Tomatoes can be hurt by a number of diseases or pests. If disease has been a problem in your area, look for varieties that are resistant. Rotate tomato crops every year and remove all plant material at the end of the season and burn it or send to a landfill.
How tomatoes are grown and what fertilizer is used affects the flavor. Too much water or too much nitrogen makes them bland. Too much compost produces more leaves and fewer tomatoes.
Cloudy weather (decreased light) and high nitrogen decrease sugar. Fruit maturing during longer days have more sugar than fruit maturing late in the season under shorter days. Water stress increases sugar concentration.
If foliage is damaged by disease or reduced by insect feeding or excessive pruning the capacity to produce sugars and acids is decreased. Tomatoes harvested at the mature green stage will have less sugar and more acid than tomatoes harvested near table ripe.
Worms are large 2-3" long green caterpillars with white stripes. A horn protrudes from the back of the worm. They can defoliate a tomato very quickly. Their calling card is black droppings on leaves. They should be picked off by hand as soon as they are seen and destroyed. Weekly sprays of pyrethrum/rotenone combination organic insecticide will control most pests.
These are fat, gray worms that live in the soil curled up in a semicircle. At night, they crawl to the surface and chew tomato seedlings off at soil level. Be alert for them while you are in the garden and remove them by hand. To prevent cutworm damage, you can make protective collars for each tomato plant. Bury the lip of cup in the soil and the cutworm will not be able to reach the tomato stem. The tomato horn worm does considerable damage to the foliage. This pest appears later in the season. Worms can get up to 4 inches long or more, yet their markings allow them to blend with the leaves. To control, pluck them off by hand and dispose of them. Colorado potato beetles also defoliate plants. They can be more destructive than the tomato hornworm. Fruitworms can spoil a lot of fruit. Seven or rotenone will control these pests.
VERTICILLIUM AND FUSARIUM WILTS
These are soilborne diseases that cause yellowing, wilting and premature death of the plants. Leaves turn yellow toward the bottom of the plant and work upward, often on one side. The only practical control is to use resistant varieties and plant in a new location. Symptoms are you will visit your garden one morning and plants will have wilted overnight. A symptom similar to wilt disease is caused by Black Walnut trees. Roots of these trees give off a toxin destructive to tomatoes.
This disease is characterized by dead brown spots that start on the lower leave and spread upward. This fungal disease typically shows up during periods of frequent rain, high humidity, and warm temperatures. Bottom leaves are affected first, with irregular dark brown spots and concentric dark rings that look like a bull's eye. These spots are surrounded by yellow leaf tissue. Eventually leaves turn yellow and fall off, exposing tomatoes to sun scald. Older fruit may develop dark, leathery sunken spots with concentric markings. Mulch plants to prevent disease spores from splashing up during irrigation. Avoid overhead watering, especially late in the day. Remove fallen leaves and diseased parts. Don't plant tomatoes, peppers, or eggplants in the same spot for three to four years. Apply mancozeb (Dithane) or copper before the symptoms are seen as a protection against attack. Look for blight resistant varieties.
This disease is a very destructive disease of tomatoes. Fortunately, the disease is not a problem most years since it only occurs when spring weather is cool and wet. Foliage and fruits are susceptible to late blight at every developmental stage.
Symptoms: On leaves, the disease begins as greenish black, water-soaked, irregular blotches which rapidly develop into large purple-black, papery lesions. The lesion margin is often thin and pale yellow. During moist conditions, white, glistening, web-like, fungal growths often appear on the lower leaf surface at the lesion's edge. If cool, moist conditions persist, blight will spread rapidly and kill the plant.
On fruit, gray-green, water-soaked, greasy spots appear near the stem end. As lesions develop, they become brown and wrinkled. When cool, moist conditions exist, lesions quickly expand, covering up to half of the fruit's surface. Decay may extend several inches deep into fruit. When cracking occurs on fruit skin, a delicate white web of fungal growth may develop in this area. Soft-rot bacteria often invade cracks, causing a soft water rot.
Control Measures for Early Blight, Late Blight, and Septoria Leaf Spot *At the end of the season, remove or burn old tomato and solanaceous weeds such as horsenettle, jimsonweed, and nightshade to prevent disease carryover.
*Plant disease-free seeds or transplants.
