If sugarcane aphid populations are allowed to hit 250 per leaf, they’ve reached a point of no return and farmers will suffer economic loss from numbers that high, says Michael Brewer, Texas AgriLife Extension entomologist at Corpus Christi.
“Things happen fast, but the plant doesn’t die immediately,” he told audiences recently at both Bryan and Commerce, Texas, during meetings of the Texas Plant Protection Association and the Texas Ag Technology Conference, respectively.
Emphasizing the importance a once-unknown pest has taken on in just three years, he said, “If you see plants responding to the infestation, it’s too late. At 500 aphids per leaf, the situation is bad.” He advises preparing to initiate spray applications at 50 to 100 aphids per leaf.
For the latest on southwest agriculture, please check out Southwest Farm Press Daily and receive the latest news right to your inbox.
“This is a new beast,” he told the Commerce audience. It likely migrates into the area from overwintering sites in South Texas where they hold up on johnsongrass through the colder months. He says the aphid is the same species as one that infests sugarcane, but is not the same. “This one is hardly ever seen on sugarcane — it’s a new race. We see it occasionally on corn, but we haven’t seen reproduction.”
It’s the rapid buildup that causes concern, Brewer says. “It can go from 50 to 500 aphids per leaf in less than two weeks. It can go from 250 to 500 in about a day, or maybe two days. It’s important to detect the aphid early, at 10 to 25 per leaf; at that level, there is time to react. We prefer that growers react within days — if they wait three weeks from that 10 to 25 aphid number, they will have significant damage.”
LONG DISTANCE TRAVELER
Brewer recalls that there was “a small problem in the Gulf Coast of Texas” with the pest, and within two years, 90 percent of the sorghum production in the United States and Mexico had been affected. “It’s now a permanent resident in the lower Gulf coast area of Texas and the Mexican Gulf coast. The winged population can travel north, 100 or 1,000 miles.”
That ability to migrate resulted in the aphid being classified as “a problem for 50 percent of our Texas acreage in 2014, with economical infestations. But we only had 15 percent production loss. We do have control options.”
Management begins with scouting. “Begin scouting 20 days after planting,” Brewer recommends. He advises growers to continue that schedule until, or if, they identify sugarcane aphids on the crop. “Once they are identified, scout twice a week,” he says. “Tolerance now is less than 50 aphids per leaf, and after detection growers face a two-month window of concern.”
He says early application, initiated around the 50 aphid level, may be enough to get growers through the season. “South Texas growers are mostly managing the pest with one spray application.” Sivanto, at 4 ounces per acre, may be the best bet for 2016, depending on the outcome of a Section 18 Emergency Exemption request to the EPA from the Texas Department of Agriculture to use Transform again.
“Transform is in the courts,” Brewer says. “For now, it is not available. Nufos is effective at high rates. Pyrethroids are not effective.” Sivanto has a full label for sugarcane aphid control in grain sorghum.
Late-season infestations may need an insecticide application with a harvest aid product to prevent the honeydew secreted by the aphid from gumming up harvest and elevator equipment.
MULTIPLE PESTS ADD COMPLEXITY
Dealing with multiple insect pests — aphids, head worms, and others — at the same time also creates management dilemmas, Brewer says, and tank mixing Sivanto with products to target head worms may be necessary.
He likes the idea of alternating chemistries when multiple applications are necessary for aphids, but says the complicating factor of treating other pests at the same time may make that more complex. He recommends using Sivanto early, before infestations get out of hand, with the hope of managing the population with one application. But, if a second spray is needed with a product for head worms, a second application of Sivanto may be the best bet.
Brewer says economic spray threshold may be somewhat a moving target, and will depend on crop condition, time of the season, and presence of beneficial insects. “But 50 aphids per leaf is a good number until we learn more.” Also, several grain sorghum hybrids have shown some resistance to the pest and may be useful as preventive measures.
“Hybrid choice is important,” Brewer says. “Host plant resistance, natural enemies, and decent rainfall all help manage sugarcane aphids.”
He says protecting forage sorghum may be less complicated. “Forage sorghum producers will seldom need to apply an insecticide more than once. Farmers may elect to alter cutting time, however.” He says sooty mold, which builds up on the honeydew, will not harm livestock, and he’s seen no evidence that it significantly affects hay quality.
“Sugarcane aphid control is feasible — but challenging,” Brewer says. “Damage occurs only from general plant decline. The aphid is not a vector for the virus and is not toxic. We can control sugarcane aphids, and the future looks good for hybrid resistance. We can do this.”
Modified IPM approach useful for sugarcane aphid control
A modified integrated pest management approach, including selecting “soft” chemistries to control in-season grain sorghum pests, may be a reasonable approach to managing sugarcane aphids, says Justin Chopelas, a crop consultant from Odem, Texas, who spoke at the recent Texas Plant Protection Association annual conference at Bryan.
Protecting the flag leaf is a critical goal, he says. “From there, the aphid moves into the head. They move quickly, and conditions that favor the sorghum plant also are good for the aphid. A good fertility program, for instance, is a positive factor for the sugarcane aphid.”
Chopelas says several beneficial insects, including the ladybug beetle and the Syrphidae (hover) fly, “can be effective. The Syrphidae is an “aphid eating machine,” he says.
Insecticide application, however, will be necessary with higher populations. “We have to pay attention and develop a methodology to start insecticide applications when it’s the right time to ‘pull the trigger.’”
Sivanto has a viable label, Chopelas says, and is effective. For other in-season pests — head worms, stink bugs, and others — soft chemistries may help preserve beneficials that prey on the aphids. Head worms may be more difficult to manage and may require pyrethroids. “Once we start with hard chemistries, such as pyrethroids, we are locked in,” he says.
“We have learned more about sugarcane aphids each season, and it appears that a modified IPM approach, using soft chemistries and beneficial insects, can be effective.”
Late-season scouting is also recommended, Chopelas says, to prevent aphids from moving into the sorghum heads and building to levels that create enough honeydew to affect harvest operations.