— Jeff Whitworth and Holly Davis
Dr. Brent Bean, Director of Agronomy with the United Sorghum Checkoff Program (USCP), recently distributed the latest list of sorghum hybrids considered tolerant to the sugarcane aphid. To find USCP’s list of the most current hybrids, please visit: http://www.sorghumcheckoff.com/farmer-resources/grain-production/hybrid-selection
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.
–by Dr. Jeff Whitworth and Dr. Holly Schwarting
Chinch bug populations throughout north central and south central KS are not going away. These small sucking insects may still cause plant lodging, especially in these areas where moisture has been lacking
A small colony of sugarcane aphids was detected in Dickinson County on 30 Aug. The colony was on the underside of one leaf on whorl-stage sorghum. Tom Maxwell, Saline Co. Agricultural Extension Agent reported finding sugarcane aphids in Saline, Seward, and Ottawa Counties, also on 30 Aug. To see the current 2017 Sugarcane aphid distribution map, please visit MyFields: https://www.myfields.info/pests/sugarcane-aphid
For monitoring and management considerations for sugarcane aphids, please refer to the Sugarcane Scout Card: https://www.myfields.info/sites/default/files/page/ScoutCard%20KSU%20v05312017.pdf
Or see the 2017 Sorghum Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF742.pdf
–by Dr. Jeff Whitworth and Dr. Holly Schwarting
Chinch bugs continue to be very active in both corn and sorghum throughout north central Kansas. Both nymphs and adults are present.
Many adults are still mating, which indicates that there are more eggs, nymphs, and adults yet to come. One consolation relative to the numerous chinch bugs in sorghum fields is that the four spotted egg eater, Collops quadrimaculatas, seems to be plentiful as well. They have been collected in samples while sweep sampling alfalfa and are also present in sorghum fields. These little beetles are predacious on insect eggs, and it has even been reported that they feed on chinch bug eggs. Not sure they will be able to provide a great deal of control on chinch bug populations but it sure can’t hurt!
Corn leaf aphids are also very plentiful throughout north central Kansas. These aphids usually feed on developing corn tassels and silks, but probably are more commonly associated with, or at least noticed in, whorl stage sorghum. These aphid colonies sometimes produce enough honeydew, and it is so sticky, that often the sorghum head gets bound up in the whorl and therefore doesn’t extend up properly. These colonies are not usually dense enough on a field-wide basis to justify and insecticide application. These plentiful aphids are also serving as a food source for many predators, i.e. lady beetles, green lacewings, etc.
Corn earworms are still plentiful in corn but as they mature, pupate, and become adults they most likely will migrate to sorghum to feed on developing kernels (between flowering and soft dough), and soybeans where they will feed on developing beans within the pods.
For more information on sorghum and soybean pest management, please consult the KSU Sorghum Insect Management guide: https://www.bookstore.ksre.ksu.edu/pubs/mf742.pdf
And the KSU Soybean Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF743.pdf
–By Dr. Sarah Zukoff, Dr. J.P. Michaud, Dr. Brian McCornack and Dr. Wendy Johnson
The sugarcane aphid (SCA) has now been reported in Sumner County. Sorghum producers in Kansas should begin scouting their fields on a routine basis. More information on scouting and thresholds for treatment can be found in the Agronomy eUpdate article “Start scouting soon for sugarcane aphid” from July 7, 2017, and at the myFields web site at: https://myfields.info/pests/sugarcane-aphid
Figure 1. Current status of the SCA. The map indicates only the counties in which the SCA has been found, and does not indicate how many or how few aphids were found in that county. Source: https://www.myfields.info/pests/sugarcane-aphid
Chemical control
Two insecticides are labeled for use on sugarcane aphid on sorghum in Kansas this season:
Sivanto (flupyradifurone)
4.0 – 7.0 fl oz/acre (0.052 – 0.091 lb ai/acre)
Transform (sulfoxaflor)
0.75 – 1.5 oz/acre (0.375 – 0.75 oz ai/acre)
Field trials show good efficacy of the above materials against the sugarcane aphid. Both have the ability to penetrate leaves through translaminar movement and kill aphids feeding on the undersides.
Maximum efficacy will be achieved by application in a large volume of water, preferably 20 gallons per acre or GPA (minimum 10 GPA) by ground or 5 GPA from the air. Laboratory trials indicate that Transform (sulfoxaflor) is relatively safe for important aphid predators such as lady beetles and lacewings and thus can be considered IPM-compatible. This is true to a lesser extent for Sivanto (flupyradifurone), but various trials have indicated a much longer period of residual activity for this material.
Both insecticides have annual application limits and growers are advised to rotate them if follow-up applications are required. Note also that preharvest intervals will be a factor to consider when treating late-season infestations, so applicators should read labels carefully and keep a log of all treatments for each field. Because Transform and Sivanto are absorbed by leaves and eventually metabolized by the plant, reinfestation can occur if large numbers of winged aphids continue to settle in the field.
