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Corn Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Have received several inquiries relative to corn earworms in field corn and there does seem to be a good infestation of them throughout north central Kansas.  100% of the ears we have randomly checked currently are, or have recently been, infested with corn earworm larvae.

Many of these larvae are still relatively small and thus will be feeding for another week or two.  The two most common questions received this week relative to these pests are; 1) Will a rescue treatment work?  The answer – no.  Once the larvae have hatched from eggs deposited on the silks and moved into the husk, they will be protected from contact insecticides.

 

 

2) Will they re-infest these corn ears?  The answer – no.  Field corn will be too tough by the time these larvae finish feeding, pupate in the soil, emerge as adults, mate, oviposit, hatch, and larvae initiate feeding.  But, the adults of this generation will move to soybeans (soybean podworms) and/or sorghum (sorghum headworms) to oviposit and larvae can do considerable damage by feeding on soybeans within the pods and/or directly on the kernels of the heads of sorghum plants.  So, the larvae currently in corn are the “spring board” for the next generations moving into soybeans and sorghum.

 

European Pine Sawfly

–Dr. Raymond Cloyd

Yesterday (April 17, 2017) European pine sawfly, Neodiprion sertifer larvae were detected feeding on my “indicator pine” in Manhattan, KS (I was totally excited!). Young caterpillar-looking larvae are 1/4 inch in length and olive-green in color with a black head (Figures 1). Mature larvae are >1.0 inch long with green stripes. The larvae are gregarious or feed in groups on needles of a variety of pines, especially Scotch, red, and mugo pine. When disturbed, each individual larva will arch their head and abdomen (last segment of an insect body) back, forming a “C-shape” (Figure 2), which is a defensive posture to ward-off predators.

Figure 1. Young European Pine Sawfly Larvae

Eventually, larvae will strip the needles of mature foliage, leaving only the central core, which is white and then turns brown (Figure 3). In general, larvae complete feeding by the time needles emerge from the candelabra. Therefore, those really is only a minor threat of branch or tree death resulting from sawfly larval feeding. However, the loss of second- and third-year needles will be noticeable in landscape trees; thus ruining their aesthetic appearance. In late spring, larvae drop to the ground and pupate in brown, leathery cocoons located at the base of trees. Adults, which are wasp-like, emerge in fall and lay eggs in needles prior to the onset of winter. There is one generation per year in Kansas.

Figure 2. European Sawfly Larvae In A Defensive Posture (Arching Head And Abdomen Back)

Sawfly larvae look-like caterpillars; but, they are not caterpillars (Order: Lepidoptera). Sawflies are related to ants, bees, and wasps (Order: Hymenoptera). The primary way to distinguish a sawfly larva from a caterpillar is by the following: 1) sawfly larva have prolegs (fleshy abdominal legs) on every abdominal segment whereas caterpillars are missing prolegs on the abdomen and 2) caterpillar larva have hairs or crochets on their feet whereas sawfly larva do not have hairs or crochets on their feet.

Figure 3. Feeding Damage To Pine Caused By European Pine Sawfly Larvae

Sawfly larvae are not caterpillars, therefore, the bacterial insecticide, Bacillus thuringiensis subsp. kurstaki (sold as Dipel) will not directly kill sawfly larvae. Dealing with sawfly larvae involves hand-picking (you can wear gloves if you wish) or dislodging larvae from plants by means of a forceful water spray. If necessary, there are a number of insecticides that may be applied to suppress European pine sawfly populations including: acephate (Orthene), azadirachtin, carbaryl (Sevin), spinosad (Captain Jack’s DeadBug Brew and Conserve), and any pyrethroid insecticide (e.g., bifenthrin, cyfluthrin, and lambda-cyhalothrin). Be sure to read the insecticide label to make sure that sawflies are listed. For more information regarding European pine sawfly management contact your county or state extension specialist.

 

Squash Vine Borer

By Dr. Raymond Cloyd

We have received inquiries regarding cucumber and squash plants wilting and collapsing, and a recent visit to the Manhattan Community Garden (Manhattan, KS) provided evidence that the larvae of the squash vine borer (Melittia cucurbitae) are indeed active inside plants. Squash vine borers feed on squash, pumpkin, cucumber, and muskmelon.

