Pests

Identifying late-season caterpillars feeding in corn ears

By:  Christina DiFonzo, Michigan State University Extension, Department of Entomology

In the last two weeks, I’ve had many calls, texts and pictures of caterpillars in corn ears (hey, at least some fields have ears). It is important to correctly identify which species are feeding in infested fields, not just to make the right management decision but to be sure that Bt traits are working as expected.

The body surface of corn earworm is rough with small, black spines and dark spots. It varies in body color (brown, yellow, pink, green) and has prominent colorful striping. Photo credits: C. DiFonzo, C. Bauer and M. Roth.

The body surface of corn earworm is rough with small, black spines and dark spots. It varies in body color (brown, yellow, pink, green) and has prominent colorful striping. Photo credits: C. DiFonzo, C. Bauer and M. Roth.

I made a tip sheet with pictures, “Identifying late-season caterpillars feeding in the ear,” with helpful ways to identify the three lepidoptera species that I am getting questions about. Some of the pictures came from FonzFacts recipients.

Of the species of concern, western bean cutworm and European corn borer are expected. Western bean flight peaked last week; catch was high in some traps, low in others. Both egg masses and larvae are present in fields. Western bean cutworm can eat through all Bt traits, except the Vip3A protein. Ears in Agrisure Viptera corn should be clean or nearly so compared to other hybrids.

Meanwhile, corn borer moths are starting to fly. Thus far, my trap counts are low. Second generation infestation and feeding may occur in non-Bt and organic corn, and there are many reports of that this year. However, it would be very concerning to find a European corn borer infestation in Bt corn beyond a few refuge plants. Contact a company agronomist and Michigan State University Extension educator if you have such a field so that it can be documented and samples taken. See the Great Lakes and Maritime Pest Monitoring Network website for trap counts for these two species.

Corn earworm has been an unexpected surprise this year in Michigan, surrounding states and Ontario. I confess that I’ve ignored this insect for 20 years because it’s been hard to find in field corn in Michigan after the widespread use of certain Bt traits. Earworm overwinters in the southern U.S. where it is a regular pest of cotton and corn. The first surprise this year was that it moved northward much earlier than normal—in June rather than mid- to late July.

Another surprise are infestations in Bt hybrids that should control it, specifically those with the Cry1A.105 plus Cry2Ab2 combination found in VT Double Pro, VT Triple Pro and SmartStax. It’s true that earworm resistance to Cry1A.105 x Cry2Ab2 was found in sweet corn, and recently reported in collections from field corn in North Carolina; entomologists in the south are concerned about earworm resistance increasing to the both toxins. The earworms infesting our fields this summer originated in the south. As my colleague Pat Porter from Texas says, “You are inheriting our moths,” (and by default, any resistance issues they carry).

But it is a false notion that just because there are resistant earworms in the south, infestation of VT Double Pro corn in Michigan is “normal” and not worth investigating. I’ve never seen a case of heavy earworm infestation in a VT or Smartstax field, ever, so it isn’t “normal” to me. An explanation that I have heard is that Cry1A.105 plus Cry2Ab2 is labeled only for “suppression” of earworm. This is not correct. A quick googlization of VT Double/Triple Pro or SmartStax shows that earworm is still listed as a pest controlled, and a phone call to entomologists in the south confirms the same information in that region. Under normal circumstances, Cry1A.105 x Cry2Ab2 should control earworm. In addition, the Vip3A protein should provide excellent control, and observations from the field so far show that is the case.

The bottom line is if you are scouting fields and finding caterpillars, be aware that they could be earworm. If it’s a Bt hybrid, check the trait package to determine which species should be controlled. If the damage levels are unexpected, then it’s important to investigate and try to explain why. Furthermore, companies are under an obligation to document and report cases of unexplained damage, and take samples if necessary. If something doesn’t look right, contact a company agronomist and an MSU Extension educator sooner rather than later so the field can be visited.

Japanese Beetle Treatment Guidelines

BY: John Obermeyer, Purdue Extension

News flash … Japanese beetle have been emerging and can be seen throughout the state on corn and soybean plants. OK, not that news worthy. How about … some areas of state are seeing tremendous numbers of beetles while some areas aren’t that excited. Again, old news, as this happens every year. Here is a headline sure to grab attention … Japanese beetle – their presence and damage is usually perceived worse than it is. Please refer to the following treatment thresholds.

Field Corn: Japanese beetle feed on corn leaves, tassels, and silks. Generally, leaf and tassel feeding can be ignored. If beetles are present and feeding on corn silks, an insecticide should be applied only if on average the silks are being cut off to less than 1/2 inch before 50% pollination has taken place. This rarely happens on a field-wide basis. Don’t be overly excited by this pest’s tendency to clump on a few ears within an area and eat the silks down to the husks. With sufficient soil moisture, silks will grow from 1/2 to 1 inch per day during the one to two weeks of pollen shed. Silks only need to be peeking out of the husk to receive pollen. Besides, beetles are often attracted to silks that have already completed the fertilization process even though they are still somewhat yellow. Check for pollen shed and silk feeding in several areas of the field, Japanese beetles tend to be present only in the outer rows of the field. Don’t be influenced by what you think you may see from windshield surveys! Get out into fields to determine beetle activity. Be sure to walk in beyond the border rows before drawing any conclusions.

