Kansas State University

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Extension Entomology

Category: Field Crops

Field crop pest and beneficial organisms.

Soldier Beetles

–by Dr. Jeff Whitworth

Have had several inquiries regarding soldier beetles (please see fig 3 provided by Kaysie Morris). These beetles are quite common throughout Kansas and most commonly noticed in late summer as the adults are highly mobile, relatively large, and are very active searching for and feeding on pollen. Thus, they can be very common on any crop, or weed, that is pollinating, especially sunflowers, sorghum, and cucurbits such as cantaloupes and watermelons. Soldier beetles are often mistaken for blister beetles because of their size and shape but are not in the same taxonomic family and thus, produce no cantharidin, the chemical that causes external blisters in humans and other problems in livestock when ingested. However, soldier beetles are harmless.

Figure 3 soldier beetle

 

Green Cloverworms

–Dr. Jeff Whitworth

Green cloverworms are still feeding on soybean leaves, and therefore still causing some concern, especially in double-cropped soybeans (some fields were being treated with insecticides on 2 Sep). As stated previously, green cloverworms can be very voracious leaf feeders. However, rarely, if ever, do they cause enough damage especially at this time of year (and plant developmental stage) to justify an insecticide application. Plus the soybean canopy usually harbors many different types of beneficials and they will be negatively affected by an insecticide application. Green cloverworms also seem to be very vulnerable to natural controls (please see figs 1 & 2, of fungus-infected green cloverworm larvae, provided by Mr. Tom Maxwell), which often effect great control on green cloverworm populations.

Figure 1 Fungal-infected green clover worms most commonly turn white as seen in this photo.

 

Figure 2 Fungal-infected green cloverworm after leaf feeding

 

SUGARCANE APHIDS

–by Dr. Jeff Whitworth

Sugarcane aphids also are present in most fields throughout southcentral and northcentral Kansas, but mostly only in small, scattered colonies (fig. 4). Beneficials are also very common, but it doesn’t seem like there are as many as there have been in the last couple of weeks. This could be because there are substantially fewer corn leaf aphids, in most fields, for beneficials to feed on. Sugarcane aphid monitoring should continue.

Figure 4  Sugarcane aphids on the back of a leaf (Picture by Amy Meysenberg)

SORGHUM HEADWORMS

–by Dr. Jeff Whitworth

Sorghum headworm populations have not been as substantial, yet this year, compared to the last few years throughout southcentral and northcentral Kansas. There are still a few larvae  (fig. 3), and many fields have not yet developed past the susceptible stage, however, and thus there could still be problems with “headworms”. Please remember the “susceptible” timeframe or stage of sorghum is flowering to soft dough. Headworms can cause 5% loss/worm/head.

Figure 3 Sorghum headworm larvae  (Picture by Amy Meysenberg

 

SOYBEAN PESTS

–by Dr. Jeff Whitworth

Green cloverworms (fig. 1) are still very common throughout soybean fields in northcentral and southcentral Kansas. Green cloverworms are voracious leaf feeders and can cause considerable defoliation (mostly if/when feeding on smaller plants) and this defoliation is often readily apparent and easily observed and thus can cause some concern. All fields monitored, even double cropped fields, did have green cloverworm populations. However, all fields seem to have great plant stands with substantial canopies. Nevertheless, these larvae still seem to be causing some concern around the area; however, no fields were even close to a treatment threshold.

Figure 1 Green cloverworms  (Picture by Amy Meysenberg)

In addition, some fungal-infected green cloverworms were also observed. Figure 2 illustrates the type of defoliation which may be caused by green cloverworms (leaves on the right in the picture) vs. leaf feeding damage caused by adult bean leaf beetles (on the left side of picture).

Figure 2 Defoliation damage to soybeans  (Pictures by Amy Meysenberg)

 

No corn earworms/soybean podworms, or signs of pod feeding were noted–none, yet!

 

SORGHUM

–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

–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

–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

–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

–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)