THE USE OF CHEMICAL AIDS IN PRE-HARVEST DEFOLIATION OF PHASEOLUS VULGARIS L. AND THEIR EFFECT ON CROP YIELD
The chemicals used were ethephon, potassium iodide, bromodine, endothal and harvade and were applied either alone or in combination. Results indicated that all chemicals, whether applied alone or in combination, reduced the number and weight of leaves. When ethephon was applied alone the leaves turned yellow prior to defoliation. Application of the other chemicals, either alone or in combination with ethephon, resulted in leaf dessication followed by defoliation. The most effective defoliation treatments caused the greatest reduction in leaf weight. Combining ethephon with potassium iodide or applying endothal alone resulted in a greater reduction in leaf weight than in leaf number. It is suggested that this may facilitate the separation of leaves from pods in the cleaning drum of the harvester.
Some chemicals reduced the fresh weight of pods. It is suggested that this reduction may be acceptable, provided there is a compensatory improvement in the recovery rate of pods relative to that of the untreated crops. The most effective defoliating treatments were not always those which caused the greatest reduction in fresh weight of pods. None of the chemicals caused a reduction in pod number which indicated a differential selectivity of vegetative and reproductive plant parts.
Ethephon activity was shown to be temperature dependent when applied either alone or in combination with endothal.