Over the past two growing seasons, a difficult new insect pest of grain sorghum has been found across the mid-south. This new pest is the sugarcane aphid, Melanaphis sacchari (Figure 1).
Do not confuse this pest with the yellow sugarcane aphid, Sipha flava, which has been around the lower Mississippi river valley for several years. These are two completely different insects. Before we go any further, it is important that you understand that at present, NEITHER of these aphids have been found in Kentucky. My concern is one of preparation, as both of these aphids are found in western Tennessee and southeastern Missouri. The information that follows is specific to the sugarcane aphid, which has been shown to be a very damaging pest on grain sorghum. What I can tell you about this pest is a compilation of information obtained from my Extension entomology colleagues in states to the south of Kentucky. We are fortunate to have information developed by my colleagues in Tennessee, Missouri, Arkansas, Mississippi, Texas, and Louisiana to draw upon before this pest shows up in Kentucky; IF it does show up in Kentucky. So here is the story:
First Discovery and Distribution of Sugarcane Aphid
In July of 2013, the state of Louisiana discovered a new species of aphid in grain sorghum that had not previously been noted as a pest of grain sorghum in the mid-southern region. This turned out to be sugarcane aphid (SCA), which produced economically important problems in Louisiana and Texas. In 2014, SCA rapidly spread throughout much of the South including Mississippi, Arkansas, Tennessee, and Missouri, causing severe yield losses in many fields of grain sorghum.
No one really knows how this happened. It could be that SCA adapted to feeding on grain sorghum or it could be the introduction of a variant of SCA that was already adapted to grain sorghum. Some taxonomists suggest that the aphid may be a new species. Additionally, SCA may feed on sorghum grown for forage, sweet sorghum, and Johnsongrass. The SCA was first verified in Tennessee in early August of 2014, although it was subsequently apparent that it was present prior to this in some counties of western Tennessee. This species was confirmed in nearly all counties of western Tennessee by the end of the 2014 growing season, and it was likely present in other areas of the state at low numbers. Fortunately, for our Tennessee neighbors, it was late-planted fields that were primarily affected in 2014 owing to the relatively late arrival of SCA in Tennessee. Other southern states along the Mississippi River had similar experiences.
You will notice in Figure 2 that sugarcane aphid (SCA) data are not listed for Kentucky and Missouri.
The insect has not been collected in Kentucky, but it has been identified in Missouri. In 2014, SCA was found in Pemiscot and Dunklin Counties, MO. These counties are south and west of the Kentucky line and, thus, not directly on the Kentucky border. So, thus far, the aphid has not been collected as far north as Kentucky within the Mississippi River valley. This is good news, but may not be much protection as the aphid has been reported in Oklahoma and Kansas, which are further north than the Kentucky–Tennessee state line. Not good news for Kentucky; however, those areas are much less humid than the Purchase Area of Kentucky, so there may not be a direct comparison. SCA is now confirmed in 11 states and may spread further.
Comparing Common Aphid Species that Feed on Sorghum
Based on information from a Texas A&M publication (see References, below) the sugarcane aphid is gray to tan or light yellow. Unlike other common aphids (Figure 3) feeding on sorghum, sugarcane aphids have dark, paired, tailpipe-like structures called cornicles at the rear, and their tarsi (feet) are dark at high magnification. The dark cornicles and tarsi contrast distinctively with the lighter body color of the sugarcane aphid (Figure 3).
Sugarcane aphids differ from other aphids that attack grain sorghum in the following ways:
- Greenbugs have a distinctive darker green strip down the back that SCA does not have.
- Yellow sugarcane aphids have hairs on the body (seen with magnification).
- The legs and head of corn leaf aphids are dark.
Spread and Feeding of Sugarcane Aphids
Infestations begin when sugarcane aphids cluster on the under surface of lower leaves, then move to upper leaves. If not controlled, they may even infest the grain sorghum head. Colonies may grow quickly in favorable conditions and produce large quantities of sticky honeydew. It is believed that this sticky substance may help protect the aphids from some predator. Honeydew deposits will support growth of sooty mold fungi.
