Published: April 27, 2008 12:31 am            

Where is leaf rust

This time last year, wheat producers were getting showered upon by rain and also by spores — leaf rust spores from Texas.

The biology lesson from high school came to be remembered. We had the leaf rust spores to be the causal agent. We had a favorable environment by being a wet leaf surface and cool, wet weather. We also had two very susceptible hosts (wheat varieties) for the disease to survive upon. As a result, there was to be a very heavy leaf rust infection in northwest Oklahoma.

We are at that time again where producers are faced with the same situation as they were a year ago. While we have a greater spread in the wheat varieties we have planted this year, there still is a large number of both Jagger and Jagalene planted. We have been drier than last year, but that may be changing with the rainfall in the middle of last week and the forecast is for more this week. Leaf rust appears to be at lower levels than last year, but what I am hearing is the rust is just later in its arrival than last year.

I would like to comment on the questions that Oklahoma Cooperative Extension Service educators are answering to provide some help for producers.

When should a producer apply a fungicide? Most fungicides are labeled to be applied from flag leaf emergence to the wheat head being completely emerged. If a producer had planted wheat on Oct. 1 and had enough moisture to emerge the wheat, we are in the middle of those growth stages mentioned.

What products should I be looking at? There are five products you should consider. These are Tilt, PorpiMax, Quilt, Stratego and Headline. A comparison of these products may be obtained from your county extension educator by asking for Current Report 7668.

What are the benefits of using a fungicide? OCES has been working with foliar fungicides for about 20 years now. Some of those years have been a light rust infestation and several of those years were like last year when rust covered just about everything. Over those 20 years, OCES has seen a 10 percent yield increase on a susceptible variety by the use of a foliar fungicide. In 2006, which is considered a light year for leaf rust, OCES data was seeing a yield loss of 5 to 7 bushels by not using a fungicide to protect the yields of Jagger and Jagalene.

What varieties should I consider using a fungicide on? If your wheat fields are planted to Jagger or Jagalene, you should very seriously considering the use of a fungicide. More resistant varieties like OK Bullet, Endurance, Duster, Overley and Fuller still are considered resistant at this time. You may see some rust develop on the flag leaves of those varieties, but yield impacts will be less than the 10 percent discussed with Jagger and Jagalene.

For more information about how to use a foliar fungicide and which wheat varieties are susceptible or resistant, stop by your OCES Extension Office for the Current Report 7668 and the latest update on the Wheat Variety Comparison Chart.



Gribble is Oklahoma Cooperative Extension Service northwest area agronomist.