Sugarcane aphid (SCA) has been collected in two western Kentucky Counties. County Extension agents Ben Rudy (Fulton County) and Trent Murdock (Graves County) have collected SCA from grain and sweet sorghum respectively. Identity was confirmed by Dr. Lee Townsend, Extension Entomologist with the University of Kentucky (UK) in Lexington. Thus far, only the two infestations have been reported. The infestation in Fulton County is below treatment threshold, but the infestation in Graves County is much larger.
Regardless of population size, this does confirm that this new sorghum pest, which likely migrates in from the Deep South, can reach Kentucky during (if late) in the production season. Sugarcane aphid is a threat to all forms of sorghum (grain, forage, sweet) and will infest many other grasses, including Johnson grass, which can act as a host for reproduction and a source of infestation.
Even though this pest in now present in Kentucky, it is important to remember that it is relatively late in the season. Early planted sorghum may escape economic damage from SCA altogether. It is the late planted crop that is most at risk. In either case, it is important to consider that even if the grain crop is made, an aphid population large enough to produce large quantities of honeydew may result in difficulty at harvest.
Scouting for Sugarcane Aphid
Treatment thresholds are based on the experience of our colleagues further south. Make sure you have sugarcane aphid and not one of the other aphids that may be found on sorghum (e.g. yellow sugarcane aphid, corn leaf aphid, green bug).
To detect early infestation, weekly check one leaf on each of 50 plants scattered across the field.
- If SCA is not present, check again in 1 week. Start scouting more frequently once SCAs have been found in your field(s).
- If SCA is present, scout 2 times per week and use a threshold of an average of 50 to125 SCA per leaf on 50 leaves taken from plants scattered across the field. If this number is exceeded, an insecticide application is warranted.
Management With Insecticides
It is vitally important that one does not begin insecticidal control before it is warranted. Once the first insecticide application is made, the many and various natural enemies that are feeding on SCA will be killed, and the SCA populations will be left to increase unhindered by these natural controls.
Most of the insecticides labeled for use on sorghum provide poor control of SCA. Lorsban, dimethoate, and malathion are registered for control of aphids on grain sorghum, but are not as efficacious against SCA as the newer products.
Sivanto 200 SL (Bayer)
This insecticide may be applied at 7-day intervals at 4 to 7 ounces per acre with a maximum use of 28 ounces per acre for the whole season. It has a pre-harvest interval of 21 days for dried grain, straw or Stover and 7 days for grazing, forage, fodder, or hay.
This product may be used against SCA based on the manufacturer’s Section 2(ee) recommendation. My understanding is that use of a 2(ee) recommendation requires that the applicator have a copy of the label in hand while making the application. Copies of the 2(ee) recommendation may be available from your dealer. If not, you can obtain a copy of the Sivanto 200 SL 2(ee) recommendation posted to the UK Extension Entomology webpages or from Agarian.com.
Transform WG (Dow)
Several states received a Section 18 Emergency Exemption in 2014 and again in 2015 for the use of this product against SCA in grain sorghum. Kentucky does NOT currently have this exemption. It is my understanding that the Kentucky Department of Agriculture Division of Environmental Services has or soon will submit a request for use of this product to the US Environmental Protection Agency (EPA). At this writing, that exemption has not been granted, so use of this product in Kentucky for SCA on grain sorghum is not allowed. If that exemption were to be granted, application of Transform would be limited to two applications per season, at least 14 days apart at a rate of 3 ounces per acre for a total use of 6 ounces per season. Transform has a 14 day pre-harvest interval for grain or straw and 7 days for grazing of forage, fodder, or hay.
Avoid Development of Resistance
Aphids reproduce at a very fast rate and in large numbers, which raises concerns about their developing resistance. It is vitally important that we protect the products that we have by not over using them. Do not apply early. Do not apply unless the threshold is met and do not apply more material than the label allows.
By Doug Johnson, Extension Entomologist