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Extension Entomology

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Soybean Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

 

Thistle caterpillars have not all pupated or emerged as adults yet in north central Kansas.  However, probably the majority of the larvae have finished leaf feeding and the adults have initiated oviposition.  There are still large numbers of adult butterflies navigating throughout soybean and sunflower fields.  Thus, scouting for the larvae should be an ongoing endeavor for probably another three weeks.

 

At the same time there are starting to be pretty good populations of green cloverworms in these same soybean fields.  Fields in the early to mid-reproductive stages are less tolerant to defoliation.  Populations last year caused considerable skeletonizing and resulted in many acres being treated.  However, there were also numerous fields that had green cloverworms controlled by an entomophagous fungus.

 

 

 

 

This highly visible white fungus will probably attack the green cloverworms again this year and may even do so, so effectively that insecticide applications are not necessary.  However, please keep in mind there is a lag time between a green cloverworm infestation of soybeans and larval infection by the fungus leading to their destruction.  But, they usually slow down or stop feeding soon after becoming infected, even if not actually killed for a few days.

Soybean stem borers seem to be relatively numerous around north central Kansas as well.  Oviposition by the females in the stem, at the site of the petiole attachment, is continuing.  Many eggs have already hatched and larvae are tunneling downward in stems where they will internally girdle around the interior of the stem and end up in the base of the taproot where they overwinter.

 

 

 

 

Spider mites are still present in north central Kansas, but so far seem to be very spotty.  These populations need to continue to be monitored during the plant’s reproductive stages.

 

 

Corn earworm larvae (soybean podworms) seem to just be getting started in south east Kansas and can cause considerable damage quickly by feeding on seeds within the pods.

 

 

Soybean aphids were first reported on 11 Aug, 2017, from the KSU Research Farm at Ashland Bottoms, just south of Manhattan, KS, by Rene Hessel and Bill Schaupaugh. These aphids have been found in the state every year since their first detection in 2002.  Beneficial’s are usually very active around these aphid colonies and help keep them from flourishing.  However, these small aphids need to be monitored periodically, especially in soybean fields treated for other pests, as these treatments may reduce the beneficial’s, and thus, any control which they may have provided.

For management of all these soybean pests, and others, please refer to the KSU Soybean Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF743.pdf

 

 

Sorghum Hybrids with Resistance to Sugarcane Aphid

A number of sorghum hybrids have now been identified which express variable, but quite significant, levels of resistance to sugarcane aphids (SCA).  Below is a list of those which are potentially suitable for planting in Kansas, based on having early to med-early maturity.

Growers are encouraged to contact their seed suppliers for more detailed information on the agronomic characteristics of these lines.  All of these hybrids express fortuitous resistance to SCA; that is, they happen to have traits that greatly reduce their suitability as a host plant for the aphid.

Conventionally, a source of aphid resistance is first identified in some odd land race of the crop and then intentionally bred into commercially acceptable parental lines, resulting in a wide range of hybrids that all express the same trait.  Success with this approach is usually only temporary because reliance on a single trait exerts strong selection on the aphid population to evolve virulence; often only a small genetic change in the aphid is required and the trait is no longer effective.

In contrast, every example of fortuitous resistance is most likely due to completely different traits that have a similar end result for the aphids, albeit via different mechanisms: reduced immature survival combined with slower rates of growth and reproduction.  The use of multiple resistance traits will dilute the strength of selection acting on the aphids because a single genetic change is no longer likely to confer virulence to all these different traits.  Thus, the outlook going forward is very positive as we would expect these traits to remain effective for some time.

The use of resistant hybrids is encouraged because they serve to synergize the impact of natural enemies and reduce the need for spraying.  Slower aphid population growth means more time for predators to arrive in sufficient numbers and consume all the aphids before they can reach densities sufficient to escape biological control.  It also means that management decisions are not quite so urgent as aphids approach threshold numbers that may require an insecticide application.  But do not expect resistant plants to be aphid-free; they will still get infested, but the aphids will not thrive. Some hybrids may even need to be sprayed once, so be sure to scout early and scout often.

