The sugarcane aphid continues its northern march through Southwest grain sorghum fields, putting the crop at risk of severe damage if growers fail to make timely insecticide applications.

Damage may include lost production as well as harvest problems from the sticky honey dew secreted by the pests. The secretion sticks to leaves and grain, clogging combines and creating problems at elevators. The honeydew also may provide an ideal growth medium for mold.

Last week the sugarcane aphid, or white aphid, was identified in San Saba and Coleman counties in Texas, marking the first time the insect has been found west of Interstate-35, says Charles Allen, Texas AgriLife extension statewide integrated pest management coordinator.

More recently, Tom Royer, Oklahoma State University Extension entomologist, identified the pest, along with the more common yellow sugarcane aphid, in Oklahoma grain sorghum.

He warns sorghum producers to be watchful for both pests.

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Damaging pest hits Oklahoma

Both types of aphids colonize the surfaces of the lower leaves of sorghum, and then move up to newer leaves. Feeding causes red or brown leaf discoloration on both sides of the leaf.

“Despite their names and common plant hosts, they are different in appearance and differ in how they cause damage to sorghum,” Royer said.

Yellow sugarcane aphids are more of a problem in sorghum seedlings, he said, where even small colonies can kill plants and reduce plant stands. As sorghum grows, the plants typically become more tolerant to the aphids. 

“Yellow sugarcane aphids don’t often build up into large numbers in maturing sorghum. If they do, greenbug treatment thresholds are recommended as a guideline for their control.”

The sugarcane aphid can cause serious damage to maturing sorghum.

“This aphid developed large populations in sorghum, supporting the growth of a black fungus called ‘sooty mold’ and producing significant amounts of sticky honeydew that coated leaf surfaces and interfered with harvest operations by clogging combines and slowing the movement of material through the machines,” Royer said.

He added that honeydew also interfered with the separation of grain from stalks and leaves so grain was left on the ground. Texas producers reported up to 50 percent losses in 2013.

“We have had little experience with this aphid and are relying on data and recommendations generated from Texas, Louisiana and Mexico,” Royer said. “When populations of sugarcane aphids increase rapidly, insecticides may be needed to prevent yield losses and honeydew buildup before harvest.”

Current recommendations are to treat if 30 percent to 40 percent of plants are infested, defined as at least one colony of aphids on a plant.

“We are currently looking to evaluate insecticides for effectiveness in Oklahoma,” Royer said.

Texas plot tests conducted in Beaumont and Corpus Christi indicated Dimethoate 4E applied at one pint per acre and Lorsban 4E applied at one quart per acre provided acceptable control. However, other tests conducted in the Lower Rio Grande Valley looking at Lorsban 4E and Dimethoate 4E produced only about 50 percent control. 

“It is important to remember Dimethoate has a 28-day pre-harvest interval, and Lorsban at the one quart rate requires a 60-day pre-harvest interval,” Royer said. “Tests also showed pyrethroids, such as products containing lambda cyhalothrin, were ineffective.”

Emergency exemption

Oklahoma obtained a Section 18 Emergency Exemption Label for the use of Transform WG that is in effect until Oct. 31, 2014. It has been effective in tests when used at a rate of 0.75 ounce per acre, and is registered for application at 0.75 to 1.5 ounces per acre.

“Dr. David Kerns, LSU Extension entomologist, has told us most applications in Louisiana have been going out at one ounce per acre,” Royer said.

Reports from South Texas and more recently from Northeast Texas sorghum producers and Extension specialists indicate Transform has been effective in depleting heavy populations of the sugarcane aphid within a few days of treatment.

Specialists also agree that more study is needed to determine an effective treatment threshold but agree that the 30 percent to 40 percent infestation rate is a good starting point.

Oklahoma’s current control recommendations for yellow sugarcane aphids would be:

● 5-leaf-stage through mid-whorl stage: Visible damage on leaves (red spots/yellow leaves) but before any entire leaves are killed on 20 percent of plants.

● Boot through heading stage: Death of one functional leaf per plant.

● Heading through soft-dough stage: Death of two functional leaves per plant.

“State sorghum producers should consult OSU Current Report CR-7170, Management of Insect and Mite Pests in Sorghum, and look under greenbug control for information about registered insecticides they can use to help control yellow sugarcane aphids,” Royer said.

The current report can be accessed at all OSU Cooperative Extension county offices or online at http://osufacts.okstate.edu through OSU’s Division of Agricultural Sciences and Natural Resources.

Aphid characteristics

Also, growers should be aware of the differences between the two aphids.

Characteristics are:

The yellow sugarcane aphid

Yellow sugarcane aphids are bright yellow with many hairs on their body and no extended cornicles. They have long been recognized as pests of sorghum and sugarcane in the United States, from southern Texas and Louisiana to Florida. They are occasional pests of sorghum in Oklahoma but do not normally overwinter in the state.

The sugarcane aphid

Sugarcane aphids are light yellow, with dark, paired “tailpipes” called cornicles and dark “feet” called tarsi. Oklahoma entomologists first noted their state presence in Bryan County in 2013. The pest also has been viewed in southern and eastern Texas, southwestern Louisiana and eastern Mississippi.

Extending range

Sugarcane aphids have extended their range this year across Texas. 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. And now it has been identified west of I-35 for the first time. AgriLife Extension agents Rick 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, Allen said.

Rick Minzenmayer, AgriLife Extension entomologist for Runnels and Tom Green counties, said the pest is rapidly expanding its range and its newly acquired taste for grain sorghum.

“The pest left the Rio Grande Valley and moved into the Blacklands and Northern Blacklands areas of Texas earlier this summer. They were found last week in Coleman and San Saba counties,” Minzenmayer said. “Now, they’ve moved west into Runnels, Tom Green and Concho counties.

“Currently, no Concho Valley fields have been treated, but the infestations are being monitored regularly and when the crop-damage threshold is reached, an insecticide can be applied,” he said. “The Texas Department of Agriculture has issued a Section 18 emergency use permit for Transform insecticide. It is the only insecticide currently available that will provide 90-plus percent control.”

“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 Dr. 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 thus reducing both quality and yield.

Growers had difficulty controlling this aphid with labelled insecticides last year, Allen said. The Section 18 emergency 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,” Allen says. “Treatments can be made up until 14 days before harvest.” 

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

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

Villanueva said the biology of the insect makes it a “much more serious threat (than other aphids). 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.”

Now, entomologists from South Texas, Louisiana, central and Northeast Texas, Oklahoma and West Texas are encouraging sorghum producers to watch fields closely and be ready to treat these pests before populations build to damaging levels and before honeydew secretions create harvest problems.