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Extension Entomology

Tag: north central Kansas

Alfalfa Weevils

–by Dr. Jeff Whitworth

Alfalfa weevil activity has increased significantly in the last week throughout North Central Kansas. The recent warm weather has really stimulated egg hatch thus there are large numbers of very small 1st instar larvae just starting to feed, plus older, larger larvae (fig. 1) that have been feeding for a week or so. However, some fields have very low infestation levels, while others have already reached the 100% infested level. Recent freezing temperatures appeared to have killed some top growth in some fields, which can be mistaken for insect damage.

Thus, sampling each field is always prudent, but even more so this year. We have gotten many questions recently about the predicted cold weather and its effect on the weevils, but remember, alfalfa weevils are cool weather insects. Temperatures into the mid 20’s for a couple hours may kill small larvae, as we saw in 2018, but probably won’t affect the eggs or adults. Then, anytime the temperatures are over about 45°F, the larvae feed and do so 24/7 as long as temperatures are above 45°F. Many fields were treated this week and probably should be whenever the treatment threshold is reached as the predicted temperatures for the next 10 days looks like it will slow the feeding activity down but probably not be cold enough to kill very many larvae. Have also gotten the question about spraying for army cutworms and that effect on alfalfa weevils. If both occur at threshold or one or the other does and you make an application of an insecticide you should get pretty good control of both. However, remember, cooler weather will slow down the effect of the insecticide.

 

Also, check this super neat picture of biological control at work (fig. 2). A turkey harvested by a Kansas youth hunter on 6 April had a crop completely filled with large army cutworm larvae.

 

Alfalfa Update – alfalfa weevil, Lady beetle larva, Pea aphids

— by Jeff Whitworth and Holly Davis

Alfalfa weevils sampled this week were in all stages of larval development, although no pupae or adults were noted in any fields.  Actually, no adult alfalfa weevils have been detected yet this year.  Also, there is relatively little defoliation, at least so far, in north central Kansas.

No infestation levels exceeded 20% this week and most alfalfa is 10 – 16 inches tall and should grow better after recent rains.  Alfalfa weevil infestation levels in north central Kansas have not been this low, overall, for many, many years!

Pea aphids are still present in all fields sampled but not in population levels that cause concern.  Hopefully, they are currently just providing food for lady beetle populations.  So, at the present time, it does not seem that alfalfa is at risk for damage by alfalfa weevils or pea aphids.  For more information on alfalfa pest management, please see the Alfalfa Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/mf809.pdf

Soybean Stem Borers

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Dectes (soybean) stem borer damage is becoming more and more apparent as soybean harvest is delayed throughout north central Kansas.  The dectes stem borer was first detected infesting soybeans in Kansas in about 1985 in south central parts of the state.  Annually, the adults emerge from soybean stubble, where they overwinter as larvae, around the 4th of July.  They mate and deposit eggs around soybean leaf petioles.  The small larvae bore into the plants and feed, making their way into the main stem.

Dectes stem borer larvae are cannibalistic, so as these larvae come into contact with others only one survives to tunnel down the main stem to the base where they girdle around the interior of the stem, typically just prior to harvest.  This girdling activity often goes unnoticed.  However, the stems are weakened and wind will blow girdled plants over.  Fields with significant infestations will have serious lodging, as we are seeing now in parts of NC KS.  Harvesting these lodged plants is very difficult at best, and if harvest is delayed further, the grain lying on the ground may be lost to rodents, disease, etc.  Infested fields should be harvested as soon as possible, hopefully before any additional lodging occurs!  There is no preventative or rescue treatment available for dectes stem borers in soybeans.

For more information on the biology of the dectes stem borer, please visit Dectes Stem Borer, MF2581: https://www.bookstore.ksre.ksu.edu/pubs/MF2581.pdf

 

Soybean Update — Green Cloverworms

— by Dr. Jeff Whitworth and Dr. Holly Schwarting

 

Green cloverworm larvae have been very numerous throughout north central and south central Kansas for the past 30-45 days.  However, the larval stage and the leaf defoliation that they’re known for, has pretty much ceased as most larvae have entered, or are entering, pupation.

 

 

A few green cloverworm larvae can still be found in late planted beans and alfalfa, but for the most part, their feeding will soon cease.  The most common question is, with all these green cloverworm adults around, will they be in the same fields next year?  They do not overwinter in Kansas and most soybean fields will be rotated, so the answer is no.  If the same fields are infested next year, it will not be because of the green cloverworms that survived the winter in that field.

 

Soybean Update – Thistle caterpillars, Stink bugs, and Soybean Aphids

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Thistle caterpillars have mostly vacated their webbed cells and are or have pupated.  That is why there are huge numbers of painted lady butterflies flying around on most rural roads throughout north central Kansas.  Hopefully, these butterflies will head south for overwintering and will not start laying eggs in soybean or sunflower fields.  However, fields need to continue to be monitored for small thistle caterpillars, especially double-cropped soybeans. Additionally, monitor for the continued presence of green cloverworms, although these populations seem to be declining quite rapidly around north central Kansas.

