Evaluation of an experimental biopesticide to control Asian citrus psyllid on orange, Summer 2023

The Asian citrus psyllid (ACP) is the most destructive insect pest in Florida citrus because of its ability to vector huanglongbing. Therefore, vector management is required in multiple environments where citrus is planted and infested with ACP. This trial was conducted in a 5-year-old orchard at the Southwest Florida Research and Education Center planted with sweet orange “Valencia” orange trees at a plant density of 480 trees/acre. Young shoots needed for ACP reproduction were induced by mechanical pruning approximately 2 weeks before sprays were initiated. Five treatments plus an untreated check were assigned to 10-tree plots in an randomized complete block design experiment with 4 blocks contained within two rows of trees. Plots were separated by a single untreated tree and the treated rows were separated by an untreated buffer row of trees. Treatments were applied on 5 and 12 September using a Durand Wayland AF100-32 air blast speed sprayer operating at 1.9 mph and 300 psi equipped with 3 # 4 John Beane ceramic nozzles delivering 100 gpa. Sprays were conducted during the morning hours when wind and temperatures were low. The daily temperature for the trial averaged 79.1 °F and 7.61 in of rain was recorded with the heaviest on 9, 17, and 19 September. There was no drift from any pesticides used in the neighboring fields.

Adult and nymph populations of ACP were monitored on 5 sampling dates, 2 after the first application and 3 after the second application. Six trees per plot were sampled for adults by conducting a standard “tap” sample made by tapping a randomly selected branch three times and counting insects that fell onto a white plastic clipboard. This was done in two locations on each sampled tree. Nymph populations were assessed by collecting 12 randomly selected shoots per plot and counting nymphs using a stereomicroscope in the laboratory. Data were square root (+0.5) transformed and analyzed using Proc GLM. Treatment means were separated using LSD (P = 0.05).

At 3 and 6 days after the first spray and 3 days after the second spray, ACP adult numbers were significantly reduced in all treated plots compared to untreated control (Table 1). By 7 and 14 days after the second spray, none of the treatments caused significant reductions in ACP adults compared to the untreated control. Comparisons across all evaluation dates for plots treated with Barrett 30 revealed a general trend towards reduced adult ACP populations following applications at a rate of 1% or 2% compared to 0.5%, but no cases where 2% or 4% resulted in statistical reductions compared to 1%. For nymphs, populations at 3 days after the first spray were 21% to 53% lower in treated plots, though these reductions were not statistically significant (Table 2). At 6 days after treatment, Micromite + 435 oil and Barrett 30 at 2% treatments had significantly less nymphs per shoot than the untreated control. At 3 days after the second spray, treatments of Micromite + 435 oil and Barrett 30 at all three rates had shoots with significantly less nymphs than shoots in the untreated control but the treatment effect was not observed at 7 and 14 days after treatment (Table 2).

Barrett 30 at the 4% rate caused severe burning of the new flush and after the second application. Severe leaf drop of both old and young leaves also occurred at this rate. Some leaf drop was observed at 2% but no visual phytotoxic effects were apparent at the 0.5% and 1.0% rates.

This research was supported partly by industry funding.