This malady is caused by 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 usually recover. However, the fruit may become catfaced or develop in a plum shape, and may be hollow and seedless. To avoid herbicide injury, do not spray when wind may carry spray drift toward tomatoes or other sensitive crops.
In addition, spray at low pressures, use a coarse-spray nozzle, and apply the spray as close to the ground as possible. Avoid applying other pesticides in sprayers that have previously contained herbicide because traces of herbicide are likely to remain in the sprayer even after thorough rinsing.