Apple and peach leaf and stem surface morphology and soybean oil retentionas influenced by simulated rainfall and soybean oil emulsions

Environmental factors such as rainfall may reduce the efficacy of foliar-ap plied soybean [Glycine max (L,) Merrill] oil in reducing pest mortality. Gr eenhouse studies mere conducted to investigate the influence of rain on the retention of soybean oil and the influence of soybean oil and rainfall on surface morphology of apple [Malus sylvestris (L.) Mill var, domestica (Bor kh.) Mansf.] and peach [prunus persica (L.) Batsch (Peach Group)] leaves an d stems. 'Contender' peach and 'Golden Delicious'/Malling 27 apple trees we re grown in 19 L pots in a greenhouse (23 +/- 9 degrees C) and sprayed with soybean oil (1%) emulsified with the adjuvants Latron B-1956 or K1, Twenty -four hours after treatment, the trees were subjected to simulated rainfall of 0.0, 0.25, 1.25, or 2.54 cm, A negative linear relationship existed bet ween rainfall and oil retention. Peach leaves receiving 0.25, 1.25, and 2.5 4 cm rainfall retained 81%, 38%, and 18% of the applied oil, respectively. Oil retention by apple leaves was also negatively related to rainfall, For both species, a negative linear relationship existed between oil retention on stems and rainfall. There was no effect of emulsifier on retention of 1% soybean oil after rain on apple leaves or on the retention of 8% to 11% so ybean oil on the stems of apple and peach. Scanning electron microscopy rev ealed that epicuticular wax occurred as striations on apple and peach leave s. The wax morphology on peach and apple stems appeared as thin plates and platelets, respectively. The was morphology of leaves and stems of both tre es was not affected either by the soybean oil emulsions or rain. Both emuls ions induced stomatal closure in leaves and peach stems, however, stomates opened after rainfall of 1.25 or 2.54 cm, The lenticels appeared to be unaf fected by either emulsion. Results illustrate that rainfall of 2.54 cm mash ed off a major portion of the applied oil. Thus, respraying may be needed u nder natural climatic conditions with rainfall greater than or equal to 2.5 4 cm to restore the efficacy of applied soybean oil.