The persea mite, Oligonychus perseae Tuttle, Baker & Abbatiello (Acari: Tetranychidae), a pest of avocado, was first discovered in Israel in the autumn of 2001. It has since spread to most avocado growing areas in Israel. To establish an economic injury level (EIL), based on the percentage of leaf area damaged (PLAD), we conducted an extensive field study. For three consecutive seasons we created distinct pest infestation levels on the Hass avocado cv., by applying acaricides (spirodiclofen and abamectin) at 50, 100, and 250 mites per leaf levels, along with non-sprayed controls in a replicated block design. At harvest time we evaluated the level of leaf damage and fruit yields across treatments. In two out of the 3 years, trees sprayed at 50 and 100 mites per leaf levels had similar PLAD values, differing from trees treated at the 250 mites per leaf level and the non-treated control, the latter pair also being similar. Over the 3 years, mean yield attained at the two higher infestation levels was reduced by 20% in comparison to the mean yields recorded for plots sprayed at the lower thresholds. Accordingly, we suggest that scouts adopt an action threshold (AT) of 50-100 mites per leaf. Future research is needed to refine this AT. Mean annual cumulative mite days (CMDs) of the two higher levels was ca. 13500 ± 700 per leaf. Using the linear regression equation PLAD = 0.0009CMDs + 2.42, describing leaf damage as a function of CMDs, we estimated an EIL of ca. 15 PLAD.
Zilberstein, M., and Pinkas, Y. 1987. Detached root inoculation-a new method to evaluate resistance to Phytophthora root rot in avocado trees. Phytopathology 77:841-844. A screening method was developed to differentiate between rootstocks of inoculated root segments is followed by measuring electrical conductivity avocado (Persea americana) resistant and susceptible to root rot disease; of the root-bathing solution at 24, 48, and 72 hr after inoculation. the method is applicable to fruit-bearing trees. Large numbers of Variability between replicates was reduced by zoospore concentrations horticulturally outstanding trees, or those that survive in infected groves, above 104/ 10 root segments. The difference in electrolyte leakage between can be screened quickly and simply without sacrificing or damaging the thick and thin roots was offset by expressing electrical conductivity as a tested trees. Detached young (white) avocado root tips are suspended in function of root weight rather than of length. Avocado Duke 7 and G6 double-distilled water and incubated with zoospore suspension of (resistant) root segments leaked significantly less than those of six Phytophthora cinnamomi at 24 C in the dark. Electrolyte leakage from rootstocks (susceptible) at 48 and 72 hr after inoculation.
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