Pest
Management Home Page Dr. John F. Baniecki Blight is a general term. It has been used to include those diseases which show up as wilting of the plant, spotting or death or distortion of the leaves, spotting or rotting of fruit, injury to the roots, or all of these. These "blights" can be caused by a number of different agents. There are several blights that affect tomatoes in home gardens in West Virginia. While some are of minor concern, others are very important and may result in complete destruction of the crop, if not controlled. Wilts The wilt diseases are caused primarily by the soil-borne fungi, Fusarium and Verticillium, which invade the plant through the root system. First symptoms appear on leaves at the bottom of the plant. These leaves turn yellow or brown and then die. Leaves higher on the stem become dull in color and may appear droopy or wilted. With Fusarium, this is most likely to appear during hot weather, usually shortly before the first fruits ripen. The entire plant gradually turns yellow or brown, wilts and dies. It will have a complete collapsed appearance. When the stem is cut open, dark brownish streaks can be seen inside in the woody tissue under the green stem. The only real control of this disease is to plant adapted, resistant (VFN hybrid) tomato varieties. It is also wise to rotate tomatoes to different areas of the garden and plant only in well-drained soil to prevent build-up of the wilt fungi. Early Blight And Late Blight These diseases are both caused by fungi which have wind-blown spores. They grow and infect plants rapidly when conditions are right for their development. Early blight first appears as small, irregular, dark brown spots on the leaves. The disease moves progressively upward. These enlarge into circular spots with target-like markings. Lower leaves are attacked first. The leaf tissue around the spots turns yellow. When the disease is severe, leaves fall off. If not controlled in the leaf stage, stems and fruit may also be infected. Fruits will develop dark leathery spots near the stem end. Early blight is favored by rainy periods with warmer temperatures. Plants infected with late blight first develop greenish-black, water-soaked blotches on the leaves. Under moist conditions, these blotches enlarge rapidly. A white, fuzzy growth of fungus may also be seen on the undersides of the leaves. Infected plants eventually wither and die. Elongated black cankers develop on the stem and leaf petioles. On the fruit, water-soaked spots develop, enlarge rapidly and turn a blotchy greenish-brown. A whitish mold may cover the infected tissue during moist weather. Late blight is favored by rainy, foggy periods with cooler temperatures. For disease control use only disease-free transplants. If early blight or late blight has been a problem and favorable weather conditions occur follow a 7-day fungicide spray schedule with chlorothalonil (Daconil 2787), mancozeb, or a copper fungicide. Anthracnose A fungus causes this rot of ripe tomatoes. Infected fruit first shows small, circular, water-soaked spots. These appear as if the fruit was bruised by pressing with the thumb or a pencil eraser. As spots enlarge, they become sunken and often develop rings of darker color - giving a target-like appearance. Small black specks often develop in the center of spots. Soft rot often develops. For disease control, practice rotation in the garden. Avoid poorly drained soils. Staking or mulching will also reduce the disease. Follow a fungicide spray program using chlorothalonil (Daconil 2787), mancozeb, or a copper fungicide. Root Knot Root-knot is caused by microscopic eel worms, called nematodes. Worm-like creatures hatch from eggs in soil or on roots and enter roots where they feed. Severely infected plants appear stunted and sickly. They wilt easily in dry weather, but may recover at night for a period of time before dying. Nematode damage also makes plants more susceptible to and increases severity of Fusarium wilt. Yield may be reduced up to 80 percent. Damage is most severe in light, sandy soil. The major symptom is knots or galls that cover the roots. These vary from slight swellings to knots of 1/16 to 3/4 inch in diameter. For nematode control, do not plant in soil where infected crops have been grown within the past two seasons. Examine the plants carefully for knots or galls on the roots. Verify presence of nematodes and dispose of transplants. Plant resistant tomato varieties. Soil Rot These fungi are widespread and present in the soil. They frequently occur when fruits lie on the soil and/or rain repeatedly splashes soil on them. Fruits develop large, cracked, rotten spots. Such spots are sometimes sunken and may have alternating bands of light and dark brown color. As spots enlarge, they frequently break open. To avoid soil rot, grow plants in well-drained soil. Use a mulch or stake plants to prevent fruit from touching the soil. Follow a regular spray schedule using chlorothalonil (Daconil 2787) or mancozeb or a copper fungicide. Mosaic There are several virus diseases that affect tomatoes. However, the most common one is "tobacco" or "tomato mosaic" discussed below. This virus is highly infectious. It is spread mainly by handling plants. The virus survives in commercial brands of tobacco and may be transmitted on the hands of smokers. Pepper and other garden plants are also affected. Plants are stunted and will bear fewer, smaller fruits than normal plants. A yellow-green mottling occurs on the leaves and occasionally on fruit. Leaves are sometimes curled and have slightly "malformed" appearance. However, this should not be confused with herbicide (2, 4-D) injury. The only control is sanitation. Avoid excessive handling of plants. Do not smoke while handling plants. If you smoke, wash hands with laundry soap and water before handling plants. Other ProblemsBlossom-end Rot Fluctuating moisture supply and lack of available calcium contributes to blossom-end rot. It is most prevalent during prolonged dry periods that occur while plants are making vigorous growth or after periods of unusually abundant rain (or heavy watering). High application of nitrogen fertilizer also increases the problem. Dark, sunken, leathery spots occur on the blossom-end (bottom) of the fruit. Such spots vary in size, but may cover half the fruit. To discourage blossom-end rot, grow plants in well-drained soil. Apply proper amounts of lime and superphosphate (based on a soil test). Avoid excessive use of nitrogen. Maintain uniform soil moisture supply by timely and thorough watering. Mulch or cultivate shallowly during dry periods. Cat Face The cause of this disorder is not fully understood, but it appears related to extreme heat or cold, drought, or contact with hormone-type weed killer. Fruits are extremely malformed and scarred on the blossom (bottom) end. There may be irregular swollen or sunken areas and bands of scar tissue. Fruit may also be cracked or split. To help alleviate the problem, grow locally recommended varieties. Sunscald This problem occurs during, hot, dry weather, especially on staked tomatoes. Large, slightly sunken areas occur on the fruit. These have a whitish or tan color. Mold often develops on the surface of affected areas and entire fruit may later rot. To help in reducing the problem, water and fertilize to keep plants vigorous. Handle fruit carefully. 2, 4-d Injury Tomatoes are extremely sensitive to 2, 4-D weed killer. Fumes and spray drift may injure plants mile or more away. Leaves and stems become considerably curled, distorted and twisted. Margins of leaves are wavy or frilled. Some blossoms drop without setting fruit. Tomato fruits may crack open or cat face. Avoid using 2, 4-D near the garden area or spraying on windy days. Always use a different sprayer for fungicides and insecticides than on the one used for weed killers. Leaf Roll This occurs when tomato plants are pruned severely. It is also common when heavy rains maintain an excessive amount of moisture in the soil for a prolonged period. Plants show upward rolling of leaflets of the older leaves. To help control this problem, plant tomatoes on well-drained soil as the trouble is less likely to occur there; however, it may occur on any soil during periods of continued and heavy rainfall. |
