or Fusarium wilt. Plants that die should be removed and destroyed. Crop rotation is of limited value as the vascular wilt fungi may survive in the soil for several years. Using resistant cultivars is the most practical way for home gardeners to prevent losses due to vascular wilts. Resistant cultivars are available in seed catalogs and at garden centers. The letters V and F following the cultivar name denote cultivars resistant to Verticillium and Fusarium wilts.   Resistant varieties may become infected, but the disease will not be as severe as with susceptible varieties, and a reasonable yield should still be obtained.  

Bacterial Spot

Bacterial spot is caused by at least four different species of the bacteria Xanthomonas (X. vesicatoria, X. euvesicatoria, X. gardneri, and X. perforans)., and it can affect both tomato and pepper. The infection starts as small circular to irregularly shaped spots that appear greasy.  As they enlarge, they often become surrounded by a yellow halo. Initially, they can look similar to spots caused by Septoria, but they will not develop gray-brown centers.  The disease affects leaves, fruit, and stems. Spots on fruit will first appear as raised black spots that will later become large sunken scab-like areas.   

The bacterium overwinters on the surface of seeds, in infected debris, and in soil. It is commonly brought into fields on infected transplants. Warm, rainy
weather favors rapid spread of bacterial spot. 

In addition to general disease management tactics, starting with disease-free transplants and seed is important. Crop rotation is important, especially since peppers can also serve as a host for this disease.  Avoid handling plants (pruning and tying, for example) any more than is necessary because wounds caused by handling allow bacteria to enter plants. Sprays of a fixed copper product can reduce the spread of the disease if applications begin when the first symptoms appear and are rotated with chlorothalonil or sulfur products. More information on the control of this disease can be found in this article: Bacterial Spot on Pepper and Tomatoes.

Bacterial Speck

Bacterial speck is caused by Pseudomonas syringae pv. tomato. This disease does not affect peppers. The disease affects leaves, fruit, and stems. In contrast to bacterial spot, this disease will cause tiny black specks (1/16-inch diameter) surrounded by yellow halos. The specks that develop on young green fruit are slightly raised, 1⁄32 to 1⁄16 inch in diameter, and have well-defined margins. The specks are considerably smaller than the spots
caused by bacterial spot and do not penetrate the fruit. Although bacterial speck seldom reduces yields significantly, it can harm fruit quality. Infection is favored by cool (less than 70°F), wet conditions. 

Management of bacterial speck is the same as those used for bacterial spot.  

Bacterial Canker

Bacterial canker is caused by Clavibacter michiganensis subsp. michiganensis, and can be one of the most destructive and difficult-to-manage diseases of tomatoes.  The first noticeable symptom is wilting of plants and browning on the edges of the leaves. Sometimes stems can turn brown; later, they can split open, revealing a brown color. The pith (mushy stuff in the middle of the stem) may be completely discolored and 'mealy.' Fruit may also show small spots (1/8 inch across) with a raised brown center and a whitish margin or halo, often called bird's-eye spots.  

Bacterial diseases that cause wilting can be distinguished from fungal diseases caused by Verticillium or Fusarium by checking for bacterial streaming. Bacterial streaming consists of bacterial masses 'oozing' out of vascular tissues, and this may be observed by slicing stems and placing them in water. If whitish or yellowish strands are observed after a couple of minutes, the wilting is most likely caused by bacteria.  

Bacterial canker can survive the winter in plant debris, weed hosts, and wooden stakes. It may also occur from contaminated seed sources and transplants and be spread mechanically by pruning and de-suckering. Secondary spread may also occur by splashing water and by handling plants. Once the bacteria enter the vascular tissue, the disease progresses rapidly. Plants infected late in the season may show little reduction in yield; however, plants infected early may die and set no fruit.   

The most effective way to control bacterial wilt is by ensuring you have clean seed and a certified disease-free transplant. After harvest, remove infested debris and sterilize all supports and equipment. When handling or pruning plants, tools should be disinfected between cuts unnecessary wounding should be avoided. Crop rotation can also help.  

