The tomato is the most popular vegetable in the home garden. Though widely grown, tomatoes are subject to a number of diseases and physiological disorders. Environmental stresses produce several common physiological disorders of tomatoes.
Plants fail to set fruit. Cause: 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. Control: Water the plants deeply once a week during dry weather. Fruit set should increase when temperatures moderate. Hormone sprays, such as "Blossom Set", may prevent some blossom drop due to low temperatures. However, the resulting fruit are often misshapen. Hormone sprays do not prevent blossom drop due to high temperatures.
A brown or black spot develops on the blossom end of the fruit. Secondary organisms invade the affected tissue and cause the fruit to rot. Cause: Blossom-end rot is caused by a lack of calcium in the developing fruit. Wide fluctuations in soil moisture levels impair calcium uptake by the root system. Excessive nitrogen fertilization may also contribute to blossom-end rot. Control: To reduce blossom-end rot, mulch and water plants during dry weather to maintain uniform soil moisture levels. Avoid over-fertilizing with nitrogen.
Initial symptoms are shiny white or yellow areas on the sides of the fruit exposed to the sun. Later, the affected tissue dries out and collapses, forming slightly sunken, wrinkled areas. Secondary organisms invade the affected areas causing the fruit to rot. Cause: Sunscald occurs on fruit exposed to the sun during periods of extreme heat. Control: Grow tomatoes in wire cages. Plants grown in wire cages provide good foliage protection. Also, control foliar diseases of tomatoes which defoliate the plants and expose the fruit to direct sunlight.
Radial and concentric cracks develop at the stem end of the fruit. Cause: Heavy rainfall or irrigation following a long, dry period promotes rapid growth during ripening. This growth results in cracking. Fruit exposed to direct sun are most susceptible. Fruit cracking is most common on the large-fruited varieties, such as 'Beefsteak.' Control: Cracking can be reduced by providing a uniform supply of moisture to the plants. Mulch and water the plants during dry weather. Also, plant crack-resistant varieties, such as 'Jetstar.'
The blossom end of the fruit is puckered and scarred. Cause: Cloudy and cool weather at blooming time may cause the blossom to stick to the developing fruit, resulting in catfacing. Catfacing occurs most commonly on the large- fruited varieties. Damage from the herbicide 2,4- D may produce similar symptoms. Control: No effective controls. Catfacing should decline with the arrival of warmer weather.
The outer wall of the fruit is normal, but the tomato is hollow inside. One of the seed cavities is usually empty. Cause: Extreme high or low temperatures, excessive nitrogen fertilization, and heavy rains may interfere with normal pollination, resulting in puffy fruit. Puffiness occurs most frequently on early fruit. Control: No effective controls. Puffiness should decline later in the summer.
This article originally appeared in the July 18, 1997 issue, p. 114.