Evaluation of Systemic Chemicals for Avocado Thrips and Avocado Lace Bug Management

We are evaluating systemic insecticides for the management of current and newly emerging pests of California avocados. Studies are being conducted in commercial avocado groves, under normal agronomic practices. Trees are treated using a variety of techniques – soil application, trunk injection – to establish the methods that will provide the best uptake of insecticide for the protection of the trees. Our primary research focus is on the avocado thrips and the avocado lace bug. Despite its recent introduction, the avocado thrips is already an established pest of avocados in California. The avocado lace bug is a more recent introduction, and has not yet established widely within the avocado growing regions. Current management practices for avocado thrips are centered on the use of foliar insecticides. Several foliar treatments are available (Agri-Mek, Success, and Veratran D) for the control of avocado thrips. However, the number of products is limited, the mode of application can be difficult (helicopter use on steep hillsides, applications near urban regions), and there are risks of resistance development, particularly to Agri-Mek due to it also being used against persea mite during the summer. Systemic neonicotinoid insecticides are relatively easy to apply (via established sprinkler irrigation systems or by modern trunk injection systems), and have a mode of action that has not been in use for the management of avocado thrips. A new mode of action would substantially lower the resistance risk associated with Agri-Mek, and alleviate operational difficulties in the use of foliar treatments. To measure insecticide uptake, we are using two techniques. First, we collect leaves that are attractive for avocado thrips and avocado lace bug feeding and conduct bioassays by exposing the insects to these leaves for a pre-determined period of time. Leaf punches from these bioassay leaves are also used to quantify the levels of pesticide present within the leaves. In this way, we are able to compare the levels of mortality in our bioassays with the quantity of insecticide that is present in those same leaves. With this information, we can establish activity thresholds for the insecticides, and subsequently evaluate the capacity of different application strategies at achieving these required concentrations. Insecticides that fall short of the activity thresholds will not be recommended for use within the avocado industry. We are also testing the fruit on these trees to ensure that there are acceptable residue levels present that would not compromise the management effort. It is important to growers that their fruit not be contaminated with pesticides as a consequence of any pest management effort. To address these concerns, we have established a residue analysis program in collaboration with Dr. Robert Krieger at UC Riverside.