299 Response of Mature Peach Trees to Grass Competition

Abstract

Peach tree size has been restricted when trees were grown continuously with grass after tree planting. However, control of excess vegetative growth of fruit trees was inconsistent when grass was planted beneath mature trees. This research determined the effect of seven grasses on growth, leaf nitrogen concentration, and yield of 8-year-old peach trees and on weed abundance. Two cultivars (`Loring' and `Redhaven') of peach [Prunus persica (L.) Batsch] trees were planted in separate orchards in 1987 in a split-plot design with grass as a main effect and time as the subplot. Nine treatments were installed as ground covers beneath peach trees in 1995: Festuca arundinacea, Lolium perenne var Manhattan II; L. perenne var. Linn; Agrostis gigantea, Dactylis glomerata, Phleum pratense, Bromus carintus, weedy control, and herbicide control (simazine, glyphosate). In general, grasses reduced vegetative growth and yield in `Loring' and `Redhaven'. For example, compared to herbicide treatments, orchardgrass reduced sprout length by 27% in `Loring' and by 15% in `Redhaven'. Fruit-bearing branch length was reduced with orchardgrass by 30% in `Loring' and 19% in `Redhaven'. Orchardgrass affected fruit yield more than vegetative growth, reducing yield by 37% and 24% in `Loring' (predominantly in the 2- to 2.5-inch size class) and `Redhaven' (predominantly in the >2.5-inch size class), respectively. All grasses were not equally competitive, `Linn' perennial ryegrass never significantly affected growth or yield. Weedy treatments also did not differ from herbicide treatments in peach tree growth and yield. Grasses and weeds consistently reduced peach tree leaf nitrogen by 17% compared to herbicide treatment, but weed density was not correlated with reductions in yield and vegetative growth. The results indicate that peach cultivars respond differently to grass competition but the relative competitiveness of grass species was similar for both cultivars. Grass competition can reduce growth of mature peach trees but this reduction did not translate to reduced pruning time per tree.