The Plant Disease Clinic has been receiving several samples, especially coniferous trees, with the new growth shriveling and turning brown. Several factors can cause this type of injury but the most likely cause is heat stress. The cool spring this year delayed new growth on many plants. The young, emerging tissue on plants is vulnerable to many stresses. Young tissue is usually not actively involved in transpiration. Transpiration is the fancy name for how plants cool themselves. Because the new growth cannot cool itself adequately, heat injury can be the cause of sudden foliar collapse during exceptionally hot weather in late spring or early summer.
Not much can be done for trees once the injury has occurred. To help prevent heat injury in the future, mulch around trees with an organic mulch and water the trees during dry periods. While heat stress is the probable cause of much of the new growth-browning, it is important to remember that root-related problems, foliar disease and chemicals can also cause this type of injury.
This article originally appeared in the July 26, 1996 issue, p. 132.