Effects of Temperature and Humidity on Foliar Absorption and Translocation of 2,4-Dichlorophenoxyacetic Acid and Benzoic Acid.

Little is known concerning the effect of humidity on the absorption of foliarly applied materials or their subsequent translocation. It is generally believed that the higher the humidity at any one temperature, the larger the amount of a foliarly applied material that penetrates the leaf per unit time. Most of the evidence for such an effect has been obtained indirectly. Koontz and Biddulph (16) found that the amount of phosphorus translocated from a given compound seemed to be related to the drying time of the solution on the leaf. By adding glycerine to the treatment solution, the translocation of P32 from an application of KH,PO4 solution was increased. Other workers have reported increased penetration of foliarly applied materials by additives which increase moisture retention. The recent review by Currier and Dybing (7) covers this work. It has been suggested that thin aqueous films on the leaf surface are important in promoting the absorption of nutrient sprays, the existence of the film depends upon the vapor pressure gradient at the leaf surface (4). In general, increasing temperature, within physiological limits, has been found to result in increased penetration. Rice (19) using red kidney bean plants studied the absorption of the ammonium salt of 2,4-D. He found that the amount absorbed was positively correlated with temperature over a three-level range of 46 to 580 F, 79 to 820 F and 86 to 920 F. Other workers using soybeans as the test plant found that with increasing temperature, there was an increase in the absorption of the sodium salt of 2,4-D (5,10). Barrier and Loomis (2) reported a temperature effect on the absorption of 2,4-D by soybean seedlings, but no effect upon the absorption of P32. Increased rates of absorption with increasing temperature have been reported for Co60 (9) and manganese (18). Known quantities of maleic hydrazide have been applied on several species of plants; the time course of absorption followed as it was affected by temperature and humidity (21). A variation in temperature at controlled humidities was found to have less effect on the absorption rate than a variation in humidity at controlled temperatures. Either an increase in