Kansas State University

search

Extension Entomology

Category: Field Crops

Field crop pest and beneficial organisms.

Wheat Update – armyworms, grasshoppers

–by Dr. Jeff Whitworth

Some fields have already established good stands of wheat this fall. However, there are also some pretty well established fields of volunteer wheat (see pic provided courtesy of Jay Wisby). There have been reports of armyworms and grasshoppers causing concern in some wheat fields that are struggling because of lack of moisture, but the recent cold weather should control both armyworm and grasshopper feeding.

 

 

Alfalfa Update – aphids, potato leafhoppers

–by Dr. Jeff Whitworth

Pea aphids (see pic) are and have been returning, or at least increasing in numbers, to many alfalfa fields throughout north central Kansas. These are primarily cool weather aphids and are usually the last ones still feeding in the fall on alfalfa and the 1st ones in the spring. However, with the advent of cool/cold weather this late fall feeding should be negligible. Potato leafhoppers (see pic), for the most part, have emigrated, or at least are not present in easily detectable numbers, so “hopper burn” (see pic) and its consequences, should not be problematic this fall/winter.

 

Pea aphids

 

Potato leafhopper

 

Hopper burn

 

Alfalfa and Soybeans

–by Dr. Jeff Whitworth

Green cloverworm adults (see pic) have been very common in soybean and alfalfa fields the last couple of weeks, and this has caused concern about potential green cloverworm infestations next year. However, green cloverworm adults are, or have been, migrating to the southern US for overwintering. Thus, since they do not overwinter in Kansas, infestations next year will depend on wherever the adults come back to, so predicting future infestations after overwintering adults return from the southern US are not possible.

Adult green cloverworm

 

 

 

Wheat

–by Dr. Jeff Whitworth

 

Some reports are being received mainly from south eastern/south central Kansas relative to “worms” feeding on early-planted wheat. First, it is usually better to plant wheat as late as possible to help avoid all wheat pests, whether pathogens or insects. The “worms” reported so far, have been either armyworms or fall armyworms, both of which will do about the same type of damage. They feed on leaf tissue and consume more, as they get larger, thus it is best to monitor wheat fields early to detect any larvae while they are still small. They usually do not reduce wheat stands, just remove the leaf tissue, but under stressful growing conditions plant stands may be impacted. Under good growing conditions, plants should be only temporarily affected. However, if there are 8-10 worms per sq. ft. and the worms are small, i.e., less than ½”, treatment may be justified. Remember also, if the leaf feeding continues into the winter it might be caused by army cutworms, which will feed all winter anytime temperatures are over 45 F, and into the spring. However, armyworms and fall armyworms will only feed until the 1st hard freeze, but not through the winter.

 

Sorghum

–by Dr. Jeff Whitworth

Most sorghum throughout north central Kansas is past the soft dough stage, thus not susceptible to “headworms.” However, a few late-planted fields, just coming into the “boot” stage, have sporadic small colonies of sugarcane aphids (SCA) (see pic of SCA’s from Saline and Dickenson counties (pic3)). However, there seems to be significant numbers of beneficials, but these late developing fields should still be monitored as these populations can “explode” quite quickly.

(Pic 3) SCA Colony

 

 

Soybeans

–by Dr. Jeff Whitworth

Most soybeans in north central Kansas, even double cropped fields, are getting to the stage where the pods are hardened enough to protect the beans inside (see picture of pod feeding scar by bean leaf beetles and an adult bean leaf beetle (pic1). Woollybear caterpillars (pic 2) are becoming more noticeable as the soybean leaves start to senesce, the caterpillars are getting larger and thus more visible, and as they move to the ground, looking for overwintering sites.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Sorghum Update—headworms, corn earworms, fall armyworms

–by Dr. Jeff Whitworth

Much sorghum has been treated throughout north central Kansas for headworms (corn earworms and/or fall army worms) and most treatments seem to have been very effective. Again, Sorghum is most vulnerable to headworms from flowering to soft dough, so past the soft dough stage headworm treatment will not be necessary.   The headworm shown (see pic1) has approximately 7-10 more days of feeding before pupating. Still no reports of sugarcane aphid problems – but monitoring should continue because in 2016 insecticide applications were still justified into late September.

