- Agronomic: sorghum (sweet)
- Pest Management: integrated pest management
Kentucky is the largest producer of sweet sorghum in the country, with an estimated 2,000 acres producing $16-$27 million yearly gross revenue. Sweet sorghum is an important source of income for many growers and is the subject of numerous yearly festivals in Kentucky. Until recently, sweet sorghum had no regularly occurring arthropod pests requiring management. In 2015, the sugarcane aphid (SCA), Melanaphis sacchari, was found infesting sorghum fields in Kentucky. Unmanaged infestations caused up to 100 percent yield loss.
SCA does not overwinter in Kentucky and migrates north every summer from overwintering populations in southern Texas. SCA on grain sorghum can reproduce rapidly under ideal conditions, leading to tens of thousands of SCAs on plants. In grain sorghum, high numbers of SCA reduces plant sap, thus lowering yield. Honeydew (sugary secretions produced by aphids) can also lead to a buildup of sooty mold on the leaves, impeding photosynthesis. SCA is believed to cause similar damage to sweet sorghum as on grain sorghum.
Without effective management, SCA threatens the economic standing of growers in Kentucky and has led many growers to cease sweet sorghum production. In 2017, the Southern Region Information Exchange Group of IPM included SCA as one of it IPM priorities. Management plants for SCA in grain sorghum (plant resistance and insecticides) have been developed, but tactics for managing SCA on sweet sorghum in Kentucky are limited.
The only management recommendations for SCA in Kentucky sweet sorghum are Sivanto Prime sprays and early crop planting. Action thresholds of Sivanto Prime are based on grain sorghum trials. Currently, use of Sivanto Prime on sweet sorghum needs an emergency use exemption label, section 18, given by the Environmental Protection Agency whichmuch be renewed yearly. Another limitation to the use of Sivanto Prime is it is not used by growers who avoid insecticides not approved by the Organic Materials Review Institute. No organic insecticides are specifically labeled for sweet sorghum, growers must instead rely on insecticides like insecticidal soap, the effectiveness of which on aphids is inconsistent. Cultural management through early planting can allow harvest to be reached prior to SCA reaching damaging levels. However, early planting is impractical for growers, such as the Amish and Mennonites, who rely on horses to provide the power for processing sweet sorghum, as early planting harvest is during August when it is too hot for horses.
In general, pest management strategies that integrate biological controls reduce the amount of chemical inputs needed, reduce yield loss from pests and improve the overall sustainability of the crop system. To improve the sustainability of sweet sorghum, tactics are needed to increase the abundance of natural enemies. Natural enemies are attracted to SCA infestations, however, SCA population growth rapidly outpaces natural enemies.
We propose the integration of predatory green lacewing releases with insecticidal soap spray applications for SCA management. Predator releases will give organic growers another option to manage SCA, buffering against the inconsistency of insecticidal soap.
Success of insecticidal soap depends on direct contact with the pest before the soap dries potentially needing multiple sprays if coverage is not complete or when pest numbers recovers. Delaying or preventing SCA from reaching the action threshold by increasing predation early in the season when SCA is colonizing sweet sorghum fields may reduce the number of sprays required. Green lacewing is available from commercial insectaries for aphid suppression. Mass releases of green lacewings as eggs suffer from high mortality and larval stage releases are extremely time consuming, but adults can be released in large numbers readily. Adults feed on nectar, pollen and honeydew, the latter is used to locate oviposition sites. Their larvae feed on aphids. One larvae may consume up to 100 SCA during its preimaginal development. Green lacewing is native to the eastern U.S., and performs well in the temperature and humidity of the region. Contact with direct or residual insecticidal soap sprays has a low mortality on all lie stages of green lacewing.
Project objectives from proposal:
On-farm studies will take place in the Mount Vernon Amish community in Hestand, KY. Four growers in this community have been identified as participants for field trials.
Field Management: Sweet sorghum is planted in May with an expected harvest in late August or September. Growers will apply insecticidal soap sprays to all field trials at a 2 percent concentration based on SCA action thresholds development by Kansas State University for conventional insecticides on grain sorghum.
Treatments: Treatments will be control fields which only receive insecticidal soap sprays as needed and releases of green lacewing adults in combination with needed insecticidal soap sprays.