Control of Chilli Thrips with Botanical Insecticides

Chilli thrips are important pests of roses and other ornamental plants causing feeding damage that results in characteristic leaf and bud scarring, discoloration, and deformation. The objective of this test was to compare efficacy of foliar spray applications of five experimental botanical extracts [GWN-9996, GWN-10285, GWN-10300, GWN-10301, GWN-10302], and AzaDirect (1.2% vol/vol azadirachtin) to that of a commercial standard, Conserve TM (spinosad) against mixed life stage infestations of chilli thrips on container-grown Knock Out ® roses.

The trial was conducted at the University of Florida’s Mid Florida Research and Education Center, Apopka, Florida, from August to September 2014. The study was set up in an RCB design with four replicates (blocks). Plants were grown in 3 gal pots spaced at 0.5 m and watered using a micro irrigation system and fertilized every other month with Osmocote Plus 15:9:12 slow release pellets at the recommended rate. Plants were artificially infested with laboratory reared insects at a rate of 20 per plant, two weeks before insecticide treatments. Applications were made using a 1.75 l, pump action Flo-Master sprayer with a hollow cone nozzle calibrated to deliver 200 gpa. Plants were sprayed to run-off; sprays were directed at foliage terminals, buds and flowers and some runoff made it to the potted soil media. Most of the experimental formulations were not readily miscible in plain water; a wetting agent (Triton X-100) at a concentration of 0.02% vol/vol was used in all treatments. Check plants were sprayed with water alone or water with Triton X-100, to distinguish any effects of the wetting agent. A total of five applications were made at 0, 6, 13, 20, and 27 days after first treatment (DAT). Insect counts were made before the first application and approximately weekly (before each spray) until 35 DAT. Counts were made on thrips life stages extracted in 50 ml ethanol (70% vol/vol) from two randomly selected plant terminals (3–5 leaflets each) per plant. Pest injury in each treatment was assessed by visual inspection of five foliar terminals per plant to identify thrips feeding scars and/or characteristic deformation. Data were subjected to ANOVA and when appropriate, means separated by Tukey’s HSD test at P  < 0.05.

No treatment differences were observed in the pre-spray thrips counts. Only spinosad significantly reduced thrips numbers on plants. Compared with water checks, the number of thrips numbers was reduced by ≥92% in spinosad treatment plants at 6–34 DAT ( Table 1 ). The proportion of foliar terminals with visible thrips damage was also significantly lower in spinosad treatments plants at 12–34 DAT ( Table 2 ). There were no significant differences in the number of thrips or the level of plant injury among the GWN experimental compounds or AzaDirect and the check treatments in this test. The wetting agent did not have a significant effect as the number of thrips and the level of plant injury were similar between water only and water plus wetting agent treated plants. No phytoxicity was observed in this study.

 

Table 1
Treatment/formulation Rate/100 gal Application # thrips lifestages/two terminals


 

Pre 6 DAT 12 DAT 19 DAT 27 DAT 34 DAT 
Water check — 0, 6, 13, 20, 27 DAT 23.3 30.3b 51.8bc 56.0bc 87.5b 50.8b 
Water/Triton-X 100 0.02% vol/vol 0, 6, 13, 20, 27 DAT 25.0 31.0b 53.8bc 25.5b 48.5b 67.5b 
GWN-9996 12 fl oz 0, 6, 13, 20, 27 DAT 26.0 19.3b 37.0b 49.8bc 33.5b 31.3b 
GWN-10285 12 fl oz 0, 6, 13, 20, 27 DAT 41.3 45.0b 48.8bc 68.5bc 80.0b 30.0b 
GWN-10300 12 fl oz 0, 6, 13, 20, 27 DAT 9.3 25.5b 24.3b 66.8bc 58.3b 29.5b 
GWN-10301 12 fl oz 0, 6, 13, 20, 27 DAT 31.0 33.3b 40.8bc 49.0bc 37.5b 42.8b 
GWN-10302 12 fl oz 0, 6, 13, 20, 27 DAT 39.5 37.0b 129.8c 131.8c 126.3b 59.5b 
AzaDirect (1.2%) 16 fl oz 0, 6, 13, 20, 27 DAT 56.5 33.0b 48.8bc 32.5bc 64.8b 23.8ab 
Conserve SC 6 fl oz 0, 6, 13, 20, 27 DAT 24.0 2.3a 0.3a 3.5a 3.0a 2.5a 

Column means with different letters were separated via Tukey’s HSD at P  < 0.05 after log n  + 1 transformation.

Table 2
Treatment/formulation Rate/100 gal Application Proportion of foliar terminals with damage


 

Pre 6 DAT 12 DAT 19 DAT 27 DAT 34 DAT 
Water check — 0, 6, 13, 20, 27 DAT 1.00 0.90ab 0.90b 1.00b 1.00b 0.90bc 
Water/Triton-X 100 0.02% vol/vol 0, 6, 13, 20, 27 DAT 0.90 0.90ab 0.75b 0.95b 0.95b 1.00c 
GWN-9996 12 fl oz 0, 6, 13, 20, 27 DAT 0.90 0.80ab 0.75b 0.95b 0.95b 0.65abc 
GWN-10285 12 fl oz 0, 6, 13, 20, 27 DAT 0.85 0.90ab 1.00b 1.00b 1.00b 0.90bc 
GWN-10300 12 fl oz 0, 6, 13, 20, 27 DAT 0.95 0.65ab 0.95b 0.90b 0.95b 0.90bc 
GWN-10301 12 fl oz 0, 6, 13, 20, 27 DAT 0.80 1.00b 0.90b 0.95b 1.00b 0.85bc 
GWN-10302 12 fl oz 0, 6, 13, 20, 27 DAT 0.95 0.95ab 1.00b 1.00b 1.00b 0.90bc 
AzaDirect (1.2%) 16 fl oz 0, 6, 13, 20, 27 DAT 0.95 0.95ab 0.95b 0.95b 0.85b 0.60ab 
Conserve SC 6 fl oz 0, 6, 13, 20, 27 DAT 0.90 0.55a 0.00a 0.10a 0.15a 0.05a 

Column means with different letters were separated via Tukey’s HSD at P  < 0.05 after arcsine transformation.

Authors: Gary. L. Leibee  Moh Leng Kok-Yokomi  Luis F. Aristizabal  Steven P. Arthurs Celso Morales-Reyes

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