Effect of different water regimes on the efficacy of aldicarb in the control of citrus rust mite, Phyllocoptruta oleivora

Citrus is an economically important fruit crop grown worldwide. Because citrus are evergreen, they are mainly grown in regions with tropical and subtropical climates, where they are infested by a score of arthropod pests. In many citrus producing areas, the control of arthropod pests in established orchards represents over 50% of total production costs. Most of the citrus produced in Texas is destined for fresh fruit market, thus in addition to ensuring crop yield, the aesthetic value of fruit must be preserved. The soil-applied systemic pesticide, aldicarb (TemikRTM) has been one of the most commonly used miticide in South Texas citrus production for CRM control. Anecdotal reports by some growers of poor pest control have raised concerns over the efficacy of aldicarb in CRM control. Like any soil-applied systemic pesticides, the efficacy of Temik is dependent on the uptake of the active ingredient by citrus trees, which in turn is affected by soil moisture content. Soil moisture level prior- or post-Temik application, might be a determining factor for the efficacy of aldicarb. Because aldicarb can degrade in the very alkaline soils of South Texas, the timing of irrigation post-Temik application might also be an important factor. The overall goal of this study was to evaluate the effects of soil moisture content pre- and post-application on the efficacy of Temik in CRM control. A factorial experiment was conducted to evaluate the combined effects of soil condition (dry or wet) pre-application of Temik and different timings of irrigation (0, 2, 7 and 14 days) post-application on the efficacy of aldicarb for CRM control. Weekly monitoring of the pest population on the leaf and fruit were and the results showed that the CRM control was best achieved under the moist soil condition pre-application of aldicarb with no post application irrigation. Highest infestation levels and densities of CRM on leaf and fruit were observed when irrigation was given the same day as aldicarb application under moist soil condition, probably as a result of aldicarb leaching. Whereas, under dry soil conditions, the timing of irrigation post-application did not significantly affect CRM infestation. Results from this study suggest that the best irrigation management plan to effectively control CRM with aldicarb is moist soil condition pre-application with no irrigation post application. Overall, aldicarb application reduced the infestation levels of CRM on leaves and fruit. Leaf samples were analyzed for presence of aldicarb biweekly using the Enzyme Linked Immuno-Sorbent Assay (ELISA) test. Trace amounts of aldicarb were found in all the treatments that received aldicarb. Studies on the dispersion patterns of CRM on citrus showed that the mite is aggregated on both leaves and fruit. The strong and significant relationship between CRM mean densities and proportion of infested fruits and leaves suggested that a presence or absence sampling plan can be used in sampling CRM in citrus orchards in lieu of the tedious counts of CRM numbers.