The invasive sugarcane aphid (SCA) Melanaphis sacchari has arrived to Kentucky almost a month ahead of its 2015 appearance (KPN). Sugarcane aphids have caused yield losses of 30% to 100% for sorghum growers since 2013 in many states of the U.S. Sugarcane aphids affected severely grain and sweet sorghum fields last year in Georgia, South Carolina, Missouri, Tennessee, and Kentucky.
Last Friday (7/15/16), a small number of sugarcane aphids were detected in a field of sweet sorghum in Trigg County (Figure 1). A single SCA aphid also was found on a sorghum field at the Research and Education Center in Princeton (Caldwell Co.) on 07/19/16 after a thorough search. Although the numbers are still low, populations may pick up soon. So far in the U.S., all SCA populations are composed of female individuals. Each female can produce 6 to 12 nymphs per day, and in less than 1 week it can complete its life cycle. This rapid life cycle can cause quick outbreaks of SCA populations.
Insect Description
Sugarcane aphids can be identified by their grey to tan yellow body color. Also, their cornicles or “tailpipes,” feet, and antennae are dark (Figure 2). Sugarcane aphids feed on the lower surface of the leaves, and their feeding produces yellow to red or brown leaf discoloration, which is visible on both sides of the leaf. Indirect damage is caused by the abundant honeydew, which may support the growth of black, sooty mold fungi. Honeydew coated leaves can stick to the inner parts of harvest equipment, preventing efficient movement of crop material through the machine and causing choking or damages to combines.
Figure 1. An adult sugar cane aphid (pink arrow) and first instar nymphs (blue arrows) detected on a sweet sorghum field in Trigg County, KY on 07/15/16. (Photo: Raul T. Villanueva, UK)
Figure 2. Alate (migrant) and wingless adult SCA, and their nymphs. Notice the dark color on cornicles or “tailpipes”, tarsi of feet, and antennae. . (Photo: Raul T. Villanueva, UK)
Monitoring
To monitor for SCA:
- Walk 20 to 30 feet into the field
- Select 10 plants randomly while walking along 50 feet of a row
- Check two leaves per plant, one near the bottom (2nd or 3rd leaf from the ground) and one near the top (a leaf under the flag leaf)
- Tally the numbers of SCA present in each leaf.
Repeat this in at least 4 or 5 different sites per field (a total of 80 to 100 plants per field). Take the average of all these leaves. If this average is between 30 to 135 aphids perleaf up to boot stage of development, then make an insecticide application.
Johnson grass is a host of SCA, and the management of this grass should be part of the strategies to control SCA. The description of the insecticides for the control of SCA in grain and sweet sorghum is described below.
Management
For grain sorghum
Growers targeting SCA can apply flupyradifurone (Sivanto Prime ™, Bayer) at a rate of 4 oz./A under a Section 2(ee) label in several states including Kentucky. Flupyradifurone can be applied up to 28 oz/A annually, with a minimum 7-day re-treatment interval.
Sulfoxaflor (Transform WG™, Dow AgroSciences), is another effective product against SCA. The Environmental Protection Agency (EPA) limits applications of sulfoxaflor to two per acre per year. A minimum treatment interval prevents applications less than 14 days apart, and no more than 3.0 ounces of sulfoxaflor per acre per year is allowed. I heard that a section 18 exemption will be granted this week (07/20/16) by EPA to allow the use of sulfoxaflor in grain sorghum in Kentucky.
For sweet sorghum
There is no effective registered product against SCA in sweet sorghum in Kentucky yet. However, I heard that soon EPA will have an exemption for an insecticide that can be used to target this pest in sweet sorghum.
Disclaimer
The University of Kentucky does not endorse the products mentioned, nor does it disapprove products not listed here. Please check the insecticide label for the proper rates. This information may not apply to pest management for states other than Kentucky.
By Raul Villanueva, Extension Entomologist
Kentucky Pest News 