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Extension Entomology

Category: Alfalfa

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.

 

 

Grasshoppers increasing in Western Kansas

Posted on by Sharon Schroll

–by Anthony Zukoff — Southwest Research and Extension Center

Weather patterns can have a significant impact on grasshopper populations year to year. Hot, dry summers increase survival of nymphs and adult grasshoppers, leading to increased egg production during the growing season. Cool, wet weather promotes fungal pathogens that can reduce egg and nymph survival, but if the following spring is warm and wet, egg hatching will increase and more nymphs survive.  So, several years of hot, dry summers followed by warm, wet springs can eventually lead to large populations of grasshoppers in some regions.

As the weather in western Kansas continues to be hot and dry this summer and areas of drought increase, larger populations of grasshoppers going into the fall season could be possible.  This year’s USDA Rangeland Grasshopper Hazard map (Figure 1) may explain the recently observed buildup of grasshoppers along field edges and in grassy areas.  As non-crop sources of food are exhausted, grasshoppers will shift their grazing over to anything still growing in the landscape.  In areas with greater grasshopper pressure seedling alfalfa and wheat could be at risk.

Before planting alfalfa, treatment should be considered if there are 15 or more grasshoppers per square yard around the planting area. Once planted and growing, consider treatment if 3-5 grasshoppers per square yard are found in the seedling alfalfa stand.

Vegetated borders around areas where wheat will be planted should be scouted 10 days before planting. Consider treating those borders if there are 7 to 12 grasshoppers per square yard. Once growing, 3 or more grasshoppers per square yard within the field can destroy seedling wheat stands. If grasshopper populations are low to moderate, seed treatments can protect emerging wheat plants for several weeks if products are applied at the highest registered rate.  Seed treatments will be less effective under severe grasshopper pressure.  Avoid planting too early as this will help reduce the time that wheat will need to be protected.

In either crop, depending on the products used and severity of the season’s grasshopper buildup, multiple applications might be necessary. Please refer to the most recent Alfalfa and Wheat Insect Management Guides for specific control information.

Alfalfa Insect Management Guide:  http://www.bookstore.ksre.ksu.edu/pubs/MF809.PDF

Wheat Insect Management Guide:  http://www.bookstore.ksre.ksu.edu/pubs/mf745.pdf

 

Figure 1.  Areas shaded in orange and red could experience increased grasshopper pressure through this fall.

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)

Alfalfa Caterpillars

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth — Field Crops

Alfalfa caterpillars are currently very common in both alfalfa and soybean fields. They are shy and extremely well camouflaged (see fig 2) and therefore rarely noticed. They are voracious leaf feeders, however, populations rarely reach densities in either crop to warrant an insecticide application. These larvae are the feeding stage of the common yellow or white butterflies often seen flying around either soybean or alfalfa fields where they can be seen often dipping down into the canopies to deposit eggs or gathering around water to drink. This activity, coupled with often large numbers of these butterflies, sometimes causes concern to growers. Howe

Figure 2. Alfalfa caterpillar  (picture by Cody Wyckoff)

 

 

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)

Potato Leafhoppers

Posted on by Sharon Schroll

–by Jeff Whitworth — Field Crops

Potato leafhoppers (PLH) started their annual migration back into Kansas about 7-10 days ago, at least in numbers that could be noticed. Potato leafhoppers are small lime green, wedge-shaped plant sucking insects (see pic 1-nymph) that have a characteristic white spot between their eyes on both adults (see pic 2) and nymphs. Adults have wings and readily fly when disturbed. Nymphs do not have wings but will quickly move to the underside of leaves or jump into the leaf litter below the canopy when disturbed. Females deposit eggs in stems and the tiny nymphs emerge ready to feed. Both nymphs and adults suck plant juices and in so doing inject a toxin into the plant. Signs of potato leafhopper feeding on alfalfa leaves then is often called “hopper burn”. This starts out as a yellowing at the leaf tip (see pic 3) but if feeding continues, it may cause the whole leaf/stem/plant to turn yellow and wilt which may significantly reduce nutrient quantity and quality. PLH is usually affect the 2nd-4th cuttings. Swathing is probably the best way to control PLH populations but if populations exceed the treatment threshold and the alfalfa won’t be ready to swath for 3 weeks or so, then an insecticide application may be justified.

Picture 1: PLH nymph

Picture 2: PLH Adult

Picture 3: “Hopper burn” on alfalfa leaves

 

Alfalfa Pests

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth — Field Crops

Most alfalfa around north central Kansas, has been swathed at least once and some fields even twice. Adult alfalfa weevils were very common in many fields up until about 10 days ago, which caused considerable concern. When temperatures finally approached and/or exceeded 80-85 °F, however, most adults migrated out of the fields and should not cause any more concern, or return in large numbers, to alfalfa fields, until September. Adult alfalfa weevils do feed just a little-but not anywhere as voraciously or as long as the larvae (see pic 1-alfalfa weevil larva noted still in the field on 8 June, 2021)

Picture 1 Alfalfa weevil larva

 

Picture 2 Grasshopper Nymph

Very few actual pests have been noted in alfalfa fields over the last couple of weeks. However, grasshoppers are hatching and these small nymphs (see pic 2) should be closely monitored. Adult leafhoppers have started migrating back into the state so as fields start to grow back after cutting these should be monitored also. Fortunately, there seem to be good numbers of lady beetles (see pic 3-lady beetle larva; pic 4-lady beetle pupa; and pic 5-adult- -this adult has the neatest name in entomology in my opinion–twicestabbed lady beetle) which should help control any aphid problems going forward.

Picture 3 Lady beetle larva

Picture 4 Lady beetle pupa

Picture 5  Lady beetle adult (Twicestabbed lady beetle) – two distinct red spots on their back

(All Photos by Cody Wyckoff)

 

Alfalfa Weevils

Posted on by Sharon Schroll

–by Jeff Whitworth — Field Crops

The only alfalfa weevils observed this week were relatively mature larvae (see fig. 1) and thus most feeding damage should be about finished. All alfalfa fields monitored had been treated, with one exception. This year’s overall alfalfa weevil infestations seemed considerably reduced compared to most of the past years. This, coupled with good growing conditions, allowed plants to keep up with alfalfa weevil feeding resulting in less defoliation then usual as seen in fig. 2 (The plant on the left was typical of an untreated field which was adjacent to a treated field from which the plant on the right was removed from).

Figure 1 Alfalfa weevil larvae (picture by Cody Wyckoff)

Figure 2 Alfalfa defoliation       Left: untreated field   Right treated field (Cody Wyckoff)

Alfalfa Pests (pea aphids, alfalfa weevil pupa)

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth

 

Alfalfa weevils have been actively feeding and developing quite rapidly throughout south central and north central Kansas during the last 7-10 days. However, infestation levels have not increased very much. The most significantly infested fields monitored during this period reached the 55% level, i.e. just over 1 larva/2 stems. Most fields were between 25-35% infested, with about 75% of the larvae at least in the late 1st- 3rd instar stage. Some fields have been sprayed and it seemed to provide good knockdown (see fig. 1 of dead larvae). All fields not treated had prepupae and pupae (see fig. 2). Alfalfa weevil larval sampling/monitoring should continue for at least another 10-14 days.

 

Pea aphid populations have decreased significantly in the last 7-10 days in the untreated fields.

Figure 1: Dead Larvae (photo by Cody Wyckoff)

Figure 2: Alfalfa Weevil Pupa (Photo by Cody Wyckoff)