 

Japanese beetle “parties” on selected ears may give false impressions of pollination problems for the whole field

Japanese beetle “parties” on selected ears may give false impressions of pollination problems for the whole field.

 

Soybean: Soybean plants have the amazing ability to withstand considerable leaf removal (defoliation) before yield is impacted. The impact of defoliation is greatest during pod fill because of the importance of leaf area to photosynthesis, and ultimately to yield. Therefore, approximately 15-25% defoliation from bloom to pod fill can be tolerated before yields are economically affected This defoliation must occur for the whole plant, not just the upper canopy. The beetles often congregate in areas of a field where they are first attracted to weeds such as smartweed. Typically, if economic damage occurs, it is only in these areas. Therefore, spot treatments should be considered. Don’t be overly alarmed by these bright, iridescent beetles that feed on the top canopy of the soybean plants. Consider that as they feed their defoliation allows for better sunlight penetration into the lower plant canopy!

 

Japanese beetle will move to new feeding locations, notice how the new growth of these plants have very little damage

Japanese beetle will move to new feeding locations, notice how the new growth of these plants have very little damage.

 

Kill the beetles to prevent grubs?: Japanese beetle develop from grubs that fed on organic matter and/or the roots of plants last fall and this spring. Therefore, it seems logical that killing adult beetles one year should prevent grub damage the next. At least some farmers have explained this to me to justify sub-economic damage in a field. However, it simply doesn’t work that way. Entomologists for decades have been trying to understand this fickle creature. Basically, the adults feed, mate, and lay eggs when and where they want to. The grubs are just as unpredictable. Research attempts to correlate grub presence to crop damage have been inconclusive. Damage does occur, but we are just not usually able to predict when or assess how much. Consider that each beetle mates and lays eggs several times during its oviposition period. To prevent egg laying in a field, one would need to treat multiple times during July and August, which is not economic or practical. If you are wondering, seed-applied insecticides, i.e., Poncho and Cruiser, provide some suppression of white grubs

Bagworms

By Ed Lentz, OSU Extension

The continuous rain this spring may cause us to forget that insects are still active. Often these insects may be controlled if insecticides are applied at the correct time. One of these insects that has reached that critical time for control are bagworms.
Bagworms can be a serious problem in town and on the farm. Bagworms can take out 20 foot tall trees in rural windbreaks, large evergreens in yards, and smaller shrubs around homes and businesses. .
Bagworms began to hatch from their protective cocoons several weeks ago. A few bagworms do little harm. However, many bagworms on a shrub or tree can cause excessive defoliation. A severe infestation may kill the plant within one or two seasons.
Bagworms do the most damage on arbor vitae and cedars, but will attack pines, junipers, spruce and at least 130 other trees and shrubs. They may not harm the deciduous trees, but they spread from these trees to more susceptible evergreens.

Bagworm

Larvae will begin feeding and start to build a camouflage bag with plant parts within a few weeks after hatching. They will continue to feed and eventually build a bag that is one to one and half inches long. Any dried and gray bags seen at this time will from last year. However, upon close examination, larvae can be seen with small new bags
Most of the emerging larvae will feed on same tree that contained their overwintering home. Others will form silk threads and allow the wind to carry them to adjacent trees. This is the most common way that bagworms spread from tree to tree in a windbreak planting. Rain events may have diminished the movement from tree to tree.
The most effective control of bagworms is to apply insecticides about two weeks after the first bagworms begin to hatch. This insures that all of the eggs have hatched from overwintering bags on the tree and the insects are in the crawler stage.
The Hancock County area has reached that two week point and spraying should begin on infected trees and shrubs. Spraying insecticide is an effective control until the larvae have made bags about ¾ inch in length, which generally occurs in late July.
Most foliar applied insecticides should provide effective bagworm control especially when applied to small larvae. One may want to consider the biological insecticide Bacillus thuringiensis var. kurstaki (Bt). Bt products are more environmentally friendly since they are selective for larvae of many moths, such as bagworms, without harming beneficial insects.
However, Bt products have short residual activity and may require more than one application for control. Also, complete vegetative coverage is important for Bt products since the worm has to actually ingest the insecticide while feeding to be effective.
Bt products would work well at this time. However, if spraying is delayed until mid-July, one may need to switch to more traditional insecticides. The non-Bt products generally are more effective since the product only has to come in contact with the larvae. Whatever product is selected make sure it is labeled for bagworms and the tree or shrub.
Control will become more difficult once the larvae stop feeding and attach their protected mobile home to the tree. Hand removal becomes the only effective method of elimination at this time.
Bagworms generally attach their protective home to a stem around mid-August and then pupate inside. About a month later male moths will emerge and mate with females in the bags.
Females never leave the bag. After mating a female will lay 300 to 1000 eggs in the bag, die, and form a mummified body around the egg mass for extra winter protection.

Bagworm

Eggs will hatch the following spring to start the next generation. Tiny emerging larvae (crawlers) will start to emerge late May and early June depending upon air temperature and accumulating heat units.
Bagworms have become more a problem in recent years for our area. It was thought that numbers had increased from milder winters and warmer springs. However populations have continued to increase even after severe winter conditions.
If not controlled, bagworms can eventually kill a row of large trees in windbreaks, evergreen borders and valuable landscape plants. For more information on bagworms, visit the following websites: http://ohioline.osu.edu/factsheet/HYG-2149-10 and https://extension.entm.purdue.edu/publications/E-27/E-27.html