Septoria Leaf Blotch of Wheat

Figure 1. Septoria leaf blotch leaf lesions.

I recently visited a wheat field with a crop consultant. The consultant was confident that the wheat had Septoria Leaf Blotch disease (Septoria tritici, Mycosphaerella graminicola); he was familiar with the leaf symptoms (Figure 1) and the region has a history of problems with Septoria. He was also noticing, however, some lesions on the glumes (Figure 2), and wondered if there was another disease present. It turns out that the lesions on the glumes are also a symptom of Septoria and can be seen if wet weather occurs after heading.

Septoria is a serious problem of wheat because, as lesions coalesce, particularly lesions on the flag leaf, it can reduce the photosynthetic capacity of the plant and reduce grain filling, thereby reducing yields. Septoria is most problematic in rainy years and in early-planted fields. Early-planted fields have a longer period of exposure if the disease is present on crop residues or volunteer plants. Crop rotation can help manage against Septoria in future plantings, but planting more tolerant varieties and properly-timed fungicide applications are also good management practices. Septoria ratings are not a regular part of the UC statewide variety testing program, but ratings are available from 2011 and 2012. (On the previous links, click on Table 3.) Fungicides, like Mancozeb and Propiconazole, should be applied between tillering and heading, with the purpose of protecting the flag leaf. Septoria only infects wheat, so other small grains like barley, oats, and rye are not affected by the disease. 

Figure 2. Septoria lesions on glumes.

The field that I visited was likely an early-planted field, and the disease seemed worse on the edges and on the south side of berms where the conditions were likely a little bit warmer and the plants advanced a little bit faster. The field is completely headed out, and the grain is in the milk stage, nearing the soft dough stage. The million dollar question is, with the forecast of rain later in the week, is it worthwhile to spray a fungicide? If it does rain, the disease may spread, showing more lesions on the flag leaf. With grain at the milk to soft dough stage, the grain may be able to mature even if the disease gets worse. Making the decision on whether to apply a fungicide at this time is a hard call to make for a farm advisor or consultant because it really comes down to dollars and cents. In this case, however, product labels say not to apply the product after 10.5 Feekes, or full heading, so this particular field is beyond the stage when a fungicide should be applied.

Information on products and practices is for educational purposes only and does not constitute an endorsement or recommendation by the University of California.