David Kerns and I have been receiving numerous phone calls this week about problems with applications of pyrethroids tank mixed with Transform for control of midge and white sugarcane aphid. The use of a pyrethroid for control of sorghum midge is a common practice in Louisiana; however, pyrethroids are very toxic to beneficial insects and are very likely to flare white sugarcane aphids in grain sorghum. Co-appliations of Transform and a pyrethroid have led to white sugarcane aphids recolonizing fields very rapidly and often resulting in poor control of aphids overall.
Therefore, automatic insecticide applications for midge should be avoided, and applications should only be made if midge are present. The Louisiana threshold for midge in sorghum is at 25 – 30% bloom, treat for one or more midge per head. If midge and sugarcane aphids are present, tank mixed applications of chlorpyrifos and Transform will offer good midge control while also reducing the risk of flaring aphids. Chlorpyrifos may not be quite as effective as a pyrethroid for sorghum midge and large populations may require a second application 3 – 4 days later. Transform tank mixed with Dimethoate is another option for midge and aphid control; however, producers should be prepared to follow up with a dedicated midge application 3 – 4 days later.
Also, pyrethroid applications for the headworm complex in grain sorghum are strongly discouraged. Pyrethroid resistance is very common in sorghum webworm and corn earworm in Louisiana, and insecticides such as Belt or Prevathon should be used for headworms. These chemistries are Lepidopteran specific and will not harm beneficial insects or flare sugarcane aphids.