The sugarcane aphid has been reported in many locations in the Southeast. Sorghum producers are advised to scout grain sorghum fields now and treat sugarcane aphids as needed. The invasive insect shows up and causes the most damage late in the season, especially on double-crop sorghum plantings.
University of Georgia Extension entomologist David Buntin gives sorghum producers some timely tips on controlling sugarcane aphids in 2015:
1) Aphids usually infest sorghum until later in the season and early planting may avoid very large infestations. In other words, late, double-crop plantings are at greater risk of severe infestations.
2) Trials in the Delta region last year found that insecticide seed treatment would limit seedling infestations for 30 – 40 days after planting. All registered neonicotinoid insecticides are effective including thiamethoxam (Cruiser), clothianidin (NIpsIt Inside, Poncho) and imidacloprid (Gaucho others).
3) Fields can quickly be inspected for the presence of aphids by looking are on the underside of leaves. Once aphids are detected, scout at least once, preferably 2 times per week, because aphid numbers build very quickly. Shinny lower leaves with honeydew are a clear sign of infestation.
4) SCA and their honeydew attract large number of beneficial insect predators such as lady beetles, syrphid fly larvae and lacewings. No aphid parasites were observed in Georgia last year but a parasitic wasp is present in TX and LA and could move eastward. No aphid fungal disease has been observed either. Generally the rapid rate of increase in aphid populations overwhelms the beneficial insects and severe plant damage usually occurs.
5) Several threshold levels are being used in the Delta region for 2015. One conservative threshold is 25% infested leaves with 50+ aphids per leaf at whorl from preboot stage through dough stage. In MS, the threshold at pre-boot and boot stages is 20% infested plants with large aphid colonies (100+) and localized areas of heavy honeydew present. From bloom through dough stage the threshold is 30% infested plants.
I think either of these sets of thresholds will prevent serious yield losses and would suggest using whichever threshold is easiest for you to use.
6) PYRETHROID INSECTICIDES ARE NOT EFFECTIVE and may flare infestations by killing all the aphid predators. Regardless of the insecticide, rapidly expanding populations are difficult to control. Foliar insecticide options for SCA are Transform WG, Sivanto, Chlopyrifos (Lorsban Advanced, Nufos. DO NOT USE CHLORPYRIFOS ON SWEET SORGHUM.), or Dimethoate ( Dimethoate, Cygon).
7) Use tips and GPA for maximum coverage especially lower in the canopy. A minimum of 10 gpa by ground and 5 gpa by air is highly recommended.
8) For sorghum midge try to avoid routine pyrethroid sprays for sorghum midge. Instead scout and treat at 1 adult per panicle. Chlorpyrifos (1 pint per are) for low to moderate infestations. Early plantings often avoid serious midge infestations. For fall armyworm in the whorl, the threshold is 50% infested whorls. Use Belt, Prevathon or Lannate which are specific to caterpillars. For headworms, corn earworms fall armyworm, sorghum webworm, the threshold is 1 worm per head and use Belt, Prevathon, Beseige or Lannate.
9) A treatment may be needed if large numbers are in the head to prevent damage to combines. Hybrids with taller stalks and more space between the grain and upper leaves may make harvest easier by reducing the amount of leaf material going through the combine. Large infestation producing large amounts of honeydew and sooty mold may interfere with harvest desiccants. Transform WG can be applied up to 14 days before harvest.