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Extension Entomology

Category: Wheat

Armyworms|

— by Dr. Jeff Whitworth and Dr. Holly Davis

Armyworm larvae are apparently getting large enough now to cause noticeable feeding damage in a few places in southeast and north central Kansas.  Armyworms prefer grasses; thus they are now feeding on brome.  They should not be a problem while these good growing conditions are allowing the plants to outgrow the armyworm feeding.  However, this is the 1st generation of this common pest and we usually have 2-3 per year.

If conditions remain good for plant growth, armyworms should not be a problem.  However, they sometimes feed in wheat and when the leaves start to senesce, they move to the beards to feed and /or clip the heads, which can be problematic if there are large numbers.  After wheat and other grasses senesce, the armyworms often move to corn and sorghum where they may cause some alarm by feeding on the leaf tissue between the leaf veins or feeding in the whorl which may contribute to the ragged-looking leaves as they grow out of the whorl.

 

 

Wheat Aphids and Mites

–by Dr. Jeff Whitworth and Dr. Holly Davis

 

Most wheat fields we sampled around north central Kansas between 2-6 May had populations of bird cherry-oat aphids which were relatively easy to find.  They were in 100% of the sampled areas, however, not on 100% of the plants within those areas.  They are relatively easy to see, because of their dark color, if you examine the lower portion of the plants.  There are no symptoms or signs of their feeding nor would we expect there to be any because of the good growing conditions so far.  The populations are not yet at the density to warrant any concern.

Some winter grain mites were also noted but are nothing to worry about.  Winter grain mites are usually in their summer aestivation, or dormancy, period by now as they prefer cool, cloudy weather.  Thus, they will not be a problem moving forward into this growing season but the fact that there are still a few around is indicative of the cloudy, cool conditions we have experienced thus far this spring.

 

 

It is still NOT recommended to add an insecticide to a fungicide application just to save application costs and to kill the few aphids that are present.  This will do much more harm than good in the long run.  For more information relative to wheat pest and their management, please see the Wheat Insect Management Guide available here: https://www.bookstore.ksre.ksu.edu/pubs/mf745.pdf

 

Wheat Aphids

–by Jeff Whitworth and Holly Davis

We are getting calls relative to wheat aphids in many fields throughout south central and north central Kansas.  So far they are mainly bird cherry-oat aphids but a few greenbugs as well.  This is normal for this time of year.  These aphids migrate in, or are blown in, all spring on southern winds.  However, at this time of year/ this stage of wheat development, there is little to worry about relative to aphid feeding.  Also, the weather has been conducive to wheat growth so any aphid population buildup should not significantly impact the wheat.  Any viruses aphids may vector should not impact the wheat at this developmental stage enough to significantly reduce yields.  Aphid populations now will provide a food source and thus help many beneficial insect populations establish for later season aphid invasions.

It is not a good practice to mix a little insecticide in with a fungicide treatment “just in case”, as this is deadly to beneficial insects, i.e. lady beetles, lacewings, etc.  that will provide help later in the growing season on other crops.  Yes, it does save on the cost of an insecticide application but will probably do much more harm than good at this time of year.  For more information on wheat insect management, please refer to the KSU Wheat Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/mf745.pdf

Volunteer Wheat

–By Dr. Jeff Whitworth and Dr. Holly Schwarting

Again, please remember every moisture event prompts the growth of volunteer wheat.  This volunteer wheat needs to be controlled at least 2 weeks prior to planting to help mitigate all wheat pests;  pathogens, mites, and insects.

 

Volunteer Wheat

–by Dr. Jeff Whitworth and Dr. Holly Davis

 

It is once again time to control volunteer wheat!  This needs to be done at least 2 weeks prior to wheat planting and will help mitigate problems with Hessian flies, wheat curl mites, wheat aphids (Russian, bird cherry-oat, greenbug, etc.) and diseases.

