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Extension Entomology

Category: Field Crops

Field crop pest and beneficial organisms.

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)

Cattail Caterpillars

–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

–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

–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

–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

–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)

 

ID to last week’s bug

–by Frannie Miller

 

Squash bug – Squash bugs use their piercing-sucking mouthparts to suck the sap out of plants leaves. This feeding can lead to the plants to wilt. These pests prefer to feed on zucchini, winter squash, and pumpkins, but will also attack members of the cucurbit family, such as cucumbers, cantaloupe and watermelon. It is important to detect the presence of these pests early, in order to try to control their population.

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)

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