 

Phytophagous stink bugs, both brown and green, are increasing in many soybean fields.  Either may insert their mouthparts into the seed within the pods and suck out juice from the developing seed.  However, there are also brown stink bugs that are predatory on pests like the yellowstriped armyworm (shown below) which has been killed and is being utilized as a food source by this beneficial stink bug.

 

Soybean aphid populations are still present in all fields examined this week in north central Kansas, but are not increasing in density or coverage.

 

 

For management decisions for all soybean pests please see the 2017 Soybean Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF743.pdf

 

Soybean Update – Green Cloverworms, Thistle Caterpillars, Stink Bugs, Soybean Aphids, and Beneficials.

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

 

Insect activity is still increasing around north central Kansas.  One positive, bean leaf beetles seem to be at really low densities in most fields, at least so far.  Green cloverworm larvae are at various developmental stages but there are still many early instars.  This means there probably is considerable defoliation to come because, as the larvae get larger, they simply eat more leaf tissue.  However, as green cloverworm populations increase, they are often infected with an entomophagous fungus which decimates their populations.

 

There also are many areas with significant infestations of thistle caterpillars and garden webworms.  Both species web leaf tissue around and over themselves, creating a relatively secure area from which they feed on leaves.  Many thistle caterpillars are really small right now and may not be noticed yet.  So, continued monitoring is important, especially with soybeans just entering the reproductive stages of development.

 

Green stink bugs are relatively common in both conventionally planted and double-cropped soybeans.  There are eggs, nymphs, adults, and mating adults all present at this time so sampling needs to be conducted periodically as these bugs can feed on the beans while they are developing inside the pods.

Soybean aphids were detected in double-cropped soybeans in Dickinson Co. on 24 August. Many soybean fields have significant populations of green lacewings and lady beetles, both of which may help control soybean aphids if and when they migrate into these fields.  So, as always, please take these into consideration if insecticide applications are contemplated.

 

For more information of thresholds and management options for these pests, please refer to the KSU Soybean Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF743.pdf

Sorghum Update – (chinch bugs, corn leaf aphids, corn earworms)

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

 

Chinch bugs continue to be very active in both corn and sorghum throughout north central Kansas.  Both nymphs and adults are present.

 

Many adults are still mating, which indicates that there are more eggs, nymphs, and adults yet to come.  One consolation relative to the numerous chinch bugs in sorghum fields is that the four spotted egg eater, Collops quadrimaculatas, seems to be plentiful as well.  They have been collected in samples while sweep sampling alfalfa and are also present in sorghum fields.  These little beetles are predacious on insect eggs, and it has even been reported that they feed on chinch bug eggs.  Not sure they will be able to provide a great deal of control on chinch bug populations but it sure can’t hurt!

 

Corn leaf aphids are also very plentiful throughout north central Kansas.  These aphids usually feed on developing corn tassels and silks, but probably are more commonly associated with, or at least noticed in, whorl stage sorghum.  These aphid colonies sometimes produce enough honeydew, and it is so sticky, that often the sorghum head gets bound up in the whorl and therefore doesn’t extend up properly.  These colonies are not usually dense enough on a field-wide basis to justify and insecticide application.  These plentiful aphids are also serving as a food source for many predators, i.e. lady beetles, green lacewings, etc.

 

 

Corn earworms are still plentiful in corn but as they mature, pupate, and become adults they most likely will migrate to sorghum to feed on developing kernels (between flowering and soft dough), and soybeans where they will feed on developing beans within the pods.

For more information on sorghum and soybean pest management, please consult the KSU Sorghum Insect Management guide: https://www.bookstore.ksre.ksu.edu/pubs/mf742.pdf

And the KSU Soybean Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF743.pdf

 

 

Soybean Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Spider mites are infesting soybeans relatively early this year in several areas in north central Kansas.  These mites damage plants by feeding on individual plant cells, usually starting on the undersides of lower leaves.  Under less than ideal growing conditions, these mites can turn leaves brown and cause them to die in a few days.  Mite populations can build up quickly and if treatment does become justified please use enough carrier to penetrate into the canopy and reach the undersides of leaves.  Also, realize that if using an insecticide to control other pests, the predators will likely be significantly reduced which may allow mite populations to increase.   For more information on spider mite management, please see the Corn Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF810.pdf

 

 

Sorghum Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

 

Chinch bugs are very active in double cropped sorghum in north central Kansas.  They are also numerous in corn but the field corn is mature enough that chinch bug feeding should be of little consequence.  However, young sorghum plants, especially under less than ideal growing conditions may be seriously stressed.

For more information on chinch bug biology, management decisions, and insecticides registered to control chinch bugs please see the Sorghum Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/mf742.pdf

and Chinch Bugs: https://www.bookstore.ksre.ksu.edu/pubs/MF3107.pdf

 

 

Soybean Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Adult bean leaf beetles are present, but scarce, in soybean fields in north central Kansas as of 20 July.  This indicates that the majority of the population is in the larval stage, feeding on soybean roots, and/or is pupating in the soil.  There are also some garden webworms and a few painted lady, or thistle caterpillars, in some fields, but not enough to be of concern.

 

 

For more information on treatment thresholds and management options, please see the Soybean Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF743.pdf

 

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