Entomologists believe some grain sorghum varieties are more tolerant of sugarcane aphids than others. But they’re not sure which ones are a fit for being designated as resistant or tolerant and which ones aren’t.
That’s why researchers at the LSU AgCenter are conducting trials with grain sorghum varieties that are believed to be resistant at the Northeast Research Station at St. Joseph and other locations, according to David Kerns, who is based at the Macon Ridge Research Station in Winnsboro, La
“What we’re doing is looking at the efficiency of some of the hybrids that may or may not have some resistance to this pest; whether it’s tolerant or whatever,” said Dr. Kerns, who shared a stop with Sebe Brown, Extension entomologist with the LSU AgCenter’s Northeast Region, at the Northeast Research Station Field Day.
“We have 18 hybrids, a known susceptible and a known resistant hybrid. It’s not a commercial hybrid. It came out of a breeder’s program. So we have two things that we know how they’re going to respond because we looked at them last year.”
The other varieties or hybrids in the test have “some suspicion” of resistance to sugarcane aphids, said Kerns.
“Now all the companies will tell you ‘we think they’re tolerant; we just don’t know to what degree,” he said. “We don’t know at what level we still need to treat it, etc., etc.”
In the test, each hybrid will be planted in split plots. “We will let one-half of the plot be eaten by aphids, and we will spray the other half and keep it aphid-free,” said Dr. Kerns. “For each hybrid, we will have a direct comparison of the impact of aphids on a supposedly resistant line vs. one that we’ve kept free. So maybe we can help quantify how much resistance is in those hybrids.”
LSU AgCenter researchers are also studying economic thresholds for when to spray or not spray sugarcane aphids, on seed treatment efficacy and at other alternatives to the insecticides currently being used to control the aphids.
One of the concerns is how well the current products are controlling the pest. “I can tell you now based on very limited data – I’m not ready to make it more than it is – the populations we’re seeing tend to be slightly less susceptible to the products we looked at last year,” says Kerns.
On the other hand, some consultants and growers have said the sugarcane aphid populations don’t seem to be hitting grain sorghum as hard as they did last year.
“There are reasons for that,” says Kerns. “No. 1 we’ve had some torrential rains and wind to go along with them that tend to wash the insects off the plants. No. 2 the beneficials are doing a lot more for us this year than they did last year.
“If you’ll look you’ll see little black specks on this leaf,” said Kerns, displaying a long leaf blade from a milo plant. Those are parasitized aphids. There’s a little wasp that stings these aphids, and a little maggot will develop in that aphid.”
For more on sugarcane aphids, go to http://agrilifeextension.tamu.edu/solutions/sugarcane-aphid/.