Viruses

The most common virus disease in Iowa is tomato spotted wilt virus (TSWV), but others can occur, including Tobacco Mosaic Virus (T), Cucumber Mosaic Virus (CMV), and Impatiens Necrotic Spot Virus (INSV).  

Symptoms for viral diseases can vary and are notoriously difficult to pinpoint.  In general, plants often become stunted in growth with reduced yields.  Leaves can develop leaf curling, yellow or green mosaic patterns, or a bronzing appearance. Fruit are also affected with mosaic patterns, streaking, or mottled areas.  Some plants may be infected and show no visible symptoms.  TSWV causes distinctive yellow ringspots on mature fruit. Foliage can also be affected; plants are usually stunted, and tip leaves show a purplish discoloration. 

Viruses are typically spread by thrips, aphids, or leafhoppers (thrips frequently spread TSWV)

There is no cure for infected plants. The first step in control is to discard diseased plants. Many viruses that infect tomatoes also infect peppers and potatoes, so avoid planting these crops next to each other. Insect management may also be beneficial in the transplant and early-season phases.

Physiological Disorders

Physiological disorders are problems not caused by a living organism like a fungus, bacterium, virus, or insect.  Instead, they are the result of environmental stresses on the plant.  


Blossom End Rot  |  Fruit Cracking  |  Catfaced Fruit  |  Sunscald  |  Blotchy Ripening  |  Physiological Leafroll  |  Failure to Set Fruit  |  Slow Ripening  |  Hollow Fruit  |  Black Walnut Toxicity  |  Herbicide Injury  


Blossom End Rot

Blossom end rot is a common problem on tomatoes.  It appears as a brownish-black spot on the fruit opposite the stem (the blossom end or bottom). Secondary organisms invade the brownish-black spot and cause the fruit to rot. Blossom end rot is most common on the earliest maturing fruit that ripens in July and early August. It can also be seen on other vegetables such as pepper, eggplant, summer squash, and watermelon. 

Blossom end rot is caused by a calcium deficiency in the developing fruit. Wide fluctuations in soil moisture levels impair calcium uptake by the root system of the tomato plant.  Excessive nitrogen fertilization may also contribute to blossom end rot. 

To reduce blossom end rot, water tomato plants on a weekly basis during dry weather to provide a consistent supply of moisture to the plants.  (Tomato plants require about 1 to 1½ inches of water per week during the growing season.)  Mulch the area around the tomato plants to conserve soil moisture.  Avoid over-fertilization.  Iowa soils contain plenty of calcium, so adding calcium will not solve the problem. 

Pick and discard fruit affected with blossom end rot.  Removing the affected fruit will allow the tomato plant to channel all of its resources into the growth and development of the remaining fruit.   More information on control of this disorder can be found in this article: Blossom End Rot.

Fruit Cracking

Fruit cracking is a common problem on tomatoes.  Cracks usually appear at the top or stem end of the fruit.  Cracks radiate out from the stem (radial cracks) or circle the fruit in concentric rings (concentric cracks).  Fruit cracking is associated with wide fluctuations in soil moisture levels.  Heavy rain or deep watering after a long, dry period results in rapid water uptake by the plant.  The sudden uptake of water results in the cracking of ripening fruit.  Generally, fruit cracking is most common on the large, beefsteak-type tomatoes. 

Fruit cracking can be prevented by supplying the tomato plants with consistent moisture during the summer months.  During dry periods, a thorough soaking once every seven days should be adequate for most tomato plants.  Conserve soil moisture by mulching.  Tomato varieties differ considerably in the amount and severity of cracking under climatic conditions.  Plant tomato varieties with good crack resistance, such as ‘Jetstar,’ ‘Mountain Spring,’ and ‘Mountain Fresh,’ among others. 