 

Pic2: These two larvae were collected from a Heligen treated field. The dead (smaller) larva is obviously pathogen-affected. If Heligen is responsible for the death of this larva, then it looks like the application was well timed to kill the larva before it caused much damage.

Photo by Cooper Wyckoff)

 

 

 

 

 

Soybean Update—podworms, corn earworms, sorghum headworms

–by Dr. Jeff Whitworth

 

Most soybeans around north central Kansas are now well into the mid to late reproductive stages. There doesn’t seem to be much potential for any massive infestations by defoliators and even if there was, as the soybeans get farther along in their development the leaf tissue becomes less needed. However, the direct pests, those that feed on the marketable product, are still very active and some are even increasing. Bean leaf beetle adults are active, feeding on pods, however, there do not seem to be as many as in past years. Soybean podworms, i.e., corn earworms/sorghum headworms, are very common and seem to be increasing in numbers in some areas. Treatment thresholds are usually considered to be 1 larva/row foot, with small worms, i.e., less than ½ inch (see pic1) and they are feeding on the seeds (beans). These larvae feed for roughly 2 weeks before pupating. As the larvae develop larger than the one shown here (see pic 1) they consume more as they get bigger and this feeding will continue for about another 7-10 days at these temperatures

 

 

 

Sorghum Update—cattail caterpillars, sugarcane aphids, headworms

–by Dr. Jeff Whitworth

Cattail caterpillars are still abundant throughout North Central Kansas causing considerable leaf feeding (see pic). Sugarcane aphids are still migrating into Kansas. However, up to now only small colonies and sporadic infestations have been reported. Every report, so far, also has reported good numbers of beneficials associated with and seemingly reducing the colonies that do get established. These aphids will probably continue to migrate into the state for some time yet but, hopefully, the beneficials will keep them under control. However, sorghum “headworm” populations are really becoming active and thus, if fields are treated with a conventional insecticide it will probably kill the headworms, any sugarcane aphids that may come into contact with a treated surface, and most, if not all of the beneficials. Yes, the conventional insecticides used for “headworms” will kill the sugarcane aphids. However, there are some problems with this. 1st, many of the aphid colonies will be on the undersides of the leaves and many of these leaves will be in the middle region of the plant, somewhat sheltered by higher leaves. 2nd, these insecticides are contact insecticides, thus, they need to contact the insect to kill it. However, all the beneficials will be very active searching for aphids, thus they have a high probability of coming into contact with, and being killed by, the insecticide. Then, number 3, the aphids reproduce parthenogenically thus these populations will increase quite rapidly if there are no beneficials hindering them. So, they will recolonize much quicker than the beneficials and thus start stressing the plants. However, “headworms” cause 5% loss/worm/head and they feed on the marketable product, thus if they get to the treatment threshold something needs to be done.

Now, there is a product available that uses a virus that is relative specific for corn earworms (Heligen) or fall army worms (Fawligen). If you are not sure which species is present in your field, you can mix these two products together. These two products then, could be an alternative to the conventional synthetic organic insecticides and thus, spare the beneficials to help control sugarcane aphids if they do start to migrate into Kansas in large numbers.

These products do need to be treated a little differently than the more common insecticides. 1st – timing is very important in any management program but even more so with these products then the regular insecticides. These virus compounds take a few days to actually work on the pest vs. the common insecticides which kill on contact. Thus, the Heligen or Fawligen compounds need to be applied as soon as the 1st (see pic. 3 day old larvae – smaller ones vs 6 day old larva – larger one) hopefully, very small worms are detected to give it a chance to work before the worms cause too much damage. This then highlights one of the problems with these products i.e., detecting the very small larvae in your bucket (see pic) because they blend in very well with all the pollen, florets/ etc. that shakes loose.

Also, these products are more sensitive to sunlight which can deactivate the virus within 24 hours after application. Virus containers that are sealed should not be exposed to direct sunlight for more than 2 hours, or in temperatures over 95℉. Product should be mixed in water with a pH of ≤ 8.0, and enough carrier used to adequately spread the product over the entire target. If you decide to try these products, it is best to leave an untreated check strip – which you should do with any products.

 

 

Subscribe By Email

Get every new post delivered right to your inbox.

This form is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.