*Follow a regular spray schedule using a fungicide. Fungicide treatments should begin 7 to 10 days after transplanting and continue at 7 to 10 day intervals until harvest.
*Keep tomato plants healthy and vigorous by following a good fertility and weed control program.
It's characterized by numerous small black spots on the leaves. The centers of these spots later white and tiny black dots appear in the white centers. The disease starts on the bottom leaves and become more severe during wet weather. Heavily diseased leaves turn yellow, wither, and drop in large numbers, starting at the base of the plant. The fungus survives in infected plant debris left on the soil surface or buried in the soil. Under favorable conditions in the spring, the fungus produces spores that are carried by wind and splashing rain. Secondary disease cycles can occur as long as the weather remains favorable. Infection and subsequent defoliation can be severe during prolonged periods of warm, wet weather.
Management- Crop rotation and clean tillage (for example, plowing) help reduce the risk of disease by reducing the amount of primary inoculums (spores) in the immediate area. Tomato varieties susceptible to wilt diseases may be more prone to leaf spots. Apply recommended fungicides when conditions favor disease.
BLOSSOM END ROT
It is a dry, leathery brown rot on the blossom end of the fruit. It is one of the most common complaints. It is caused by a combination of a calcium deficiency in the developing fruit and a wide fluctuation of soil moisture. The problem becomes more pronounced in hot weather. It begins as a light tan water-soaked lesion on the blossom end of the fruit. The lesions enlarge and turn black and leathery. The open wounds can act as an avenue for attack by fungi such as fusarium. This can drastically lower the yield and marketability of the fruits. Fluctuating moisture supplied to the soil during the dry periods, and low calcium levels in the fruit, are the major causal factors. To control blossom end rot, assure an adequate and consistent supply of moisture from fruit formation to maturity, and use mulch (grass clippings, plastic, straw, or shredded newspapers) to conserve moisture. Avoid frequent shallow watering, water deep and then wait five or more days before watering again.
Proper mulching increases the number of days between watering. Although lack of moisture generally causes this condition, ironically enough too much moisture may also encourage it. For example, several days in a row of steady rain and storms may cause the rot; it is the lack of consistency in moisture patterns that is at fault here, which tends to wreck havoc with the calcium levels in the plant. There are products on the market that can be sprayed on the leaves to help the problem. Fruit that is already affected cannot be saved. There are certain varieties of tomatoes, which are resistant to blossom end rot. Look for them when planning your crop.
Poor color or sunscald occur when high temperatures retard the development of full red color in tomatoes exposed directly to the hot sun. Shading the plants during the hottest part of the day and looking for types that say they have good foliage cover will help.
The name isn't the only thing strange about catfacing. So are the deformed and misshapen fruits that result from it. No one knows for certain what causes catfacing, but it's related to problems with flower formation. The blossom sticks to the side of the fruit, resulting in puckering. Temperatures below 50 degrees F at flowering or fruit set can cause catfacing. So can extreme heat, excessive soil nitrogen, drought, and growth-hormone-type herbicides. Heirlooms and tomatoes with large fruit are most susceptible to catfacing.
Are your tomato leaves curling? Do they feel leathery? Leaf curl can happen in hot weather, especially after a fluctuation in moisture levels. Heavy pruning also causes this problem. Fortunately, leaf curl won't affect your tomato production.
Do your tomatoes have concentric or radial cracks? This happens when fruit grows quickly during a period of rapidly changing weather conditions, such as high temperatures and drought followed by a rainy spell. Always maintain consistent irrigation during dry spells, and mulch plants to conserve moisture. Or try crack-resistant varieties.
Are blossoms dropping off your plants? Tomatoes are picky about temperatures when setting fruit. If the weather is too warm (above 85 degrees F to 90 degrees F) or too cool (below 55 degrees F), pollination suffers and blossoms drop off. Early-season varieties can handle a little * chill, and heat-tolerant tomatoes can take warmer temperatures. Too much nitrogen fertilizer can also cause blossom drop, as can heavy rains and dry winds.
The other causes for blossom drop are: lack of pollination, too much or too little nitrogen, humidity is too low or too high, lack of water, stress from insect damage or disease and to heavy fruit set.
Tomatoes grow best if daytime temperatures range between 70 F and 85 F. The following are things to do to help avoid blossom drop: Ensure pollination, go easy on the fertilizer, work around the humidity, water deeply, once a week, during dry weather, and keep the tomato plants healthy.
