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Extension Entomology

Month: August 2016

Sorghum Pest Update

— by Dr. Jeff Whitworth, Dr. Holly Schwarting and J.R. Ewing

Much sorghum throughout north central Kansas is at least in the soft dough stage and thus has passed through the most susceptible stages for sorghum headworm infestations.  However, any sorghum yet to head out will still be susceptible to these headworms as there will still be at least one more generation.

All four aphids species, corn leaf, greenbugs, sugarcane, and yellow sugarcane, are still in every sorghum field we sampled throughout north central Kansas.  All populations seem to be increasing but there are relatively healthy populations of beneficials present as well.

SCAwLB

Soybean Pest Update

— by Dr. Jeff Whitworth, Dr. Holly Schwarting and J.R. Ewing

Green cloverworms have been causing considerable concern throughout the eastern 2/3rd’s of Kansas.  This has resulted in many acres treated to limit defoliation caused by these fragile little green and white striped worms.  Fungal-infected green cloverworms are also relatively common.  This fungus usually helps regulate green cloverworm populations, but remember, there is a lag time before the fungal infection decimates the larval populations, unlike an insecticide which usually works very quickly.

GCW fung

GCW defol

 

There are also a few yellowstriped armyworms still causing defoliation.  However, one yellowstriped armyworm larva collected in south east Kansas, brought into the lab appearing healthy, succumbed to a pathogen, probably a virus, within 3 days.  So, there are other factors working to help control many pest populations, i.e. fungal and viral pathogens.

YSAW viral

 

Corn Earworms/Sorghum Headworms/ Soybean Podworms – Helicoverpa zea (Boddie)

— by Dr. Jeff Whitworth, Dr. Holly Schwarting and J.R. Ewing

There has been much activity this year by this particular insect, starting in whorl stage corn and moving to sorghum (both whorl and heading stages) and now in soybeans.

soybean podworm pod

Likewise, there has been some concern that all this activity and resultant insecticide applications have cause an increase in insecticide resistant Helicoverpa zea populations.  So, thanks to great effort on the part of Ethan Kepley, consultant in south east Kansas, who collected all the Helicoverpa zea larvae in one morning from an untreated soybean field, and Steve Freach, FMC, who was kind enough to transport all the larvae directly from the field to our lab, it was possible to conduct a bioassay.  The results of this insecticide bioassay are shown below.

 

Approximately 300 corn earworm/soybean podworm/sorghum headworm, Helicoverpa zea (Boddie), were collected from an untreated soybean field in south east Kansas.  Larvae (mixed sizes but predominantly relatively large instars, which are known to be more difficult to kill quickly) were equally divided into 6 treatments (Table 1).  Larvae were placed individually in small petri dishes that had been coated with the selected insecticide at the rate listed and set aside to dry for 4 hours prior to adding the larvae.  All treatments were individually evaluated 24 hours after the larvae were placed in the petri dishes.  Larvae were evaluated as live: no apparent effect; moribund: larvae very sluggish, little or no movement unless prodded and then only very slow, unnatural movement, and; dead: no movement even when prodded.  From this bioassay there does not appear to be any insecticide resistance to those insecticides and rates utilized (Table 1).

 

Treatment % of Larvae Live % of Larvae Moribund % of Larvae Dead
Hero @ 6 oz/a 0 3.4 96.6
Lorsban @ 2 pts/a 0 8.6 91.4
Mustang Maxx @ 4 oz/a 0 10.9 89.1
Baythroid @ 2.8 oz/a 0 15.5 84.5
Warrior II @ 1.6 oz/a 0 3.4 96.6
Untreated 87.5 9.4 3.1 (parasitized)

 

 

Mimosa Webworm

— by Dr. Raymond Cloyd

Now is the time of year when mimosa webworm (Homadaula anisocentra) larvae (=caterpillars) are feeding and creating their protective habitat on honeylocust (Gleditsia triacanthos) and mimosa (Albizia julibrissin) trees. The larvae (=caterpillars) are 1/2 inch in length when fully-grown, and rapidly move backward when disturbed (Figure 1).

Figure 1. Mimosa Webworm Caterpillars Feeding On Leaves (Raymond Cloyd)

Fig 1. Mimosa Webworm Caterpillars Feeding On Leaves (Raymond Cloyd)

 

The caterpillar webs leaves together on the ends of branches (Figure 2).

