Posted on May 23, 2016
The sugarcane aphid, first discovered in grain sorghum late in the 2013 growing season, is capable of causing substantial damage to the crop if left unmanaged. However, with timely management, its effects can be minimized.
To protect sorghum from potential early season infestations, Brent Bean, Sorghum Checkoff agronomist, advises growers to consider planting seeds treated with an insecticide seed treatment.
"Any of the commonly used insecticide treatments such as Poncho, Cruiser and Gaucho are effective and should give up to 40 days of sugarcane aphid control," Bean said. "In addition, there are several commercial hybrids available that have some degree of tolerance to the sugarcane aphid that growers may want to consider."
Once sorghum has emerged, it is recommended to scout sorghum fields at least once a week for signs of the aphid. Once aphids are found, fields should be scouted 2-3 times a week. Sugarcane aphids excrete honeydew, a sticky, shiny substance on the lower leaves, which is often the first sign of a sugarcane aphid infestation.
Loss of plant sap, caused by the sugarcane aphids feeding on sorghum leaves, takes away nutrients from the plant that would otherwise be utilized for plant health and grain yield. Sugarcane aphid feeding, along with black sooty mold and other secondary diseases, eventually cause the leaves to turn yellow and die. The result is often uneven or lack of head emergence, poor grain set, and possibly an increase in lodging. A yield loss of up to 100 percent is possible if high aphid infestation levels occur prior to heading and are left untreated.
Depending on the growing region and the growth stage, growers are encouraged to treat for aphids as soon as the action threshold is reached. A general guideline is to apply an insecticide when 25 percent of the plants have been infested with 50 aphids per leaf, but there are specific threshold levels suggested for different growing stages and geographical regions, so local experts should be consulted.
For example, in the Texas High Plains, growers are advised to take action when 20 percent of the plants are infested with localized areas of heavy honeydew and established aphid colonies at the pre-boot and boot stages. At the heading, soft dough and dough stages, the advised threshold is when 30 percent of plants are infested with heavy honeydew and aphid colonies. When the grain black layer growth stage is reached, it is suggested to spray when honeydew presence is heavy and there are established aphid colonies in the head. At this point, treat only to prevent harvest problems.
However, regardless of the threshold level used, it is critical that insecticide application occurs as soon as possible to avoid a severe loss. Applications targeting lower infestation levels are likely to be more effective and prevent an escalating population of aphids that will be much more difficult to control.
Two products proved to be very effective during the 2015 growing season—Sivanto Prime by Bayer CropScience and Transform WG by Dow AgroSciences. Sivanto Prime is available for use in 2016 under a federal 2ee label. Transform was recently approved for use in 2016 under a Section 18 label in Alabama, Arkansas, Georgia, Kansas, Louisiana, Mississippi, Missouri, North Carolina, Oklahoma, Tennessee and Texas.
One of the benefits of both Transform and Sivanto prime is they are not harmful to beneficial insects, which is important for the control of sugarcane aphids. Care should be taken in adding other insecticides to the mix that could be harmful to beneficial insects. Additionally, movement of Sivanto prime and Transform in the plant is minimal, making coverage essential for adequate control.
If sugarcane aphid presence is significant in the sorghum head or on the upper leaves, harvesting can be impeded due to honeydew. Many producers have opted to spray an insecticide to eliminate the risk of harvest issues. In Texas, both Sivanto and Transform have a pre-harvest interval of 14 days. If desired, both insecticides can be mixed with pre-harvest desiccants.
"It is extremely important to have multiple products available to treat the sugarcane aphid," Bean said. "By rotating chemistries, we can avoid insecticide resistance and maintain control of the pest."
For those sorghum growers who experienced the sugarcane aphid for the first time in 2015, and maybe had to spray 2-3 times, it may be easy to get discouraged. However, Bean said growers everywhere should be encouraged by the experiences of those in South Texas and in Louisiana who have had the most experience with this pest and continue to successfully grow grain sorghum.
"This is a strong indication that growers are learning to effectively and economically manage the sugarcane aphid," Bean said. "As with all other crop pest crises, the sugarcane aphid will be effectively dealt with by using sound integrated pest management practices."