Effects of long term use of several herbicides on apple trees

Abstract

The effects of four systemic herbicides, simazine, diuron, amitrole, and 2,2-DPA were studied when used at strengths in excess of current recommendations on mature apple trees. The herbicides were applied annually for six seasons. In a very dry season severe injury, defoliation, and yield reduction were caused by 2,2-DPA; the heavier the rate, the more severe the damage, and even the lowest rate caused some damage, Injury was not repeated in normal seasons. Diuron at greater than recommended rates resulted in slight injury in the fourth season and yield reduction in subsequent years. The damage became severe in following seasons but the recommended rate caused no reduction in yield and only slight leaf symptoms. Apart from slight leaf chlorosis in the very dry year, tolerance to simazine was good and amitrole treatments caused no injury in any season.