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Extension Entomology

Category: Soybean

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

 

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!

 

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)

 

Soybeans—false chinch bugs

–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)

 

DECTES (soybean) Stem Borer

–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)

 

BEAN LEAF BEETLES

–by Dr. Jeff Whitworth

Adult bean leaf beetles are very active throughout north central Kansas at the present time. They typically chew round/oblong holes in leaves (note fig. 4 with bean leaf beetle at the tip of the arrow) and deposit eggs in the soil around the base of soybean plants. There are two color phases of adult bean leaf beetles (fig 5), a tan phase and a reddish phase, but both have six black spots surrounded by a black border on their backs. Both color types can be seen in fig 5.

Figure 4 Soybean leaf damage from beetles (Cody Wyckoff)

Figure 5 Bean leaf beetles (Cody Wyckoff)

Soybeans—Bean leaf beetles

–by Dr. Jeff Whitworth

Bean leaf beetles (fig. 6) overwinter in Kansas as adults. They are usually first found in late winter/early spring in alfalfa fields because as the temperatures start to warm these adults become more active and actually feed a little on alfalfa foliage. However, there are not enough to cause any problems in these alfalfa fields. However, every year they are impressive because of their super ability to detect the very first germinating soybean plants, whether volunteer or planted. They can apparently detect these early plants from many miles away. As these first germinating plants are found by these adult beetles from many different overwintering sites, they can do some quite noticeable leaf feeding damage (fig. 7). These plants are usually mainly on border rows as the adults fly to and start to feed on the first plants they find from distant overwintering sites. These oval/oblong holes can cause considerable concern, especially if only border rows are examined and growing conditions are stressful. Please remember these young soybean plants are very resilient at absorbing this early season defoliation without any subsequent impact on the plants or yield, as long as the defoliation is less than about 50% in the vegetative stages and good growing conditions return. These adult beetles then lay eggs in the soil and around the base of these plants where they hatch and the larvae feed on the roots/root hairs. These adults then emerge in mid-summer and start feeding on new leaves and/or, more problematic, sometimes on the pods.

Figure 6. Adult Bean Leaf Beetle (red color phase)

Figure 7. Damaged Soybean Seedlings (Cody Wyckoff

Alfalfa and Soybeans

–by Dr. Jeff Whitworth

Green cloverworm adults (see pic) have been very common in soybean and alfalfa fields the last couple of weeks, and this has caused concern about potential green cloverworm infestations next year. However, green cloverworm adults are, or have been, migrating to the southern US for overwintering. Thus, since they do not overwinter in Kansas, infestations next year will depend on wherever the adults come back to, so predicting future infestations after overwintering adults return from the southern US are not possible.

Adult green cloverworm