The sugarcane aphid (SCA) has not been found as of yet on sorghum in Kansas. There have been a few confirmed reports of the sugarcane aphid in Oklahoma and Texas, which means the aphid is slowly making its way north (Figure 1). Activity is generally light so far, but the situation on the ground can change quickly with this 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
What can we expect this season? It’s impossible to know for sure at this time. Infestations in Kansas in 2017 were sporadic, and most issues were late season (Figure 2). But in 2016, sugarcane aphids were a significant problem on grain sorghum in Kansas, Texas, Oklahoma, and most southern states, and fields were justifiably sprayed to protect yields.
Figure 2. The distribution of SCA in 2017.
Since aphids have been found in Oklahoma, it is advisable to begin scouting while sorghum is still in the pre-boot stage. Early detection is key to the management of this pest, but treatments should be based on established thresholds. One, heavily infested plant does not equal a yield loss. Applying insecticides too soon can result in repeated applications, which occurred during the 2015 season. See scouting and treatment recommendations below.
Scouting time
Plants are vulnerable to infestation by SCA at any growth stage, but Kansas sorghum is most at risk from boot stage onward. The ability of sugarcane aphid to overwinter on Johnsongrass and re-sprouting sorghum stubble represents challenges to the management of this pest in more southerly regions.
In 2017, the SCA overwintered as asexual females on Johnsongrass rhizomes in south central Texas and northern Mexico. Infestations begin when swarms of winged aphids settle in a field and begin to establish colonies, which usually occurs after a large storm front pushes aphids from south to north. Once winged adults deposit nymphs, these immature aphids can mature in less than a week, lack wings, and have a much higher reproductive rate than their winged mothers. Established colonies of wingless aphids quickly become large and crowded, which causes winged forms to develop, until the final generation is exclusively winged once again. Thus, the trend will be for Kansas to receive SCA only after infestations to the south mature and produce winged migrants. Growers are advised to plant sorghum as early as agronomically feasible to maximize plant growth and maturity before aphids arrive. In 2017, large flights of winged sugarcane aphid arrived in Kansas somewhat later than in 2016 and a smaller area of the state was affected, despite cold wet spring weather in the south that delayed the aphids initially. It remains to be seen how the 2018 season will develop, but given the slow march across Texas and Oklahoma, we expect to see something similar to last year.
Sampling method
- Once a week, walk 25 feet into the field and examine plants along 50 feet of row:
- If honeydew is present, look for SCA on the underside of a leaf above the honeydew.
- Inspect the underside of leaves from the upper and lower canopy from 15–20 plants per location.
- Sample each side of the field as well as sites near Johnsongrass and tall mutant plants.
- Check at least 4 locations per field for a total 4 locations per field for a total of 60-80 plants.
If no SCA are present, or only a few wingless/winged aphids are on upper leaves, repeat this sampling method once a week thereafter.
If SCA are found on lower or mid-canopy leaves, begin twice-a-week scouting. Use the same sampling method, but be sure to include % plants with honeydew. Estimate the % of infested plants with large amounts of SCA honeydew (shiny, sticky substance on leaf surface) to help time foliar insecticides for SCA control on sorghum (Table 1).
Table 1. SCA thresholds
|
Growth Stage |
Threshold |
|
Pre-Boot |
20% plants infested with localized area of heavy honeydew and established aphid colonies |
|
Boot |
20% plants infested with localized area of heavy honeydew and established aphid colonies |
|
Soft dough |
30% plants infested with localized area of heavy honeydew and established aphid colonies |
|
Dough |
30% plants infested with localized area of heavy honeydew and established aphid colonies |
|
Black Layer |
Heavy honeydew and established aphid colonies in head *only treat to prevent harvest problems **observe preharvest intervals |
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 maps seen in Figures 1 and 2.
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 free myFields.info account using the link above. 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.
Sarah Zukoff, Entomologist, Southwest Research-Extension Center
snzukoff@ksu.edu
J.P. Michaud, Entomologist, Agricultural Research Center-Hays
jpmi@ksu.edu
Brian McCornack, Entomologist
mccornac@ksu.edu
Wendy Johnson, myFields Coordinator, Entomology Extension Associate
wendyann@ksu.edu
Tags: insects sorghum grain sorghum