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Extension Entomology

Category: Soybean

Grasshoppers

Posted on by Sharon Schroll

–by Jeff Whitworth — Field Crops

As noted before, grasshoppers seem to be really numerous this year throughout northcentral Kansas. We have seen, or heard about, more grasshopper-riddled fields (see pic 1) then we have maybe in the last 15-20 years. The species responsible for most of the crop damage is the common, relatively large, yellow, differential grasshopper (see pic 2). These grasshoppers are still feeding a little, but are also moving to grassy/weedy/undisturbed areas where they are depositing eggs in the soil. These eggs will then hatch next spring and the young nymphs can start feeding on any nearby crops.

Picture 1: Grasshopper riddled field (pic by Cayden Wyckoff)

Picture 2: Differential grasshopper (pic by Cayden Wyckoff)

 

 

Worms, Worms, Worms (Fall armyworms, armyworms, Alfalfa caterpillar)

Posted on by Sharon Schroll

–by Jeff Whitworth — Field Crops

 

 

“Worms” have been voraciously feeding throughout at least the eastern 2/3’s of Kansas for about the last 3 weeks. However, they have only recently gotten large enough to cause considerable damage and thus concern. The main problem in alfalfa, so far, seems to be a combination of fall armyworms (see fig 1), armyworms (see fig 2), and somewhat surprising, alfalfa caterpillars (see fig 3).

Figure 1: Fall armyworm

 

Figure 2: Armyworm

 

Figure 3: Alfalfa caterpillar

Alfalfa caterpillars are usually quite common in alfalfa and soybeans, however, not at the densities detected this year. Alfalfa caterpillars pupate then emerge as the common yellow (see fig 4) or white butterflies usually seen flying around alfalfa and soybean fields.

Figure 4: Adult alfalfa caterpillar

Regardless of which larval species, it is apparent that the majority of the larvae are relatively mature and thus will be/or are pupating soon. Pupation will probably take 4-5 days. Then the adults will emerge, mate and start depositing eggs. These eggs will hatch, and then in 4-7 days the new, but very small, larvae will start the feeding process all over again. Armyworms (fig 2) will attack mainly grasses, i.e. brome, late-planted sorghum, wheat, etc. Alfalfa caterpillars (fig 3) will mostly stay in alfalfa or soybeans, before they get too mature, and fall armyworms (see fig 1) may feed on just about any crop. However, sorghum should only be susceptible to “headworms” from flowering until soft dough. All three species may have at least one more generation, if not more, until a hard freeze puts a stop to them.

 

 

Soybean Pests

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth — Field Crops

The pest situation, so far anyway, looks really encouraging throughout most of northcentral Kansas. Very few pests in sorghum, including chinch bugs, have been noted or reported at least as of 22 July. Sorghum seems to be all over the place, however, as far as developmental stages are concerned. There is some double-cropped sorghum that has just recently germinated (also some that was just planted late due to the weather) all the way to some that is just reaching the boot stage. So there is a long ways to go yet–but so far, the pest situation looks good.

 

Soybeans also seem to have relatively few pests so far this year. There are a few stink bugs (which will be depositing eggs soon) and Dectes stem borers (see fig 1 -adult green stinkbug and Dectes stem borer) neither of which are causing any problems yet–but may in the future before harvest. There are a few bean leaf beetle adults just emerging (see fig 2-bean leaf beetle adult eating hole in leaf) so these populations need to be monitored throughout pod set. There also seem to be relatively more spined soldier bugs (see fig 3) than usual this year. These are often confused with phytophagous stinkbugs but these” look alikes” are predators on other insects.

Figure 1. Adult green stinkbug and Dectes stem borer (pic by Cody Wyckoff)

Figure 2. Bean leaf beetle adult eating hole in leaf (pic by Cody Wyckoff)

Figure 3. Spined soldier bug (pic by Cody Wyckoff)

 

Beneficial’s

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth — Field Crops

Beneficial’s continue to be very active throughout all crop fields in the eastern half of Kansas (please see fig 4–pink spotted lady beetle depositing eggs, 15 July). Thus, the practice of just adding an insecticide into any tank mix with fungicides and /or herbicides “just in case” is NOT recommended. Please ensure any targeted pest meets, or is close to, a treatment threshold before utilizing an insecticide application.

