COOPERATORS: Upper Coastal Plain Research Station personnel
Location: Upper Coastal Plain Research Station, Rocky Mount, NC
Soil Type: Nahunta sandy loam
Variety and Tillage: ST 474; conventional till; ripped and bedded
Planting Date: May 14, 2003
Row Spacing: 36 inches
Previous Crop: Corn
Insecticide: Temik 15G, 5.0 lb. product at planting for thrips control.
Experimental Design: Plots were 4 rows by 40 ft., with 10-ft. alleys and 4 replications arranged in a RCBD.
Data Analysis: All field data were entered into Gyllings ARM 6.1 software and analyzed via ANOVA and DMRT with LSD (0.05) values shown in the tables.
Application Information: Treatments were applied with a CO2-powered back pack sprayer calibrated to deliver 10.0 gpa @ 70 psi with 1 Spraying Systems TX-8 hollow cone nozzle per row. An initial overspray of Orthene was made on July 24 to enhance subsequent bollworm establishment. An early application was also made to each of the four biological insecticides (Dipel, Condor, Deliver, and Lepinox) on July 31. All treatments were sprayed on August 4, 12, and 21.
Sampling: On August 20 , following the August 4 and 12 applications, 25 squares and 25 bolls were randomly-selected per plot (100 each per treatment), and examined for live bollworms and their damage. On August 27, following the third and final August 21 application, 25 bolls per plot (100 per treatment) were examined for live bollworms and boll damage.
Bollworm:Budworm Ratio: Forty bollworm/budworm larvae were taken from the outer rows of the untreated check on August 20 and examined for species determination.
Bollworms constituted 83% of the Helicoverpa/Heliothis population in the untreated check cotton on August 20. Therefore, tobacco budworms may have been a slight contributing factor in the results.
At the August 20 fruit assessment, all of the non-biological treatments were inseparable statistically, but showed significantly less square damage the check or the biologicals. This difference was the same for boll damage on this date. Bollworm pressure was high by this time, attested by the 56% bollworm damage to squares and the 29% boll damage and 13% live bollworm in bolls.
On August 27, all of the non-biological treatments were inseparable statistically for boll damage, although a trend toward higher boll damage was apparent with Steward alone, Karate Z, and Tracer. All of the biological insecticides except one (Dipel) showed boll damage inseparable from the 51% boll-damaged untreated check.
Very few significant yield differences were found between the non-biologicals. The yield loss of the Asana + Bidrin tank mix compared to Asana alone may be explained by slightly higher disruptive impact of the organophosphate in the tank mix in a test of high bollworm and low plant bug and stink bug pressure. Bidrin plus pyrethroid tank mixes continue to an option here in situations of bollworm pressure in association with high stink bugs levels, particularly brown stink bugs.
The high bollworm levels common to a significant number of late season insecticide screening tests carried out here and at other North Carolina make locations often translates into poor bollworm control liquid Bt formulations. Of the products in this class evaluated, only Dipel showed significantly better yields than the untreated check; however Dipel also sustained numerically greater boll damage than the other three biologicals.