Catfaced Fruit

Cloudy and cool weather at blooming time may kill certain cells that should develop into fruit, resulting in deformities called catfacing. This results in the blossom end of the fruit becoming puckered and scarred with irregular bulges and leathery scar tissue. Catfacing occurs most commonly on the large-fruited varieties and is most often observed among first-formed fruit. There are no effective controls for this disorder. Catfacing should decline with the arrival of warmer weather.

Sunscald

Sunscald occurs on fruit exposed to the sun during periods of extreme heat.  Initial symptoms of sunscald are the development of shiny white or yellow areas on the fruit.  Later, the affected tissue dries out and collapses, forming slightly sunken, wrinkled areas.  Secondary organisms invade the affected areas, causing the fruit to rot. 

Fruits most subject to sunscald are those that have been exposed suddenly to the sun because of pruning, natural spreading of the plant caused by a heavy fruit load, or loss of foliage from diseases.

Losses due to sunscald can be reduced by growing tomatoes in wire cages.  Cage-grown tomato plants provide good foliage protection for the fruit.  Also, control foliar diseases and avoid heavy pruning or shoot removal.

Blotchy Ripening

Blotchy ripening occurs due to the absence of red pigment in localized areas of the fruit.  These areas appear as yellow or gray-green patches
on otherwise normal-colored ripening fruit. When these fruits are sliced open, brown discoloration is often apparent.

Several factors may contribute to the lack of red pigments, including weather, growing conditions, and nutrient levels. Factors such as high soil moisture, high humidity, low temperature, soil compaction, and excessive fertilization can impede the development of red pigment in the fruit. Low potassium levels in plants and prolonged cloudy periods or inadequate light intensity have also been associated with the disorder.

To minimize the incidence of blotchy ripening, follow proper cultural practices to maintain nutritional balance and plant vigor. If commercial fertilizers are used, select balanced formulations and avoid over-application.

Physiological Leafroll

Physiological leafroll occurs when the edges of the leaves roll upward and inward. Sometimes, the curling continues until the leaf margins from either side touch or overlap. The leaves may also become thickened, giving the foliage a leathery appearance.  Some leaves on the plant may not exhibit rolling.

Leaf roll often occurs after a heavy rain, plants have been severely pruned, or the plant’s roots have been damaged by deep cultivation.  Leaf roll does not reduce crop yield or quality.  Leaf roll is usually a temporary problem (although occasionally, it can persist most of the growing season).  Plants typically recover on their own. 

Failure to Set Fruit & Blossom Drop

There are many potential reasons for plants to fail to set fruit. High day and night temperatures will reduce flower production on tomato plants, reducing the number of fruit produced. Extremes in temperature and dry conditions may result in poor pollination and cause the flowers to drop from the plant without setting fruit. Blossom drop on tomatoes occurs when night temperatures are below 55 F or above 75 F. 

To reduce issues of poor fruit set and bloom drop, water the plants deeply once a week during dry weather. The fruit set should increase when temperatures moderate. Hormone sprays like "Blossom Set" may prevent some blossom drop due to low temperatures but yield inconsistent results. The resulting fruit are often misshapen, and they do not prevent blossom drop due to high temperatures.

Slow Ripening

Once fruit set has occurred, it normally takes 45 to 55 days for tomato fruit to develop and ripen fully.  Cool temperatures during tomato fruit development will slow maturity.  Tomato fruit may require an additional 7 to 10 days to mature when daytime high temperatures are consistently in the 60s°F and 70s°F.   

Puffiness or Hollow Fruit

This physiological disorder is characterized by fruit where the outer wall of the fruit is normal, but the tomato is hollow inside. One of the seed cavities is usually empty. This is typically the result of extreme high or low temperatures, excessive nitrogen fertilization, or heavy rains.  These conditions may interfere with normal pollination, resulting in puffy fruit. Puffiness occurs most frequently on early fruit. 

There are no effective controls. Puffiness should decline later in the summer.