Figure 2. Mimosa Webworm Webbing On Branch End (Raymond Cloyd)

Fig 2. Mimosa Webworm Webbing on Branch End (Raymond Cloyd)

Webbing typically starts at the tops of trees and serves to protect caterpillars from natural enemies (parasitoids and predators) and insecticide spray applications. Heavily-infested trees are brown or scorched in appearance (Figure 3) as the caterpillars skeletonize the leaf tissue. Caterpillars eventually fall from trees on a silken strand before pupating. Mimosa webworm pupates in bark crevices or pupae will be glued to structures (e.g. building). In regards to controlling mimosa webworm infestations, it may be too late although initial damage may be minimal. Insecticides that may be used to suppress mimosa webworm populations, in which the caterpillars are exposed, include: acephate (Orthene), Bacillus thuringiensis subsp. kurstaki (Dipel), spinosad (Conserve), carbaryl (Sevin), and several pyrethroid-based insecticides (e.g. bifenthrin and cyfluthrin). Read the label of each product to ensure that “webworms” are listed on the label. High-volume spray applications are essential in order to contact the caterpillars inside the protective webbing. If trees are already heavily-infested with webbing then it may be too late to apply an insecticide. If possible, selective pruning can quickly remove isolated or localized infestations of mimosa webworm.

Figure 3. Mimosa Webworm Feeding Damage (Raymond Cloyd)

Fig 3. Mimosa Webworm Feeding Damage (Raymond Cloyd)

 

Fall Webworm

— by Dr. Raymond Cloyd

The fall webworm (Hyphantria cunea) is prevalent throughout Kansas with webs noticeable on certain trees and shrubs, which is the start of the second generation. Fall webworm nests are typically quite evident in August and September, with silk webbing enclosing the ends of branches and associated foliage or leaves (Figures 1 and 2).

Figure 1. Fall webworm nest on birch tree (Raymond Cloyd)

Fig 1: Fall webworm nest on birch tree by Raymond Cloyd.

Fall webworm larvae (=caterpillars) are pale-green to yellow to nearly whitish in color with black spots (two per each abdominal segment).

Figure 2. Fall webworm nest and accompanying feeding damage (Raymond Cloyd)

Fig 2: Fall webworm nest and accompanying feeding damage (Raymond Cloyd)

The caterpillars are covered with long, white hairs (Figure 3). They feed on a wide range of trees, including: birch, crabapple, maples, hickory, pecan, and walnut. Fall webworm caterpillars, unlike eastern tent caterpillars, remain within the enclosed webbing and do not venture out to feed. Caterpillars consume leaves, resulting in naked branches with dirty webbing attached that contains fecal deposits (“caterpillar poop”). Although feeding by fall webworm caterpillars may ruin the aesthetic appeal of infested trees; the subsequent damage is usually not directly harmful to tree health because trees are primarily allocating resources for storage instead of producing new vegetative growth. The most effective means of dealing with fall webworm infestations is to simply prune-out the webs that enclose the caterpillars. Insecticide sprays may not be effective because the caterpillars remain in the webbing while feeding; thus reducing exposure to spray residues. If insecticides are too be used then be sure to use high-volume spray applications that penetrate the protective webbing or use a rake to disrupt or open-up the webbing so that the insecticide spray contacts the caterpillars.

I need to acknowledge Jeff Otto of Wichita, KS for bringing to my attention that fall webworm was active.

Figure 3. Close-up of fall webworm caterpillar (Raymond Cloyd)

 

 

Fig 3. Close-up of fall webworm caterpillar (Raymond Cloyd)

 

Sorghum Pests Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Double cropped sorghum may still have some ragworm feeding during the whorl stage (see photo).  In addition, there will probably be at least one more generation of headworms and thus later planted sorghum needs to be monitored for headworms between flowering and soft dough when it is vulnerable.  Also, continue monitoring for aphids as there still seems to be a pretty good mixture of greenbugs, corn leaf, yellow sugarcane, and sugarcane aphids.  Some of the fields treated for headworms have reduced numbers of beneficials so they may not be there in sufficient numbers to help control these aphids.  However, some of the fields sampled this week that were sprayed for headworms at least 2 weeks ago had pretty good populations of beneficials already building back up.

sorghum headwormsfall armyworm_sorghum

 

 

Soybean Pests Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Green cloverworm larvae have been rapidly increasing all throughout the eastern 2/3rds of Kansas.  These worms are very well camouflaged and usually feed on the underside of leaves, thus are not always evident until holes start showing up in leaves.

