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Variety, infection level dictates fungicide use

Leaf rust (Puccinia recondita) is a devastating foliar disease that infects both hard and soft red winter wheat in Northeast Texas. The first line of defense is development and introduction of resistant varieties. Over time, the leaf rust organism mutates to form new races that will threaten existing “resistant” varieties. The “fallback” position then becomes application of a foliar fungicide to protect yield during the grain filling period.

A primary research effort at Texas A&M-Commerce is evaluation of foliar fungicides to control both stripe and leaf rust in soft red winter wheat. We use highly susceptible varieties that often magnify the effects of fungicides on these diseases. For stripe rust, we conduct tests on AgriPro Patton and Pioneer 25R78, two SRWW varieties that are highly susceptible to stripe rust but quite resistant to leaf rust. We conduct leaf rust research on Pioneer 25R49 and Pioneer 25R54, two SRWW varieties with poor leaf rust resistance but excellent stripe rust resistance.

The primary purpose of these tests is to evaluate fungicide performance. Highly susceptible varieties make it easier to determine which fungicides perform best on both diseases. Research has shown that some materials are effective on both types of rust, while others are more effective on either stripe or leaf rust.

Economic Evaluation of Tebuconazole for control of Leaf Rust in Five Commercially Grown SRWW Varieties in Northeast Texas

A parallel research initiative is to evaluate profitability of foliar fungicides on commercially grown SRWW varieties. For these studies, we are evaluating fungicide profitability on Pioneer 25R47, Pioneer 25R57, Terral LA 841, AgriPro Coker 9553, and AgriPro Magnolia.

Highlight Summary - Fungicide Profitability Study

• At the Royse City location, a positive return on fungicide investment was achieved on Pioneer 25R47, Pioneer 25R57, Coker 9553, and Terral LA 841. We lost money by spraying Magnolia, even though a light leaf rust infection was observed on the flag leaf.

• Light to moderate leaf rust infection levels were observed at the Royse City location. Leaf and stripe rust levels in Pioneer 25R47 and Terral LA 841 were very low. The yield increases in the sprayed Terral LA 841 and Pioneer 25R47 are likely due to control of glume blotch, Stagnospora nodorum.

• Disease pressure was very low at the Leonard location and it was not profitable to spray a fungicide on any of the five selected varieties except Terral LA 841.

• When both locations are averaged together, a low cost fungicide (Folicur®) was marginally profitable in 2009 on the most commonly grown varieties in this region.

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