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Sugarcane aphid in Kansas sorghum, 2017

by –J.P. Michaud, Brian McCornack, Wendy Johnson and Sarah Zukoff

 

As we reach the midpoint of September, it is becoming clear that the impact of sugarcane aphid (SCA) in Kansas will be only a fraction of what it was in 2015 or 2016.  Multi-state monitoring efforts using myfields.info to track SCA have reported SCA in 138 different counties in 8 states in 2017; the first record in Kansas was on August 1 in Sumner Co. You can track county movement by visiting the myFields distribution map, or sign up for an account to receive an email alert when SCA has been detected in your area. Only southwestern Kansas has had some fields with infestations heavy enough to warrant treatment, and many others have remained below threshold (see our Scouting Card for more information).  A large proportion of the earlier planted fields are now mature enough to be safe from yield losses, even though SCA may be able to survive on these plants for some time.  At this point, only the latest planted fields that have not yet filled grain remain at risk, and lower overnight temperatures are slowing aphid activity.  Remember, SCA can survive overnight freezes and continue to feed on plants as long as they have any green tissue remaining, although without any further impact on yield if grain fill is complete.

 

Decreased acreage

 

A substantial decrease in sorghum acreage this year, especially in the regions of central Kansas that were most affected in 2016, has likely impeded northerly movement of the aphid this year.  Reduced sorghum acreage, much of it converted to soybeans and dryland corn, has meant the aphid must traverse longer distances to reach suitable plants on which it can establish populations capable of producing the winged migrants that enable further spread.  But several other factors have likely been even more important.

 

Improved management

 

There has been a much higher level of awareness among sorghum growers, and much better preventive and remedial management of the aphid in the southern regions that are the source of aphids for Kansas infestations.  The widespread adoption of seed treatments in south Texas effectively prevents the infestation of young plants for up to a month or longer.  An increase in the acreage planted to the many hybrid varieties expressing resistance to the aphid has greatly impeded its ability to produce large populations so quickly.  Timely scouting and identification by concerned growers has resulted in the early discovery and effective treatment of fields that did exceed economic thresholds, which in turn reduced the number and size of alate swarms that dispersed northward in 2017. Look for more help on scouting and determining treatable infestation levels here: KSU Scout Card

 

Evolving natural enemies

 

Just as pest species can evolve new behaviors (for example, attacking a new host plant), so beneficial species can quickly evolve new pest/host plant associations.  An example of this is provided by the Asian multicolored lady beetle, Harmonia axyridis, which last summer produced very large populations in Kansas sorghum for the first time, feeding primarily on SCA.  This lady beetle was not found in sorghum previously, but was drawn into fields by abundant SCA, and is now responding to sorghum as a habitat containing many types of suitable prey.  This year we have found it regularly feeding on corn leaf aphids and greenbugs, in the absence of SCA, something we had not previously observed.  Similarly, H. axyridis did not frequent soybeans until the arrival of soybean aphid in 2002, whereupon it quickly became a key source of mortality for this aphid, and has remained a regular resident of soybean fields ever since.  While the example of H. axyridis is quite obvious and visible, many changes in the responses of other aphid natural enemies in the sorghum agroecosystem are more subtle, but also important.  For example, the greenbug parasitoid, Lysiphlebus testaceipes, appears to be gradually overcoming SCA immunity to parasitism, and we are starting to find some successfully mummified SCA.  Aphid natural enemies are now colonizing sorghum faster, and in greater numbers, in response to SCA.  Surveys for SCA in central Kansas revealed many small colonies of greenbug, corn leaf aphids, yellow sugarcane aphids, and English grain aphids, all approaching extinction due to heavy predation and parasitism.  Lacewings and hoverflies were especially abundant, with adults flying everywhere and several lacewing eggs on almost every lower leaf, independent of the presence of any aphids.

 

In summary, we are clearly advancing from the epidemic phase of the SCA invasion to the attenuation phase, and considerably faster than we might have expected.  Vigilance will be required for the next few years, and appropriate monitoring and management will need to be maintained, but it is quite possible that 2016 will mark the high point for SCA problems in Kansas and we will not see another year that bad again.

 

Photo caption:

 

A colony of sugarcane aphid showing evidence of substantial predation.  Note ‘bloodstains’ (aphid hemolymph) along leaf midrib and the fact that aphids are widely scattered rather than forming a compact colony.

Sorghum Update – Sugarcane aphids

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Sugarcane aphids are still present in sorghum fields examined over the last week but, like soybean aphids, seem not to have increased in densities or coverage.  However, continued monitoring is prudent.

 

To see the current sugarcane aphid distribution map please visit MyFields: https://www.myfields.info/pests/sugarcane-aphid

For management decisions please refer to the 2017 Sorghum Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF742.pdf

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 aphids still hanging on!

–The KSRE Field Crop Entomologists Team

Sugarcane aphid populations continue to persist in sorghum across much of Kansas, but cooler temperatures are slowing them down considerably. However, monitoring populations is still strongly encouraged as infestations can grow quickly if temperatures warm up. Winged aphids are moving from early planted sorghum fields to late planted fields, so pay close attention to whether infestations are winged or wingless. Wingless aphids have the potential to increase rapidly, but several factors, including presence of natural enemies, can help slow population growth. In all cases, be sure to monitor populations closely. Bottom line: scout often.

photo-sep-20-12-28-09-pm
Winged aphids (alates).

