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Extension Entomology

Category: Alfalfa

Garden Webworms

Posted on by Sharon Schroll

–by Jeff Whitworth — Field Crop Entomologist

Garden webworms (fig. 2) have just about finished feeding on soybeans and/or alfalfa (where they have been much less noticeable). They will pupate in the soil for the next 4-7 days then the moths will emerge to start depositing eggs in acceptable host plants. From a crop perspective this time of year, hopefully they will have little impact as the soybeans have developed far enough that these worms won’t defoliate enough to affect yield. But the really late-planted soybeans or those that may be moisture stressed may still have some concern, so monitoring should include these defoliators starting soon.

 

Figure 2: Garden webworm mature larva (picture by Steve Freach)

 

 

Potato Leafhoppers

Posted on by Sharon Schroll

–by Jeff Whitworth — Field Crops, Entomology

The 1st potato leafhoppers were detected in northcentral Kansas on 10 June, but probably started immigrating in a few days prior to that. They will continue this immigration for about another month. As of 14 June, however, only adults were active (see fig 1) but they are depositing eggs which hatch into very tiny nymphs in approximately 4-7 days. Much alfalfa, however, has just been swathed, or soon will be, and this will help mitigate potato leafhopper damage by removing eggs/nymphs before they cause any damage (see fig 2-often called “hopper burn”). However, adults will continue to migrate into these fields- so monitoring should continue as the new growth emerges.

Figure 1. Adult potato leafhoppers

 

Figure 2. Hopper burn

 

 

Army Cutworms (wheat, alfalfa)

Posted on by Sharon Schroll

–by Jeff Whitworth, Field Crops – Entomology

I have received a few calls within the last 10 days about “Miller moths” flying around lights at night and flying/running into the house when an outside door is opened the 1st thing in the morning. Those, at least from my experience and the specimens I have seen, are adult army cutworms (see pictures by Cayden Wyckoff). Like most adult cutworms, the army cutworm is a relatively thick bodied but otherwise nondescript moth. These moths are even more nondescript after losing wing scales while flying and/or hiding under objects during the day. They are a relatively agile, quick moving moth, and in Kansas always seem to be present just before and/or during Memorial weekend. As far as crops go, the army cutworm feeds on wheat or alfalfa since those were the crops growing last fall when the female moth was depositing eggs. Thus, since last fall the larvae have fed all winter and spring, pupated, emerged as adults, and are/or have headed for over- summering sites, usually somewhere in the Rocky Mountains. These same moths then, at least the ones that survive the summer, will be heading back this way in late summer or early fall and depositing eggs in wheat and alfalfa fields along the way. After depositing their eggs, these adult moths expire, but have started the next generation.

 

Adult army cutworm

 

Alfalfa Weevils and Caterpillars

Posted on by Sharon Schroll

–by Jeff Whitworth–Field Crops Entomology

 

 

Alfalfa weevils continue to cause concern around the state, but that shouldn’t last much longer. After checking many fields in north central Kansas, from 20-23 May, it is obvious that alfalfa weevil infestations have been very problematic–but has run its course, for the most part.  All fields sampled had alfalfa weevil larvae (see fig. 1), whether previously treated or not.  All fields, including 2 untreated, had less than a 2% infestation of larvae and adults.  There were still a few adults (see fig. 2) hanging around in these unswathed fields which is common as the uncut alfalfa canopy does provide shade for these adults until it is swathed.  After swathing these adults usually emigrate from the alfalfa fields and not return until early fall.  Adult alfalfa weevils do feed- but at a much reduced rate compared to larvae.

 

Alfalfa caterpillars (see Fig. 1) are also becoming more common in alfalfa fields throughout the state. These develop into the common white or yellow butterflies, again usually very common around both alfalfa fields and, later on, soybean fields.  However, these larvae do not usually cause enough damage to be of any consequence.

 

Figure 1: Alfalfa weevil larvae (smaller larvae with dark heads) and Alfalfa caterpillar (larva on the left)

Figure 2: Alfalfa weevil adult

Wheat Pests

Posted on by Sharon Schroll

–by Jeff Whitworth – Field Crop Entomology

Wheat (and alfalfa) continue to develop slowly throughout north central Kansas. Wheat mites, mostly winter grain and brown wheat mites, are still active throughout the central part of the state, but both species are slowly transitioning into their summer, non-feeding, stage (i.e., mite count in several fields averaged 50-60 winter grain mites per plant on 10 April, but only 7-10 per plant on 20 April).  They have been feeding and thus competing with the plants for the little moisture that is present, thus we are often seeing the kind of feeding damage as in figure 1. Hopefully, adequate moisture plus the transition to the mite’s non-feeding stage will help these areas recover.

 

Figure 1 Mite damage on the Dickinson Co. line (picture by Jay Wisbey)

 

Alfalfa Pests (alfalfa weevils, pea aphids, cowpea aphids)

Posted on by Sharon Schroll

–by Jeff Whitworth, Field Crops Entomology

Alfalfa weevils (see fig 1) have been hatching from eggs over about the last two weeks.  However, they have not been developing very quickly, nor has the alfalfa, at least throughout north central Kansas. There will be more larvae.  This is always a problem for producers, to treat early or not, especially with less foliage to accept the insecticide.  If your treatment threshold is reached, irregardless of time it’s probably prudent to make an insecticide application as soon as possible.  Less foliage may mean better coverage and therefore kill.  But, it also probably means less foliage to accept the spray and thus there may be a little less residual control.  But this is always part of alfalfa weevil management.

