Foliar insecticide treatments in tomato for lepidoptera larvae control, 2022

In Feb 2022, land preparation for the field site began with 500 lbs of 10-10-10 (per acre) fertilizer incorporated into Tift pebbly clay loam 6-foot beds, which were then covered with white plastic mulch. On 20 Jun, tomato plants, hybrid ‘Longboat’ (TYLCV resistant), were transplanted in a single row and maintained with standard cultural practices at the Lang-Rigdon Farm, Georgia Coastal Plain Experiment Station in Tifton, GA. Treatment plots were measured to 60 ft in length and replicated 4 times with all tomato plants staked and tied. The fungicide Manzate (mancozeb) was sprayed over the top, while Ridomil Gold (mefenoxam) was injected into the drip system to reduce foliar disease. Drip irrigation occurred weekly with 30 gal/acre of 7-0-7 liquid fertilizer injected every other week. Weekly pest scouting commenced on 8 Jul using a 30-s inspection per plant method across 10 whole plants per plot. Leaf samples for whitefly adults were counted from 3 leaves (one per plant, 3–6 leaf nodes) for 10 plants per plot using the leaf turn technique. An insecticide application of 53 gallons/acre spray volume, using 5 TX 18 nozzles per row and 2.5-gallon mixture per treatment for sprays, occurred on each of these days, 3, 10, 23, 30 Aug, and 6, 13 Sep, throughout the test period. The spray injection rig was done at 25 psi for 7 min and a 30-min wash in-between injections. Only a single harvest damage rating on 27 Sep was recorded. Lepidopteran feeding, the most significant damage category recorded, caused damage directly or indirectly. Thus, we only divided the USDA standard tomato sizes into “clean” (non-lepidopteran damage) and lepidopteran-damaged fruit. The yield and scout data were analyzed using GLM and LSD tests mean separation (SAS Institute 1990).

Beet armyworms and tobacco hornworms were mainly detected during this test (38% and 26%, respectively, of the Lepidoptera larvae overall). Overall, the incidence of beet armyworm and tobacco hornworm was 0.7 larvae per 10 plant samples, well above the previously published treatment threshold of 1 larva per 40 plants in Georgia tomato. There were significant treatment effects on overall lepidopteran larvae (Table 1), but no significant separation in individual treatments. No significant differences were detected between the various treatments with and without the adjuvant Silwet. Proclaim 5SG (emamectin benzoate) 2.8 oz/a + Silwet 0.1% v/v alone performed marginally better vs. the no adjuvant counterpart over all sample dates (Table 1, last column). Across all sample dates, the lepidopteran larval count was lower in all treatments, i.e., Proclaim, Coragen (chlorantraniliprole), and Radiant (spinetoram), compared with the check; however, the only significant effect on tomato yield was that the Radiant treatment yielded more clean fruit and overall fruit weight than the check (Table 2).¹

Footnotes