In visiting with Joe Martin, wheat breeder at Kansas State University Agricultural Research Station in Hays, a few varieties of wheat on the station will be fully headed by the end of this week.

That means the wheat will start to shed pollen or pollinate in three to five days after fully headed. Once pollination begins, according to the label, it is too late to spray any of the labeled fungicides for wheat.

More susceptible varieties to leaf rust such as Jagger, Jagalene, Overly, TAM 110 and TAM 111 might be good candidates to spray for leaf rust. Currently, we are just seeing low levels of leaf rust on the lower leaves of the above mentioned varieties.

Given the current weather conditions, there still is a favorable chance of leaf rust moving up the plant onto the flag leaf of susceptible varieties. If temperatures continue to warm up as forecasted, that should not slow down the progression of leaf rust. In fact, it actually will speed up the progression of leaf rust because it prefers warm weather (65 to 80 degrees) with some humidity -- which we continue to have. Stripe rust is favored by mild weather (50 to 75 degrees) with some humidity.

The earlier rust appears in the life cycle of wheat, the greater the potential for substantial yield losses.

Losses are greater when leaf rust infects the flag leaf at flowering (30 percent loss with 65 percent flag leaf infestation) than when leaf rust infects the flag leaf at the soft dough stage (7 percent loss with 65 percent flag leaf infestation).

The flag leaf accounts for about 70 percent to 80 percent of the final yield, so keeping it healthy especially early on is important. Even though the wheat is behind in growth as compared to the normal average, it appears that in Ellis County leaf rust might not be on the flag leaf by flowering. Its potential affect on yield at this time is anyone's guess.

Consider economics and yield potential. For example, 10 percent loss in yield on 30 bushel per acre wheat at $6 per bushel is a loss of $18 an acre, which does not cover the cost of the fungicide application. However, 10 percent loss on 60 bushel/acre wheat at $6 per/bushel is a loss of $36 per acre.

On Wednesday, I visited with Mark Ploger, Pratt County agent, and he indicated in Pratt County there is about 20 percent to 40 percent leaf rust infestation on the lower leaves of susceptible varieties, and therefore some growers in that county are spraying.

Continue to scout your wheat fields. Considerations to make before spraying are current yield potential, susceptibility of variety to leaf rust, when the rust appears in the life cycle of the wheat and severity of rust on the flag leaf, and probably the most unknown variable is expected price.

Further information on leaf rust can be obtained from Identifying and Managing Wheat Rusts (MF-2723), Foliar Fungicide Efficacy Ratings for Wheat Disease Management 2008 (EP-130), and Wheat Variety Disease and Insect Ratings 2007 (MF-991) at www.ellis.ksu.edu

Stacy Campbell is Ellis County agricultural agent with K-State Research & Extension.