Trunk Absorption of a systemic Chemical by Coffee.
During investigations in 1951 on the control of Planococcùs kenyae (Le Pelley) on coffee in Kenya, a proprietary preparation (Hanane), stated to consist mainly of bis(dimethylamino)fluorophosphine oxide, applied to the soil in a groove round the base of the tree gave inconsistent results, and the effect of applying it to the trunk was accordingly tested in 1952. This was done by removing loose bark from a section of trunk about 4 ins. wide and a few inches above the level of the soil, placing a band of oiled silk, 6 ins. wide, round the trunk with its top edge tied tightly round the lower edge of the scraped area, covering the scraped area with a double thickness of surgical lint soaked in the diluted insecticide, and pulling the oiled silk over it so that any liquid not immediately absorbed by the lint would collect in the fold. When a tree was treated in this way with 32.5 gm. active ingredient in 250 cc., the leaves began to show injury after five days and the tree was almost defoliated after 14, though in earlier tests in which the chemical was applied to the soil at the same or higher rates it caused little or no damage. Two infested trees of which the trunks were treated with 2 or 5 gm. active ingredient, respectively, in 200 cc: were not injured and the infestation was reduced after two weeks and completely controlled after 12, though untreated trees were still infested; in further tests, dosages of up to 10 gm. active ingredient in 200 cc. gave good control and caused little damage to the trees, though there was some yellowing of the foliage on most. At 8 gm. in 200 cc., complete control was given in two weeks whether the bark was first removed to expose the cambium or only lightly scraped, but in the first case the tree became almost completely defoliated after three weeks, whereas in the second there were no phytotoxic effects. When dosages of 3 or 6 gm. in 200 cc. were applied to the trunks after slight abrasion or to the soil in a shallow groove round the base, a metal cone being used to prevent rapid lateral dispersal, there was no injury to the trees but the lower dosage caused no significant changes in mealybug populations. The higher dosage caused a gradual decrease in population and gave almost complete control in eight weeks when applied to the trunks; it was ineffective when applied to the soil, but a second application after three weeks gave fair control. Application to the trunk without the waterproof and absorbent bands was unsatisfactory, doubtless owing to the volatility of the chemical, and absorption and translocation were best when the area of the trunk to be treated was first well scraped to expose the cambium in several places.