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.
Diseases | Physiological Disorders | Insect & Animal Pests | More Information
Diseases
Tomatoes are a favorite garden crop, but they can be affected by a variety of diseases that reduce plant health and yield. Learning to recognize common symptoms and understanding how diseases spread are the first steps toward effective management and a successful harvest. Learn more about the various diseases, including blights, wilts, cankers, viruses, and more, in the article below.
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 ripened 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.
More Information
- Tomato Diseases and Disorders (publication)
- Growing Tomatoes in the Home Garden
- Tomatoes (publication)
- Crop Rotation in the Vegetable Garden
Photo Credits: 1: Chelsea Harbach; 2: Brenda Kennedy, University of Kentucky, Bugwood.org; 3: R.W. Samson, Purdue University, Bugwood.org; 4: Paul Bachi, University of Kentucky Research and Education Center, Bugwood.org; 5: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org; 6: Howard F. Schwartz, Colorado State University, Bugwood.org; 7: Don Ferrin, Louisiana State University Agricultural Center, Bugwood.org; 8: Eric R. Day, Virginia Polytechnic Institute and State University, Bugwood.org