No. 2/April 3, 1998
Intense Black Cutworm Moth Capture Reported
An intense capture of black cutworm moths was reported by Mike Roegge, crop systems educator with the Adams/Brown Extension unit in Quincy, during the weekend of March 28 and 29. Captures of moths have been common in east-central Illinois. Aaron Grote, with United Prairie located in Ivesdale, Champaign County, reported that cooperators have been regularly capturing moths since March 26. Bottom line--the moths are here! We will report in later issues of this Bulletin heat-unit accumulations for the different regions of the state.
What is an intense capture? An intense capture occurs when nine or more moths are caught during a 1- to 2-day period. Following an intense capture, it is important to keep track of heat units. After 300 heat units (base 50 degrees F) have accumulated (beyond an intense capture), black cutworm larvae have the potential to begin cutting plants. Black cutworm larvae must reach the fourth-larval instar to begin their cutting activity. Before this stage of development, early instars feed on leaves, creating small holes on the leaf surface. Cornfields most susceptible to cutting and economic losses are those with plants at the 4-leaf stage of development.
Most fields in Illinois never require an insecticide treatment for black cutworms. However, certain fields are at greater risk of injury by thisinsect pest than others. Black cutworm moths are attracted to weedy areas in fields.
The availability of actively growing (green) weeds creates very attractive ovipositional (egg-laying) sites for moths. Soybean residue is more attractive than corn residue, and bare soil is unattractive for oviposition. Corn grown in rotation with wheat also is at greater risk from cutworms, especially if weeds were present during the egg-laying activities offemale moths.
Certain weeds are more attractive than others when it comes to egg laying by black cutworm moths. Fields that have winter annual and perennial weeds prior to final tillage and planting are most at risk to an infestation of black cutworms. Those fields with common chickweed,mouse-eared chickweed, bitter cress, shepherd's purse, yellow rocket, and pepper grass are likely candidates for the development of a black cutworm infestation.
A rescue treatment may be warranted in commercial corn when at least 3% of the plants are cut and larvae are still present. In seed-production fields, rescue treatments may be needed if 3 to 5% of the plants have leaf feeding and two or more cutworms are found per 100 plants. This threshold is based upon the premise that for each 1% of plants with leaf feeding, 3 to 5% of the plants may be subject to cutting at a later date.
In general, rescue treatments have performed better, compared with insecticides applied before or at planting. Please take a look at our black cutworm trial (Table 1) established in 1997. Many of the compounds performed very well in our experiment despite the fact that we infested the barriers with plenty of third and fourth instars, stages of the cutworm that are just beginning to pose a cutting threat. Also, please note that the transgenic hybrids did not perform in this trial. In fact, cutting was typically more severe than in the control (Pioneer 3489). All five Bthybrids contained the Cry9C protein. Finally, because this trial was experimental in nature, please consult product labels for information on rates and methods of application for insecticides you may choose to use.
Table 1. Cumulative mean percentage of corn plants cut per barrier by black cutworm larvae 7, 15, 20 days after manual infestation (DAI), Urbana, Illinois, 19971
|Mean Percentage of Cut Plants|
|Insecticide||Rate2||Application3||7 DAI||15 DAI||20 DAI|
|Regent 4SC||0.13||microtubes at planting||13.33||15.00||16.67|
|EXP83 Bt||---||at planting||18.33||20.00||20.00|
|97VCE Bt||---||at planting||21.49||25.06||25.06|
|97VCB non-Bt||---||at planting||17.82||25.63||25.63|
|EXP85 Bt||---||at planting||25.00||26.67||26.67|
|97VCB Bt||---||at planting||28.33||31.67||31.67|
|97VCE non-Bt||---||at planting||32.50||37.50||35.95|
|EXP83 non-Bt||---||at planting||36.67||45.00||45.00|
1 Barriers were infested with 15 black cutworm larvae (third and fourth instars) per barrier on May 29.
2 All rates are specified at lb(AI)/acre, based upon a 30-inch row spacing.
3 Pre-plant treatments were applied on April 28, planting-time treatments on May 15, pre-emerge treatments on May 21, and rescue treatments on June 1.
Mike Gray (firstname.lastname@example.org) and Kevin Steffey (email@example.com), Extension Entomology, (217)333-6652