Tomato Plant Pests & Diseases:

Tomatoes have a built-in insect repellent called solanine that will repel many insect pests. The tomato hornworm is probably the most serious pest of tomatoes, although Japanese beetles, cutworms and other insects will also bother the plants. Many of these can be controlled by interplanting with flowers or other crops. Nematodes can be discouraged by planting marigolds, or even planting tomatoes where marigolds grew the year before. Virus-free nasturtiums will trap aphids.

The hornworm, a green worm with white stripes, is also attracted to dill, and is easier to spot on those plants than on the tomato. It can be hand-picked and dropped into a can of kerosene. Some easy-to-make sprays such as red pepper or onion and garlic also serve as insect repellents.

Cutworm damage can be prevented by placing a paper collar around the stem, about an inch above and below ground level.

Many diseases plague tomatoes, but only a few are of major importance.
- Blossom drop
- Blossom end rot
- Curly top
- Damping off
- Early blight
- Fusarium wilt
- Growth cracks
- Late blight
- Leaf roll
- Root knot
- Septoria leaf spot
- Soil rot
- Sunscald
- Tobacco mosaic virus
- Verticillium wilt

Tomato Diseases & Problems

• Blossom drop:
  
  Tomato plants often fail to set a normal crop of fruit because the blossoms drop off just when the flowers have matured. This may occur wherever tomatoes are grown, but the trouble seems to be especially prevalent where soil moisture is low and plants are subjected to hot, drying winds. Such conditions prevent blossoms from setting fruit, as do sudden periods of cool weather or beating rains. Loss of blossoms also results from infection by parasitic bacteria or fungi.
  
  Since large-fruited varieties of the Ponderosa type are very susceptible, do not grow these where summers are going to be hot and dry. Instead grow resistant varieties in hot climates, especially in the Southwest. Irrigate, if possible, and avoid excessive applications of nitrogen, especially during early growth. To help pollination and fruit-set, shake the flower trusses on a warm, sunny day to help distribute the pollen.
  
  
• Blossom-end rot:
  
  This is a common, nonparasitic disorder of tomatoes. A water-soaked spot first appears near the blossom end of the tomato when the fruit is about 1/3 of the way to maturity. The spot enlarges and browns until it covers up to half the surface, and gets dark and leathery, flat, or even concave as it continues to grow. No soft rot of the tomato occurs unless it also has been attacked by bacteria or fungi.
  
  
  
  Blossom-end rot characteristically strikes during a long, dry spell after the plants have grown quickly and well during the earlier part of the season. Sometimes it appears after rainy periods. A deficiency of calcium is the basic cause of the trouble, but that condition is aggravated by excessive water or nitrogen. An excessive amount of total salts also causes blossom-end rot because the effective amount of calcium salts available to the plant is reduced.
  
  Control should begin with a soil test very early in the spring or fall to find out whether there is already a shortage of lime in your soil. To raise the pH value of the soil by one unit, use about 1/2 lb of finely ground limestone for each 10 sq. ft. If soil pH needs to be raised more than one unit because it tests below 6, apply more lime. Add a little at a time and expect effects to last about 3 years. In a dry climate, be especially careful not to make your soil too alkaline.
  
  

• Curly top:
  
  Also called Western Yellow Blight, curly top is destructive to both tomatoes and sugar beets, and can trouble beans, spinach, squash, peppers, and table beets. It is carried by beet leafhoppers from weedy, abandoned lands. Attacks may occur at any stage of the tomato's growth, causing leaflets to roll and turn over to expose their undersurfaces. Foliage becomes stiff and leathery. The petioles of the leaves curl downward. Branches and stems become very erect and the veins get purple in places. The plants are stunted and very few fruits ripen normally. Early tomatoes probably suffer more from curly top than late varieties, but both are affected.
  
  Control is difficult because the range of the leafhoppers is very wide. Set out transplants after the heaviest leafhopper infestation has passed. Plant more closely than usual. You can also plant in double-hill plantings, with 2 plants set 6 inches apart in hills planted in 42 inch rows. Yield is increased and damage decreased in this type of planting situation.
  
  If you have only a small area of tomatoes, shading of the entire area with slats or by using a muslin-covered frame will repel a fair number of the insects, as well as arrest the effect of the disease if it has already started.
  
