-5- 



£or this weed. A delayed- tillage practice involving late planting has provided 

 the best control. But such a practice fits soybeans better than it does corn. 

 AAtrex (atrazine) , applied either preemergence or posteraergence, has given some 

 temporary control. 



We have also received several samples of Jerusalem artichoke. This is a peren- 

 nial sunflower from the northwestern part of the state. This weed is fairly 

 susceptible to 2,4-D or Banvel. 



PLANT DISEASES 



PROGRESS REPORT ON SOUTHERN CORN LEAF BLIGHT 



Southern corn leaf blight (SCLB) was identified this past week on volunteer corn 

 growing in Champaign, Coles, and Marion Counties. All infections are probably 

 race T, but this is being checked by inoculating greenhouse plants. The recent 

 rains may have spread Eetminthosporium maydis spores from clumps of volunteer 

 corn to nearby seedling corn. Small, round- to-oval leaf lesions, with reddish- 

 purple or reddish-brown borders, will appear about mid-week if infection has 

 occurred . 



These infections are not expected to spread to any great extent. Certainly, no 

 epidemic can or will occur until tassel time, or later. At that time, night tem- 

 peratures are in the 70' s, dews are heavy, and the canopy of corn leaves slows 

 down air movement. All of these conditions favor rapid infection, multiplication 

 of the fungus, and the spread of the disease. Infected volunteer corn- -if you 

 search for it- -can probably be found now in fifty or more Illinois counties. 



We do not expect SCLB to be as serious this year as in 1970 because a much higher 

 percentage of the fields are planted with resistant N corn, highly tolerant blends, 

 and T-cytoplasm corn that yielded well in 1970 where the blight was severe. In 

 addition, relatively few H. maydis spores will be blown up from the Gulf States, 

 because most of their production is in N or ¥2 corn. We continue to pick up a 

 few of the H. maydis spores each week at both Dixon Springs and Urbana. 



The states now reporting SCLB in fields or in volunteer corn include Florida, 

 Mississippi, and Texas. The infected areas are small, and the blight is not 

 spreading anywhere in the South as rapidly as it did in 1970. Because of the 

 recent widespread rains, all states where SCLB was severe in 1970 will probably 

 report infections within the next week or two. 



BACTERIAL BLIGHT OF OATS 



The Plant Disease Clinic has recently received several oat specimens with bacter- 

 ial blights. The symptoms appear as either gray-brown centered lesions with a 

 broad, light-green area fading to a straw-colored halo (Halo Blight) or water- 

 soaked streaks and blotches that turn brown and extend for the length of the 

 leaf without a halo (Bacterial Stripe Blight) . The infected leaves die-back from 

 the tips, giving the infected areas and even complete fields a brownish cast. No 

 loss in yield or grain quality is expected. The affected oat fields should appear 

 normal in another week or so. 



Both of these bacterial blights are favored by cool, rainy weather and are checked 

 by warm, dry periods. The causal bacteria overwinter in infected seed, plant ref- 

 use, or soil, and are transmitted by rain and wind and insects. Because of recent 

 legal action, seed treatments containing mercury cannot be recommended. Consequently, 