green cloverwomr larva

soybean defoliation

There has been concern relative to this leaf feeding but generally it is not until the density reaches 10-12 larvae/ row ft. with about 30% defoliation, and larvae are still small (1/2 inch or less) that an insecticide application may be justified.  However, in past years when those cloverworm densities have been achieved there has been an entomopathogenic fungus that rapidly decimates the populations.  This seems to be starting this year, as the first fungal-infected green cloverworm larvae were noticed on 23 August in several counties in Kansas.  This fungus causes the green cloverworm larvae to stop feeding after 12-24 hours of infection and causes death 24-48 hours later.  Sometimes, these infected larvae still look alive even in death, which is one of the characteristics of this fungus.  There will probably be at least one more generation of green cloverworms to come.

fungal GCWfungal GCWs

Don’t forget to continue monitoring for adult bean leaf beetles, stink bugs, and podworms, all of which may feed on pods and/or seeds.  There will probably be one more generation of podworms this year.  For more information on soybean pests please see Soybean Insect Management 2016, available here: https://www.bookstore.ksre.ksu.edu/pubs/MF743.pdf

 

Cicada Killers

–by Dr. Raymond Cloyd

We have received numerous inquiries regarding large wasps flying around. These are the eastern cicada killer, Sphecius speciosus, which is actually a beneficial insect due to regulating dog day cicada (Tibicen pruinosa) populations. The cicada killer hunts and provisions each cell within a nest with a cicada, which becomes the food source for young cicada killers or larvae. Cicada killers are an urban nuisance pest, especially when nesting, sometimes in large numbers, in a bare area or area around a structure. People get concerned because cicada killers resemble giant yellowjackets.

Cicada killers are approximately 2.0 inches in length and black, with yellow-banded markings on the abdomen. The head and transparent wings are reddish brown (Figure 1).

Figure1CicadaKillerAdult (Daniel Gilrein)

Figure 1: Adult cicada killer (Photo Credit: Daniel Gilrein)

Cicada killers are not dangerous, but they are intimidating. These are ground-nesting solitary wasps, with the female digging a 6 to 10-inch burrow (1/2 inch in diameter) in the ground; usually in sandy or loose soil. A pile of soil or sand, depending on the soil type, typically surrounds the entrance. The female locates and stings a large insect such as a cicada or katydid and then brings the immobilized “prize” back to the burrow (Figure 2).

Figure2CicadaKillerFemaleTransportingParalyzedCicadaToBurrow (Raymond Cloyd)

Figure 2: Adult female cicada killer transporting paralyzed cicada to burrow (Photo Credit: Raymond Cloyd)

burrow (Figure 2).

The female then places the paralyzed insect into a chamber and lays an egg on the body of the paralyzed insect; sometimes the female places two paralyzed insects in a burrow but lays an egg on only one. The female cicada killer eventually covers the burrow, digs another, and repeats the process. The egg hatches into legless grub-like larva that consumes the paralyzed insect. Full-grown larvae overwinter in the burrow, pupate in the spring, and emerge as an adult during the summer (July and August).

Male cicada killers establish aerial territories and patrol for intruders. A male cicada killer wards off other males that enter his territory and attempt to mate with females. Anyone else, such as a human, walking into the territory is typically confronted by a very large wasp that hovers in front of the face and “zips” to the side and back. However, after determining that the “intruder” is not a rival, the male cicada killer ignores the individual. However, as a person walks across a lawn, fairway, or other area where these wasps are nesting, the process is repeated through each male’s territory. Cicada killers are unlikely to sting a person. Wasp and bee stingers are modified egg-laying devices (ovipositors), so males are unable to sting. Females may sting if crushed by being stepped on with bare feet or grabbed with bare hands.

Cicada killers are more common in areas with bare soil, so mulching, planting ground covers, or sodding may reduce potential problems. Cicada killers can also be a problem in well-maintained areas such as irrigated and regularly fertilized turfgrass. They are a major problem when nesting in areas accessible to or frequented by the public. Applying carbaryl (Sevin) or a pyrethroid-based insecticide containing the active ingredient permethrin, bifenthrin, cyfluthrin, and/or lambda-cyhalothrin to the burrowed area should kill females in golf course sand traps. Once the females are gone, males eventually leave. In home yards, sandboxes should be covered with a tarp when not in use since this deters cicada killers. Sand below swings, jungle gyms, or other playground equipment can be replaced with bark mulch or shredded tires.

Managing cicada killers in volleyball courts and baseball infields is more of a challenge because people with minimal clothing and exposed skin are diving and sliding onto the ground, which makes it difficult to recommend using an insecticide on a volleyball court. In these cases, the use of a geotextile fabric placed beneath the sand may create enough of a barrier to prevent cicada killers from creating burrows. The recommendations mentioned above will only be effective if cicada killer populations are not excessive.

 

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