-7- 



Yield losses are greatest when severe infection reaches the flag leaf and stem (culm) . 

 Black spore pustules produced during the overwintering stages are now present on sus- 

 ceptible wheat leaves, but they cause little damage. 



Rust spreads most rapidly during periods of heavy dews, light rains, and high humidity 

 and when the temperature is 70 degrees F. or above. The disease is spread by wind- 

 blown summer spores (urediospores) . 



Stem rust, caused by Puaainia graminis tritioi, can now be found in southern Illinois, 

 south of Brownstown. The infection pustules produced on stem-rust -infected plants 

 have ragged edges where the epidermal layer of cells has torn open to expose and re- 

 lease the urediospores. The varieties Arthur and Benhur are resistant to known races 

 of stem rust fungi in Illinois. The Bluebay variety is susceptible. See RPD 108, 

 "Stem Rust of Small Grains and Grasses," for information on disease cycle and control. 



SCAB OF CEREALS 



Scab or head blight is just beginning to appear on wheat heads. Gibberella zeae, the 

 scab fungus, causes the kernels to blast or become shriveled and distorted. Severe 

 infection occurs during flowering and shortly after, when the weather is warm and moist. 

 If the weather is dry following emergence of the head, small grains will be nearly scab- 

 free. 



Scab -infected heads or kernels will be bleached or discolored when compared with healthy 

 spikelets that remain green and mature uniformly. During warm, wet weather, masses of 

 light-pink to salmon-colored mold may form on infected glumes or lemmas of the spike- 

 lets, especially near the base of the kernels. In addition, the tiny black perithecia 

 of Gibberella zeae may often be found scattered on the head. 



Infected kernels may be shrunken and wrinkled, and have light test weight, with a rough 

 and flaky appearance. See RPD 103, "Scab of Cereals," for more details. 



SEPTORIA LEAF BLOTCH AND GLUME BLOTCH OF WHEAT 



Septoria tritiai infections can now be observed on wheat heads, especially in fields 

 that have heavy leaf infections. If most of the leaves are killed before the grain 

 reaches the soft -dough stage, the grain will probably be lightweight and shriveled. 



Septoria nodorwn causes the "glume blotch" phase of the disease. Unlike Septoria leaf 

 blotch , the glume blotch disease is favored by warm , moist weather - ! Glume blotch loss- 

 es are greatest when excessive rainfall occurs between flowering and grain harvest. 



Small, irregular grayish or brown blotches appear on the chaff, usually near the top 

 one-third of a glume. As the blotches age, their centers turn greyish-white and are 

 sprinkled with tiny, black pycnidia (fruiting bodies of the Septoria fungus) . The 

 pycnidia are similar in size and shape to the perithecia of Giberella and can confuse 

 the non- specialist. 



All Illinois wheat varieties are susceptible and there are no control measures that can 

 be applied at this time. See RPD 105 (Revised), "Septoria Leaf Blotch and Glume Blotch 

 of Wheat," for control measures. 



SEEDLING BLIGHTS AND ROOT ROTS OF SOYBEANS 



Poor emergence, damping-off, and seedling blights or rots continue to occur. Dry 

 weather will prevent some of these problems, but puts stress on others. For example, 

 plants that have wilted are unable to recover because of poor or rotted root systems. 



