Foliar Sprays of Labeled and Experimental Insecticides to Control Asian Citrus Psyllid on Grapefruit, 2017

Asian citrus psyllid (ACP) is the key pest in Florida citrus, primarily due to its role as a vector of huanglongbing or citrus greening disease. We conducted a trial at the Southwest Florida Research and Education Center in an orchard of ‘Ray Ruby’ grapefruit trees bud grafted to ‘Smooth Flat Seville” planted in 2013 at a density of 262 trees/acre. We evaluated nine treatments and an untreated check using five tree plots that were organized into an RCB design with four replicates in eight rows, with each treated row (block) flanked by untreated buffer rows. Treatments were applied on 9 Oct 2017 using a Durand Wayland AF100-32 air blast speed sprayer operating at 1.9 mph and 300 psi equipped with three #4 John Beane ceramic nozzles delivering 100 gpa. This trial was conducted on new foliage that grew in response to defoliation by Hurricane Irma on 10 Sep 2017. The density of ACP adults was evaluated 5 days prior to treatment and then adults, nymphs, and eggs were evaluated 3, 7, and 11 DAT. Nymphs (both dead and alive) and eggs were counted on ten randomly selected shoots per plot using a stereomicroscope in the laboratory. The density of ACP adults was assessed on 3 trees per plot using the stem tap sampling method six times on each tree. For each tap, adults were counted on a white plastic clipboard placed under a randomly chosen limb struck three times with a short length of PVC pipe. Data were subjected to ANOVA and means were separated using LSD (P = 0.05).

Prior to treatment the average adult ACP density was 0.33 per tap. All treatments significantly reduced ACP adult density on 12 Oct except for Thyme Guard, Harvanta, and 3106 + AB at the 55- and 11-oz rates (Table 1). Significant adult control on 16 Oct was seen only from the Minecto Pro, Voliam Flexi, and Abba Ultra treatments, and by 20 Oct, no differences were observed. It appeared that there was a great deal of ACP dispersal following the hurricane which may explain the rapid cessation of treatment effects.

Significantly fewer eggs compared with the check were only seen with the Voliam Flexi treatment on 12 Oct and nothing later (Table 2). All treatments reduced nymphs for the 12 and 16 Oct samples except for Thyme Guard and Venerate. There were no differences among remaining treatments. By 20 Oct, all treatments reduced nymphs except for 3106 + AB at the 5.5 oz rate and Venerate. More dead nymphs were seen on 12 Oct with the Minecto Pro, Voliam Flexi, and Thyme Guard treatments compared with the check.

No phytotoxicity was observed. This research was supported by industry gifts of pesticide and funds.