Issue No. 9, Article 8/May 25, 2007
Wheat: What Were Those Spots and Stripes?
Wheat fields in Illinois have been showing an array of diseases this season, some not too common for us. A couple of fungal spots and stripes have been present that you may not be familiar with: tan spot (caused by Pyrenophora tritici-repentis) and Cephalosporium stripe (caused by Cephalosporium gramineum).
Spots. Tan spot is not typically an economic disease in wheat in Illinois, and while it can appear all season, it is seen mostly in early spring on the lower leaves of the wheat plant when weather conditions have been cool, cloudy, and humid: just the conditions we saw this spring. Several producers saw this disease when scouting for freeze damage. Other conditions favoring development of tan spot are conservation tillage and continuous wheat.
Lesions caused by the tan spot organism develop on both the upper and lower surfaces of the leaf and appear as small, yellow-to-tan brown flecks. The initial lesions expand into lens-shaped, tan lesions with dark borders surrounded by yellow. The lesion may have a dark brown spot in the center.
Typical early tan spot lesions (photo courtesy of L. Ortiz-Ribbing).
Management for tan spot in wheat is typically not recommended in Illinois, although if the disease continues to develop in the field and infects the flag leaf before beginning flowering (Feekes 10.5) and conditions favor disease development, a fungicide may be warranted.
Advanced foliar lesions of tan spot (photo courtesy of L. Ortiz-Ribbing).
Please see page 139 of the 2007 Illinois Pest Management Handbook for fungicide recommendations. (If you still need a copy of the handbook, it is available for online purchase through University of Illnois Pubs Plus. Be sure to read and follow all label rates and restrictions regarding the time of application on wheat. Cultural practices that destroy wheat stubble and crop residues reduce the survival of this pathogen and are effective for managing tan spot. It is also advisable to rotate with nonhost crops.
Stripes. The second disease uncommon to Illinois was reported by Crop Production Services in some headed wheat fields around Ferris. Symptoms of Cephalosporium stripe can occur from jointing to heading as one to four yellow stripes per leaf, often extending the full length of the leaf and sometimes continuing down the leaf sheath and stem.
Cephalosporium stripe field symptoms (photo courtesy of L. Ortiz-Ribbing).
As the leaf ages, the yellow stripes eventually turn reddish brown, and gradually the leaf withers and dies. Wheat plants with Cephalosporium stripe are typically stunted or dwarfed in appearance and produce white, poorly filled heads with shriveled kernels.
Fluctuating winter temperatures, wet soil, and continuous cropping of cereals and grasses favor development of Cephalosporium stripe. Managing this disease and reducing the inoculum for disease development in subsequent years can be accomplished by rotating to a nonhost crop (corn or legumes) for at least two years and by managing crop residue and grassy weeds. When rotation with a nonhost crop is not practical, removing or plowing under residue to a depth of below 3 inches will help decompose crop residue and manage the fungus. Tillage of this nature is advised only on soils that are not prone to erosion.--Loretta Ortiz-Ribbing and Suzanne Bissonnette