Feeding damage results in yellow to red or brown discoloration on both sides of sorghum leaves. Infestations on young plants may result in plant death, while very late infestations may prevent grain from forming.
Heavily damaged plants can result in clogging harvest equipment and difficulty in moving the grain through machines. The sticky leaves may prevent grain from separating from the stalks and leaves. Combines may require service to wash off the honeydew and remove lodged stalks form the heads.
Insecticidal control options for SCA are limited in grain sorghum. Most currently labeled insecticides are marginally effective.
- Most of the neighboring states that have had problems with this insect have sought and received a Section 18 Emergency Exemption for use of Transform WG™, a Dow product, against sugarcane aphid on sorghum and ONLY sugarcane aphid on grain sorghum. I have provided the Kentucky Department of Environmental Services (within the Kentucky Department of Agriculture) with biological information concerning this pest as they consider submitting a Section 18 Emergency Exemption for Kentucky; again, this information was obtained largely from our sister states. It is important for all concerned to realize that if this exemption is granted to Kentucky, a collection of follow-up information will be required, such as, but not limited to: number of treatments, number of acres treated, timing of treatments, and application methods, etc. If this information is not supplied to EPA, the Emergency Exemption will be revoked.
- In addition, Sivanto 200 SL (a Bayer CropSciences insecticide), has just recently been labeled for use on grain sorghum. Though sugarcane aphid is not listed on the label, Bay CropSciences has issued a 2ee label for use against sugarcane aphid. Originally Kentucky was not included in the list of states which may use the 2ee label, but after communicating with individuals at the company, Bayer CropSciences has agreed to add Kentucky to their 2ee label; this label will be available in 2015.
Other Management Options
Beyond rescue insecticide applications, what can you do to prevent / mediate this pest? Our colleagues in Mississippi have published an outline for SCA control on grain sorghum that seems to be the best approach (See Catchot, Gore and Cook in references, below). Briefly:
- Plant early.
- Use high plant populations and narrow rows.
- Use insecticide seed treatments.
- Avoid all disruptive sprays.
- Use tips and GPA to maximize coverage to the bottom of the canopy.
- Scout two times per week when the first aphids are found.
- Watch for late season head colonization.
Remember: Kentucky is NOT Mississippi. Mississippi and the other more southern states will have much more insect pressure and a larger number of pest species than Kentucky. I realize that some of these points are too late to be implemented. Nevertheless, avoiding unneeded sprays and consistent scouting are likely to be very important. Given the previous 2 years, if we have a problem, it will likely occur in the later maturing fields. It will be important to detect SCA as early as possible. This will give producers time to react.
I would like to end on a shameless advertisement. Though I have put considerable time into trying to determine what needs to be done to help Kentucky producers avoid, or at least moderate, this pest, I want everyone to understand: if it were not for my colleagues in the more southern states working in a cooperative manner we probably would not know that this problem is on our horizon. Though it is hard to put a value on something like this, the presence of the Cooperative Extension Service and the Agricultural Experiment Station is why you have this heads-up before this pest becomes a problem!
- Brown, S. D. Kerns, and J. Beuzelin.2015. Sugarcane Aphids: An Emerging Pest of Grain Sorghum. Pub. 3369. [Link]
- Catchot, A. J. Gore, and D. Cook. 2015. Management Guidelines for Sugarcane Aphids in MS Grain Sorghum 2015. [Link]
- Seiter, N., G. Lorenz, G. Studebaker, and J. Kelly. 2015. Sugarcane Aphid, a New Pest of Grain Sorghum in Arkansas. FSA7087. [Link]
- Stewart, S. 2015. Sorghum – Thinking About Sugarcane Aphid Control in 2015.
by Doug Johnson, Extension Entomologist