Author: Frank Byrne and Joseph Morse

We have further refined methods for evaluating field populations of avocado thrips and persea mite for resistance to abamectin, spinetoram, and fenprothrin. It appears to us that abamectin resistance is evolving with both avocado thrips and persea mite but it has not proceeded far enough such that field failures are common – instead, one sees a shortening of field efficacy (for example, spring avocado thrips treatments used to control persea mite through the summer and fall in the Ventura region; most years it no longer does and a second treatment with a miticide is needed). Unfortunately, PCAs and growers often retreat with abamectin (sometimes with an alternative) when thrips or persea mite control is inadequate with an initial treatment. While the lack of efficacy of the first application may be due to abiotic and/or operational problems,  the possibility that resistance could be involved is often not given enough consideration.

We are extremely concerned about abamectin resistance developing in populations of one or both of avocado thrips and persea mite. We have “gotten the word” out regarding the danger of resistance but to date, we are still quite concerned that most PCAs are overusing abamectin and not trialing/ using the above alternatives to the degree they should (i.e. practicing proactive resistance management). If abamectin resistance develops, the concern is that the next most popular one or two materials would then be overused, also leading to the eventual loss of those products to resistance. For example, we believe fenpropathrin (Danitol) would fail due toresistance quite quickly.

Over the period 2012-2016, we have responded to industry and pest control advisor requests for information and targeted research. We believe it is partially due to our research on chemical control of avocado thrips and persea mite that the industry has been able to deal with these two pests effectively and without excessive damage most (but not all) years over the recent past.