-J.P. Michaud and Sarah Zukoff

2017 Entomology/Plant Pathology Agent Training Dates and Locations

–by K-State Extension Entomology Team

February 7, 2017: Scott City, KS; William-Carpenter 4-H Building, 608 North Fairgrounds Road, Scott City, KS 67871

 

February 22, 2017: Salina, KS; 300 West Ash, Room 109, Salina, KS 67402

 

March 14, 2017: Emporia, KS, Bowyer Building on the Fairgrounds, 2700 US Highway 50, Emporia, KS 66801

 

 

 

Late-Season Update on the Sugarcane Aphid in Kansas

— by J.P. Michaud, Sarah Zukoff and Brian McCornack

 

The sugarcane aphid (SCA) has been causing a range of harvesting problems in central Kansas.  In some cases, sticky honeydew has been gumming up combines, sometimes bringing harvest to a halt, or slowing combine speeds.  Fortunately, provided the grain has hardened, you can wait for a week or so and this honeydew will be weathered by the elements (and sooty mold) so that it is no longer sticky. The sooty mold that grows on it is not toxic, and so is not a concern for the cattle for those who plan to graze the stubble.  However, palatability and nutritional value of the stubble may be somewhat reduced if aphid infestations have been heavy.

 

A more widespread problem is that aphid infestations in maturing panicles have caused uneven ripening of the grain, which in turn has caused uneven drying. Harvest has been delayed in some cases because grain moisture measurements in a field can be so variable that a decision to harvest is difficult to make.

 

Back in late September, we observed a sudden cold snap in SW Kansas (overnight low = 39 deg F) that caused significant aphid mortality (Photos 1 & 2).

photo1

Photo 1. SCA summer forms killed by 39 deg F cold shock, Garden
City, KS, Sept. 28, 2016 (Sarah Zukoff). Dead aphids are black.

 

photo2

Photo 2. Close-up of summer forms killed by cold shock (Sarah Zukoff).

 

This suggested that large numbers of aphids might be killed by low temps that were still well above freezing.  However, as day length shortens and temperatures get gradually cooler in the fall, we can see the aphids transition to a ‘winter phenotype’ with biology quite different from the pale yellow forms we see in summer. The aphids become much darker in color, slower to grow and reproduce, longer lived, and much more cold tolerant. This was evident in a field in Rooks County (thank you Cody Miller!) that had two successive freeze events last weekend (overnight lows were 23 and 26 deg F, respectively), and yet had remarkably high numbers of aphids still alive as harvest began on Tuesday.  It is possible that aphids lower down within the crop canopy were buffered somewhat from the extreme lows,  However, even though all the leaves were killed by the freeze, many aphids remained alive on the stems and in the leaf axials, with freeze-killed aphids appearing black and shriveled (Photos 3-5).

photo3

photo4

photo5

Photos 3, 4 & 5. Winter phenotype SCA that survived 2 freeze events, Rooks
County, KS, Nov. 15, and those that did not (black). (photos Ahmed Hassan).

The winter phenotype of SCA is clearly adapted to survive short, sub-tropical winters by remaining alive on any green plant tissues or vegetative regrowth, as they have been doing in south Texas (Photo 6).  Of course this will not happen in Kansas, so all the aphids will disappear once the plants are completely dead.

photo6

Photo 6. Overwintering colony of SCA in south TX, Dec. 2013 showing
dark coloration of winter phenotype (photo Raul Villanueva)

 

Great variation in hybrid susceptibility to SCA has been evident in a number of performance tests this year, with many seed companies identifying one or more lines with substantial resistance and/or tolerance to these aphids.  Farmers are should seek advice from seed company representatives on which of their hybrids have performed best under aphid pressure.

