By Keith Waldron and Ken Wise (NYS IPM)
Western Bean Cutworm (WBC) has been moving east from the Great Plains states across the US. It was found in New York in 2009. It attacks corn and dry beans feeding on the kernels and the pods. This pest has been found to reduce yields in dry beans up to 15 percent and research studies have shown that one larva per corn plant can result in 3.7 to 15 bushel per acre loss. In 2010 we started a WBC pheromone trapping network across the state. In 2010 we caught about 700 moths in 65 traps but in 2017 we caught about 35,000 moths in 101 traps. In recent years we have had economic damage from WBC in field corn in Northern and some Western NY fields. In some cases we have measured up to 100 percent ears damaged by larvae. The cryF1 BT and conventional hybrids do not have resistance to the WBC. WBC is going to continue to increase across the state and is starting to become a major new pest of corn. Management options, including transgenic options, are discussed later in this document.
Moths start appearing in late June to early July and peak in population later in July or early August.
- Are brown to grayish
- have a wing-span of a 1-1/2″.
- have a white bar on the edge of forewing
- have two cream-colored spots middle of forewing
- have a boomerang spot near the posterior end of the forewing
Western Bean Cutworm Moth Identification
The moths will mate in late July and start laying eggs on the upper surface of corn leaves. The moths prefer to lay eggs on pre-tassel corn. Eggs when first laid are white and will turn tan over time. When the eggs turn a purplish color they are close to hatching. As the life cycle takes place within one growing season this pest can be a problem in every year of the rotation.
Eggs are white when first laid (Photo by Mike Hunter-CCE)
Eggs turn tan then purple just before hatching-(Photo by Mike Hunter-CCE)
Once the tiny larvae hatch they will eat the rest of the egg shell. These 1st instar will look for shelter in the leaf axil or whorl of the plant feeding on pollen, tassels and silks. All larvae eventually travel to the corn ear to feed on the kernels. The first instar larvae are dark with a black head.
First instar Western Bean Cutworm larvae (photo by Mike Hunter-CCE)
Over time they will turn lighter tan to a light shade of pink. Stripes will develop the full length of the body. There are 6 instars of this larvae. 4th-instar and larger larvae, ½ to 1-1/2 inches long, are readily identified by 2 black “rectangles” behind the orange head, and a generally smooth skin or cuticle (i.e. lacking tubercles, warts, or bumps). The 6th is most conspicuous and often found feeding on mature ears, usually the tip but sometimes the sides.
Mature Western Bean Cutworm Larvae
Entry holes and/or frass are not always visible, so scouting for larvae must include removing husks. Several larvae may be found on a single ear, because these caterpillars (unlike corn earworm) are not cannibalistic. In late summer and early fall, 6th instar larvae drop off the plant and burrow into the soil, where they construct an earthen chamber using salivary gland secretions. Sandier soils allow for larvae to penetrate deeper into the soil profile that increases winter survival and avoidance of tillage implements. They will remain in a quiescent state (pre-pupa) throughout the winter and will pupate and complete development during the following spring and early summer.
Western Bean Cutworm entered the ear of corn
Western Bean Cutworm Life Cycle
WBC Monitoring Methods
Pheromone Trapping Network
This is a group of agricultural professionals that have volunteered to monitor the flight of WBC moths in New York. In 2017 we had 20 people and 101 traps across the state.
Green “Universal” bucket traps are used to trap male moths. These traps are the same type used for trapping black cutworm and armyworm. Traps, WBC specific pheromone lures, insect killing strips, laminated ID card, mounting posts and necessary hardware and monitoring protocols are used to accomplish this task. Pheromone lures should be replaced every two to three weeks. Keep pheromone lures in a freezer until use.
- Traps should be deployed by the second week in June. Traps should remain deployed for 12 weeks.
- Position the trap in a convenient and accessible location along an edge of a corn field (either field corn or sweet corn) or dry bean. Keep the traps at least 30 ft from a hedgerow or woodlot—such habitats could be repellent to the moths.
- Hang trap from a stake so that the trap is approximately 4 feet off the ground.
- Trap should hang freely with stiff wire (like a section of a coat hanger) so that they do not move much in the wind. When traps are hanging they should be as straight up and down as possible to keep water from getting inside.
