Insecticidal Control of Sugarcane Aphid, 2015 *

Sugarcane aphid, Melanaphis sacchari (Zehtner), was first observed as pest of sorghum in the United States in 2013 in Texas. It has since spread throughout the Southeastern United States. Sorghum ( Sorghum bicolor (L.) Moench) ‘RV 9782’ (Terral Seed, Rayville, LA) was planted 31 Jul 2015 at the University of Florida’s Everglades Research and Education Center in Belle Glade, FL, atop raised beds on 30-inch centers in a Lauderhill Muck soil using a John Deere Max Emerge vacuum planter at 2.5 in spacing using sorghum plates. Four, 4-row blocks were planted 20 ft apart to reduce potential spray drift. Liquid starter fertilizer (300 lb/ac 11-37-0, N-P-K) was applied at planting in the seed furrow. Atrazine (2 qt/ac) was applied at-plant for pre-emerge weed control. Tecmangam (4 lb/ac) was applied at 2–3-wk intervals beginning 4 wk post plant due to the high pH (7.9) of the soil. Cultivation and side dressing with liquid fertilizer at 300 lb/ac (19-0-0, N-P-K) occurred on 14 and 21 Aug. Additional herbicide (Atrazine at 2 pt/ac and Prowl H2O at 3 pt/ac) was applied for layby weed control on 21 Aug. Methomyl (16 fl oz/ac) was applied 2 Sep to reduce aphid predator and fall armyworm populations. Headline (12 fl oz/ac) and Bravo Weatherstik (1 pt/ac) were applied on 21 Sep to protect and control against multiple foliar fungal diseases. Weeds in the unplanted areas among blocks were controlled using herbicides and mowing.

Plots (4 rows × 27 ft long with 3 ft planted, untreated buffers) were established after emergence. The trial was arranged in a randomized complete block design with four replications for each of the six treatments ( Table 1 ). The crop was scouted weekly for M. sacchari beginning 27 DAP. The fifth leaf from the top-visible leaf collar (TVD+6) was used consistently for this trial, as pre-sampling in the field indicated it to be the most likely leaf to have aphids. Aphids were counted on five sample leaves per plot from the center two rows of each plot. At 27 DAP, an average of 10.3 aphids were found on sampled leaves. At anthesis (70 DAP), aphid numbers had increased to 33.4, finally reaching the treatment threshold. On 16 October 2015, treatments were applied in water at 23 gpa using a high clearance, self-propelled sprayer. Teejet 8003 flat fan nozzles were used and nozzle spacing was 15″. Two nozzles on 15″ drops and angled at 45° were arranged at 30″ intervals along the boom to improve lower canopy coverage. Posttreatment counts were performed 10 and 27 DAT. ANOVA was performed using natural-log transformed means. Post hoc means separation was evaluated if ANOVA indicated a significant ( P  < 0.05) source affect (i.e., block, treatment). Results in Table 1 are presented using untransformed means.

At 10 DAT, aphids in the untreated plots had increased nearly 10-fold, while aphids were reduced to means of less than six per leaf in four of the treatments ( Table 1 ). Transform, Sivanto, Centric, and Endigo all prevented the 10× increase observed in the untreated plots. Lorsban Advanced did not differ from the untreated plots. At 27 DAT, M. sacchari numbers had surged in all treatments ( Table 1 ). There was very significant variation among treatments and blocks due to large variations in predator densities and entomopathogenic fungi. Aphid density in the Sivanto plots was significantly lower than the other treatments at this second posttreatment sample date suggesting that this treatment provided longer residual control than the other treatments.

Author notes