Alternate bearing in the pistachio (Pistacia vera L.) is brought about by abscission of inflorescence buds during July and August when seed growth and development take place. There was rapid accumulation of sugars and conversion to fat in the nuts at that time, but sugar and starch levels in the bark and wood of nut-bearing branches were not appreciably different from those in similar tissues of non-bearing branches. The inflorescence bud-drop phenomenon does not appear the result of carbohydrate deficiency.
A number of pre-emergence soil residual herbicides were tested at 2 locations on varieties of young peach, plum, cherry, pear and walnut rootstocks. The greatest variation in response resulted from differences in location. Important differences in varietal response were also obtained with the various herbicides in light soils. Simazine appeared sufficiently safe to trees in heavier soil but gave variable weed control. Diuron gave about the same degree of weed control but more safety than simazine on young trees. Of the uracil herbicides tested, DP-733 was the least toxic to the fruit tree species tested, while bromacil and isocil were generally the most toxic, except to peach trees. Of the commercial uracil herbicides, only DP-732 (terbacil) was of sufficient interest for further study.