Figure 4. Pink Spotted Lady Beetle depositing eggs (pic by Kaysie Morris)

Whiteflies

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth — Field Crops

Whiteflies (see fig. 3) are very common in soybeans throughout most of the eastern half of Kansas. This is not uncommon, but they seem to be more plentiful this year. However, there is no treatment threshold or even any problems that have been determined from these tiny whiteflies in Kansas soybeans. Potato leafhoppers are also still very common in soybeans where they also never seem to have much impact.

Figure 3. Whitefly

 

Also, at least for the last week, most soybean fields seemed to have very few defoliators.

 

Click Beetles

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth — Field Crops

Click beetles (fig 1) are becoming very active and this activity will continue for at least the next month. There are several species of click beetle in Kansas that can be a pest of crops. The larvae of these species are generally called wireworms and may feed on roots, root hairs, germinating seedlings, etc. In other words, just about any plant parts found underground including seeds can be damaged by click beetle larvae. The adults, of all species, are often attracted to lights at night or may be found under plant residue in fields. Insecticide seed treatments do really well at protecting seeds and seedlings, from planting up to about 28 days post-planting, from wireworm attack.

Figure 1.  Click beetle   (picture by Cody Wyckoff)

 

Green Cloverworms

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth — Field Crops

 

 

Green cloverworms are quite common right now in most alfalfa and soybean fields throughout north central Kansas. They are in various stages of development (see fig. 1), i.e. sizes are variable, but most will be pupating within a week or two. The adult moths will then emerge, mate, and start depositing eggs, probably mostly in soybean fields. This next generation of green cloverworm larvae then maybe more significant as they are voracious leaf feeders and can quickly cause noticeable defoliation in soybeans. Populations of green cloverworms have occurred in significant densities periodically in past years as to cause considerable concern. Defoliation of 50-60% during the vegetative stage may justify an insecticide application. However, there is often an entomopathogenic fungus that attacks green cloverworm larvae when the larvae reach significant densities. This fungus can really decimate these larvae and thus help control their populations.

Figure 1.  Green Cloverworm   (pic by Cody Wyckoff)

Dectes Stem Borers

Posted on by Sharon Schroll

–by Jeff Whitworth — Field Crops

The 1st adult Dectes stem borers (see pic 4) were observed in soybean fields on 21 June. These adults are usually 1st observed a week or two prior to the 4th of July and so this year is no exception. As the adults emerge, they usually aggregate on weeds around soybean field borders for a few days then disburse throughout the soybean fields where they deposit their eggs in petioles and stems over the next 6-8 weeks.

Picture  4: Adult Dectes stem borer

Pictures by Cody Wyckoff

Bean Leaf Beetles

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth — Field Crops

 

Many soybeans have been planted recently and seem to be doing really well under good growing conditions. Most (if not all) fields with germinated beans have a few bean leaf beetle adults feeding on them (see pic 6). However, seedling soybeans can withstand considerable defoliation, especially under these good growing conditions, without any adverse effect. These adults usually cause round or oval holes in leaves (see pic 7) but it takes approximately 6-8 beetles/row foot to justify a rescue insecticide application. These adults will feed a little on leaf tissue then start depositing eggs around the base of soybean plants where the larvae feed for 2-3 weeks.

 

Picture 6  Bean leaf beetle adult

 

Picture 7  Soybean leaves with round or oval holes from Bean leaf beetle feeding

(All Photos by Cody Wyckoff)

 

SOYBEAN – bean leaf beetle

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth

Most soybeans have developed well past the point of being susceptible to soybean pests (excluding lodging due to Dectes stem girdling). However, there are still some late-planted fields that have pests feeding on the pods. See (fig 3) of grasshopper feeding bite site and bean leaf beetle chewed hole. However, grasshoppers should be dying soon and thus not causing much actual damage. The bean leaf beetles will soon be migrating from these soybean fields to overwintering sites.

Figure 3. Soybean pod damage by grasshopper and bean leaf beetle (Cayden Wyckoff)