Yield loss due to aphid feeding can occur up through black layer. However, most losses caused by sugarcane aphid occur between boot stage and up through soft-dough (50% dry weight in the seed) stage; more data is needed to understand losses between hard dough and black layer, but seed weight (grain quality) and total yield may be reduced. Further details about sorghum growth and development can be found here (MF3234.pdf).

photo-aug-30-12-18-10-pm
Lady beetle eggs in a sorghum head.

Harvest of early-planted sorghum is underway, and late-planted fields are only a couple of more weeks from being ready (depending on weather conditions). Most decisions to spray for sugarcane aphid this time of year are aimed at avoiding mechanical issues associated with high aphid numbers and honeydew coating leaves and heads. Although buildup of honeydew can cause significant harvest problems, this is not an inevitable outcome. Weathering can reduce honeydew stickiness, so once grain is fully ripe, delaying harvest for a week or two may be an option, provided there is no indication of lodging. As lower leaves senesce or die off, aphids migrate to the upper leaves and eventually into the heads. We have observed this behavior in several fields this fall. However, colder overnight temperatures will significantly retard aphid growth and reproduction, and significant aphid mortality may occur before freezing.

Aside from honeydew and potential mechanical issues, lodging can also be associated with high aphid populations. It is important to understand that sugarcane aphid is not the only pest in sorghum this fall. We have observed high levels of 2nd generation chinch bugs feeding behind panicle leaf sheaths, which can also weaken stalks and cause lodging. In addition, from a plant physiology standpoint, during the last weeks of grain filling sorghum stems tend to shrink due to natural plant remobilization process, affecting final stalk strength.

When making a decision to treat so close to harvest, growers should consider four main factors: 1) overnight temperatures, 2) stage of crop maturity and potential yield, 3) aphid density, and 4) and the preharvest interval for registered insecticides. If the aphids have been heavy, but your grain has turned color, you may want to wait until the honeydew weathers to become less sticky before trying to harvest it. Read and follow the insecticide labels. For Sivanto and Transform, the preharvest interval is 2 weeks. Follow forecasted temperatures for upcoming weeks. Cooler nights will slow populations. We’ve observed aphids killed by 10 hours at 46F in a small lab study, but more data are needed to understand what low temperatures, for what period, will kill them under field conditions.

photo-sep-28-4-36-32-pm
Sugarcane aphids after exposure to freezing temperatures.

Again, monitoring fields and relying on more than a single sampling event will provide additional information for making a treatment decision. The only reason to treat aphids past black layer is to avoid potential harvest issues. Killing aphids this fall will not impact aphid populations next year in Kansas. This is a migratory pest and will not overwinter in Kansas.

Transform approved for use in Kansas to control sugarcane aphid

—by the KSRE Field Crop Extension Entomology Team

This week, Kansas received a section 18 approval for the use of Transform (sulfoxaflor) against sugarcane aphid for 2016, which will give sorghum growers two effective materials to manage aphid infestations. Note, there are differences in price between these two products, which should be factored into any treatment decisions, especially when multiple applications may be necessary.

Recent reports have sorghum receiving insecticide treatments for relatively light populations of sugarcane in south Texas, but the aphid is beginning to slowly move north, so the potential exists for much earlier infestation of Kansas sorghum this year. There are also confirmed reports that the aphid overwintered on Johnsongrass rhizomes just north of Lubbock, TX. This is about about 80 miles further north than in 2015. Reports from Texas indicate some of the cultivars rated as resistant seem to be holding up well, probably with the assistance of good natural enemy populations.

The Sorghum Checkoff has a list of ‘tolerant’ (= resistant) hybrids, but it does not indicate any regional adaptations for the hybrids. We have not yet ranked Kansas-adapted hybrids for resistance to sugarcane aphid, but efforts are underway to evaluate hybrids this summer. We strongly recommend that growers and extension agents contact their local entomology specialists for advice, as management recommendations will vary regionally.

Scout early, scout often, and know before you spray!

 

Preplant considerations for the sorghum sugarcane aphid

sca bowlingA new report from Robert Bowling (TAMU) revealed that sugarcane aphids (SCA) are building in southern Texas volunteer sorghum and may soon start to move into Central Texas. What this means for Kansas and Oklahoma sorghum is still unknown at this point, but it is worth noting the aphid got a much slower start last year. In preparing for possible SCA aphid infestations, there are a few important things farmers should consider prior to planting sorghum this season:

  • Plant as early as possible to give plants a head start on the aphids, which tend to arrive later in the growing season.
  • Currently, the insecticide Sivanto (Bayer) is the only chemical labeled for Kansas sorghum for managing sugarcane aphid infestations. Last season in 2015, Kansas had a Section 18 approval for the insecticide Transform (Dow), and although a 2016 Section 18 has been requested, this has yet to be approved for Oklahoma or Kansas.
  • Efforts are underway to screen hybrids for resistance to SCA, but few are being sold as resistant so far. However, data collected so far suggests that a number of varieties rated as resistant to greenbugs also express resistance to SCA – but not all of them.
  • Farmers can expect SCA to arrive in Kansas as early as July, depending on weather conditions and wind direction. Be sure to monitor the spread of the aphids northward migration via updates from this blog, county agent updates, and twitter.

Read Dr. Bowlings full article here: https://drive.google.com/file/d/0B4lb0hWyS3iMaGV5dVVIcUd1YUE/view?usp=sharing

-Sarah Zukoff and JP Michaud

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