Seed treatments have been growing in popularity because of their ease of application — no in-furrow boxes to be filled or calibrated, etc. — relatively low expense and effectiveness.
But seed treatments may not always be the best option, especially if cotton producers have high populations of specific types of nematodes in their fields, a scientist with the Louisiana State University AgCenter says.
Charles Overstreet, Extension specialist with the AgCenter in Baton Rouge, says site-specific farming techniques may offer a way for growers to reduce the cost when they need to apply nematicides with higher efficacy such as soil fumigants and non-fumigants.
“One of the things we’ve been working with for a number of years is the site-specific application of fumigants and non-fumigants because they’re expensive,” Overstreet said. “You can’t afford to put them out where you don’t need them. You need to put them exactly where they’re needed to get the maximum benefit.”
Speaking at Cotton Incorporated’s 2008 Crop Management Seminar in Robinsonville, Miss., Overstreet said seed treatments do offer producers advantages such as ease of application (most are applied on the seed by seed companies), timeliness and by providing multiple types of protection against insects, diseases and nematodes.
Chemical manufacturers have begun offering combinations of products, including Avicta Complete Cotton, which contains an insecticide (Cruiser), a nematicide (Avicta), and a fungicide (Dynasty CST), and Aeris Seed-Applied System, which contains Gaucho Grande, thiodicarb (as a nematicide), and an optional fungicide, Trilex Advanced.
He said cotton producers should ask three questions about seed treatments: Why would you use them to protect cotton? How effective are they? When should they be used?
“Obviously, seed treatments are easy to use,” he notes. “The materials are on the seed. You get the seed planted, you get a stand and you should have the chemicals out there, exactly where you need them. But what are you willing to sacrifice to get the benefits of seed treatments?”
If he was asked to provide a ranking, he said he would list untreated seed as being the worst, Temik and seed treatments somewhere in the middle and the fumigants — Telone, K-Pam and Vapam — as being the most effective.
Nematologists see numerous comparisons of seed treatments and nematicides against Temik. He showed a 2006 study conducted by Gary and Kathy Lawrence for the 2007 Beltwide Cotton Conferences.
“You can see a lot of ups and downs,” said Overstreet. “Sometimes they work really well, sometimes they don’t. Sometimes the Aeris is better than Temik and sometimes Temik is better than the Aeris. Obviously, they are effective to some extent, and that’s the important thing here.
“My take on seed treatments is that they do have a place. But you should only use them when you have low populations of nematodes — maybe slight to moderate — depending on the type of nematodes and depending on what kind of soil you have.”
Growers have some places in their fields “where seed treatments and nematicides are just not going to work for you, and you need to know that ahead of time,” says Overstreet. “Don’t get in a situation where you plant some of these fields that have either high levels of nematodes or the fields are at high risk of nematode injury.”
Crop rotations can also have an impact on a grower’s choice of nematodes control materials. Some crops will provide a positive response or a reduction of certain types of nematodes while others will simply maintain those populations.
“Corn obviously has become a big crop for us in the Mid-South, and it does a great job of knocking down reniform nematode populations,” he notes. “But it does a lousy job of knocking back populations of root-knot. You should know what type of nematodes you have in the field so you know what kind of population change you can expect.
With crop rotations, one year is good, but two years are better if growers can plant a non-host or resistant crop in their rotation, says Overstreet, who has been studying nematodes in Louisiana for nearly 30 years.
Farmers need to sample their fields using zone-sampling or grid-sampling techniques to determine populations and types, he said. He listed these rules of thumbs for when to use seed treatments and lower rates of nematicides:
• Fields which have been sampled for nematodes (the grower has received reports on population levels and type).
• Fields where nematode problems have not been observed and cotton yields are high.
• Fields where the grower plans to supplement the use of seed treatments with some other type of nematicide.
Precision farming research by LSU AgCenter scientists has shown farmers can apply fumigants preplant to areas in the field with high populations of root-knot and reniform nematodes using variable rate applications.
Farmers may want to consider applying the more expensive fumigant materials based on soil types alone, he said, displaying a map that had been color-coded according to soil types.
“You might want to apply a fumigant to the light side of this map (with sandier soils) because those are the areas that are likely to have higher populations of nematodes,” he said. “You could skip the fumigants on the darker side of the field and use a seed treatment over the entire field.”