Disease pressure remains low in most Texas wheat fields, but growers should be prepared to apply fungicides if conditions favor infection. Current positive profit opportunities for wheat may encourage producers to protect the crop.

Most wheat is approaching Feekes 9 (flag leaf emergence) in Northeast Texas. Some of the very earliest maturing varieties are in Feekes 10 (boot stage). Stripe rust (Puccinia striiformis) infection levels are relatively low across the region, but we have noticed a trace of stripe rust in the lower canopy of some susceptible varieties in our nursery at Leonard.

Statewide reports also indicate low levels of stripe rust. The most susceptible commercial variety widely planted in this area is Pioneer 25R78 SRWW. Stripe rust usually appears earlier than leaf rust and may require an earlier fungicide application.

Leaf rust (Puccinia triticina) infections remain low across the region and state. The most susceptible widely planted varieties include 2145 HRWW and Pioneer 25R57 SRWW.

If conditions remain dry, both rust diseases will be suppressed. However, all it takes is moisture in the form of heavy dews to trigger an infection cycle. The following conditions should be met before making a decision on applying a fungicide to control leaf rust:

  1. A susceptible variety.

  2. Good yield potential (40 or more bushels per acre). Most area wheat meets this requirement.

  3. Evidence of rust pustules on the lower leaves but not the flag leaf.

  4. Later applications (Feekes 10 to 10.5.1) have usually been more productive than earlier one (Feekes 8-9).

We have an excellent arsenal of fungicides for rust management. Quilt, Stratego, and Headline have all provided excellent protection from both stripe and leaf rust. Propiconazole, sold as Tilt or Propimax, has also provided good protection from both diseases.

Fungicides will provide only about three weeks of protection. The higher fungicide rates will provide longer protection than lower rates. However, the 10.5-ounce rate of Quilt has been as effective as the 14-ounce rate over the past two years. The key is to apply the materials before infection is observed on the flag leaf.

Given the attractive wheat prices this year, growers are showing more interest than usual in foliar fungicides. At $4.00 wheat, it doesn't take many bushels to pay for the fungicide and cost of application. Below is a summary of our 2005 and 2006 foliar fungicide work on leaf rust. Stripe rust was not a problem last year.

Foliar fungicides for control of leaf rust in SRWW 2006

Leaf rust (Puccinia triticina) is a devastating foliar disease that infects both hard and soft red winter wheat in this region. The first line of defense is development and introduction of resistant varieties. Over time, however, 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. Following is a summary of our 2006 foliar fungicide research for leaf rust control.

Highlight Summary

  • Yield increases ranged from 6.9 to 15.2 bushels per acre with a foliar fungicide application.

  • All of the fungicides produced a significant increase in bushel weight.

  • All of the fungicide treatments produced significantly more grain than the untreated check but were not significantly different from one another.

  • Over the past 20 years, fungicides have returned an average of $2.00 to $2.50 for every dollar invested where susceptible varieties were sprayed in the presence of moderate to high leaf rust infection levels. In this study, the fungicide returned $1.55 to $3.42 for every dollar invested.[2]

  • Split applications of Quilt, Stratego and Folicur were not significantly better than a single application of any fungicide. There has been no advantage to split applications to control leaf rust in either 2005 or 2006. However, our best stripe rust treatments in 2005 were split applications.

  • The split applications of Quilt, Stratego, and Folicur were applied at Feekes 8 (April 4) and Feekes 10.3 (April 17) at Leonard. The early single applications were made at Feekes 8 (April 4) and the later single applications were made at Feekes 10.3 (April 17).

  • There were no significant differences between the low and high rates of Quiltand Stratego.

  • All of these materials provided economically effective control of leaf rust and a positive return on investment, regardless of rate.

[1] VIRULENCE SCALE:

1 = Spore “hits” but no pustules

2 = A few weak pustules surrounded by large necrotic margin

3 = Larger pustules, surrounded by moderate necrotic margin

4 = Profuse, robust pustules, surrounded by small or no necrotic margin

[2] Assuming $3.60 wheat and a fungicide cost of $16.00 per acre

[3] Assuming $3.60 wheat, a $4.00 application cost, and foliar fungicide suggested retail prices. Actual fungicide prices may vary.

Funding from the Texas Wheat Producers Board supported this work.