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Extension Entomology

Category: Wheat

Be on the lookout for this new wheat pest…

Posted on by Sarah Zukoff

SSipha-maydis-216797ipha maydis is a new invasive aphid that was recently found in Colorado and could potentially be found in Kansas.

“Wheat and barley are this aphid’s preferred hosts, although it can feed on many weedy grasses, corn and sorghum. It is a particular concern in wheat and barley since it can kill leaves and transmit barley yellow dwarf virus.”

Read more about this potential threat here:

http://wci.colostate.edu/shtml/Sipha.maydis.shtml

https://smallgrains.ces.ncsu.edu/2016/04/new-invasive-aphid-of-wheat-now-in-south-carolina/

-Sarah Zukoff

Wheat Aphids

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Wheat aphids, primarily bird cherry-oat and greenbugs, continue to migrate into Kansas on southern winds.

GB adult and nymphs

BCOA nymphs

The most common question this last week then is whether to add insecticide to a fungicide application to kill the aphids.  First of all, we do not recommend pesticide applications unless justified, and the mere presence of aphids in wheat does not justify an insecticide application.  Aphids need to be at densities of 20+ aphids/tiller when wheat is in the boot to heading stages before aphids begin to impact wheat simply due to their feeding.  Even then, their feeding is more impactful on plants that are already stressed by less than ideal growing conditions and when there are few beneficials present, i.e. lady beetles, lacewings, parasitic wasps, etc.  Recent rains seem to have really helped alleviate the previous dry conditions- so growing conditions are not stressing the wheat.  When an insecticide is added to a justified fungicide application, the insecticide will kill the aphids, as well as all the beneficials.  The aphids will continue to migrate into the state but the beneficials will be gone and much slower to re-populate.  Foliar insecticide applications made to control aphids with the aim of reducing the transmission of Barley yellow dwarf viruses has not been proven and thus is not recommended.  At the present time there seem to be good populations of lady beetles and parasitic wasps in wheat fields to help mitigate aphid populations.

lady beetle larva

aphid mummy

Wheat Update

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Received a report from north central Kansas about a small wheat field infested with ca. 20 aphids/tiller, but the aphids weren’t identified.  All wheat fields we visited in the last week had aphids, including bird cherry-oat, English grain, and/or greenbugs.  However, we were only finding about 1/10 plants or less and beneficials (lady beetles, lacewings, and parasitic wasp activity) were present in all of these fields.  Most wheat averaged Feekes 6-8 and no other pests really have been noted.

Wheat Aphids

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

We checked several wheat fields in north central Kansas this past week.  Once again, very few pests of any kind were detected.  As last week, there are a few aphids present, but not in any significant numbers.  With continued strong south winds, aphids will continue to migrate into the state.

greenbug

BCOA small

Wheat Insects

Posted on by Sharon Schroll

— by Dr. Jeff Whitworth and Dr. Holly Schwarting

We checked several wheat fields without finding much insect activity. There are a few greenbugs and bird cherry-oat aphids but not really enough to worry about yet. There are also many green lacewings and lady beetles present and feeding on these aphids which will help reduce populations.

Hessian fly in wheat-check your fields now

Posted on by Sarah Zukoff

Recent visits to Edwards county wheat fields revealed spotty but heavy infestations of hessian fly. One field (LCS Mint variety) in particular was planted on Sept. 25th which was just a few days shy of the “fly-free” date of October 1st in Edwards county.  In this field the adults likely emerged from the adjacent wheat stubble and then infested the nearby wheat seedlings in mid-late October. If the farmer would have planted after Oct. 1st, some egg laying would still have occurred in this field because many of the adults emerged later than the fly-free date. Although this is still a good rule of thumb, the term “Hessian fly-free date” is not completely correct anymore since hessian fly adults can be caught flying up until December in some places in Kansas now. This infestation is likely not limited to Edwards county since large populations of hessian flies were detected in many areas in south-central Kansas last spring. The adults were detected by sweeping wheat fields that were located near wheat stubble or in continuous wheat. Farmers should check now for the puparia or ‘flaxseed’ stage (see below) and will need to weigh further input costs if infested fields are found.