Adults are “clear wing” moths 5/8 inches long. The front wings are covered with scales whereas the hind wings are transparent because they do not have scales. Hind wings have red-brown hairs along the edges. The body is orange-red, with gray bands and three black markings along with orange-red hairs on the abdomen (Figure 1).

Figure 1: Squash vine borer adult
Figure 1: Squash vine borer adult

Moths are active during the day with females depositing eggs on the stem near the soil level or on stems or petioles when plants begin to flower. The eggs are red-brown, flattened, 1/30 inches in diameter, and are typically located at the base of plants (Figure 2).

Figure 2: Squash vine borer eggs located at base of plant
Figure 2: Squash vine borer eggs located at base of plant

A single female is capable of producing up to 200 eggs. Larvae that hatch from eggs are white, with a dark head capsule. Young larvae are 1/4 to 3/4 inches in length and taper toward the end of the abdomen (Figure 3).

Figure 3: Young larva of squash vine borer
Figure 3: Young larva of squash vine borer

Mature or fully-grown larvae are 1.0 to 1.5 inches long (Figure 4).

Figure 4: Mature larva of squash vine borer larval feeding
Figure 4: Mature larva of squash vine borer larval feeding

Larvae that hatch from eggs immediately tunnel into the base of plants. The larvae feed for 30 days in the plant stem, and increase in size as they mature. Typically there is only one larva per stem; however, multiple larvae may be present in a single tunnel in the stem. Mature larvae leave plants and burrow into the soil to pupate by constructing brown, silkened cocoons in which they overwinter. Squash vine borer overwinters as a mature larva in the cocoon that is located 1.0 to 2.0 inches in the soil. In early spring, the adult (moth) emerges from the soil. Squash vine borer has one generation in Kansas.

At this point, squash vine borer larvae are feeding within the internal vascular tissues inhibiting the plant’s ability to take-up water and nutrients; consequently, resulting in sudden wilting of vines and plant collapse (Figure 5).

Figure 5: Plants wilting due to squash vine borer larval feeding
Figure 5: Plants wilting due to squash vine borer larval feeding

Once the larvae are inside the plant, there is little that can be done to control them or prevent damage. The tunnels inside infested plants are packed with moistened frass (fecal matter) (Figure 6).

Figure 6: Moistened frass or fecal matter inside infested plant stem
Figure 6: Moistened frass or fecal matter inside infested plant stem

Yellow-green sawdust-like frass can also be found around feeding sites at the base of vines or plants (Figure 7)

Figure 7: Frass or fecal matter near tunnel entrance of squash vine borer larvae
Figure 7: Frass or fecal matter near tunnel entrance of squash vine borer larvae

,which will be a direct indication that larvae have entered the plant.

Since the larvae are feeding inside the plant there is not much that can be done to kill the larvae; however, there are number of plant protection strategies that can be implemented during the remainder of the growing season, including: sanitation and physical control.

Sanitation: remove and dispose of all wilted plants before the larvae leave and enter the soil. Discard all plant debris such as vines and fruits after harvest.

Physical control: rototilling in fall or spring will directly kill squash vine borer pupae or bring the pupae to the soil surface where they are exposed to cold weather or predation by birds. In addition, the process of deep plowing will bury the pupae deeper in the soil profile thus inhibiting adult emergence. Another technique that may have limited use in large plantings but may be feasible for smaller plantings is to locate infested stems and vines, create slits at the base of the plant, and then use tweezers to remove and destroy the larvae inside. The plant base should then be covered with moist soil, which stimulates the production of secondary vines and/or root growth; thus helping the plant to re-establish.

There is a new up-dated extension publication on squash vine borer (MF3309) that contains current information on plant protection with images of the insect (both adult and larva) and plant damage. You can download a PDF from the following website:

http://www.bookstore.ksre.ksu.edu/pubs/MF3309.pdf

Rose Sawflies: Out With a Vengeance!

