SMOOTH PIGWEED INTERFERENCE IN NEWLY PLANTED PEACH-TREES

The effect of smooth pigweed (Amaranthus hybridus L. on the growth of newly planted peach (Prunis persica [L.] Batsch var. Persica) trees wa s investigated at the Rutgers Research and Development Center, Bridget on, NJ, in 1985 and 1986. Intraspecific and interspecific competition were evaluated for two consecutive years. Full season weed interferenc e treatments at 0.25, 0.5, 1, and 2 weeds/sq yd were established in Ma y, and compared with populations of 2 weeds/sq yd established in June, July, or August. Intraspecific competition occurred in full season we ed populations both years. Weed dry weights per plant decreased as the weed population increased in 1985. Both weed height and dry weight we re lower in 1986, however, weed height increased as the population inc reased. Weed height and dry weight decreased when establishment occurr ed later in the season. Tree nutrient status, trunk diameter, and fres h weight were adversely affected by weed interference. Leaf nutrient a nalysis indicated that N, Fe, and Cu levels were reduced by 0.5, 1, or 2 weeds/sq yd planted in May, and by 2 weeds/sq yd planted in June. T runk diameter and tree fresh weight were only reduced by 2 weeds/sq yd planted in May.