Farm Talk

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November 19, 2013

Do wheat fungicides pay?

Parsons, Kansas — Holed up between planting and harvest, a gang of desperados is lying in wait to steal wheat yields.

Included in that murderer’s row of yield killers are fungal diseases bent on picking the pockets of growers — when conditions are right.

“Fungicides do pay off, but not every year,” Kansas State University Extension Specialist Doug Shoup told producers in Columbus, Kan., last week. “You have to be aware of the potential for disease — variety susceptibility, weather, stage of growth, disease levels and other factors.”

Principal fungicide targets include leaf rust, powdery mildew, septoria leaf blotch, tan spot and stripe rust.

Leaf rust and stripe rust normally don’t over-winter in the area but blow in from the south, Shoup said.

Powdery mildew and tan spot are fairly common in area fields and septoria leaf blotch has become a bigger problem in recent years — partly because the area’s most popular hard red winter wheat, Everest, has lost some of its foliar disease resistance.

Shoup emphasized that wheat streak mosaic and barley yellow dwarf, while severely damaging to wheat, are viral diseases not affected by a fungicide.

Farmers can choose between two fungicide types — triazoles and strobilurins — or combinations of the two.

In general, strobilurins are strictly preventative and must be applied before disease symptoms appear, Shoup said.

Triazole fungicides are considered to have slightly better curative activity, depending on the disease that is present. Small differences in curative activity don’t always translate into increased yield, however, he added.

Both types, applied at the correct rate, provide residual activity for about 21 days. Strobilurins are a little stronger past 21 days, he added.

Regardless of the product, Shoup stressed, fungicide efficacy is always better if applied when the targeted disease is still at low levels.

“The decision of whether or not to apply a fungicide is probably more important than which product you use,” he said. “It’s tough to pinpoint one product over another because every year and every situation is different.

“If you simply applied a fungicide every year, some years you’d hit a home run and other years you’d get no yield response.”

The key to sorting out when a fungicide treatment will pay off and when it won’t lies in assessing disease potential, he explained.

Start with variety susceptibility, Shoup suggested. A variety with a better fungal disease resistance package, like WB-Cedar, is less likely to need a fungicide treatment compared to more highly susceptible varieties like Overley and Jagalene, for example.

But that’s not the only consideration. Disease pressure varies from year to year and producers need to be aware of disease presence in other areas — particularly to the south — as well as locally.

Local weather also plays an important role, Shoup said. Moderate temperatures and frequent rain set the stage for disease problems.

Stage of growth is another consideration. The later the infection occurs, the less impact on yield.

And then there’s the question of whether the crop’s yield potential and grain prices justify the additional input investment.

Application timing is critical, the agronomist cautioned. The goal, he said, is to protect the plant’s last two leaves and producers using a single application approach should spray between flag leaf emergence and flowering.

“That’s probably going to give you about a three-week window,” Shoup said. “But remember that the flag leaf needs to be completely out because fungicides are not systemic — they have to be on-target.”

Acknowledging that some growers in intensive management systems opt for two fungicide applications — including an early treatment at green-up — Shoup said most yield response comes from the later application.

Kansas State University has 20 years of data on the efficacy of fungicide applications across the state. On average, Shoup said, fungicides provided a 10 percent yield advantage with most treatments ranging from a 4 to 14 percent yield advantage. The full gamut, however, runs from 0 percent to 40 percent and the research focuses on susceptible varieties.

Last summer at the Southeast Agricultural Research Center, Armour showed a 10.34-bushel response to a fungicide application while Everest and Fuller got 13.65- and 19.52-bushel boosts, respectively.

Those results may not be typical, Shoup said, but it does indicate the potential yield response when fungal diseases are a threat.

Identifying that risk level is the challenge wheat growers will face as this season’s crop progresses toward harvest. £

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