TechNotes Tips - 07.25.02

Drought stress conditions in many parts of the country have made weed control difficult. In many instances repeat applications are needed. The difficulty arises under conditions where the weed is not actively growing. With the case of most weeds, especially broadleaf weeds, the herbicide needs to be absorbed and translocated through the plant. Weeds that develop under drought stress have a thicker cuticle compared to weeds developing under conditions of adequate soil moisture. A thicker cuticle makes it more difficult for the herbicide to be absorbed. In addition, a slow growing weed is less likely to translocate herbicides as rapidly as an actively growing weed.

Brown patch on tall fescue lawns is active under hot humid conditions. Conditions favorable for disease development are nighttime temperatures above 70 F and high humidity. Practices to minimize the severity of the disease include not over fertilizing with nitrogen, maintaining adequate phosphorus and potassium levels, and minimizing irrigation in the evening. Irrigating in the evening hours extends the period of moist conditions that favor disease development.