Figure 1 Alfalfa weevil larvae and leaf damage

 

We also see conspicuous aphid populations all around the state—both pea (see fig 2) and cowpea (see fig 3). These aphids are causing concern, especially in areas where moisture is lacking.  However, these aphids usually do not buildup to the density to actually reduce yield but more often provide a food source for many beneficials if left untreated.

Figure 2 Pea aphids

Figure 3 Cowpea aphids (received from Ed Beason)

 

 

“Worms” (continued) —–Fall Armyworms

Posted on by Sharon Schroll

–by Jeff Whitworth — Field Crops

 

 

“Worms” (larvae of armyworms, fall armyworms, etc.) are still causing considerable concern, at least throughout the eastern 2/3rd’s of Kansas. They have slowed a little over the last couple of weeks, as many have been pupating, mating, egg laying, etc. Therefore, if you have experienced significant “worm” activity in the last month or two, it will be a great time to start monitoring those vulnerable areas, i.e. seeding wheat, brome, alfalfa, etc. to detect any new “worm” infestations while the worms are small before they can do much feeding. The picture on the left is a brome field in Saline County that had a significant infestation of armyworms and was sprayed approximately 2 weeks prior to this picture and there was no rain between spraying and the date of this picture. The picture on the right is a patch of that same pasture that could not be sprayed.

(Pictures provided by a rancher in Saline Co.)

 

Also, we have conducted 2 separate insecticide efficacy trials against armyworms, one in brome and one in volunteer wheat. The raw data from the trial in brome are presented here. Analyzed results of both trials will be available on the KSU Entomology website, hopefully, in the near future.

 

 

    Total worms/ft2/4 Reps
Treatment Rate 19 Sept (7 dat) 26 Sept (14 dat)
Fastac CS 2.4 fl. oz/a 0 1
Besiege XL 8.0 fl. oz/a 0 2
Stallion 6.0 fl. oz/a 0 2
Grizzly Z 2.5 fl. oz/a 0 0
Lorsban 4E 1.5  pint/a 3 3
Check (control) – 25 26
Check (control) – 18 20

 

Grasshoppers

Posted on by Sharon Schroll

–by Jeff Whitworth — Field Crops

Grasshoppers continue to be quite numerous in some alfalfa fields, and late-planted soybeans (see pic. 2). As these crops senesce or dry down, these grasshoppers sometimes move into wheat fields when the newly planted wheat starts to germinate where they can be a real hindrance to establishing a good stand.

Adult Grasshopper (there are many different kinds currently in the fields – this is a Differential Grasshopper)  (pic by Cayden Wyckoff)

 

WORMS, WORMS, and MORE WORMS (army cutworms, fall armyworms)

Posted on by Sharon Schroll

–by Jeff Whitworth — Field Crops

 

2021 might be called the “year of the worm”. Starting in late winter/early spring, 2021, there was considerable activity by army cutworms. Most of the problem was caused by the larvae decimating thin strands of wheat and/or alfalfa. Then, since late spring/early summer, a combination of armyworms and fall armyworms have been causing serious concern and damage in lawns, pastures, and alfalfa fields throughout about the eastern 2/3rd’s of the state. Army cutworms spend the summer in the Rocky Mountains but start to migrate back into Kansas in early fall every year. The larvae may feed on just about any plants but mostly affect wheat and alfalfa, as these are usually the only plants actively growing this time of year. Armyworms, probably more so than fall armyworms, may continue to cycle through another generation or even two as they overwinter in Kansas, and thus it will probably take a “hard” frost or freeze to stop them. Fall armyworms, since they don’t usually overwinter in Kansas, may migrate south after this generation become adults-but there could be another, or at least partial generation. Armyworms infest primarily grasses, i.e. sorghum, corn, brome pastures, lawns, and often this time of year, wheat, but occasionally alfalfa, etc. Thus, if armyworms are the problem they could be around through another generation or maybe even two depending upon the weather. So, if armyworms are relatively small (see pic 1) they will probably feed for another 10-14 days then pupate (stop feeding). If they are relatively large (see pic 2) however, they will probably pupate in the next 3-7 days. There will probably be at least one more generation of armyworms. Fall armyworms (see pic 3) have a little wider host range, which includes alfalfa, soybeans, corn, sorghum, wheat, etc., but don’t usually overwinter in Kansas, thus, hopefully, will be heading south after these larvae finish feeding and become moths. Also, in the next 30-60 days army cutworm moths should have returned from their summer Rocky Mountain retreats to deposit eggs throughout at least the western 2/3rd’s of the state and thus, these tiny worms will start feeding on wheat and/or alfalfa all winter.

Picture 1: Small Armyworm (pic by Cayden Wyckoff)

Picture 2: Larger Armyworm (pic by Cayden Wyckoff)

Picture 3: Fall Armyworms (pic by Jay Wisbey)

 

 

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)