While late season cold fronts and substantial rains have delayed grain sorghum from being planted in coastal and southern regions of Texas, Texas A&M AgriLife Extension crop specialists warn that overwintering sugarcane aphids (SCA) could be problematic for young sorghum plants shortly after emergence.
Robert Bowling, Assistant Professor and Extension Specialist at the Texas A&M Research and Extension Center in Corpus Christi, says overwintering sugarcane aphids may move to the base of live plants during cold environmental conditions. Because of milder winter temperatures in most coastal areas and in southern regions of Texas, some of these aphids survived the winter and are poised to move back into sorghum fields in early spring.
Host plants for these aphids include any sorghum species—grain sorghum, forage sorghum, Sudangrass and haygrazer. The aphid needs a live host to overwinter and can be readily found on volunteer sorghum or Johnsongrass near sorghum fields.
While overwintering aphids have not been reported in all coastal areas of Texas, Bowling warns that they have been reported as far north as Matagorda and Wilson counties and in other middle and lower Coastal Bend areas and Deep South Texas.
Mike Brewer, an Extension entomologist at the Corpus Christi Research and Extension Center, told producers at a meeting in January that he expected an early start to aphid problems this year because of successful overwintering.
"Aphids are known to infiltrate very young sorghum plants not long after emergence, so sampling and identifying aphid populations is the first and most important task required to manage what promises to be another difficult year dealing with aphids in Texas," Brewer said.
He and Bowling agree the best early defense against aphids moving into sorghum fields is early detection. Scouting fields becomes a critical aspect of pest management, and this particularly holds true for the sugarcane aphid, which is prolific in its reproduction cycle.
"In two weeks’ time after spotting aphids on your sorghum, sooty mold can start forming on sorghum leaves under good growing conditions. In another 3 to 4 weeks you can get a dead plant if the field is not treated," Brewer explained.
Brewer says sampling sorghum fields can be a time-consuming process but suggests a system of estimating aphid density as a method to speed the scouting process and one that has proven successful in larger fields and test plots.
Bowling warns that the rapid growth rate of this aphid makes the pest particularly hard to control. Random sampling in the field may turn up very small numbers of aphids on the underside of lower leaves of sorghum, but in a few days population numbers can accelerate beyond threshold.
The good news for sorghum growers this year is that two insecticides have been approved for use on sugarcane aphid in sorghum. Last year Dow AgroScience's Transform was extremely effective against aphids in sorghum and was available for use after the EPA approved a Section 18 emergency use label. According to Extension agents up and down the coast, Transform provided adequate protection even in fields heavily infested with SCA.
EPA has approved a Section 18 emergency use label for Transform in the 2015 sorghum crop.
Also approved is a new product from Bayer CropScience, Sivanto. Numerous efficacy studies have revealed that Sivanto provides good sugarcane aphid control in sorghum when used at Section 2ee labeled rates of 4 to 7 ounces per acre. Bayer CropScience indicates that this product is compatible with many beneficial insects and predatory mites. Sivanto has a pre-harvest interval (PHI) of 21 days for dried grain, stover or straw, and 7 days for forage.
The Transform Section 18 runs through October 31 and allows for two in-season applications for sugarcane aphid in sorghum. Labeled rates range from 0.75 to 1.5 ounces per acre. The Section 18 allows for two applications per acre per year and not to exceed 3 ounces per acre. A higher rate range is recommended for heavy sugarcane aphid populations. This product has a 14 day PHI for grain or straw harvest and a 7 day PHI for grazing or forage, fodder, or hay harvest. Insecticide applications are suggested when sugarcane aphid densities average 50 to 125 aphids per leaf.
Bowling advises producers to check fields and areas surrounding fields with forage sorghum, Sudangrass, and haygrazer carefully as the SCA can build populations to high numbers in a very short time.