Saying it was inevitable, Texas AgriLife officials in Weslaco are reporting a rapid buildup of sugarcane aphids (SCA) in Cameron, Hidalgo and Willacy County grain sorghum.
Recent scouting efforts have uncovered growing numbers of SCA in recent days causing Valley AgriLife officials to issue an alert to area sorghum growers on Wednesday.
"On Wednesday, surveys in all three counties revealed an abundance of sugarcane aphids. While many sorghum fields are being harvested there are still many that have a ways to go, so please be aware of this late Sugarcane aphid outbreak and check your fields prior to harvest to prevent gumming of harvest equipment," AgriLife IPM agent Danielle Sekula Ortiz warned growers in an email alert.
Officials say the outbreak is developing rapidly after extensive rain showers and cooler weather helped to deter SCA development up until late last week.
Raul Villanueva, an entomologist at the Texas A&M AgriLife Research and Extension Center at Weslaco, reported early last week that predicted high populations of the sugarcane aphid in sorghum had so far failed to develop.
“Based on our experience last year, we were expecting explosive populations of the aphids to inflict serious damage to this year’s crop,” he said.
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Robert Bowling, Texas AgriLife Extension entomology specialist in Corpus Christi, has consistently warned that detecting sugarcane aphids on lower sorghum leaves, even in small numbers, could be the signal to rapid development.
Winter survival a factor
At a pre-plant meeting in Corpus Christi in April, Bowling told farmers the South Texas sub-tropical climate, sugarcane allowed aphids to survive the winter year by taking up residence in Johnsongrass and voluntary sorghum, and that could mean heavy infestations of the pests early in the year. He also warned that once the pests were active in sorghum plants, population numbers can explode rapidly.
"In late 2013 we identified this aphid for the first time primarily in Texas and Louisiana. We did have a report of a case in Mississippi and one in Oklahoma, but that was the extent of the problem at that time; we had reports covering four states and 38 counties," Bowling said. "By the end of 2014, the sugarcane aphid actually moved to surrounding sorghum production states for a total of 12 states and 340 counties."
Cooler temperatures in March, heavy rains in April and floods in May kept farmers out of their fields and delayed planting in not only the Lower Rio Grande Valley (LRGV) but also into the Coastal Bend and Southeast Texas. But it was these same cooler temperatures and heavy rains that helped to prevent sugarcane aphids from developing until hot weather set in beginning the last week of June.
Until then, sorghum fields in both the Rio Grande Valley and the Coastal Bend were nearly sugarcane aphid free, even into late June.
Since the Valley received less rain than the mid- and upper coast, sorghum began to reach final growth stage in the Valley about three weeks ago. In early July harvest began in fields that were planted early.
Substantial acreage remains vulnerable
Even in the Coastal Bend, sorghum planted in May has now reached final growth stage, and a few fields were defoliated last week in preparation of harvest.
AgriLife officials in the Valley warn that in spite of ongoing harvest in Deep South Texas, a substantial number of acres have not reached harvest stage and these fields are subject to serious SCA infestation. The same is true in the Coastal Bend and Southeast Texas, where sorghum is further behind as a result of heavy April and May rains.
"We are seeing more winged adults (alates) in the flag leaves (in the Valley) reproducing rather quickly. This stretch of dry hot weather with abundant sunshine seems to be the cause in this recent SCA outbreak," Ortiz added.
She said scouts are finding many predators and seeing parasitism as well, but they seem to be lagging behind the rapid growth of SCA over the last week.
Crop officials up and down the coast are now warning Texas growers to step up scouting of sorghum fields and prepare for a possible late season outbreak.
Treatment options include the non-neonicotinoid insecticide Transform, a Dow AgroSciences product granted a limited EPA Section 18 emergency use permit in grain sorghum again in 2015 (with a 14-day pre-harvest restriction), and Bayer CropScience Sivanto, which performed well in a number of trials conducted across South Texas last year (21-day pre-harvest restriction applies apply for use in grain sorghum).