–by Dr. Raymond Cloyd

We are receiving numerous questions regarding insects feeding and completely devouring rose plants. These insects are sawflies, and there are at least two species that attack roses during this time of year: the rose slug (Endelomyia aethiops) and bristly rose slug (Cladius difformis). Rose slugs are the immature or larval stage of sawflies, which are black to yellow colored wasps.

Rose sawfly females create pockets or slits along the edges of rose leaves with their saw-like ovipositor (egg-laying devise) and insert individual eggs. Larvae hatch from eggs and resemble a slug. The larvae are 1.2 cm long when full-grown and yellow-green with an orange head (Figure 1). Larvae eventually fall on the soil surface to pupate. Rose slugs overwinter as pupae in earthen cells created by the larvae. There is typically one generation per year in Kansas. Bristly rose slug larvae are pale-green and 1.5 to 2.0 cm in length. The body is covered with numerous bristle-like hairs (Figure 2). There is generally one generation per year in Kansas.

Figure 1. RoseSawflyLarvaeFeedingonRoseLeaf
Figure 1: Rose Sawfly Larvae Feeding on Rose Leaf

Figure 2. BristlyRoseSlugLarvaeFeedingOnLeafUndersideofRose
Figure 2: Bristly Rose Slug Larvae Feeding on Spirea Plant

Rose slug larvae feed on the underside of rose leaves; resulting in leaves with a skeletonized appearance (Figures 3 and 4) and eventually they create notches or holes on the leaf margins. Bristly rose slug larvae feed on the underside of rose leaves and also cause leaves to appear skeletonized. However, the larvae may chew larger holes than the rose slug.

Figure 3. DamageonRosePlantCausedByRoseSlug
Figure 3: Damage on Rose Plant Caused by Rose Slug

Figure 4. DamageonRoseLeafCausedByRoseSlug
Figure 4: Damage on Rose Leaf Caused by Rose Slug

Small infestations of either the rose sawfly or bristly rose slug can be removed by hand and placed into a container of soapy water. A forceful water spray will quickly dislodge sawfly larvae from rose plants and they will not be able to crawl back onto rose plants. There are a number of contact insecticides with various active ingredients that are effective in suppressing populations of both sawflies. However, the bacterium, Bacillus thuringiensis subsp. kurstaki (sold as Dipel or Thuricide) will have no activity on sawflies as this compound only works on caterpillars.

Oak Vein Pocket gall: Back with a Vengeance!

–by Dr. Raymond Cloyd

We have received numerous inquiries (in fact…LOTS) regarding gall-like growth on the underside of pin oak (Quercus palustris) leaves. In some cases, many pin oak trees have extensive galling on nearly all the leaves, with the leaves twisted or distorted. In fact, one tree on the Kansas State University (Manhattan, KS) campus, located behind Umberger Hall, is nearly 100 percent infested with this gall. I really think the gall makes the tree more attractive J. The culprit is the oak vein pocket gall, which is caused by the gall-midge, Macrodiplosis quercusoroca. Galls are elongated, pocket-like swellings on the lateral veins and mid-rib of pin oak leaves (Figures 1 through 3). The gall-making organism is a small fly called a midge (Family: Cecidomyiidae). Adults are 3.0 mm long and resemble small mosquitoes (but they are not mosquitoes so do not worry). Female midges attack newly developed leaves that are unfolding – just before they are flattened. After the eggs hatch, small larvae or maggots migrate to the lateral and mid-veins, and subsequently begin feeding. After several days, tissue forms and surrounds each larva. Full-grown larvae are white and approximately 2.0 mm in length. Development is completed by mid-spring to early summer. The larvae eventually emerge from the gall, fall to the ground, and overwinter or enter diapause (a physiological state of arrested development) until the next spring. There is one generation per year. There are no control measures for this gall. Remember, this is not the gall-former that the oak leaf itch mite feeds on…that is the marginal oak leaf fold galler (Figure 4).