Metopolophium festucae cerealium (Stroyan), a new aphid in Kansas wheat

— by Dr. J.P. Michaud — Hays, KS

In 1982, Stroyan distinguished a subspecies of Metopolophium festucae, sensu stricto, as M. f. cerealium based on morphological characters.  Whereas the former subspecies infests various wild grasses and is only incidental on grain crops, the latter is a potentially significant pest of cereals, especially wheat.  Although this aphid complex has been present in North America since the 1970s, it was not until 2011 that significant M. f. cerealium infestations of wheat (as well as barley and oats) were discovered in the Pacific Northwest.  The winged adults are pale yellowish with dark markings on the dorsal surface (Fig. 1), whereas apterae are pale yellow, similar in color to sugarcane aphids, but with a more elongate body shape (Fig. 2).

Fig. 1

Fig 2

On the morning of May 17, 2018, we collected a number of winged M. f. cerealium using a sweep net in wheat plots on the Agricultural Research Center-Hays.  Other aphids present included Sitobion avenae and Rhopalosiphum padi, but all three species were present in low numbers, and were attended by the usual complex of aphid predators.  It should also be noted that apterous M. f. cerealium were not found, so the winged forms are most likely very recent migrants.  It is quite possible that existing biological controls will maintain this new aphid below economic levels along with all the other species present in wheat, but farmers should be vigilant for possible outbreaks in particular fields, especially later-maturing varieties that will give the aphids more time to feed and increase their numbers.  It is also possible for these aphids to move to spring oats and barley after winter wheat matures.

Insect Management Guides, 2018

–by Jeff Whitworth and Holly Davis

 

 

 

Ms. Donna Sheffield, Communications Department, recently sent the links to the 2018 Insect Management Guides which can be found as follows:

Alfalfa, MF809: https://www.bookstore.ksre.k-state.edu/Item.aspx?catId=42&pubId=1492

Corn, MF810: https://www.bookstore.ksre.ksu.edu/Item.aspx?catId=221&pubId=20262

Cotton, MF2674: https://www.bookstore.ksre.k-state.edu/Item.aspx?catId=1081&pubId=20259

Sorghum, MF742: https://www.bookstore.ksre.k-state.edu/Item.aspx?catId=281&pubId=20260

Soybean, MF743: https://www.bookstore.ksre.k-state.edu/Item.aspx?catId=281&pubId=20261

Wheat, MF745, https://www.bookstore.ksre.ksu.edu/Item.aspx?catId=299&pubId=1463

 

Fall armyworms, Armyworms, and Army Cutworms in Wheat

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Where wheat has emerged, fields need to be checked for fall armyworms, armyworms, and army cutworms. If you see worms on your wheat this fall, the first thing to do is to determine which worm is present. Proper identification is important because they have different feeding and overwintering patterns.

We have been hearing about and seeing a mixture of both armyworms and fall armyworms on wheat and other host plants this fall. These small worms start by causing small “windowpanes” in wheat or alfalfa. No army cutworm infestations have been verified yet on wheat.

Flocks of birds in wheat or alfalfa fields in fall or early spring are often indicative of a “worm” infestation as the birds are feeding on the larvae. Fields with 25-30% of the plants showing “windowpane” feeding need to be monitored frequently as these larvae consume more as they get larger. Treatment should be applied before stands become threatened.

Fall armyworms

When scouting fields for fall armyworm damage, look for “windowpane” injury caused by tiny larvae chewing on seedling leaves. Each individual field should be scouted in several locations, including the field margins and the interior. The larvae themselves are usually too small to be easily observed after they first hatch, and hide in or around the base of seedlings. Within a few days of hatching, the larvae become large enough to destroy entire leaves.

The suggested treatment threshold is 2-3 actively feeding larvae per linear foot of row in wheat. Fields with 25 to 30 percent of plants with windowpane injury should be re-examined daily and treated immediately if stand establishment appears threatened. Larvae increase in size at an exponential rate, and so do their food requirements. Later instars do the most damage, sometimes destroying entire stands, and are the least susceptible to insecticides. Without treatment, problems can continue until larvae reach maturity or until a killing frost. Thin strands of wheat are especially at risk.

