University of Illinois

No. 2/April 4, 1997

Black Cutworm Moths Make an Impressive Early Showing

Migrating black cutworm moths exploded into Illinois during the last 2 weeks of March. So far, volunteers in 34 counties have reported first captures of moths in pheromone traps. Cooperators indicate that moths are present from southernmost Alexander County to McHenry County in northern Illinois. To east to west distribution also is impressive, with moths commonly observed from Adams to Vermilion counties. This early and wide distribution of moth captures is significantly different compared with 1996. Intense captures of moths (9 or more moths caught over a 1- to 2-day period) occurred in Alexander (March 26), Macoupin (March 29), and Randolph (March 24) counties.

Projected heat accumulations provided by Bob Scott and Steve Hollinger, Illinois State Water Survey, indicate that cutting of corn plants could occur as early as April 28 for Alexander County and April 30 for Randolph County. Cornfields are susceptible to cutting injury when plants are in the 1- to 4-leaf stage of development and black cutworm larvae have reached the fourth larval instar. Fields most susceptible to potential injury are typically infested with winter annual weeds. It's important not to react to this information by assuming that an insecticide should be applied at planting to control cutworms. Most cornfields never require a treatment for black cutworms. It is to be hoped that by knowing when cutting might occur in your area of the state, timely scouting of fields can take place, and rescue treatments applied if needed.

Last year, a trial was established to evaluate the performance of planting, preemergence, and rescue treatments for black cutworm control at the University of Illinois Foundation Shaw Farm located near Urbana. Due to the unfavorable spring weather, the test was delayed until the fall. The study was conducted by artificially infesting black cutworm larvae into confined barrier areas. The barriers consisted of steel partitions (5 inches high by 6 feet long) that were embedded in the soil to a depth of 1 inch. The test arenas were placed in the field on September 16 after corn plants had reached the first-true-leaf stage. Fifteen third to fourth larval instars were placed into barrier arenas on September 17. Planting-time treatments and preemergence treatments were applied on September 6 and 9, respectively Rescue treatments were applied on September 18, roughly 24 hours after infestation. A total of 1.3 inches of rain fell between the application of rescue treatments and the final sampling date. The areas within the barriers were kept weed free throughout the study by hand weeding. The cumulative number of cut plants in each barrier arena was determined on September 20 and 24, and October 1 and 8. These dates corresponded to 3, 7, 10, and 14 days after the infestation had occurred. The results for some of the compounds tested are presented in Table 1 below.

Rescue treatments have consistently outperformed planting-time insecticide applications for black cutworm control in our efficacy trials. This finding holds true not just for 1996. It can be argued that the use of barriers and artificial infestations offers an inherent advantage to rescue treatments as compared with planting-time treatments. However, the bottom line to the story is that rescue treatments represent a responsible and effective pest management strategy for this insect pest. Producers are better off to keep their money in their pockets and invest in rescue treatments only as needed. Remember, black cutworms are referred to as occasionalinsect pests in entomology textbooks. There's a reason for this.

Mike Gray, Extension Entomology, (217)333-6652

Table 1. Cumulative mean percent ofcorn plants cut per barrier by black cutworm larvae 3, 7, 10, and 14 daysafter manual infestation (DAI), Urbana, Illinois, 1996.


Mean percent of cut plants

 Insecticide  Rate 1 Application 3 DAI 7 DAI 10 DAI 14 DAI
 Pounce 3.2EC 0.1 rescue 5.51 5.51 5.51 5.51
 Lorsban 4E 1.0 rescue 15.06 16.84 16.84 16.84
 Lorsban 4E 0.5 rescue 16.67 24.17 26.25 26.25
 Force 3G 0.13 plt. band 2 21.67 26.67 26.67  26.67
 Lorsban 4E 1.0 plt. band 33.33 33.33  33.33 33.33
 Pounce 3.2EC 0.1 preemerge 23.33 33.33 35.00 35.00
 Warrior 1EC 0.02 preemerge 20.00 31.67  35.00 35.00
 Aztec 2.1G 0.15 plt. band 27.44 35.77 35.77 39.10
 Lorsban 15G 1.3 plt. band 35.00 40.00  41.67 41.67

1 All rates are specified as lb (AI) per acre, based on 30-inchrows.
2Applied at planting in a 7-inch band.