Distribution of Spray Deposits in Peach Trees and Number of Leaves that Constitute an Adequate Sample

The distribution of carbaryl spray deposits on individual leaves and fate of deposits applied to peach trees with gun and air-blast sprayers were studied by analyzing individual leaf discs with a new, rapid colorimetric method. The quantity of carbaryl deposit within a region of the tree ranged from 0–21.4 μg/cm2 of leaf when 50% WP of carbaryl was applied at 6.72 kg/ha using 13.7 1/tree by spray gun, and 3.4 1/tree by air-blast sprayer. The amount of deposit also varied among regions within a tree; the outer bottom leaves received larger quantities of carbaryl than did leaves from the inner bottom and top regions. There were also tree to tree variations, and carbaryl remaining 7 days after application varied from 9–47% of that originally deposited. Statistical analyses showed that with an average deposit adequate to provide satisfactory control, less than 50% of the leaves were properly covered with the spray chemical. If 95% or more of the leaves were to receive this amount of chemical, the average deposit had to be at least twice the required amount. The numbers of leaves required to keep the mean (M) within the limit of M±M/10 with 90% probability, ranged from 20–239 depending on the regions of trees sampled and methods of application.