While sugarcane aphids are a big concern in sorghum production, an agronomist says he’s looking forward to the day when they are no longer a hot topic.
“And I think we are getting closer to that day,” says Dr. Brent Bean, Sorghum Checkoff agronomist. “If you look at what’s gone on the last two years with the sugarcane aphid, nationwide things have improved considerably.”
Originally, South Texas was the “hot spot,” Bean says, but this year it is estimated that no more than 20 percent of the acres were treated for sugarcane aphid. Moving further north to the San Angelo area, he says a few more acres were treated there.
“But when growers in South Texas, or south of wherever you farm, control aphids in their fields, it helps everybody else because the population of sugarcane aphids is kept down,” Bean explains. “Beneficials have adapted to this new food source, so that’s helping. And then we’ve identified hybrids that are more tolerant to sugarcane aphid, so that also helps keep numbers down.”
One area where we continue to struggle with high infestation levels is in the Plainview, Hart area of the South Plains. “It’s unfortunate, but that region has been the hot spot in Texas for the last three or four years for sugarcane aphids and we really don’t know why that is.”
Bean answers the following questions about the sugarcane aphid and what growers need to be thinking about as harvest approaches.
What’s sugarcane aphid activity like in the Panhandle?
I’m seeing very few aphids. You can probably find them in every county if you look hard enough, but you’ve really got to look, and in some cases, look hard to find them. Now, that could change in two weeks; they can blow up quickly sometimes. But they don’t seem to blow up as quickly as what we experienced in 2015. The aphids showed up, nobody recognized them and then they blew up, and it became a disaster. You just don’t see that anymore. Usually, it’s a gradual increase, so you do have some time to check your fields and to treat.
At what stage of development do sugarcane aphids primarily affect sorghum?
During flowering or soon thereafter. That’s really the critical time to be scouting.
What products do you recommend for treatment?
We have two good products we’re using: Sivanto Prime and Transform. Both can do a good job. Which product you use depends on the stage of development of the sorghum.
When treating, are surfactants necessary?
Research shows we do not need to add surfactant, which saves on cost.
When do you treat?
The key is to watch your crop. If you do reach threshold level, then treat. In some cases, we are pulling the trigger too fast. We’re afraid they are going to blow up and don’t wait until threshold. I encourage people to wait until they get to the threshold level before they treat.
What is considered threshold for sugarcane aphids?
It varies across states but when sorghum is in the pre-bloom to the early soft dough period, and when you have 50 aphids which are roughly a quarter size colony on 25 percent of your plants, that’s when you need to treat. Randomly look, don’t go out there and say, ‘I see honeydew,’ and just scout in those spots. Randomly scout your field. Pull a leaf from the bottom and a leaf from the top, check those leaves and do that on as many plants as you feel comfortable checking, and if you are at 25 percent of plants infested with at least 50 aphids, that’s what we generally consider the threshold.
As the sorghum matures and gets into, for example, the hard dough stage, you’re not going to affect the yield much, but what they can do is affect the standability of the sorghum, so you can get some lodging later on prior to harvest.
If a grower has sugarcane aphids near harvest time, can desiccating their sorghum with Roundup or sodium chlorate control the aphids and help with harvest?
That treatment only works if you have enough time to let it dry down completely and the aphids finally die off but that’s typically not what happens. In fact, if you desiccate the sorghum it may force the aphids to look for green material and that green material is going to be in the head, so that doesn’t really help you.
What you need to do is use the lowest labeled rate of either Transform or Sivanto because all you need to do is control the aphids for short period of time, let the honeydew dry up and then you can harvest. You don’t want to spend any more money than you have to, but if you think you’re going to have an issue at harvest, use the lowest rate of insecticide that you can get by with.
As harvest nears, what should growers consider when it comes to irrigation?
Sorghum will continue to use water up to the point that it reaches physiological maturity which typically occurs about 45 days after flowering or bloom.
Keep in mind, when it gets to the hard dough stage, then it’s another 14 days or so before it’s physiologically mature, so it’s still using water. You can shut off the irrigation at hard dough stage in most soils if you have decent soil moisture.
If you don’t, the crop could use another inch or two of irrigation water to get it to physiological maturity. It may not always affect the grain yield, but it can certainly help with test weight. A late irrigation also helps maintain the stalk’s integrity, so you don’t get lodging if you’re having to wait to harvest because you’re trying to get your corn harvested or something else. Once it’s reached physiological maturity, the longer it stays in the field, the chances of lodging increase.
For more information or questions regarding sorghum production, contact Bean at firstname.lastname@example.org.