 

Fall armyworms will feed until the temperatures cool into the mid-20’s or they pupate, whichever comes first. If a killing frost does not occur soon after the treatment threshold is reached, fields may require chemical treatment.

 

Armyworms

Armyworm larvae are green to black with stripes of various colors. The head capsule is medium brown with dark markings. Most damage to wheat in Kansas occurs in southern and eastern areas of the state during warm, moist periods from late April to early June rather than in the fall. Like fall armyworms, armyworms will feed until the temperatures cool in the mid-20’s or they pupate, whichever comes first.

Most armyworm damage occurs during the last three to five days of larval feeding. When leaf feeding is observed, look for larvae curled up on the ground under litter, especially in patches of lodged plants. Treatment is usually not necessary below levels of four or five larvae per foot, but is probably justified at infestations of five to eight per foot depending upon larval maturity in relation to crop maturity.

 

Army cutworm

The army cutworm is a late fall /early spring pest in Kansas. Leaf damage by early stage army cutworm larvae  looks very similar to that of fall armyworms. However, army cutworm larvae are typically very small in the early fall – smaller than fall armyworms or armyworms. If the worms causing defoliation in wheat in the fall are relatively large, ½ inch or more, they are probably armyworms and/or fall armyworms.

Adult moths lay eggs in soil in the fall. The brown, faintly striped larvae hatch during the fall and early winter. They will feed throughout the winter (unlike armyworm and fall armyworm larvae), burrowing in the soil to escape frost and emerging again to feed during sp

Unlike other cutworms, only above ground plant parts are consumed, giving plants the ap­pearance of being grazed by cattle.

Infestations in well­-established stands will probably not require insecticide appli­cations while wheat is dormant, but some fields never green up in the spring because of cutworm feeding. Along with fall scouting, frequent inspections during warm periods in February, March, and early April are strongly encouraged, particularly when preceded by a dry fall.

Moisture availability, crop condition, and regrowth potential are all factors influencing potential losses to this pest. Late­-planted fields under dry conditions with poor tiller­ing may suffer economic damage with as few as one or two larvae per square foot.

In most fields, treatment will not be necessary until populations average four to five worms per square foot. Vigorous, well-­tillered fields under optimal growing conditions can tolerate even higher popu­lations, as many as nine or 10 larvae per square foot, without measurable yield loss. Infestations in later stages of crop develop­ment are less damaging than early ones because established plants can compensate for considerable defoliation and larvae normally finish feeding before wheat enters reproductive stages.

Mixed populations

Mostly the same insecticides are registered for control of these species of worms, but higher rates are recommended for fall armyworm. Any fields with mixed populations should be treated with the fall armyworm rate.

For treatment options, please refer to the latest K-State Wheat Insect Management Guide 2017 at: http://www.bookstore.ksre.ksu.edu/pubs/mf745.pdf

Volunteer Wheat

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Wheat is, and will continue to be planted throughout south central and north central Kansas over the next few weeks, as weather permits.  So, this is the best, and last, chance to control all volunteer wheat, which should be destroyed at least 2 weeks prior to planting the 2018 crop.  Volunteer wheat hasn’t been as persistent as in 2016, mainly because of the numerous rains that occurred in 2016 vs. this past year which has been drier.  However, there is still plenty of volunteer around and it just doesn’t take much wheat to support huge numbers of pests.  Wheat curl mites and Hessian flies are the arthropods most reliant on volunteer wheat as a ‘green bridge’.  In addition, many pathogens are also able to utilize volunteer wheat as a reservoir until it is able to infect a vector and is then transferred to cultivated plants.  Thus, eliminating this green bridge prior to planting along with delaying planting as long as possible, will go a long way toward reducing arthropod pests and pathogens in the newly planted wheat.

 

For more information on the Best Pest Management planting date as well as other pre-planting decisions, please see the 2017 Wheat Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/mf745.pdf

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