When inspecting fields for treatment efficacy, note whether any live aphids are winged or wingless, as the former may indicate continued immigration rather than control failure. DO NOT attempt to control sugarcane aphid with contact insecticides that have broad-spectrum activity; these include all pyrethroid and organophosphate materials and combinations thereof. Replicated field trials indicate these materials are not effective, harm beneficial species, and often result in higher aphid numbers than unsprayed control plots.
Sorghum headworm infestations are often present when SCA is observed in a field, since this pest migrates using the same weather events. When choosing an insecticide to control headworms, use products that are less harmful to natural enemies such as Prevathon or Blackhawk, as these have proven compatible with Transform and Sivanto and less selective materials risk flaring the aphids.
The myFields web site: Keeping updated on SCA in Kansas and reporting findings
For ongoing current information on SCA in Kansas, check out the myFields web site often in the coming weeks and months: https://www.myfields.info/pests/sugarcane-aphid
It would be helpful if producers would report findings of SCA in their fields on the myFields web site as soon as the insects are found. Reports of findings are used in developing the map seen in Figures 1.
The reports used to develop each map are, in part, those submitted through the myFields web site from account holders that also have special permissions as “Verified Samplers.” Only reports submitted by these verified samplers get mapped so that we can account for data quality. However, we do encourage any account holder to report their observations on the SCA. Web site administrators can see these reports and can contact the submitter for a confirmation, a great way to get an early detection in new areas. Web site visitors will need to: 1) sign up for an account, 2) log in, 3) to get access to the ‘Scout a Field‘ feature to make reports. The Scout a Field tool is easy, you just map the observation location and select yes or no for SCA presence.
Here is the sign up page: https://www.myfields.info/user/register
Also, if sorghum producers are interested in receiving alerts, which are triggered by new reports submitted by verified samplers, they just need to sign up for a myFields account. Signing up for an account automatically signs them up for SCA alerts, but they can also opt out of them in their user preferences. The alerts include a statewide email notice when SCA is first detected in the state, and then are localized by county as SCA moves into the state. The notices will also contain latest recommendations and contact info for local Extension experts.
–by Dr. Jeff Whitworth and Dr. Holly Schwarting
Chinch bugs are very active in double cropped sorghum in north central Kansas. They are also numerous in corn but the field corn is mature enough that chinch bug feeding should be of little consequence. However, young sorghum plants, especially under less than ideal growing conditions may be seriously stressed.
For more information on chinch bug biology, management decisions, and insecticides registered to control chinch bugs please see the Sorghum Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/mf742.pdf
and Chinch Bugs: https://www.bookstore.ksre.ksu.edu/pubs/MF3107.pdf
— by Dr. Jeff Whitworth and Dr. Holly Schwarting
Adult Japanese beetles have been detected around north central Kansas in the last 7-10 days. These adults may feed on corn, sorghum, and soybean leaves, as far as field crops are concerned, and may cause some “window paneing” much like the leaf feeding of adult corn rootworms. However, this leaf feeding usually is of little consequence. In corn, these beetles will be attracted to the silks and, as they can be very veracious feeders, may clip these silks at a pretty good rate. Fortunately, they are usually localized to small “hot spots” in some fields and thus do not really justify any insecticide application. These adult Japanese beetles may be active for another couple of weeks, after which only eggs and larvae will be present, and these life stages are not a threat to these crops.
–by Dr. Jeff Whitworth and Dr. Holly Schwarting
Chinch bugs are numerous and very active throughout north central Kansas, and have been for at least the last month. The overwintering adults deposited eggs in wheat and oats, as far as our agricultural crops are concerned, and apparently the overwintering survival was relatively high because there have been huge numbers of chinch bugs migrating from these two crops. Fortunately, most of the corn and sorghum have developed enough to be able to withstand relatively large numbers of chinch bugs as they suck plant nutrients. Chinch bug populations sampled this past week consisted of 90% nymphs (both the very small reddish orange and larger gray nymphs, both of which have a transverse white stripe).
These nymphs, for the most part, are around the base of the plants feeding behind the leaf sheaths. These bugs will feed and develop for approximately another couple of weeks, then mature into adults. Mating and oviposition then will start another generation of chinch bugs that will continue to feed in corn and/or sorghum fields. With good growing conditions, most of this feeding will go unnoticed and have little effect on yield. However, if growing conditions deteriorate but bugs continue feeding, they can cause stalk lodging, which makes harvesting much more difficult. Spraying for chinch bugs at this stage of crop development is usually not effective as most bugs are relatively inaccessible to insecticides at ground level behind leaf sheaths.
–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.
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).
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.
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.
— by Dr. Jeff Whitworth and Dr. Holly Schwarting
We have had several calls this past week about large numbers small black flies/gnats on and around sorghum heads. These are not a pest of sorghum but a type of fungus gnat and are probably attracted to the fecal material left behind from sorghum headworms. In general, fungus gnats thrive in damp conditions and the larvae typically dwell in the soil where they feed on algae, fungi, and plant roots.
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