  
• Damping-off:
  
  This wilt is caused by a fungus that attacks the stems at the ground level. The plants soon fall over and die. The disease can be combated by sterilizing planting soil and controlling excess moisture. Avoid overfeeding your seedlings and place them close to a lighted window or overhead fluorescent light.
  
  
• Early blight (Alternaria tomatophila) :
  
  Symptoms of early blight may appear first on the stems as dark, slightly sunken areas with concentric markings. Small, irregular, brown dead spots appear early in the season on the older leaves and enlarge until they are 1/4 to 1/2 inch in diameter. The spots are usually surrounded by yellow, and if there are many spots on the leaf, the entire leaf might be discolored.
  
  Most early blight injury occurs just as fruit begins to mature. High temperatures and humidity will cause much of the foliage to die and the fruit to be exposed to sunscald. This disease is easily spread. To avoid problems with early blight, sterilize soil for starting seedlings, use commercially grown seed or clean seed from your own plants, and do not crowd plants in a flat. If seedlings show signs of this disease, do not plant them in the garden.
  
     
  
  

• Growth Cracks:
  
  Cracks radiating from the stem or extending more or less concentrically around the shoulders of the fruit may seem normal, but in reality they invite infection and detract from the appearance of the fruits. Cracking often appears during rainy spells that are hot and conducive to rapid growth. Another kind of cracking comes when there is a dry period followed by a rainy period during the ripening season.
  
  To control this condition, refrain from applying water at crucial periods of the plant;s growth. Sometimes the cracks heal before harm is done.
  
  
• Late Blight (Phytophthora infestans ):
  
  A fairly common disease in certain parts of the East and on the Pacific coast, late blight occurs sporadically elsewhere. The older leaves of infected plants develop irregular, black, water-soaked patched. Eventually, leaves drop and the disease destroys the fruit. Sometimes there is a white, downy growth of the fungus on the lower surfaces of the leaves, and if the weather is warm and moist, the plant will look as if it had been enveloped by frost. Damage to the fruit is likely to occur on the upper half. The first sign is a green-gray spot which becomes brown and hard. Infected plants must be dug up and destroyed or the blight will spread to other plants.
  
     
  
  

• Leaf Roll:
  
  During very wet seasons, tomato plants frequently show an upward rolling of the leaflets of the older leaves. At first this rolling gives the leaflet a cupped appearance. Later, the margins of the leaflets touch or overlap. The rolled leaves are firm and leathery to the touch. One half to three-fourths of the foliage may be affected. Plant growth is not noticeably checked, and a normal crop of fruit is produced. Frequently leaf roll occurs when tomato plants are pruned severely, and it is very common when unusually heavy rains cause the soil to remain moist for long periods of time.
  
  To prevent leaf roll, keep tomato plants on well-drained, well-aerated soil, and protect them from prolonged periods of heavy rainfall if you can.
  
  
• Root Knot (Root knot nematode - Meloidogyne):
  
  Nearly invisible nematodes which attack the roots of various plants are found wherever tomatoes are grown - especially in areas where crop rotation is not practiced. The attack results in the formation of root knots or galls that range in diameter from a pin-head to a full inch or more. Soon the whole outer area of the root is discolored, and may rot. The results are not apparent above ground except that plant growth and yield are retarded. Infected plants wilt very easily on a hot day, and they may be stunted in appearance and somewhat yellowish. Some are nearly killed.
  
  The best control for nematodes is the planting of marigolds along with tomatoes, or, even better, put tomatoes in parts of the garden where marigolds grew during previous years. The root exudate from marigolds has a powerful inhibiting effect on nematodes, and remains effective in the soil for 3 years. Interplanting of marigolds and tomatoes is effective the same year.
  
  To control root knot, examine the roots of tomato plants, and discard any with root knots or rotten roots. Never use soil known to have had a nematode infestation the previous season. Plant marigolds instead. Burn infected plants.
  
  

• Septoria Leaf Spot (Septoria lycopersici ):
  
  Not common in the South or on the Pacific coast, septoria leaf spot occurs in the mid-Atlantic and central states, and as far south as Arkansas and Tennessee, flourishing when temperatures are moderate and rainfall abundant. The disease destroys so much foliage that plants fail to make enough food to support an abundant crop of fruit. Absence of leaves exposes the fruit to sunscald. Fungus is most evident on plants that are just beginning to set fruit.
  
