<b>By ANN HINCH<br> Assistant Editor</b> </p><p> LOUISVILLE, Ky. – Deciding how and when to treat Asian Soybean Rust (ASR) – or even the threat of it – with fungicide also involves deciding what kind to use, and how to best to apply it.</p><p> At the recent National Soybean Rust Symposium in Louisville, Tristan Mueller with the University of Florida offered a presentation on fungicide trials used on soybean test plots in Florida and Brazil, and agricultural engineer Richard Derkson of the USDA’s Agricultural Research Service talked about spray technology.</p><p> To set up the importance of trying to narrow a window of proper fungicide application, Mueller explained in his region, a field can go from ASR being detected, to 20 bushel/acre yield loss in only 15 days.</p><p> There are two basic kinds of fungicides marketed under a variety of trade names: triazoles and strobilurins. Strobilurins, he explained, should be sprayed only as a protectant, when advisable, against incoming ASR spores. Triazoles are more systemic than strobilurins, and while they work better as a protectant before the fact, Mueller said they do have some curative properties.</p><p> His field tests employed Headline, a popular strobilurin; Folicur, a triazole; Headline SBR, a co-pack; and Quilt, a premix. These were applied to soybean plants at R1, R3 and R5 stages, in a wide range from 47 days before ASR reported to 36 days after.</p><p> Overall, he said fungicide application in later reproductive stages, such as R5, works fairly equally with all brands used.</p><p> It’s in the earlier stages, especially before R3, that “really separates the men from the boys” with respect to efficacy of the chemicals. In one instance, Headline applied at the R3 stage on a Florida plot seemed to preserve some of those plants’ greenery over application of Quilt – at their later R5 stage, Mueller reported a 12 bu./acre grain advantage of Headline-treated plants over Quilt-treated plants.</p><p> If ASR infection is early enough in a soybean field’s development or a grower sprays too early, Mueller added the farmer may need to spray a second application of fungicide before harvest, to preserve yield.</p><p> If applied at the right time, and judiciously, he said, “You will be able to control this pathogen.”</p><p> He also used Topguard on application directly to soil, which is illegal except for special permission or testing. He received good results, but said even if the federal government allowed broad application, growers would have to use special equipment and methods to apply to soil.</p><p> Derksen’s tests involved using different kinds of nozzles and boom sprayers on soybean plants from both 12 and 24 inches above the ground, letting the fungicide dry and then taking samples to test residue spread on middle and lower canopy leaves. The first applications in 2005 used 15 gallons/acre of Headline at 7 mph.</p><p> The canopy-opener sprayer worked well on the mid-canopy, while the air-assist (high air pressure) sprayer did well on lower canopy. The stems didn’t retain much residue and Derksen said he didn’t include those in his study (even though they have a slight groove that can trap spores).</p><p> In 2006 applications, he kept the same speed but experimented with some new sprayers and nozzles, and varied the rate of application – some plants still received 15 gallons/acre, some received 20 or another concentration.</p><p> Naturally, he found “coverages tend to be higher with a higher application rate.”</p><p> He found the lower canopy was still covered better with air-assisted sprayers than others; with nozzles, he found smaller droplets worked well, as did the Turbo TwinJet nozzles, applying a narrower angle of coverage – 60 degrees – than a dual-jet sprayer with two nozzles covering a 90-degree angle. Deposit coverage was better on less dense canopies. |