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Extension Entomology

Category: Field Crops

Field crop pest and beneficial organisms.

SORGHUM

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth

 

Still getting many calls about corn leaf aphids and many folks seem to still be getting them confused with sugarcane aphids (see fig. 2-cornleaf aphids and fig. 3-sugarcane aphids; photo provided by Jay Wisby) just because of the amount of honeydew produced by both species. Sugarcane aphids have now been verified as far north in Kansas, at least as far as I have heard, as Saline and Dickinson Counties. None of the colonies, yet, however have reached field-wide treatable levels and beneficials seem to be plentiful around every colony so far.

Figure 2  cornleaf aphids on leaf

Figure 3  sugarcane aphids on leaf

SOYBEANS

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth

SOYBEANS

There seems to be much focus on soybeans and sorghum right now, as there probably should be.  Similar to last week, soybeans still seem to be relatively free of damage by pests. See picture of green cloverworm infected with fungus (fig. 1).  However, there has been considerable fungicide spraying around the state and many of those applications included an insecticide “just in case”- with the rationale that it may save an insecticide application cost if an insecticide may later be justified.  However, pesticide applications are very rarely, if ever, recommended “just in case” for several reasons: 1st-most insecticides commonly used for soybean pests have approximately 10-14 days residual activity, and in fact, as the plants add foliage this newer foliage will have NO residual. Thus if pests do buildup to treatable levels another insecticide application will still be required; 2nd-the more insecticide applications utilized the more pressure placed upon the pest(s) populations, thus the more and faster opportunity for pest resistance; 3rd-each insecticide application reduces non target organisms, both beneficials that may help control pests through predation and parasitism, and potential pollinators. So, from practical, environmental, entomological, and financial aspects it is just a terrible practice to add an insecticide to any kind of application unless and until it is justified by the presence of a treatable level of a specific pest(s).

Figure 1 Green cloverworm  (infected with fungus–picture by Tom Maxwell)

 

CORN LEAF APHIDS

Posted on by Sharon Schroll

–Dr. Jeff Whitworth

 

Corn leaf aphids feed on corn and/or sorghum and are usually most evident during the whorl stage of sorghum. This year seems to be a very good year for corn leaf aphids as we have received many inquiries relative to possible damage caused by corn leaf aphids. Corn leaf aphids can be found every year. However, I could find no data to show that corn leaf aphids ever occur in field-wide populations that would justify an insecticide application and as farther indication of this, there is no treatment threshold. Corn leaf aphids are usually just considered as a great host for beneficials to utilize to sustain their populations. Figure 2 is a corn leaf aphid being fed upon by a lady beetle larva. Sorghum, and soybeans, have been relatively pest free compared to past years, at least so far this year.

Figure 2. Lady beetle larva feeding on aphids (picture by Cody Wyckoff)

 

SOYBEANS – bean leaf beetles, grasshoppers

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth

Many fields were sampled throughout southcentral and northcentral Kansas over the last couple of days. There seems to be very few insect pests affecting these soybeans, so far. There are some adult bean leaf beetles, which should be monitored as beans start or continue, setting pods as these beetles can start feeding on these new pods. There are a few adult Decte’s stem borers (fig. 1), but not many oviposition holes could be found yet. The only potential problem detected this week were grasshoppers. Weedy/grassy borders adjacent to many fields are loaded with grasshoppers. These areas are still lush and green so far, thus most grasshopper infested areas are still sufficient for these grasshoppers to feed in so they have not yet migrated to crop fields. However, there are some areas that have been treated with herbicides and thus these weeds are/or have died in these areas. Grasshoppers are/have moved into crops–in this case, soybeans (fig 2-3). Continued monitoring is highly recommended and please do not make a pesticide application “just in case”, and please send me an email if soybean aphids are detected.

Figure 1 Ductes Stem Borer  (Cody Wyckoff)

Figure 2   Grasshopper hiding/ feeding (Cody Wyckoff)

 

Figure 3  “Chewed” Soybean leaf  (Cody Wyckoff)

 

VOLUNTEER WHEAT

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth

Frequent rains over the last few weeks throughout the eastern half of Kansas have really started germination of volunteer wheat (figures 4 and 5). This is the “green bridge” that most wheat pests rely upon for their existence, from the time last fall’s planted crop matured until this fall’s planted crop germinates. Thus, destroying volunteer wheat can really help mitigate most wheat pests.