Black Walnut Toxicity

Black walnut produces an allelopathic compound called juglone, which is presumed by some to cause an allelopathic response (inhibition of growth) in other plants. Very little research has been done in native or garden soils that show that juglone has any consistent impact on the growth of other garden plants.  Some plants have been observed to grow poorly near walnuts (frequently including tomatoes).  In this situation, plants often yellow, grow poorly or look stunted, and eventually die when grown near walnuts. These symptoms can also be caused by other conditions like dry soil conditions and low light (both common under the shade of any tree, including black walnut).  Learn more about juglone and its limited impact on garden plants in this article: What plants are sensitive to the juglone produced by black walnuts?.

Herbicide Injury

Herbicide injury is caused by carryover, misapplication, or drift of 2,4-D, MCPP, and other growth regulator herbicides. Tomato plants are highly sensitive to these chemicals throughout the growing season. The first symptom is downward curling of leaves and tips of growing points. Leaves often become narrow and twisted toward the tip, with prominent, light-colored veins. The symptoms are most pronounced on portions of the plant that were actively growing when the exposure occurred. In severe cases, stems and petioles become thick, stiff, and brittle with warty outgrowths. Affected plants may
recover. However, the fruit may become catfaced or develop in a plum shape and may be hollow and seedless.

If plants are damaged by herbicide, they may or may not recover, depending on the severity of the damage. All that can be done is to wait and see what happens while providing good care for the plant.  Preventing other stresses from harming the plant is the best way to minimize herbicide injury. When herbicide injury is observed, no chemical sprays or nutrient/fertilizer applications can reverse the damage. New growth may be unaffected, and long-term damage may not occur. This depends on the plant species, its overall health, and the product it was exposed to. More information on managing herbicide injury can be found in this article: Herbicide Injury to Garden Plants.

Insect & Animal Pests


Tomato Hornworm  |  Tomato Fruitworm  |  Stalk Borer  |  Stinkbug  |  Deer  |  Chipmunks, Squirrels, & Other Small Mammals


Tomato Hornworm

Tomato hornworms feed on the leaves and fruit of tomatoes and other vegetables, including eggplant, potatoes, and peppers. They can quickly defoliate portions of the plant, reduce its productivity, and heavily scar the fruit. 

The tomato hornworm is almost as big around as your thumb and can be 4 to 5 inches long. It’s bright green with a hornlike hook at one end that can be red or green depending on which of the two species you have on your plant. After feeding, hornworms move to the soil, where they pupate and spend the winter. The following summer, the pupae transform into five-spotted hawk moths and start the cycle over. 

Often, the best control option for home gardeners is to pick off the caterpillars by hand and destroy them. Finding them can be challenging, especially when small, as they are well camouflaged. Another control option is a biological insecticide, such as Bacillus thuringiensis (Bt) or a synthetic home garden insecticide.  More information on control of this insect pest can be found in this article: Tomato Hornworm.

Tomato Fruitworm

Tomato fruitworms often move from one fruit to another as they feed, and one larva may damage several fruits without consuming the equivalent of a single tomato.  Many more fruits are spoiled than are actually consumed.  They attack green fruits and typically cause neat round holes through the skin on the side of the tomato.

Tomato fruitworm moths do not survive in Iowa through the winter but instead are blown into the state from the southern U.S. each spring.  The moths lay eggs on the host plants.  Young larvae feed unnoticed on foliage until green fruits are present.  Fruitworms vary greatly in color from light green to brown.  They are marked with alternating light and dark stripes running lengthwise on the body.  There may be 2 or 3 generations of tomato fruitworms each summer.

There is no special monitoring or treatment program for fruitworms, as it is only an occasional pest in Iowa.  Carefully watch for feeding damage as fruits are expanding.  Spray only when damage levels are intolerable. Because fruitworm damage in Iowa is low, adequate control can usually be achieved by removing damaged fruit from the plant or sorting injured tomatoes during harvest. More information on control of this insect pest can be found in this article: Tomato Fruitworm.

