Sorghum Tips

Grain Sorghum Hybrids with Resistance to Sugarcane Aphid—II

This tip was provided by:

Allen Knutson, Extension Entomology, Dallas, (972) 952-9222, allen.knutson@ag.tamu.edu

Statewide–Emphasis on North, Central & South Texas

Grain Sorghum Hybrids with Resistance to Sugarcane Aphid—II

In the March 9 “Sorghum Tip” we omitted some of the explanation about grain sorghum hybrid tolerance among the various lists of tolerant hybrids published.  This is the full discussion of the Texas A&M AgriLife entomology report on work on identifying tolerant hybrids. Soon after sugarcane aphid (SCA) emerged as a pest of sorghum in 2013, growers, consultants and seed company representatives observed that some hybrids were not as heavily infested with sugarcane aphids as were other hybrids. These observations led to field research studies that confirmed that some hybrids were resistant to sugarcane aphid due to their genetic makeup.  As a result, many seed companies now market hybrids with some resistance or “tolerance” to sugarcane aphid. Planting grain sorghum hybrids with resistance to sugarcane aphid is now an important management tactic in reducing the risk of crop loss.

Beginning in 2014, Texas A&M AgriLife, with support from Texas Grain Sorghum Producers Board, began to evaluate some of these hybrids in replicated field trials to confirm resistance to SCA.  Trials were conducted in the Rio Grande Valley, Gulf Coast and north Texas and compared the number of SCA and leaf damage among the hybrids and to hybrids known to be susceptible to SCA.

These trials confirmed resistance in 14 hybrids from seven different seed companies (Table).  This list is not complete and these and other seed companies may have hybrids with resistance to sugarcane aphid.  Also, seed companies are releasing new hybrids with sugarcane aphid resistance each year, and growers are encouraged to visit with their seed representatives regarding current hybrids.

Sugarcane aphid populations increase more slowly on these resistant hybrids compared to susceptible hybrids where insecticide thresholds are set at 50 aphids/leaf.  Also, damage is lower on resistant hybrids compared to susceptible hybrids. In these trials, resistant hybrids had fewer SCA than susceptible hybrids and aphid infestations often remained below the treatment threshold of 50 aphids/leaf for susceptible hybrids, and rarely exceeded 100 aphids/leaf.  However, resistant hybrids are not immune, SCA will be present, and it is possible that under some conditions, infestations could reach damaging levels above the 100 aphids/leaf mark observed in our trials.  Thus, resistant hybrids must be scouted and if sugarcane aphid infestations exceed a revised threshold for aphid-resistant hybrids of at least 100 aphids/leaf, an insecticide may be needed to prevent yield loss or honeydew contamination at harvest.

While resistant varieties reduce risk of SCA, they are part of an overall pest management plant that includes early planting, weekly field scouting, use of thresholds and efficient insecticide use if needed, selection of insecticides applied for midge and headworms that help preserve natural enemies of sugarcane aphid, and Johnsongrass control (important host of SCA.  {Contact Dr. Knutson or other Extension entomologists for comprehensive management information.}

In addition to sugarcane aphid resistance, yield and other agronomic qualities must be considered in selecting hybrids.  High yielding, well adapted hybrids, but susceptible to sugarcane aphid, may be more profitable, and if so, can be protected from sugarcane aphid damage by frequent scouting and well- timed application of an insecticide if infestations exceed 50 aphids/leaf threshold for susceptible hybrids.

Table 1. Grain sorghum hybrids identified as having some resistance to sugarcane aphid in field trials Conducted by Texas A&M AgriLife Research and Extension entomology, 2015-2017.

Contributors: Mike Brewer, Robert Bowling, John Gordy, Allen Knutson, Danielle Sekula-Ortiz, Texas A&M AgriLife Research and Extension.