Figure 4-5 “Green Bridge” of volunteer wheat (Cody Wyckoff)

Cattail Caterpillars

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth

Cattail caterpillars are a perennial cause of concern throughout south central and north central Kansas. They are usually found on cattails, thus the name. However, every year some sorghum fields are infested. These infestations are usually most intense around field borders, and most especially in sorghum fields near water, i.e., a creek or pond, etc. The adult is a tan or dusky white, heavy bodied moth, which looks somewhat like a southwestern corn borer moth. The females usually start depositing eggs just about at the whorl stage of sorghum. However, the cattail caterpillar is rarely found within the whorl like “ragworms”, i.e., corn earworms/fall armyworms/etc. are. The cattail caterpillar is mostly found on the leaves themselves but may add to the “ragging” up of the leaves after they unfurl from the whorl (fig. 1) due to their voracious leaf feeding. The cattail caterpillar is a relatively hairy but very distinctive larva with bright orange/white/and black body markings (figures 2 and 3). A relatively high percentage of the older, larger, more mature larvae have been found to be parasitized, thus stop feeding, become very sluggish, and eventually just die from these natural enemies of these caterpillars. There is no established treatment threshold.

Figure 1 “Ragging” up of the leaves (Tom Maxwell)

Figure 2 Cattail Caterpillar (Tom Maxwell)

Figure 3 Cattail Caterpillar feeding on the edge of the leaf (Tom Maxwell)

 

Soybeans—false chinch bugs

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth

We have received several calls relative to false chinch bugs (fig. 5) damage to soybeans.  In most cases false chinch bugs may appear in large numbers in a patch or two in a field, and usually after the soybean field was treated with a herbicide.  The most common natural host of false chinch bugs are plants in the mustard family.  So when these are killed by a herbicide, the false chinch bugs congregate and may feed for a few days before dispersing.  This feeding, by removal of plant juices, usually has little to no effect upon the plants, but occasionally can be very detrimental to soybeans (fig. 6) and sometimes sorghum.

Figure 5: False Chinchbug

Figure 6: Soybeans affected by False Chinchbugs (photos provided by Rod Schaub)

 

Corn – adult western corn rootworm, corn earworm and fall armyworm

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth

Corn – adult western corn rootworm, corn earworm and fall armyworm

The first adult western corn rootworms (WCRW) (fig. 1) were detected on 5 July, 2020, in north central Kansas.  Since this first emergence there has been considerably more emergence, to the point that there are several areas of north central Kansas that are now concerned about silk clippings by these adults.  WCRW adults spend much of their time in the early morning, and then again toward evening, feeding on silks (fig. 2)—thus, shown here in a position that they are commonly found in while feeding on silks.  They may spend much of the middle, warmer, part of the day in more shaded areas, i.e., behind leaf collars, etc.  Figure 3 shows typical “goosenecking”, from the previous root feeding, which is now completed, by the larval stage of the WCRW.

 

Figure 1: Adult Western Corn Rootworm (WCRW)  ( Cody Wyckoff)

Figure 2: WCRW in position that they are commonly found while feeding on silk (Cody Wyckoff)

Figure 3: Goosenecked corn  (Cody Wyckoff)

There is also much corn earworm and fall armyworm activity in corn fields that are just now, and have just recently, started silking.  The larvae (fig. 4) observed around north central Kansas will probably feed for about another 2 weeks, then, pupate in the soil, emerge as adults which mate, and start depositing eggs.  These eggs will most likely be deposited in late planted corn, or sorghum (between flowering and soft dough) and/ or soybeans.

Figure 4: Larva feeding on corn (Cody Wyckoff)

 

Western Corn Rootworms

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth

Western corn rootworm larval feeding seems to be almost finished around the north central part of Kansas, anyway. Root monitoring yielded mostly mature larvae– but also one that had just recently pupated (see fig 2). No western corn rootworm adults have been observed yet.

Figure 2 Two WCRW larvae plus new pupa  (by Cody Wyckoff)

 

DECTES (soybean) Stem Borer

Posted on by Sharon Schroll

–Dr. Jeff Whitworth

The 1st adult Dectes (soybean) stem borers were observed on 29 June in north central Kansas (see fig. 1). This adult emergence seems to be right on schedule with past years, as we have found adults emerging right around the 4th of July since 1997. These adults usually feed a little while on pollen, then mate for about 7-14 days before disbursing to soybean (or sunflower) fields to deposit their eggs in the stems right at the petiole.

Figure 1 Adult Dectes Stem Borer (BY Cody Wyckoff)