Expecting the problem to get worse before it gets better, Texas AgriLife entomologist Dr. Mike Brewer delivered the latest news about the growing sugarcane aphid threat to Coastal Bend grain sorghum producers who gathered in a meeting last week in Corpus Christi, warning them to gear up for a fight with the pest as the current outbreak intensifies.
"Sorghum is an excellent host to this new sugarcane aphid. It reproduces like crazy in sorghum," Brewer told a packed auditorium at the Texas A&M Research and Extension Center. "If it didn't reproduce as much as it did, the plant could tolerate the aphid well."
The presentation, one of many being staged across the Coastal Bend and as far south as the Rio Grande Valley, is in response to the threat to sorghum fields across large areas of coastal Texas posed by the sugarcane aphid.
Less common aphid
Entomologists say the smaller aphid, while sporting a yellow tint as it matures, is not to be confused with the larger and more common yellow sugarcane aphid that injects a toxin into host plants.
Until confirmation last week, entomologists were not certain how to classify the 'new' aphid. But a definitive identification was reached last week by Dr. Scott Armstrong, USDA-ARS Entomologist from Stillwater, Okla.
Armstrong acquired sugarcane aphid DNA from Texas, Florida and African aphids for comparison before making a positive identification. His research confirms that the sugarcane aphid currently posing a threat to Texas sorghum is the same Melanaphis sacchari aphid found in South Africa and in Florida.
"The good news is that we are guessing the threshold for this aphid in Texas sorghum is as high as 200 aphids per leaf, or about 30 percent of the leaves on the plant," Brewer added.
The aphid enters the plant to feed on the lower leaves until population numbers force it to climb higher in the maturing plant, eventually into the sorghum head once developed.
Brewer said the primary reason this aphid poses a serious threat to sorghum is because of how rapidly population numbers can grow, almost 'overnight', and because of a prolific amount of honey dew the aphid produces on the plant, which leads to a "sooty mold" that turns the leaves black, causing irreparable damage.
"If not treated, the aphid count on a sorghum plant can quickly reach into the thousands, and at that point the plant is lost," Brewer illustrated by pointing out a heavily infected plant on display at the meeting.
Entomologists say there is little doubt the sugarcane aphid could be found for at least the best part of last year across wide areas of the Texas coast, but, for reasons unknown, population numbers did not become critical until just before harvest. Officials suspect just the right conditions contributed to the population explosion of sugarcane aphids last fall, and again this year beginning in late May in the Rio Grande Valley region. Since then, larger numbers of the aphids are blooming in sorghum fields in parts of the Coastal Bend and as far up the coast as the Louisiana border.
During harvest last year in both the lower and upper coastal bend, the production of honey dew on leaves and in the heads of sorghum was so prolific that producers say it gummed up harvesting equipment and caused major problems in many fields. A few sorghum fields were so badly infested that they were a total loss and plants were plowed under.
"We knew because of a mild winter that we were going to see a return of the aphid this year, and that's because this sugarcane aphid can winter well on Johnson grass," Brewer said.
Now that nearly 300,000 acres of sorghum in a three-county area including Corpus Christi are faring well after a late planting schedule this spring, the aphids have moved into commercial fields.
"A lot people don't realize that Nueces, San Patricio and Aransas counties are one of the largest grain sorghum growing areas in the nation," Brewer said.
Jason Ott, Texas A&M Extension agent for Nueces County, says before heavy rains that fell across the area two weeks ago, only a few of the sugarcane aphid were being scouted in area fields.
"What we had was an aphid rain," Brewer said. "After the beneficial rains greened up sorghum and cotton fields across the area, we began to see more aphids working their way into commercial crops."
At first, light populations were being reported after the rain. But within days aphid counts jumped to nearly 500 aphids per plant. That number has quickly jumped in a few fields with numbers estimated in the thousands per plant in isolated areas.
A similar aphid explosion occurred two weeks ago in Deep South Texas where fields went from manageable numbers to thousands per plant, some in just a two-day period.
Texas AgriLife Extension Integrated Pest Management specialist Danielle Sekula-Ortiz reports nearly 200 South Texas growers crowded into a special meeting about the threat in late May. Many of those attending were entomologists from Tamaulipas State just across the border in Mexico.
"They have been suffering from enormous sugarcane aphid populations over there as well and are expressing a willingness to work with us on this side of the border in hopes of getting control of the outbreak," she reported last month.
In her June 6, 2014, IPM newsletter, Sekula-Ortiz says after widespread treatment of sorghum fields over the last three weeks, population numbers of aphids "have been drastically reduced," an indication that recommended treatment strategies are working – at least for the interim.
"A panel of five of us from Texas A&M Extension collectively agree the best treatment method at the present time is a Dow AgroSciences product, Transform, which was approved for use in Texas grain sorghum in late April by USDA as part of a Section 18 emergency action," Brewer told producers last week.
He said good success has also been reported using Dimetholate, but says field trials indicate Transform provides a longer lasting residual control.
Travis Hirst and Charlcey Vineyard of Dow AgroSciences attended last week's meeting in Corpus Christi. During a visit to test plots at the research center following Brewer's presentation, they fielded questions from local producers.
Section 18 exemption
"In April of this year, we received Section 18 approval to use Transform in grain sorghum fields in Texas. The sugarcane aphid is a very invasive pest, and it is something we really needed to help in this developing outbreak," Vineyard said.
"Under Section 18 authorization, growers are allowed a maximum of two treatments not to exceed a total application of three ounces of Transform. So far we are seeing excellent results," added Hirst.
Brewer says reports indicate a single treatment of Transform is proving to provide a 14-21-day protection window in sorghum fields. That compares with Dimetholate's six-to seven-day protection window per application, according to trials.
"Scouting is the key. Grain sorghum is capable of handling a large number of this sugarcane aphid, but once we find population levels around 200 aphids per leaf, then we believe we have reached treatment threshold. While you don't want to treat too early in the game, you don't want to get behind rapidly growing populations, otherwise you are running a serious risk of heavy honey dew and sooty conditions on a plant and across a field," Brewer added.