Any disease requires three conditions before a widespread outbreak can occur. These 

 conditions are a virulent pathogen, a susceptible host, and the proper environment- - 

 or weather conditions. 



The same is true of southern corn leaf blight. 



The pathogen- -race T-- overwintered in Illinois. The two spore traps in Illinois 

 have picked up relatively few spores, indicating that 1971 infections to date have 

 primarily come from 1970 crop debris. 



Because of this it seems likely the disease will be most apparent in fields and 

 areas badly infected in 1970. 



The susceptible host is also present, but to a lesser degree than last year. In 

 1970, about 85 percent of the Illinois corn crop contained the susceptible T 

 cytoplasm- -a much larger percentage than in 1971. 



That's two of the three conditions accounted for. But one condition still remains 

 unknown: weather. Nobody knows what the weather will be. For example, in Florida 

 this year, dry cool weather at planting time seemed the reason southern corn leaf 

 blight failed to develop as it did in 1970. Widespread planting of normal (resis- 

 tant) seed also retarded development of blight in Florida this year. 



But if Illinois farmers find themselves faced with optimum conditions --humid 

 weather, too- frequent rains, heavy dews, and optimum temperatures of 60 to 80 

 degrees --even local sources of infections could develop into a serious problem. 



On the brighter side, however, unless conditions favor blight development, the 

 presence of a virulent pathogen and a susceptible host will have little effect on 

 the 1971 corn crop. 



At this point, everything hinges on weather conditions. 



CONSIDER HERBICIDES BEFORE REPLANTING 



If you are thinking about replanting corn fields because of blight or any other 

 reason, be sure to consider the herbicides you have already used. 



Two important considerations are: (1) will the herbicide remaining in the soil 

 injure soybeans, and (2) is there a legal tolerance set for any herbicide that 

 may be in the soybeans at harvest? 



If you used atrazine alone or in combination with another herbicide for corn, do 

 not replant to soybeans. The risk of atrazine injury to soybeans is high, and 

 there is no tolerance set for atrazine in soybeans. 



Sutan--if used for corn weed control- -could also cause injury if soybeans are 

 planted too soon. The manufacturer says, "If it is too late to plant to corn 

 again, soybeans may be planted providing no atrazine was used with the Sutan. 

 Do not plant soybeans sooner than 21 days after application of Sutan." 



Lasso is approved for both corn and soybeans, so there is no problem if you re- 

 plant soybeans in fields where Lasso was used earlier for corn. 



