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Extension Entomology

Month: November 2016

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).

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

 

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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).

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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.

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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.

 

 

Alfalfa Update

— by Dr. Jeff Whitworth and Dr. Holly Schwarting

Alfalfa in north central Kansas doesn’t seem to be in the overwintering mode yet.  It is still growing, albeit slowly.  But, the unusual situation this warmer-than-average fall weather has caused is with alfalfa weevils.  On 16 November, several alfalfa fields were sampled in north central KS and many adult alfalfa weevils were captured.  However, the unique situation was the sampling of many alfalfa weevil larvae. Some leaf feeding by these larvae was also evident. These insects are normally univoltine (one generation of alfalfa weevils/year).  The adults are moving, or have moved, back into the alfalfa fields by now and started laying eggs.  Eggs laid in the fall are not normally developed enough to hatch this time of year.  Late February is usually the earliest that alfalfa weevil eggs hatch.  After the coming cold front moves through and temperatures warm back up we will re-sample to determine how the cold temperatures impacted these larvae.

aw-adult-nov

 

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Also, there are many pea aphids present which is not as unusual for this time of year.  Numerous lady beetles are also present but they do not seem to be feeding on either pea aphids or alfalfa weevil larvae.

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Oak Leaf Itch Mite

–by Dr. Raymond Cloyd

We are still receiving many inquiries regarding the oak leaf itch mite (Pyemotes herfsi) and what can be done to avoid getting bitten. This is the first time in Kansas that the oak leaf itch mite has been a problem in successive years (2015 and 2016), which is likely associated with the mild winters we have experienced. Below is information associated with the oak leaf itch mite:

 

  1. The oak leaf itch mite may have originated from Europe based on documentation from 1936.
  2. There have been four major infestations of the oak leaf itch mite in Kansas: 2004, 2009, 2015, and 2016.
  3. The oak leaf itch mite is associated with the oak marginal leaf fold gall (Figure 1), which is produced by a midge gall-maker (Macrodiplosis erubescens).

 

figure1oakmarginalleaffoldgall

 

Figure 1: Oak Marginal Leaf Fold Gall

  1. Mated females of the oak leaf itch mite prey on midge larvae.
  2. Females enter galls through openings and inject a potent neurotoxin that paralyzes midge larvae.
  3. A single female can produce between 200 and 300 eggs. Females deposit eggs into a pouch or ovisac that forms at the tips of the abdomen (Figure 2). Millions of individuals can be produced within a short period of time.

 

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Figure 2: Oak Leaf Itch Mite Female Ovisac

 

  1. In seven days, immatures develop into adults (7 day life cycle). As a result, the oak leaf itch mite has one of the highest rates of population increase.
  2. Oak leaf itch mites can be dispersed via wind for hundreds of miles.
  3. Cooler temperatures and moist conditions may result in increased populations.
  4. Oak leaf itch mites emerge from the galls and fall from oak trees (primarily pin oak) from late July through fall. As many as 370,000 mites per day can fall from oak trees (yikes!).
  5. The mites bite anyone under oak trees with bite marks appearing 10 to 16 hours after exposure.
  6. In order to avoid bites, refrain from any activity under pin oak trees. Bites typically occur in the upper body region where clothing is loose; such as the neck, shoulder, and chest because the mites drop from the canopy of infested trees. The scratching, in response the bites, may result in secondary bacterial infections.
  7. People are susceptible to oak leaf itch mite bites when: 1) raking leaves, 2) sitting under infested oak trees, and/or 3) handling pets (dogs or cats) that have been around pin oak trees.
  8. Thorough bathing after exposure to infested oak trees, and washing clothing daily will reduce the number of bites.
  9. Oak leaf itch mite overwinters in protected areas or within leaves/leaf litter on the ground.
  10. Repellents such as DEET (N,N-diethyl-meta-toluamide) are not effective in preventing bites associated with the oak leaf itch mite.
  11. Wearing a Tyvek® suit (Figure 3) is one of the best ways to avoid getting bitten by oak leaf itch mites.

figure3tyveksuittoavoidbitesfromoakleafitchmite

 

Figure 3: Tyvek Suit To Avoid Bites From Oak Leaf Itch Mite.

 

18. We do not recommend burning any pin oak trees.

For more information regarding oak leaf itch mites contact the Department of Entomology at Kansas State University (Manhattan, KS).

 

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