Insecticidal Control of Fall Armyworm on Sweetcorn with BT, Insect Growth Regulators and a Synthetic Pyrethroid, 1998

P.A. Stansly, J.M. Conner, & M. A. Pomerinke
University of Florida/IFAS
Southwest Florida Res. and Ed. Center
2686 State Road 29 North
Immokalee, Florida 34142-9515
(239) 658-3427

CORN (Sweet): Zea mays (L.) ‘Primetime’
Fall armyworm (FAW) Spodoptera frugiperda (J.E. Smith)

Selective insecticides such as endotoxins of Bacillus thruingiensis and insect growth regulators offer the opportunity to better integrate chemical and biological management tactics, but must prove their ability to control damaging pests such as fall armyworm on sweetcorn. To this end, 6 raised beds 32 inches wide and 240 ft long on 6 ft centers were prepared by fumigating with 67/33% methyl bromide/chloropicrin at 300 lbs/acre, and fertilizing with a bottom mix of 700 lbs/acre 5-16-8. A single driptape irrigation line with emitters spaced every 12 inches was laid on the surface of each bed and covered with white polyethylene mulch. Beds were divided into 2, 3 row sets separated by a 15 feet of fallow land with a ditch in the middle. The center row of each 3 row set was left untreated to provide pest inoculum. The remaining 4 rows were divided into 7 single row plots in a RCB design with 4 replications. All beds were planted 31 Aug by direct seeding at 10 inch spacing. Additional fertilizer in liquid form with an analysis of 8-0-8 was injected through the irrigation system to provide a total of 150 lbs nitrogen/acre for the growing season. Four weekly spray applications were initiated 30 Sep using a high clearance sprayer equipped with 2 overhead nozzles fitted with ceramic Albuz ® "yellow" hollow cone nozzles/row with delivery pressure of 200 psi and rate of 22 GPA. Warrior 1 TM at 0.025 lb(ai)/ac was used in place all treatments except the control on 20Oct after ears had formed. A pre-treatment sample on 30 Sep of 20 plants/bed indicated 50% were damaged by FAW. Foliar damage was evaluated weekly for 2 weeks on 10 randomly selected plants/plot after the initiation of the treatments. Damage of the last three leaves in the whorl was assessed on a scale of 0 to 5 where 0 = no damage, 1 = 0 to 1% damage to leaves (total for all three), 2 = 2 to 5%, 3 = 6 to 10%, 4 = 11 to 30%, and 5 is > 30% damage. Ears were harvested 30 Oct from 25 plants in the center of each plot. Ears were evaluated for marketability noting total weight of ears in each category. Categories of fancy, standard or unmarketable were used where fancy = no damage, standard = slight damage to husk or silks only, and unmarketable = damage to ear. Fancy and standard were combined as "marketable". Data was analyzed using a GLM and means separated by LSD.

Fewer FAW were seen on all treated plants compared to the control on both sample dates. Fewest FAW larvae were seen on plants treated with Warrior at 0.025 lb(ai)/ac on both dates and over all dates although not significantly less than Intrepid at 0.05 lb(ai) Mattch or Cry-1X on 6 Oct. or Intrepid at 0.1 lb(ai)/ac or Mattch on 12 Oct. All treatments resulted in significantly more marketable ears (number and weight) than the control except for Intrepid at 0.05 lb(ai)/lb. Most marketable ears were harvested from plants treated with Warrior for all 3 sprays, although not significantly less than plants treated the first 2 sprays with Mattch. Significantly fewer unmarketable ears were harvested from all treated plants compared to the control. Fewest unmarketable ears came from plants treated with Warrior although not significantly less than plants treated the first 2 times with Mattch. Thus Intrepid and the Bts tested provided significant levels of control, comparable (at least in the case of Mattch) with that obtained with the broad-spectrum standard.

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