Do I Really Need a Special Sprayer for Sweet Corn Caterpillars? Rick Foster Department of Entomology Purdue University
Corn Earworms Primary pest of sweet corn in the Midwest Overwinter at some level in most of Indiana Migrate north from southern locations; migration can occur any time depending on weather patterns First generation (June) is usually fairly small Second generation (August) is usually very large Sweet corn harvested in late August and September is usually severely attacked by corn earworms
Corn Earworm Biology Females prefer to lay eggs singly on green silks Eggs hatch in about 3 days, depending on temperatures When eggs hatch, larvae crawl down silk into the ear tip Larvae do little or no feeding until they are inside the tip of the ear Adult activity can be measured with pheromone traps
General Management Strategy A contact insecticide must be present on the silk between the egg and the tip of the ear prior to egg hatch Problem is compounded by the growth of silks (1 inch per day) so that each day there is unprotected silks Because of silk growth, multiple applications are required
What Determines the Level of Control You Will Receive? Correct insecticide Correct timing Correct placement
Correct Insecticide 2017 Trial Results Insecticide Rate per Acre % Clean Ears Damaged Kernels/Ear Earworms/ Ear Untreated --- 7.7 b 24.0 a 1.07 a Coragen 5 fl. oz. 85.5 a 1.4 b 0.13 b Radiant 6 fl. oz. 83.0 a 2.0 b 0.17 b Mustang Maxx 4 fl. oz. 75.9 a 4.0 b 0.28 b Warrior 1.92 fl. oz 73.0 a 4.4 b 0.28 b Entrust 2 oz. 66.7 a 5.3 b 0.34 b Helicovex 1.25 fl. oz. 27.0 b 16.5 a 0.84 a
Decision Rules/Correct Timing Insecticide should be applied if: Green silks are present At least one moth per night is being caught in pheromone traps for early and late plantings At least 10 moths per night are being caught in pheromone traps for plantings that are silking at the same time as the surrounding dent corn Intervals between sprays will vary between 2 and 5 days depending on trap catch and temperatures Applications can cease when most of the silks are brown
Correct Placement What is the best way to get insecticide on the silks? Choices: Boom sprayer Boom sprayer with drop nozzles Airblast sprayer Airplane Helicopter Backpack sprayer
2017 Sprayer Type Experiment Obsession sweet corn was planted on July 7 Plots were 8 rows by 30 feet with four replications Treatments were: Untreated control Boom sprayer with drop nozzles Boom sprayer with no drop nozzles Airblast sprayer Applications were made on August 25, 28, 31, September 5 and 8. Water sensitive cards placed on silks to measure coverage
2017 Sprayer Type Experiment At harvest (Sept. 18-19), 25 ears from each of rows 3 and 6 were harvested from the untreated control, boom with drops, and boom only plots. 25 ears were harvested from each of the 8 rows of the airblast plots
Boom Sprayer with Drop Nozzles Boom covered four rows with one nozzle over the top of each row and two drop nozzles for each row, angled slightly upward 12 total nozzles for 4 rows 26.7 gallons per acre 30 psi TXVS-12 conejet nozzles
Boom Sprayer 9 nozzles spaced every 15 inches so there was one nozzle over each row and one offset 15 inches from each row 23.1 gallons per acre 30 psi TXVS-12 conejet nozzles
Airblast Sprayer John Bean 458T Pressure: 350 psi Ground speed: 4.5 mph GPA: 40 at 20 foot swath Nozzles: Turn over discs (John Bean) Tip: Ceramic whirl plates and discs Nozzles and air baffles oriented straight into the crop
Coverage: Boom Sprayer with Drops 1 2 3 4
Coverage: Boom Sprayer No Drops 1 2 3 4
Coverage: Airblast Rep 1 1 2 3 4 5 6 7 8
Coverage: Airblast Rep 2 1 2 3 4 5 6 7 8
Coverage: Airblast Rep 3 1 2 3 4 Missing 5 6 7 8
Coverage: Airblast Rep 4 1 2 3 4 5 6 7 8
Spray Coverage Sprayer Type Boom with drops Boom no drops Airblast Coverage 207 a 150 ab 47 b
Spray Coverage by Row with Airblast 140 120 100 80 60 40 20 0 1 2 3 4 5 6 7 8 Row
Earworm Control Treatment Percentage Clean Ears Damaged Kernels/Ear Earworms/Ear Untreated 50.5 9.2 a 0.58 a Boom with Drops 89.4 0.8 b 0.08 b Boom with No Drops 82.0 1.9 b 0.18 ab Airblast 76.6 2.7 b 0.25 ab
Airblast Sprayer: Earworm Control by Row Row Percentage Clean Ears Damaged Kernels/Ear Earworms/Ear 1 99 a 0.2 a 0.01 a 2 100 a 0.0 a 0.00 a 3 96 a 0.4 a 0.04 a 4 92 ab 0.6 ab 0.06 a 5 70 bc 3.5 b 0.34 b 6 62 cd 4.7 b 0.40 bc 7 52 cd 5.8 b 0.50 bc 8 42 d 6.3 b 0.63 c Boom with Drops 89.4 0.8 0.08 Untreated 50.5 9.2 0.58
Disclaimer For each of the sprayers, there are a number of variables that could be modified that might change the results
Take Home Messages In our study, a boom sprayer with drop nozzles provided better earworm control than a boom sprayer without drop nozzles In our study, both boom sprayers provided better earworm control than an airblast sprayer over 8 rows In our study, an airblast sprayer provided better control than either of the boom sprayers in the first 4 rows In our study, an airblast sprayer did not provide acceptable control after more than 4 rows The use of water sensitive cards on the silks provided an accurate prediction of the level of earworm control
Questions?