Figure 1. Oak Vein Pocket Gall
Figure 1: Oak Vein Pocket Gall

Figure 2. Oak Vein Pocket Gall
Figure 2: Oak Vein Pocket Gall

Figure 3. Oak Vein Pocket Gall
Figure 3: Oak Vein Pocket Gall

Figure 4. Leaf Marginal Fold Gall
Figure 4: Leaf Marginal Fold Gall

I want to acknowledge Matthew McKernan; Horticulture Agent (Sedgwick County; Wichita, KS) for keeping me abreast of the situation (and sending images) regarding the oak vein pocket gall in south-western Kansas.

European Pine Sawfly

–by Dr. Raymond Cloyd, Professor and Extension Specialist in Ornamental Entomology/Plant Protection

      European pine sawfly, Neodiprion sertifer larvae are out-and-about feeding on pine trees. Young larvae are 1/4 inch in length and olive-green in color with a black head (Figures 1 and 2).

Figure1

Figure 1

Figure2

Figure 2

Older larvae are >1.0 inch long with green stripes. The larvae are gregarious or feed in groups on the needles of a variety of pines, especially Scotch, red, and mugo pine. Larvae will strip the needles of mature foliage, leaving only the central core, which is white and then turns brown (Figure 3); eventually falling off.

Figure3

Figure 3

In general, larvae complete feeding by the time needles emerge from the candelabra. Therefore, those needles are not damaged. There really is only a minor threat of branch or tree death resulting from sawfly larval feeding. However, the loss of second- and third-year needles may be noticeable in landscape trees and ruin their appearance. In late spring, the larvae drop to the ground and pupate in brown, leathery cocoons at the base of trees. Wasp-like adults emerge in fall and lay eggs in the needles before winter. There is one generation per year in Kansas.

Although sawfly larvae look-like caterpillars; they are not caterpillars (Order: Lepidoptera) as they are related to ants, bees, and wasps (Order: Hymenoptera). The best way to tell a sawfly larva from a caterpillar is by the following: 1) sawfly larva have prolegs on every abdominal segment whereas caterpillars are missing prolegs on the abdomen and 2) caterpillar larva have hairs or crochets on their feet whereas sawfly larva do not have hairs or crochets on their feet.

Since sawfly larvae are not caterpillars, the bacterial insecticide, Bacillus thuringiensis subsp. kurstaki (sold as Dipel) will not directly kill sawfly larvae. Therefore, dealing with sawfly larvae involves hand-picking (you can wear gloves if you wish) or dislodging larvae from plants by using a forceful water spray. If necessary, there are a number of insecticides that may be applied to suppress populations of the European pine sawfly including acephate (Orthene), azadirachtin, carbaryl (Sevin), spinosad (Captain Jack’s DeadBug Brew and Conserve), and any pyrethroid-based insecticide with any of the following active ingredients: bifenthrin, cyfluthrin, and lambda-cyhalothrin). Be sure to read the insecticide label to make sure that sawflies are listed. For more information regarding European pine sawfly management contact your county or state extension specialist.

 

 

 

 

 

Alfalfa Weevil Update

— by Dr. Jeff Whitworth and Dr. Holly Schwarting

Alfalfa weevils are very active in south central and north central Kansas. We sampled many fields from 14 to 17 March and found small to medium sized (1st and 2nd instar) larvae in every field. Infestation levels ranged from 30% to 100+%.

AW early instar

Cooler weather over the next three days should slow down egg hatch and larval feeding activity. However, it does not look like the predicted low temperatures will be cold enough to harm either plants or weevils. Then, with the return of warmer than normal temperatures next week, the weevils will again become very active. Thus, if the winds are calm enough and fields are at or greater than 30% infested, next week seems like the ideal time to treat for alfalfa weevils. Only pinprick holes in leaves and a little feeding on terminals is evident so far. This, however, will quickly change if weevils are allowed to feed in 65+°F temperatures.

