WESLACO — Scientists at the Texas A&M AgriLife Research and Extension Center at Weslaco say sugarcane aphids appear to be moving from grain sorghum to corn and sugarcane crops.
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Until now, sugarcane aphids had only been seen in high numbers in most fields of the area’s 400,000 acres of grain sorghum, most of which is exported to Mexico as cattle feed, they said.
Dr. Raul Villanueva, a Texas A&M AgriLife Extension Service entomologist at the center, said the aphids are not thriving on corn but could pose serious problems to the area’s sugarcane crop in addition to the damage it is causing to grain sorghum.
“It could be they are not getting the nutrition they need, but they just don’t seem to develop into healthy adults on corn plants,” he said. “So they likely won’t be a persistent pest on corn, maybe just a secondary pest from time to time. But it’s a different story on sugarcane.”
Villanueva said the sugarcane aphid thrives on sugarcane plants, developing into healthy, reproductive adults, some of which grow wings to disburse to other plants or fields.
Worse yet, they are highly efficient vectors of the yellow leafvirus that until now had not been a threat to the sugarcane industry, likely due to a lack of an efficient insect to transmit the disease, he said.
“Of course, we don’t know yet, but the sugarcane aphid on sugarcane could cause yellow leaf virus to spread much more rapidly due to the presence of a more efficient insect vector such as they sugarcane aphid.”
Dr. Erik Mirkov, a Texas A&M AgriLife Research virologist at the center, said the sugarcane aphid was first detected in 1977 in Florida sugarcane and in 1999 in Louisiana sugarcane, but did not cause major problems in either state.
“It’s called the sugarcane aphid because sugarcane is its preferred host,” Mirkov said. “It completes its life cycle on sugarcane and can build up to high populations.
“Our concern is yellow leaf virus. Until now, the aphids here were inefficient in transmitting this disease, so it wasn’t much of a problem. But the sugarcane aphid is very effective in moving it around.”
As its name implies, yellow leaf virus turns sugarcane plant leaves yellow, he said. It prevents the transport of sugars produced in the leaves to the stalks where the sugar is stored. In susceptible varieties, yellow leaf virus can result in 50 percent yield losses.
“Fortunately, the two varieties that make up the majority of South Texas sugarcane are fairly tolerant to yellow leaf virus,” Mirkov said. “Studies done back in the 1990s showed that yield losses could be significant, but not horrific. But that could change.”
Aside from transmitting the virus, Mirkov said he’s concerned about this new pest because the insect itself can cause problems.
“Sugarcane aphids can grow to such huge numbers that they can overwhelm a plant,” he said. “They are sap-feeders and can deprive sugarcane plants of the nutrients and water needed to produce and survive.”
Like grain sorghum growers, sugarcane growers are not accustomed to spraying expensive insecticides on their crops, Mirkov said.
“The profit margin on both grain sorghum and sugarcanejust isn’t there for growers to be spending thousands of dollars on insecticide treatments they’re not accustomed to pay for.”
For now, Mirkov said, growers can only keep an eye on the situation and hope for the best.
“It’s happened before, but these new populations may not survive here,” he said. “They could be overwhelmed by the environment, or by predators and parasites. At this point, we just don’t know what these insects will do in the future.”
Almost 200 grain sorghum producers, many who also grow sugarcane, attended a field day at the Texas A&M center in Weslaco recently to learn about the sugarcane aphids’ biology, how to identify them and how to treat their fields for them.
Danielle Sekula-Ortiz, an AgriLife Extension integrated pest management agent at the center, said since first being detected here late last year, genetic studies are being done at Texas A&M University in College Station to determine whether the aphid is a new insect to the area or if it adapted to feed on grain sorghum.
“We may not know the answer to that for a while,” she said. “But what we do know is that grain sorghum growers need to treat their fields against this pest if they hope to harvest grain this year.
“Besides reducing yields, the insects create an abundant sticky waste called honeydew, which can cause major problems and delays at harvest time because it gums up the combines. So even if the heads have hardened, meaning they are ready for harvest, it’s important to spray to reduce the honeydew growers will have to contend with.”
Sekula-Ortiz said those who attended the field day included producers and researchers from Mexico who said the sugarcane aphid is causing major problems throughout Tamaulipas.
“At about 1 million hectares, Tamaulipas has the largest grain production area of any state in Mexcio. We agreed that because the Rio Grande is no barrier to insect movement, we’ve got to work together as a single region to manage this infestation.”