Update on sugarcane aphids and other pests of sorghum
The sugarcane aphid problem is more limited in scope this year in Kansas than in 2016, but there is still a need for vigilance in later-planted fields in central and western Kansas for a few more weeks. Grain that is now turning color is probably safe from damage. Be sure to check the myFields web site for the latest information: 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: www.myfields.info/pests/sugarcane-aphid
Other potentially destructive insects active in Kansas sorghum this year include headworms (corn earworms), chinch bugs, false chinch bugs, and lygus bugs. Grain is most at risk from these insects during soft stages.
One of the biggest challenges for sorghum producers is how to control these other insect pests without making potential sugarcane aphid problems worse by killing their natural predators. For example, we are concerned that farmers will spray headworms with broad-spectrum insecticides because these products are cheap, and in so doing, reduce natural enemy populations and flare the aphids.
We are recommending only selective insecticides for the headworms now. Two currently registered would be Prevathon and Blackhawk (Dow/Dupont). Test have shown these insecticides to be compatible with the selective aphicides recommended for sugarcane aphid control – Transform (Dow/Dupont) and Sivanto (Bayer) – and can be tank-mixed, if needed.
The threshold for the headworms hasn’t changed, but we have updated the scouting card for the SCA this year.
Figure 2. Revised scouting recommendations for sugarcane aphids in Kansas.
Figure 3. Revised thresholds for sugarcane aphids in Kansas.
The myFields web site: Keeping updated on SCA in Kansas and report findings
For ongoing current information on SCA in Kansas, check out the myFields web site often in the coming weeks: 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 are used in developing the map seen in Figure 1.
The reports used to develop each map are, in part, those submitted through the myFields web site from account holders that have special permissions as “Verified Samplers.” Only reports submitted by these verified samplers get mapped so that we can account for data quality. However, all account holders are encouraged to report their observations on the SCA, as uploaded pictures can be verified by specialists, 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.
The question of whether to spray
The question of whether to spray is a difficult one, given the current low grain prices. Consider the stage of the crop first. If your grain is already turning color, you are probably OK, but sorghum at all stages up until hard dough will be at risk from this complex of pests.
Applications costs (assuming either Transform or Sivanto is used) will range from about $12 an acre (Transform from the ground) to about $22 an acre (Sivanto from the air). There is a good chance this cost will not be recovered unless the field yields 80 bushels per acre or better – not a very encouraging proposition.
Transorm and Sivanto should also control the seed bugs, which have the potential to inflict much greater losses than the aphids, but will not control headworms, which are also having a late generation in southern regions of the state.
Growers need to consider not only the yield potential of the field, but also how much is invested in the crop. If the field is in earlier stages of development (say, just beginning grain fill), a treatment may be considered for sake of preserving the grain and the investment already made in the crop, even if it appears unlikely the cost will be fully recovered. Even in later stages of grain fill, an application may be warranted if a majority of plants are heavily infested with lots of aphids in the heads, given the risk of harvesting problems.
It is important to use a minimum of 5 gallons per acre of carrier in aerial applications, or 15-20 gallons per acre from a ground rig, in order to get good coverage of the plants. Transform and Sivanto will both penetrate the leaves and kill the aphids on the undersides. Residual activity is only about 10-14 days for Transform, but can be three weeks or longer for Sivanto. A single treatment with either product should be enough to preserve yield in plants that are in any stage of grain fill, but one should also consider that the efficacy of these materials will be significantly reduced at lower temperatures. Cooler overnight temperatures will substantially slow aphid feeding (and thus their growth and reproduction), but they can remain alive on plants as long as any green tissue remains available, even surviving successive overnight freezes. In other words, they will not die off completely until the plants do, even though they are no longer causing economic damage.
J.P. Michaud, Entomologist, Agricultural Research Center-Hays
Sarah Zukoff, Entomologist, Southwest Research-Extension Center
Brian McCornack, Entomologist
Wendy Johnson, myFields Coordinator, Entomology Extension Associate