Untreated grain sorghum in the Texas High Plains is covered with sugarcane aphids Untreated the tiny pests build populations rapidly and can destroy a grain sorghum field

Untreated grain sorghum in the Texas High Plains is covered with sugarcane aphids. Untreated, the tiny pests build populations rapidly and can destroy a grain sorghum field.

Treating sugarcane aphids in sorghum: What you need to know

Sugarcane aphids are spreading across the Southwest grain sorghum production area, adding to production costs and threatening yield and quality. Scouting and timely insecticide spray, along with biological controls are important in managing the damaging pest.

In just three years, the sugarcane aphid has gone from being a virtually unknown pest with no history of infesting grain sorghum to notoriety as one of the most — if not the most — pressing problems for Southwest milo producers.

Left untreated, the tiny yellow sucking insects can devastate a sorghum field. They reproduce rapidly, and if not controlled, can overwhelm sorghum in a few days. Their range has spread from southwest Louisiana and south Texas northward through central and northeast Texas and the Rolling Plains, into Oklahoma, over to the Texas High Plains, and all the way to Kansas. Some observers now believe the pest may be overwintering in the Texas High Plains.

A panel of Texas AgriLife Extension specialists put the problem in perspective at the West Texas Agricultural Chemicals Institute annual conference in Lubbock. Their discussion, Sugarcane Aphid: Lessons learned in 2015, explored myths and facts about the pest.

Does the aphid overwinter as far north as the High Plains? Most experts would say no. Blayne Reed, Extension integrated pest management agent for Hale and Swisher counties, says surveys he conducted early this year indicate no overwintered sugarcane aphids. But IPM agent Tommy Doederlein thinks overwintering did occur in Dawson County.

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TREATMENT THRESHOLDS

Much of the current management strategy for the aphid is based on experience in south Texas, where the pest was discovered on grain sorghum about three years ago. Entomologists there developed treatment thresholds to prevent or limit economic damage.

“Those thresholds are too high here,” says Extension Entomologist Pat Porter, Lubbock. “First applications were made at the south Texas threshold of 50 to 120 aphids per leaf.” Results using that threshold showed an inability to control aphids in the lower canopy and a need to follow with subsequent applications.

“We quickly lowered the High Plains threshold to 20 percent to 30 percent of plants infested (depending on growth stage) with honeydew present,” he says. “Insecticide coverage is critical. Early indications show little control on lower leaves, but good control on the upper leaves.”

Possible coverage limitations include canopy interception of the insecticide, inadequate carrier volume by air, and honeydew interference.

“Higher volumes helped,” Porter says. “With ground application, we recommend 15 gallons per acre minimum. For aerial application, volume should be 5 gallons per acre. Adjuvants seem to help.”

Beneficial insects may play a significant role in controlling the sugarcane aphid, but not alone. “Beneficials can wipe out survivors following a good insecticide application,” he says. “A good application, including control in the lower canopy, usually did not require a second treatment. A bad application often required a follow-up.”

PREDATOR POPULATIONS

Predator or parasite populations will vary by locations, Porter notes. In Dawson and Swisher counties, lady beetles, syrphid fly larvae, and Aphelinus wasps are the most prevalent. From Amarillo north, the Lysiphlebus wasps, syrphid fly larvae, and lady beetles are the most likely beneficials.

Following good insecticide treatments, biologicals play an increasingly important role, he says; 14 days after a good control treatment, aphids begin to rebuild populations, but “after 21 days, it’s hard to find aphids.” With the reduced population of aphids, beneficials can move in and keep pest numbers below threshold levels.

Honeydew did not seem to be a factor in insecticide efficacy, but leaf position did appear to make a difference. With leaves turned downward, spray does not completely cover the leaf surface.

Entomologists say Transform and Sivanto are the best products available to control sugarcane aphid. Sivanto has a full label, while Transform has been used the last few years on a Section 18 Special Exemption. Transform is expected to be available on a Section 18 again in 2016.

A test using chemigation as a treatment option shows promise, Blayne Reed says. “Chemigation works, but it isn’t labeled yet. Using Sivanto, seven days after treatment we found no aphids. When — and if —we get a label, Sivanto will be a good option.” A water wash treatment was not effective.

Entomologists are also looking at sugarcane aphid-resistant hybrids. “Several companies are working on resistance,” Reed says. “In damage rating tests, we have seen significant differences with some resistant lines. Resistance will buy us about 10 days on the treatment threshold.”

“I think we will have resistant lines,” Porter says, but he cautions, “We can’t consider those lines silver bullets. But resistance will mean fewer aphids on the plants, which will help biological controls do a better job.”

USE OF HARVEST AID

Tommy Doederlein, Texas AgriLife IPM agent, also tested an insecticide with a harvest aid to determine if he could lower aphid numbers, reduce honeydew levels, and keep the pests off grain. He added malathion to the harvest aid treatment. “We wanted to keep the crop viable until harvest,” he says, “and keep the aphids from the panicles. Malathion wont control aphids, but it does push them down the stalk and away from the panicles.”

With the malathion treatment, he reduced risk to panicles from 70 percent to 20 percent. “We will check to see if there is a difference in sticky panicles,” he says. “Malathion seems to be helping.”

Harvest issues this season are evident. The specialists say heavily damaged plants are already lodging, and lower yield and test weight are likely. Honeydew losses are thus far unknown.

Recommendations call for a harvest aid and an insecticide when 25 to 100 aphids are on the flag leaf.

Kerry Siders, IPM agent for Hockley and Cochran counties, is looking at hay quality from untreated, aphid-infested sorghum. “We laid it down and let it dry for two weeks,” he says. Rain during that drying time washed off some honeydew, which was a concern because of potential for the sweet, sticky material to nurture mold and mildew.

“I think it’s okay with one-fourth inch of rain to clean it up,” Siders says. “After baling this hay, I would recommend feeding it by the first of the year. Shelf life might be a problem.”

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