hessian finalhessian fly total

Hessian fly maggot feeding on seedlings in the fall can cause severe injury to plants. Infested wheat is stunted, dark green, and its leaves are broader than normal. Such injured plants will never grow past the four-leaf stage and will generally die during the winter. If tillering has begun, then only infested tillers may die.  To scout for the hessian fly in the winter months, peel back the leaf sheaths to uncover the puparia. Flies in the flaxseed stage will usually emerge in March-April as adults and will fly to nearby areas to deposit their eggs onto wheat leaves. There are no chemical management options for hessian fly maggots or those in the flaxseed stage. Managing adult hessian flies is not recommended either because emergence can be staggered over a period of several weeks yet adults live for only a few days. The best way to prevent further infestation is to plant varieties of wheat that have greater resistance to hessian flies and plant after the fly-free dates for their county.

mikes hessian flaxseed pic mikes hessian fly

For more detailed information on the Hessian fly in Kansas visit: https://www.bookstore.ksre.ksu.edu/pubs/MF2866.pdf

https://webapp.agron.ksu.edu/agr_social/eu_article.throck?article_id=691

-Sarah Zukoff

Winter Grain Mites

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

This time of year there is usually considerable interest in winter grain mites and this year is no exception.  A little refresher relative to winter grain mites:

  • Adults can be seen by the naked eye, but they are tiny.

winter grain mites_size

  • They have dark colored bodies with distinctive red legs and a red spot at the rear of their back, which is an anal pore.

Winter grain mite_close

  • There are 2 generations per year.
  • Adults will be actively feeding in the fall and spring and overwinter and oversummer as eggs.
  •  This feeding will continue as long as temperatures are cool (not cold), i.e. they are most active from 40°F to 70°F.

Feeding activities usually peak about this time of year and will cease during winter, when temperatures usually are just too cold.  This 1st generation deposits eggs in November and December and these eggs will hatch in late February to March.  This is about the time wheat is breaking dormancy, thus another time for grower concern.  Under dry conditions winter grain mite feeding may cause plants to take on a silvery appearance because mites penetrate individual plant cells and remove the plant juice, resulting in this silvery look.  Serious feeding, again in dry conditions, may result in yellowing of plants but, more commonly, just the tips. Under good growing conditions this feeding will not even be noticed.  Hot weather causes adult populations to quickly decrease.

Winter grain mite feeding

In summary, mite feeding activity will be terminated by cold weather in winter and hot weather in the spring, both of which cause eggs to be deposited into the soil to withstand the unfavorable conditions.  Winter grain mite feeding is only noticeable when wheat is under moisture stress, is reversed by adequate moisture, and rarely, if ever, results in any impact on yield.

Wheat Pests

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth, Dr. Holly Schwarting and JR Ewing

Worms (fall armyworms and armyworms) are still active in wheat and can be for another month, depending upon the weather.  If growing conditions are good, the wheat should be able to outgrow feeding caused by small worms.  Large worms have probably caused most of their feeding damage already, and hopefully, won’t be able to pupate, emerge as adults, lay eggs and have those eggs hatch again this fall.  Winter grain mites may cause some concern in the next month or so, especially under dry conditions. However, insecticide applications are rarely warranted or impact next year’s yield.  Again, good growing conditions will mitigate winter grain mite feeding damage.

Armyworms and Army cutworms in Wheat

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Several planted fields have already been sprayed to control worms.  What we have been seeing in south central and north central Kansas are a combination of armyworms (see pic) and fall armyworms (see pic).  Both of these species will do a similar type of damage.  When they are small they will feed on one side of the wheat leaf causing what is commonly called ‘window paning’.  As the larvae grow they devour more and more tissue until it may become quite noticeable and, under unfavorable growing conditions, may even severely reduce the stand (see pic).  Armyworm larvae will feed, probably for a couple more weeks, depending upon temperatures, and then pupate. If we haven’t yet had a hard freeze, they may emerge as moths and lay eggs in other wheat fields.  The first hard freeze will terminate armyworms.  Army cutworms, on the other hand, will not be terminated by the first hard freeze but will continue to develop all winter, feeding anytime temperatures are over about 45°F and will complete their development in the spring (see pic).  So, it is important to make proper identification of armyworms feeding in wheat as armyworms and fall armyworms will not be feeding throughout the winter and early spring but army cutworms will.

armyworm

 

fall armyworm

 

armyworm damage wheat

 

 

army cutworm