Following a serious 2014 outbreak of sugarcane that threatened sorghum crops in multiple states, especially in the Texas Coastal Bend and in Deep South Texas, entomologists and plant specialists from Texas A&M AgriLife Extension Service staged an educational update Monday, Jan. 12, in Corpus Christi to update producers on the latest research about the continuing threat of an aphid outbreak in the 2015 growing season.
Entomologists Robert Bowling and Dr. Mike Brewer, Texas AgriLife Research and Extension Center in Corpus Christi, talked about the escalating outbreak of the sugarcane aphid in sorghum fields, the challenges posed by the pests over the last two years, and the latest developments growers face this year.
Stephen Biles, Texas A&M AgriLife Extension Agent and IPM specialist for Victoria, Refugio and Calhoun counties, discussed efficacy trials with new and developing products that should be available this year to combat the sugarcane aphid in Texas sorghum fields.
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The event was well attended by area growers and was also available on webcast, which was attracted another three dozen producers, including farmers from the Texas High Plains.
"This aphid is nothing new in the continental United States. It was first reported in 1978 in sugarcane fields in Florida. Then again it was reported in Louisiana in 1999 in sugarcane. But in 2013 something new happened. We had either a new variant of this sugarcane aphid or possibly a re-introduction of this aphid that was reported damaging sorghum in Texas," Bowling told producers. "We also started getting reports of this aphid in Louisiana and lesser reports in Oklahoma and Arkansas [as early as 2013]."
Wide ranging infestations
Researchers say by the close of the 2014 growing season reports had began surfacing as far away as Kansas and Missouri. The aphid is also widely found in Asia, Australia, South America and now in Mexico.
"The way we start to manage this pest is first by learning to identify it," Bowling said.
In addition to specific identification characteristics of the sugarcane aphid, Bowling said the aphid is rather unique in that it is found in both winged and wingless forms. In the reproductive stage the aphid is wingless, but as population densities grow, the aphid will develop wings, a certain indication they will be migrating to new fields and new areas.
Another reason the sugarcane aphid is a rapidly growing and rapidly spreading threat to sorghum is that under the right conditions they can go from live birth to reproductive stage in as few as five days.
Brewer said the best and only control and management of an outbreak of this sugarcane aphid is by early detection.
"What makes this aphid a little special is that it found itself a good home in most grain sorghum. It's a good food for the aphid, and what happens when you have a good home and good food? You have lots of kids," Brewer said.
It is the rapid growth of aphid populations in a field that poses the biggest problem Brewer explained. Random sampling in the field may turn up very small numbers of aphids on the underside of lower leaves of sorghum, but in a manner of days those population numbers can accelerate beyond threshold.
"In two weeks’ time after spotting aphids on your sorghum, sooty mold can start forming on sorghum leaves under good growing conditions. In another 3 to 4 weeks you can get a dead plant if the field is not treated," Brewer explained.
Brewer said sampling sorghum fields can be time consuming but suggested a system of estimating aphid density can help speed the scouting process and has proven successful in field tests last year.
He emphasized that sampling/scouting fields should not be skipped because of the rapid proliferation of the sugarcane aphid under optimum conditions. If conditions are good for rapid plant growth, they are optimum for aphid population growth as well.
Perhaps of greatest concern for South Texas growers is that in spite of several cold snaps across the Texas Coastal Bend in recent weeks, there have already been reports of sugarcane aphids successfully wintering on both remnant sorghum and in Johnson grass.
To complicate matters, aphids infiltrate very young sorghum plants not long after emergence, so sampling and identifying aphid populations is the first and most important task to manage what promises to be another difficult year dealing with aphids in Texas and beyond.
"In 2013 we detected this aphid in growing numbers by late June, but by August this aphid had spread up north—one county in Oklahoma, one county in Mississippi and a number of parishes in Louisiana. I have worked with a number of invasive aphid species and have never seen rapid growth like this before." Brewer warned. "This is a very important bug in sorghum."
Brewer said once the weather warms up in the early spring, it will signal the aphids to start moving up from the lower plant in a steady trek to the top of the plant, and only by sampling and scouting fields can producers hope to know when they have reached threshold requiring treatment.
Stephen Biles discussed efficacy tests conducted across the middle Coastal Bend. All available treatment options were field tested, including new products awaiting Environmental Protection Agency (EPA) approval. Researchers also observed untreated fields for the purpose of a comparative study.
The primary products tested included Transform (Dow AgroSciences), Endigo (Syngenta), Centric (Syngenta), Sivanto (Bayer CropScience), Chlorpyriphos, and Dimethoate. Of the chemicals tested, Transform was available for use in Texas sorghum in 2014 by an EPA Section 18 Emergency Exemption Label. An exemption for use of Transform in 2015 has been submitted.
AgriLife officials say a request for Section 18 exemption is currently under consideration for the use of Sivanto in the upcoming crop year and a label is anticipated. A Section 18 exemption has also been submitted for the use of Centric.
Roundup PowerMax was also tested in the pre-harvest insecticide trial and was also combined with Transform Plus as a treatment option.
Biles conducted trials at various stages of sorghum growth, including a flag-leaf efficacy trial; milk stage, and pre-harvest efficacy trial, and at various levels of aphid infestation/density.
Overall, Dimethoate and Chlorpyriphos was determined to be the least effective for management of the sugarcane aphid in sorghum, primarily because of limitation associated with the window of use available between chemical use and harvest.
Biles reported the most effective control was achieved at all growth levels with Transform, Centric, Endigo and Sivanto, with varying levels of success for each product at various insect density levels. His conclusions indicated that aphids tend to move to the sorghum head after harvest aids are applied, and further indicate that insecticide can prevent infestation of the head when used at appropriate threshold levels.
Cause for concern
As the 2015 growing season approaches, researchers see cause for concern that this sugarcane aphid, often referred to as the white sugarcane aphid, will continue to migrate north and east and will present itself as a major problem in sorghum fields regardless of geographic location. In 2013 the white sugarcane aphid was reported in four states, or 38 counties total. But by mid- to late 2014, the aphid had been reported in 12 states and in over 300 counties.
Research further concludes that use of sorghum seed hybrids, proper scouting and sampling, and insecticide application at time of threshold helps reduce the threat of damage and crop loss from this invasive species.
Texas AgriLife officials are continuing research and field trials and will continue to provide updates as the 2015 growing season approaches and throughout the year.
To view the recorded webinar, click here.