Control: Water the plants deeply once a week, mulch heavily to maintian constant soil moisture levels, establish windbreaks as needed, avoid using excessive amounts of nitrogen fertilizers, and wait for temperatures to moderate and stabilize. Earlier timed planting can help attain fruit set prior to the on-set of high temps., and the use of protection can compensate for cool nights. Some recommend attempting hand-pollination with an artist brush or a gentle shaking of the plant/cage/support prior to the hottest part of the day will also help. Fruit set will resume when temperatures moderate.
Stunted growth and reduced fruit yields are some big problems caused by these small soft-bodied insects, which travel in colonies and suck sap from plants. Control aphids early. A strong spray of water will knock them off your tomatoes. (Allow plants to dry before evening to avoid fungal diseases.) Insecticidal soap is also effective. Aphids have many natural enemies, including parasitic wasps, lacewings, and lady beetles (which can eat several hundred aphids a day). Encourage beneficial insects in your garden by avoiding chemical pesticides. Set natural traps for ants, however, because ants protect aphids from predators and even transport aphids to plants.
BACTERIAL SPOT AND BACTERIAL SPECK
It is often difficult to tell the different between the two bacterial diseases, both of which form small spots on leaves and fruits. Since control recommendations for bacterial spot and bacterial speck are similar, it is usually not necessary to separate the two.
Symptoms. Bacterial spot symptoms can be found on all above ground plant parts of tomatoes, peppers, and nightshades. Initially, leaf-spots appear as small, circular, irregular, water-soaked, dark green area on the lower leaf surface. As spots develop, they become purplish gray with black centers. Spots on the upper leaf surface become raised. Occasionally, spots are surrounded by narrow yellow borders or halos. When leaf spots are numerous, surrounding tissue often turns brown and the whole leaf will die. Diseased tissue in the center of the lesion will dry and fall out, giving the leaf a ragged, twisted appearance.
In very wet weather, spots may grow together producing large, black areas on the leg. Disease spots on stems and petioles are slightly more elongated than leaf spots. Fruit spots first appear as small, dark, raised areas which are sometimes surrounded by water-soaked borders. As these spots age, they become slightly large (1/8 inch in diameter) and scabby. Although spots remain small and do not penetrate very deeply into fruit, large numbers of these spots will lower the quality of the fruit.
Leaf and fruit symptoms of bacterial speck are similar to those described for bacterial spot. However, bacterial speck can sometimes be distinguished on the basis of halo development. Large areas of tissue bordering the spots may become yellow or white. On fruits, tissue bordering the lesions will sometimes become white. The white or yellow discoloration of bacterial speck is much more extensive than the halo which sometimes is produced by bacterial spot. Bacterial speck will infect only tomatoes naturally.
Control Measures for Bacterial Spot and Bacterial Speck Both cultural and chemical control recommendations are available for management of these bacterial diseases.
*Do not grow tomatoes or peppers for at least 4 years in fields severely infested with bacterial spot or speck.
*Disinfect all soil, flats, and frames that are used for seedling production. *Use disease free seed and transplants.
*To ensure disease free seed, treat seed with a 0.6% acetic acid solution (3/4 ounce acetic acid per gallon of water). Place 1 pound of seeds in a cloth bag and immerse in 1 gallon of acetic acid solution for 24 hours. Keep the solution agitated and at a temperature of 75 degrees F.
*If bacterial spot or bacterial speck occurs during the growing season, treat plants with a copper maneb spray program. Always follow all directions, precautions, and restrictions that are listed on the manufacturer's label.
TOMATO SPOTTED WILT
Tomato plants infected with spotted wilt become stunted and often die. Initially, leaves in the terminal part of the plant stop growing, become distorted, and turn pale green. In young leaves, veins thicken and turn purple, causing the leaves to appear bronze. Necrotic spots or ring spots are frequently present on infected leaves. Infected stems often have streaks. Infected fruit may contain numerous ring spots and blotches and may become distorted if infected with the virus when immature. There may be no effective means of controlling tomato and spotted wilt. To reduce the source of infection, try the following:
*Control tomato spotted wilt virus infected weeds adjacent to the field.
*Apply systemic insecticides to the soil at planting to slow the initial spread of the virus into the field.
*Apply foliar insecticides later when thrips begin to build up. *Spray weeds bordering the field with insecticides.