Evaluation of the effect of foliar application of kaolin clay and calcium carbonate on populations of Diaphorina citri (Hemiptera: Liviidae) in Tahiti lime

Diaphorina citri Kuwuyama is one of the main concerns of citrus growers in the tropics because it is the pest responsible for transmitting citrus greening. The use of biorational insecticides has gained importance as an alternative for the control of arthropod populations in horticultural crops. The objective of the present study was to evaluate the foliar application of kaolin clay and calcium carbonate particle films on populations of D. citri as well as to estimate the effect of kaolin on physiological variables, such as photosynthesis, leaf temperature, relative chlorophyll content and PSII efficiency, in Citrus latifolia Tanaka trees. One set of experiments (two separate experiments) was conducted in two different municipalities (Apulo and Jerusalen, Cundinamarca, Colombia) to evaluate the effect of foliar kaolin clay sprays. Also, two repeat experiments were carried in two different farms in the municipality of Jerusalen to assess the efficacy of foliar calcium carbonate application. In all cases, a statistical design in series of experiments with analysis in different localities arranged in randomized blocks (four blocks) was used. In the kaolin clay experiment, population levels of Asian citrus psyllid were assessed in citrus trees treated with insecticide (imidacloprid) or kaolin clay and compared to population levels in control trees (no treatment). In the calcium carbonate experiment, populations of psyllid were assessed in citrus treated with calcium carbonate and compared to populations in control trees (no treatment). Foliar kaolin clay sprays showed lower population levels of adults (0.4 vs 1.1 individuals per flush), nymphs (0.5 vs 1.1 individuals per flush) and eggs (1.3 vs 4.3 individuals per flush) in comparison to control trees over the eight-week study. The calcium carbonate sprays also diminished the number of adults (0.5 vs 1.0), nymphs (5.0 vs 10) and eggs (4.0 vs 7.5) per flush at the end of experiment. Foliar applications of kaolin clay were as effective as imidacloprid for reducing populations of psyllid eggs. The use of kaolin reduced the photosynthetic rate of citrus trees by 25% compared to the other control and imidacloprid treatments (4.0 vs. 5.2 μmol m−2 s−1, respectively). Leaf temperature was reduced by approximately 5 °C in trees treated with kaolin clay. Significant differences in relative chlorophyll content (SPAD readings) and PSII efficiency (Fv/Fm ratio) were not observed. In conclusion, the use of inert particles based on kaolin clay and calcium carbonate can be considered a control strategy within an integrated management program of D. citri because they showed repellent characteristics, primarily against oviposition. The use of kaolin can also help regulate leaf temperature, especially when episodes of heat stress are expected.