We have had quite a few reports over the past few months from areas to the south of striped rust in wheat that caused concern and some that required treatment. Starting early last week and continuing through today (5/12), it looks like the striped rust has blown its way into our fields in Hale, Swisher, & Floyd in force.
In our wheat scouting over the past 10 days or so we have witnessed this plant disease move from south to north at what have become treatable levels. Conditions had been optimal for an extended period a few weeks ago for spore germination with damp, dewy mornings, cool temperatures, and some good rain events.
With the help of some southern wind and in conditions like those, the spreading fungal spores had ample opportunity to germinate in wheat with the increased humidity and moisture. These germinating spores infected many of our area what fields and symptoms are now and have been showing up in those selected fields.
Now that we are (and have been) able to see the symptoms plainly, what we need to be looking at is the flag leaf, at or preferably prior to bloom stage. Wheat can handle a large amount of foliage damage to the lower leaves without economic concern, but the flag leaf is of utmost importance as it is the primary source for feeding the head.
Up to a point we can say that the percent damage of the flag leaf at or before bloom stage should roughly equal the percent of yield loss we can expect from just about any wheat disease, including striped rust. That is up until the grain fills at soft dough stage.
Herbicide Resistance Info
Once the grain reaches soft dough stage, the economics of disease treatment diminish rapidly and even heavily damaged flag leaves should not require treatment. The above chart was developed and is promoted by Dr. Ron French, Texas A&M Plant Pathologist, Amarillo to aid in these tough economic decisions regarding wheat disease and treatment.
If following this chart, and applicable Texas A&M management guidelines, you decide your field has not completed bloom yet, is in an economic situation and requires treatment, there are several good fungicide options to do so ranging in price from a quick knock down up to multiple modes of action with a proven two weeks’ worth of residual.
Please consult all applicable labels and do watch the labeled pre-harvest intervals for your selected fungicide.