Stalk Borer

The stalk borer is an insect that attacks a wide variety of plants, including tomatoes, potatoes, peppers, corn, hollyhocks, and dahlias. The larva (caterpillar) bores into the stem and tunnels inside the stalk. (The entrance hole is small and often difficult to locate.)  Affected plants wilt and often die. However, stalk borer-damaged plants may survive when given good care.  

The stalk borer is a purple and cream-striped caterpillar with a solid purple band around its body one-third of the way back from its head. It is an early-season pest that moves from tall grassy weeds and occasionally attacks plants in the garden. An individual stalk borer may go from one plant to another, damaging several plants. The adult is an inconspicuous grayish-brown moth.  

Tomato plants that die should be pulled and destroyed. Destroying the plants may kill the stalk borers, as well. Cutting or mowing tall, weedy areas around gardens also may help control the pest. Stalk borers cannot be effectively controlled with insecticides.

Stinkbug

Stinkbugs have piercing, sucking mouthparts (like a straw), and they insert this straw-shaped mouthpart into developing tomato fruit.  The resulting damage is usually not readily apparent until the fruit begins to ripen.  Yellow cloudy spots (sometimes described as starburst-shaped) form on the fruit. Careful inspection will reveal a tiny black dot in the center of the yellow cloud (this is where they inserted their mouthpart).  Directly under the skin of the damaged areas, the flesh of the tomato is white and spongy.  The damage is dispersed in a relatively uneven pattern on the fruit.  Often, damage is more severe along garden borders or near weedy areas.

Control of stinkbugs is difficult.  Damage can be observed with relatively low population numbers.  Just a few stinkbugs can cause significant damage as they often probe in multiple locations on the fruit.  If possible, handpick from plants and squish or drown in a bucket of soapy water.  This is not easy. During the day, they are typically at ground level and, when disturbed, will drop from the foliage to the ground, making them difficult to see or catch.  Pesticides are labeled for stinkbug control, but they are highly mobile insects and usually are no longer present once the damage is noticed. This means treating is not typically very effective.  Reducing weeds in and around the garden will help to reduce populations in the area.  Most times, the damage caused by stinkbugs is minor and control is unnecessary.  The fruit is still edible (just not very attractive and maybe a bit less flavorful).  

Deer

Deer feed a wide variety of garden plants, and tomatoes are no exception.  They typically feed on the upper stems and leaves of the plant, leaving behind jagged, torn stems.  The damage often seems to appear almost overnight (because it usually does!).  

Exclusion with fencing is the most reliable method to prevent deer browsing.  Fencing needs to be at least eight feet tall to prevent deer from jumping over.  Small vegetable beds (~10 to 30 square feet) can be enclosed in six-foot fencing as deer will not jump inside a small enclosure.  Repellents can be used but often have limited success as they must be reapplied frequently (especially after rain), and deer become used to the scent over time.

More information on control of this animal pest can be found in this article: White-tailed Deer: Damage Management.

Chipmunks, Squirrels, & Other Small Mammals

Chipmunks, ground squirrels, tree squirrels, and other small mammals sometimes feed on the fruit of a tomato plant.  These animals will chew or nibble on portions of fruit sometimes leaving them on the plant and other times plucking them from the vines and carrying them somewhere else.  Often newly ripen fruit is affected although green fruit is also occasionally damaged.  Damage is often more severe during drought or dry conditions.

To prevent damage, exclusion is the best option.  Surround plants with hardware cloth or chicken wire.  Mesh bags or plastic bags with small holes punched in them can be placed around the fruit as it begins to ripen and may discourage feeding.  Harvest fruit often and pick fruit before it is fully ripe to "beat" them to it.  Scent repellents (such as predator urine) can be used but often have limited success as they must be reapplied often (including after it rains) and animals get used to the scent over time.  Taste repellents (like hot pepper) are not practical.  These repellents can make the fruit taste badly to the chipmunk, but they will also do the same for the gardener.  Occasionally, providing an alternate water source nearby can reduce damage to the fruit as often the animals are eating the tomato during dry weather or drought because of its high water content.


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Last reviewed:
April 2024