This past week we spent a few days surveying wheat fields throughout the state in order to see how the crop is progressing as well as better understand what disease related issues we may be experiencing. Most of the crop was near flag leaf emergence (Feekes growth stage 8/9) with a few fields near boot in locations further south. The good news is that of the 26 fields we looked at, none had any stripe rust, nor have I received any additional reports of this disease in the state. In general, diseases were minimal. In southwest portions of the state Septoria leaf blotch (aka speckled leaf blotch) was fairly common.
This is a residue-borne disease that is favored by cool, wet conditions and can grow and persist on small grain residues. The disease is often located deep within the lower canopy, and causes irregular brown lesions on the foliage. At the center of the lesions you will often see black structures that may resemble tiny peppercorns. These structures are why the disease has the extremely creative common name speckled leaf blotch. The disease spreads upwards predominantly via rain splash, and seldom causes significant yield impacts. This typically is due to increased temperatures that do not favor disease development as the crop develops and the flag leaf is produced. Remember, the flag leaf and green tissues above contribute the majority of carbohydrates for grain fill (over 70% from the flag leaf alone). Foliar diseases that do not reach these tissues are typically not a major concern.
Similarly, I came across a few fields with light powdery mildew. Unlike Septoria leaf blotch, powdery mildew is an obligate pathogen and requires a living host to grow and reproduce. Cool, humid (not wet) conditions favor powdery mildew development. In general, production practices that favor rapid plant growth and lush, full canopies early in the season favor this disease. For example, high nitrogen rates or manure use can result in rank growth early in the season. Powdery mildew can reproduce more quickly than Septoria, and therefore can occasionally impact early season growth or tillering in some instances. Although I did not see anything that would be of concerns and have not had any reports of severe powdery mildew, management is best achieved through selection of a resistant variety and avoiding excessive nitrogen application. Early season fungicide applications with nitrogen applications can have some benefit when a field is at high risk for disease (i.e. susceptible variety, heavy N use, disease present early, cool weather forecast for several days/weeks) but are not recommended if disease is low. Anything in the triazole (FRAC group 3), SDHI (FRAC group 7) or Strobilurin (FRAC group 11) fungicide classes will help control powdery mildew in high risk situations.
As we approach boot and heading you should keep an eye on the Fusarium Head Blight Prediction Center for updates on disease risk. I will follow up with a post on how to best use this tool on my blog in the next few days. Forecasts are calling for e moderate and potentially rainy conditions over the next 7-10 days depending on your location. In the meantime, keep an eye on your fields, and enjoy the weather!
Nathan Kleczewski Extension Field Crop Plant Pathologist University of Illinois email: email@example.com