  The first symptom of septoria leaf spot is the appearance of water-soaked spots on the older leaves. Spots are rough and circular, with gray centers and dark margins. Later, dark dots are evident in the centers where spores are produced. Eventually all the leaves are affected and drop off, leaving only a few at the stem top. Fruits are rarely attacked.
  
  
  
  To control septoria leaf spot in tomatoes, plow under all crop and weed refuse; the fungus will not over-winter on plant remains that are buried deep in the soil.
  
  
  
  
  
  
  
  

• Soil Rot (Rhizoctonia solani ):
  
  This disease can attack your tomato plants no matter where you have your garden. It is caused by the same organism that causes damping-off. The first symptom is a brown, slightly sunken spot on the fruit, with sharply outlined (not smooth) concentric markings close together. It enlarges and often breaks open.
  
  Soil rot can invade either through wounds in the tomato or through uninjured skin. It usually occurs during wet periods and on moist soils where plants cover the ground; or when the fruit has been splashed by rain. Avoid poorly drained soil, use a good mulch, and use varieties of tomatoes suitable for staking.
  
  
• Sunscald:
  
  During hot, dry weather, green tomatoes may develop sunscald. It is especially common on plants that have lost their foliage from other diseases. Symptoms, especially on young fruits, include a yellow or white patch on the side of the fruit toward the sun, which may remain yellow or turn blistery and later flatten to a large, gray-white spot with a very thin, paperlike surface. It is very likely that this spot will later become the site of a fungus infection.
  
  To control sun scald in tomatoes, protect plants from defoliation and from wilt diseases and leaf spot. If excessive loss of protective foliage occurs, put a light covering of straw over the fruit clusters.
  
  

• Tobacco Mosaic Virus:
  
  Also called tomato virus, it is found everywhere and infects many members of the Nightshade family. The green strain causes light and dark green mottling of the foliage, curling, and slight malformation of the leaflets. If seedlings or young plants are infected, mature plants may be stunted; but later attacks do not reduce the size of the plant, especially if they do not occur until the fruiting stage. Yellow strains cause yellow mottling of the leaves and sometimes of stems and fruit, as well as curling, distortion and dwarfing of the foliage. Control is advisable, expecially since an infected plant is susceptible to attack by a second virus.
  
  The tobacco mosaic virus is usually transmitted by first handling an infected plant and then a healthy one, or even by brushing against first one and then the other. Careful handling is important. Wash your hands in soap and water or milk if you are handling more than one plant. Greenhouse tomato plants are most susceptible to the virus, since they are so frequently handled. A few insects, such as the potato aphid, also transmit the virus from plant to plant. The virus will live for several years in dried stems and leaves, in greenhouses as well as in the soil, especially when one tomato crop is planted right after another in a warm climate. Garden soil does not seem to be the source of much infection, but seedlings intended for garden planting are often infected if grown in or near a greenhouse where the disease is present. The carry-over may be due to aphids. Eliminate jimsonweed, nightshade, bittersweet, matrimony vine, ground cherry, and horse nettle growing near your tomato patch. Mosaic virus is present to some extent in practically all cigar, cigarette and pipe tobaccos, so smokers are very likely to carry the virus on their hands.
  
     
  
  To control or at least reduce losses from tobacco mosaic virus, remove all infected plants among the seedlings and spray with milk any tomato seedlings suspected of contracting the disease. For full protection, repeat at least once. Burn infected plants or place in a good, hot compost heap. Sterilize soil in which seedlings are grown, especially when a new crop is put in where an old crop has recently been dug up.
  
  
• Verticillium Wilt (Verticillium albo-atrum):
  
  Verticillium wilt is a problem in the West, some of the north-central states, and in the Northeast. Unless the soil is pasteurized regularly, it can also invade greenhouses.
  
  Infected plants show a slight wilting at the shoot tips during the day and yellowing of the older leaves. Eventually, the crown of the plant loses all its leaves, the higher stem leaves look dull and the leaflets curl. Finally, only the leaves near the tips of the branches are alive. If the plant fruits, the tomatoes are very small and unattractive. When the leaves have been infected, they show yellow areas at their margins in a "V" design. Eventually, this tissue dies and the leaves drop off, but the fungus may have already invaded the vascular system and traveling through the whole plant. As with fusarium wilt, the best control is to locate seedbeds on soil that is free from the fungus. Use clean, pasteurized soil in flats, hotbeds, cold frames, and peat pots.
  
  
  
  
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