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Two pests threaten Texas grain sorghum

Harvesting grain sorghum near San Angelo Texas
<p>Harvesting grain sorghum near San Angelo, Texas</p>
Aphids and fall army worms pose threats to Texas sorghum.

Texas grain sorghum producers have dual threats to watch as fall armyworms and sugarcane aphids move into fields across the state.

The aphid, which started early in South Texas and has steadily moved north as sorghum matured, has now been identified west of I-35 for the first time, according to a report from Kathleen Phillips, Texas AgriLife media in College Station.

And Extension media specialist Steve Byrns reports from San Angelo that farmers should be alert to fall armyworm infestations in sorghum across much of the state. Each quoted Texas AgriLife Extension statewide integrated pest management coordinator Charles Allen, who works out of San Angelo.

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Entomologists across the state advise sorghum producers to stay vigilant for fall armyworms. “This is not a panic situation yet, but a growing number of reports of increasing numbers of fall armyworms from AgriLife Extension entomologists located across the state have led us to warn producers of this possible threat,” said Allen.

Entomologists Pat Porter and Ed Bynum, at Lubbock and Amarillo, respectively, are alerting AgriLife Extension personnel, consultants and farmers of the potential threat to grain sorghum and non-Bt corn in West Texas.

Bynum is running a trapping network for fall armyworms and other pests in the Panhandle.


High moth captures

“Fall armyworm moth captures are unusually high in Lipscomb, Gray, Randall and Swisher counties, and appear to be high across much of the Panhandle,” Bynum said.

“Some whorl stage grain sorghum is being treated in Lubbock and Lynn counties,” Porter said. “My non-Bt corn test plots at Lubbock have at least one fall armyworm per ear. The really troubling thing is that numbers in our fall armyworm traps this past weekend were abnormally high and may reach 1,000 moths per trap this week.

“This is 10 times higher than what we caught this time last year, and this is the July flight. The big flight usually occurs in August. We hope natural enemies and weather will keep them in check, but growers need to be aware that damaging populations may develop and be prepared to deal with them.”

Rick Minzenmayer, AgriLife Extension entomologist for Runnels and Tom Green counties, said fall armyworms and corn earworms are causing increased concern in his area of Central West Texas on both forage and grain sorghums.

“Our grain sorghum looks great and many fields have just finished blooming, but we really need to be watching for headworms (headworm refers to either fall armyworms or corn earworms),” Minzenmayer said. “A simple economic threshold for when control measures are warranted is 12 one-half inch or larger larvae per 25 heads of grain.”

Allen said more information on fall armyworms and the recommended control measures to keep them in check can be found at .


Aphids expanding territory

Sugarcane aphids have extended their range. Infestations in Northeast Texas are heavier than they were last year and came in earlier, creating increased potential for crop damage, according to IPM specialists.

Now, the pest has been identified on sorghum in San Saba and Coleman counties, marking the first time the insect has been found west of Interstate-35, says Allen.

AgriLife Extension agents Minzenmayer of Ballinger, Neal Alexander of San Saba and Michael Palmer of Coleman have found sugarcane aphid in sorghum fields near San Saba and Coleman.

“Finding sugarcane aphid further west does not necessarily mean that the aphid will move into the large grain sorghum producing areas in the Rolling Plains and High Plains, but growers need to be aware that sugarcane aphids have been found west of where they were seen last year,” Allen said. “Growers should keep a close watch on their grain sorghum fields as the plants begin to head.”

Left unchecked, the aphid sucks sap from plant leaves and deposits “honeydew,” a sticky waste that clogs harvesting equipment, said AgriLife Extension entomologist Raul Villanueva of Weslaco, where farmers already have battled the insect this season. It can also move into the grain head, slowing the ripening process, reducing both quality and yield.

The tan to cream colored sugarcane aphids initially colonize on the undersides of leaves near the bottom of plants.

“They typically move up the plant as they increase in populations. An action level that has been working well in South and East Texas is that when about 40 percent of plants infested means it’s time to spray. Plants are considered infested if they have 100 or more aphids on one of the leaves,” Allen explained.


Control option

Growers had difficulty controlling this aphid with labelled insecticides last year.

Studies in Texas and Louisiana in 2013 determined that Transform insecticide could provide effective control. A Section 18 emergency exemption label granted by the U.S. Environmental Protection Agency earlier this year for Transform allows for application rates from 0.75 to 1.5 ounces per acre.

“Good spray coverage is essential. Treatments can be made up until 14 days before harvest,” Allen said.  

The U.S. Department of Agriculture-National Agricultural Statistics Service reports 3 million acres of grain sorghum in Texas; about 1.9 million acres are west of I-35.

The Rio Grande Valley already has harvested about 400,000 acres of grain sorghum. Most of the rest of the state’s sorghum is still maturing in the field. The East Texas crop will be harvested in a few weeks. The West Texas crop is usually harvested in late-August through early October.

The sugarcane aphid was first reported in Texas in 2013 near Beaumont in sorghum fields. It was first detected in 1977 in Florida sugarcane. Some 22 years later, it was found in Louisiana sugarcane, Villanueva said.

Villanueva said the biology of the insect makes it a “much more serious threat. Like most aphid species, it is parthenogenetic, meaning populations are all female and don’t require a male to reproduce. When populations become overcrowded, some develop wings and fly off to other fields or plants to colonize there. They don’t lay eggs; they simply give birth to new female aphids — and very quickly. That’s one reason why populations can quickly spread and increase to critical levels.”

For more information, contact your local county office of AgriLife Extension.




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