The white sugarcane aphid (WSCA) has made it well into Tennessee. On August 5th, I found relatively low populations on heading grain sorghum within the city limits of Jackson. The previous nearest find to Tennessee was in northern Mississippi and across the river from Memphis (Crittenden Co., AR). Thus, it is conceivable this insect could show up in any sorghum field in West Tennessee. It is important that everyone start scouting for this insect and report suspected infestations. If you are unfamiliar with this pest, I’ve included the links to many related news articles and pest updates (below). This aphid, until a couple of years ago, was not an economic threat. However, WSCA have been reeking havoc in sorghum fields in much of the South during the last two years (and across a much wider geography in 2014).
It takes a lot of aphids to cause a problem. Unfortunately, low infestations have a history of blowing up into a major problems in a short period of time. Identification is not that difficult. Only a few aphids commonly occur in sorghum. The white sugarcane aphid is cream colored to pale yellow (pictured). They should not be confused with corn leaf aphids which are dark green in color. Greenbugs may also be present but are light green in color. Yellow sugarcane aphids may also be found but are brighter yellow and typically occur in much lower numbers. In short, it you find a bunch of pale colored aphids on your sorghum leaves, your are likely dealing with WSCA.
Damage: I stole the following paragraph from Dr. Angus Catchot (Mississippi State University). “Like most aphids, the white sugarcane aphid causes damage by feeding with piercing sucking mouth parts and secretion of honey dew. When numbers get really high, especially on stressed grain sorghum, the overall general vigor of the plant is reduced and can severely stunt and even kill plants. Excessive honey dew accumulation can result in sooty mold that blocks photosynthesis as well. It is not thought at this time that the aphid has a toxin associated with it like greenbugs. Because this aphid can persists all the way until harvest it has been reported to cause problems with combine efficiency due to excessive foliage covered with sticky honey dew going through the combine also. Generally the aphid begins to show up pre-boot stage.”
Some Take Home Points: You will find a couple of common themes if you read through the articles below.
- Heavy infestations can kill the plant. But it takes thousands of aphids to do this, at least once plants are in the boot stage. Late season infestations create a lot of honey dew, and this can create a gummy nightmare while combining the sorghum. Be thinking about WSCA if you see shiny, slick leaves.
- A common treatment threshold is to make an insecticide application when 30% of the plants are infested with localized areas of honey dew accumulation. However, treatment thresholds vary and are evolving quickly as we gain experience.
- WSCA are difficult to control and populations may bounce back quickly following an application. Currently labeled insecticides in grain sorghum are not adequate. High rates of Lorsban (24-32 oz) appear to provide decent control but are not much use for late-season infestations because of the 60 day preharvest application restriction. All the other states have a Section 18 (emergency use) approval to use Transform (sulfoxaflor, Dow AgroSciences). Tennessee will also be making this request soon, but Transform is currently not allowed in Tennessee.
- Avoid unnecessary applications for sorghum midge. The pyrethroid insecticides in particular may flare populations by killing beneficial insects. Some of my colleagues are suggesting using Dimethoate 4E (8 oz) or Lorsban (16 oz.) for midge control if necessary. These products may provide some control and would seem less likley to flare aphid populations.
- Consider using Belt or Prevathon for control of headworms in late-maturing sorghum. They are probably less likley to flare aphid populations. Besiege is a premix containing a pyrethroid, so consider avoiding this product if WSCA are present.
- The use of harvest aids like sodium chlorate to desiccate the plants has been suggested for very late season infestations when heavy honey dew is present.
Some Related Articles From Other States:
http://www.arkansas-crops.com/2014/07/14/sugarcane-grain-sorghummilo/
http://www.mississippi-crops.com/2014/07/15/treating-white-sugarcane-aphid-decision-aid/
http://www.mississippi-crops.com/2014/07/25/white-sugarcane-aphid-update-7252014/
http://www.mississippi-crops.com/2014/08/01/white-suagarcane-aphid-update-812014/
http://louisianacrops.com/2014/07/17/sorghum-midge-and-white-sugarcane-aphid-concerns/
http://louisianacrops.com/2014/06/16/sugarcane-aphid-numbers-increasing-in-grain-sorghum/