Pheromone lure placement –
- Place pheromone lure in the capped basket compartment in the top of trap – Take care not to touch the lure itself when placing lures in trap buckets.
- Replace lure every two – three weeks
- Unwrap insecticidal strip (Vaportape) and place in lower portion of the bucket, fasten an edge of the Vaportape with duct tape to keep it from falling out when checking traps.
- Vaportape should not be handled with bare hands (use gloves or forceps)
- One vaportape should last for the duration of the monitoring season. Vaportape should be replaced earlier if you feel it is becoming less effective.
- To report the counts each week use the WBC app we developed. This gives us the GPS location and you enter the number of moths in the trap each week from the field.
- A second option is to report the location of the trap using decimal degree GPS coordinates.
- Please check the traps once a week. Because we are monitoring for an insect of unknown distribution and relative time of appearance, we may record a lot of zeros.
- To report the counts each week use the WBC app we developed. This gives us the GPS location and you enter the number of moths in the trap each week
- A second option is to send data via email to email@example.com (845-677-8223 ext 149). Please report the date the trap was checked and the number of moths caught. Please send a report even if zero moths are captured.
- Please identify and record the crop stage of growth at time of sampling
- The data will be entered into a database and the results made available on the NYS IPM Program Weekly Pest Report (http://blogs.cornell.edu/ipmwpr/#)
- The great majority of the moths attracted to the traps should be western bean cutworm moths, although small numbers of yellow striped armyworm and dingy cutworm moths and other insects have been caught from time to time. For a comparison of similar looking species see: http://www.nysipm.cornell.edu/fieldcrops/tag/pestrpt/pestrpt12/images/Western-Bean-Cutworm-ID-Card.pdf. If unsure of the identification – please send a picture or actual specimen to Ken for identification.
Scouting for WBC
Scouting for WBC should begin with pre-tassel corn. Pre-tassel corn is the preferred host for egg laying WBC moths. Many times this corresponds with peak flights of moths in the last week of July to the first week in August. If you are trapping moths it has been suggested when you reach 100 moths/trap is a good indication you might want to start scouting the field for WBC.
Egg masses will be laid on the upper surface of leaves close to emerging tassels including leaves in the whorl. Check 10 – 20 consecutive plants in at least 5 random locations in the field. Threshold for field corn is an accumulation of 5% of plants with WBC egg masses and/or small larva. The accumulated threshold is when you reach 5% over the times you have scouted. An example might be if you get 3% of the plants that have eggs in week 1 and in week 2 you get 2% more. This add to a total of 5% threshold.
Egg masses are typically laid on upright leaves or those just beginning to lay over. If leaves are oriented towards the sun you can see the egg masses better on the top side of leaf or if looking at the bottom surface of leaves look for a shadow of an egg mass on the upper surface of the leaf.
Shadow of egg mass can be see while scouting (photo by Mike Hunter-CCE)
WBC eggs take ~5 – 7 days to hatch turning purple 1 – 2 days prior to hatch. Newly hatched larvae initially feed on their egg case and then make their way to silks or ears. If suitable food sources are not found the larvae will starve.
First instar larvae that ate their egg case (Photo by Mike Hunter-CCE)
Management of WBC
If a field has reached an economic threshold for grain corn (there is not a threshold for silage corn) an insecticide may be needed for controlling small larvae and eggs. Peak flight of moths are normally the last week in July or 1st week in August. Timing the insecticide is very important in killing the larvae/eggs. It is recommended that 70 to 90% of eggs should have hatched before spraying. Many times a field can have multiple egg laying events that yield different sizes of larvae at the same time. You should spray when a field reaches the 5% threshold. Note that larvae have to come in contact with the insecticide before entering the ear of corn. If the larvae have entered the ear before an insecticide is sprayed it will not control them. Other states suggest that an application should be timed when 90% to 95% of the tassels have developed and still have fresh silks. If the silks turn brown the insecticide is most likely too late.
Having the correct spraying equipment can be an issue relative to the height of corn. Aerial application is not ideal for controlling WBC. Volume of carrier is critical for the spray to penetrate the canopy.
Transgenic options: The only transgenic hybrid gene that has resistance to WBC is Vip3A BT.
Planting dates can effect when the corn plant tassels. It is thought that if the corn tassels before or after peak flight the field may not be an attractive option for egg laying moths.