AW feeding

 

 

Emerald Ash Borer In Kansas: Another Quarantined County

by–Dr. Raymond Cloyd

If you have not heard, on September 30, 2015 an Emerald ash borer (Agrilius planipennis) larva was found in a girdled trap tree in Eudora, KS (Douglas County) by the Kansas Department of Agriculture. This means that Kansas has four counties in which Emerald ash borer has been detected, and subsequently quarantined, including Wyandotte, Johnson, Leavenworth, and Douglas. First detected in 2002 in Michigan, the Emerald ash borer has been found in 23 states throughout the USA (Figure 1), and is responsible for causing the death of over 30 million ash trees. For more information regarding Emerald ash borer, contact the Kansas Department of Agriculture or the Department of Entomology at Kanas State University (Manhattan, KS).

Figure1DistributionMayofEmeraldAshBorerAugust32015

 

Figure 1: Distribution May of Emerald Ash Borer August 3, 2015

Nuisance Moths = “Miller Moths” = Army cutworm Moths

–by Dr. Bob Bauernfeind

Recent questions have been received inquiring about the annoying “miller moths”.  Also, numbers of moth captures in my (at home) blacklight trap have picked up

What are they?  Why so many?  What can I do about them?

1

“Miller moth” is an all-inclusive umbrella term used to describe any plain brown drab moth.  Because virtually all moth species have wings covered with scales, those scales are fluffed off like dust-in-the-air (as dust associated with flour milling plants).  At this time of year, the “miller moths” of note are army cutworm moths, Euxoa auxillaris.

Upon close examination, army cutworm moths definitely are not plain, brown or drab.  There are 5 morphological forms (called varieties) of army cutworm moths.  Each possesses its own intricate and distinctive wing pattern.  Adding more to the visual array, brown forms of each variety are males, whereas grayish individuals are females.

2

The seasonal life history begins in the fall of the year when moths deposit eggs in the soil in fields of fall-seeded wheat, alfalfa stands and weedy fields/patches.  Eggs may hatch within several days of being deposited, but may be delayed under unfavorable/dry conditions.  Larvae preferably feed during the dark of night, and seek shelter in the soil during daytime hours.  Army cutworms overwinter as partially grown larvae (red rectangle).

3

Each year in the central plains states, overwintered army cutworm larvae resume their feeding as temperatures moderate/become warmer.  They complete their development towards the beginning of May, after which they burrow into the ground where they create protective earthen cocoons inside of which they pupate.

4

Moth emergence usually begins by late May.  Although moths are the mature form of the army cutworm, at this point in time, they are not sexually mature.  For a period of time, moths remain near areas where they emerged.  Then an undefined stimulus (likely photoperiod driven) signals moths across the central plains states to migrate westward to the higher elevations in the Rockies. There in the cool-of-summer, they feed, accumulate body fat and attain sexual maturity.  In mid- to late September, they migrate back to the central plains where they deposit eggs (as previously described) to initiate the next generation of army cutworms.

The current complaints revolve around the moths.  Again, because moths are active during evening hours, they shun daylight.  That is, with the approach of daylight, army cutworm moths seek shelter/cover in any conceivable space.  Excluding moths is difficult because they will exploit very small openings.  Because garage doors seldom are tight fitting, when one opens the garage door, a flurry of moths may rush out.   A car window left open overnight provides an attractive entry point – and when one gets ready to drive to work, he/she will be greeted by a flurry of excited moths.  Open a polycart to deposit a trash bag and you may be greeted by a rush of moths.  Take an early morning walk and as you pass a line of shrubs, you may be startled by hundreds of excited moths darting out.  And so on.  In homes, catch or swat a moth on your wall or curtains/sheers and you will find a coating of “dust” (wing scales) left behind.

An example of the “dust” produced by army cutworm moths can be seen where moths gathered from a single blacklight trap are dumped out of a garbage can.  Talk about being up-to-your-neck in army cutworm moths!

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Another interesting tidbit about army cutworm moths:  food for grizzly bears. During summer months, bears move to the higher elevations to feast on army cutworm moths.  It was determined that single moth possesses ½ calorie of fat content.  It was further estimated that a bear obtains 20,000 calories of fat on a daily basis by consuming 40,000 moths per day.

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