 

 

Sugarcane aphid expanding to other counties in Kansas

Sugarcane aphid has been confirmed in the following counties in Kansas: Marion, Sedgwick, Sumner, Cowley, Labette, Meade, Haskell, and Ford. Populations first reported in Sumner and Cowley counties have reached threshold levels (30% of plants infested with visible signs of honeydew on leaves) and are being treated with insecticides. Scouting fields early will help determine the need for an insecticide application before losses occur. Treating too soon may increase the need for additional insecticide treatments later, as populations can rebound based on immigration events. Scout often, as densities can change quickly. Report any infestations in new counties to your local agent or using http://myFields.info.

SCA counties KS 2 Aug 2016

Figure 1. Current counties in Kansas confirmed with sugarcane aphid in green.

Recommended treatment options for SCA control are either Transform (Dow AgroSciences) at 1 oz per acre, or Sivanto prime (Bayer CropScience) at 4 oz per acre, applied in 15 – 20 gal of water from a ground rig. Application from the air will be more costly and less effective, as it will not permit application of these materials in sufficient volume to obtain the coverage necessary for good efficacy. The cost per acre is lower for Transform, and this material is also the least toxic alternative for aphid natural enemies. If headworms are present in damaging numbers (1-2 per head or more, the majority still less than 1 inch long), Blackhawk (Dow AgroSciences), Prevathon (Dupont) or Belt (Bayer CropScience) are alternatives that can be considered for controlling them. Note that Belt registration has just been revoked by the EPA, but existing stores may be used. Of the materials labelled for headworm control, these are the ones likely to have the lowest impact on beneficial species assisting with aphid control. We have found Prevathon to be compatible with Transform in a tank mix; all other combinations should be tested first for compatibility by mixing small amounts in a jar to ensure no precipitate forms. Read the label carefully before you spray.

Alfalfa Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Swathing seems to have interrupted the potato leafhopper increases that were seen prior to cutting.  All the fields sampled prior to swathing in north central Kansas exceeded the treatment thresholds.  Conversely, all the fields sampled post-swathing had potato leafhopper population well below economic injury levels, i.e. 20 potato leafhoppers per 20 sweeps pre-swathing vs. two per 20 sweeps post-swathing.  Continued monitoring would be prudent as these pests may stray around until October and continue to produce offspring.

 

Spotted alfalfa aphids are still present in alfalfa fields but at relatively insignificant infestation levels.  These aphids seem to do very well in mid-summer’s hot, dry conditions but usually don’t reach densities heavy enough to cause yield-reducing stress.

spotted alfalfa aphid

Corn Pests

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Most corn pests have come and gone throughout north central and south central Kansas, with a few exceptions.  Japanese beetle adults have been causing concern in north eastern KS, from about Topeka to the Nebraska border and east to the Missouri border.

Japanese Beetle

Green june beetle

 

These beetles are attracted to green silks and can feed so voraciously that they eat into the husks and damage some of the kernels on the tip.  These populations usually do not occur in such numbers to affect pollination over a large area of many fields.  However, in small areas they can cause concern but are relatively well controlled if a foliar insecticide is justified.  Some adult green June beetles are also feeding on corn silks and/or ‘naked ears’ and have been mistaken for Japanese beetles.  Japanese beetles usually migrate to soybean fields to feed on pollen when fields start pollinating but probably not to the extent that they affect yield.

 

Commercial Applicator Recertification Training Programs

–by Frannie Miller, Pesticide & IPM Coordinator

November 10, 2015 – Right-of-Way, Industrial Weed and Noxious Week Category 6, 7C and 9A – 8:00am to 5:00pm Abilene Civic Center, Abilene, KS.

November 12, 2015 – Right-of-Way, Industrial Weed and Noxious Weed Category 6, 7C and 9A – 8:00am to 5:00pm Agricultural Research Center, Hays, KS.

November 16, 2015 – Aquatic Pest Control Category 5 – 8:30am to 4:30pm McPherson Extension Office, McPherson, KS.

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