PLANT DISEASES 



STEWART'S DISEASE OR BACTERIAL WILT IN SWEET CORN 



The sum of the mean temperatures for December, 1970; January, 1971; and February, 

 1971, was 108.7 in the Carbondale area (85.8 at Urbana) . This temperature index 

 means that early season wilt may be destructive; also, that late-season leaf blight 

 may be severe on susceptible sweet corn and seedling field corn. (See Report on 

 Plant Diseases No. 907, Stewart's Disease or Bacterial Wilt of Sweet Corn, available 

 from the UI Department of Plant Pathology, 218 Mumford Hall, Urbana, Illinois 61801. 



The bacterium that causes this disease [Xanthomonas stewartii) survives the winter 

 in the bodies of corn flea beetles. Use an insecticide, as recommended by ento- 

 mologists, to control the spread of the beetle. Dry weather favors feeding and re- 

 production. Beetles feed on and scratch the leaf surface, permitting bacteria to 

 enter through the wounds. 



Possible bacterial wilt infection would be indicated by premature tasseling; stunt- 

 ing; narrow yellow-green streaks that turn tan; wilting during the daytime; wet, 

 chocolate-brown cavities in the lower stalk region; or yellow oozing from the cut 

 ends of the vascular tissue. 



Dent corn containing resistance to northern corn leaf blight is usually resistant 

 to Stewart's disease after the four- or five- leaf stage. (See Report on Plant 

 Diseases 201- -Stewart's Leaf Blight of Corn, available from the same source.) All 

 sweet corn varieties are susceptible in the first leaf stage. Corn that was planted 

 early may attract a large number of beetles, and susceptible seedlings may wilt rap- 

 idly as the bacteria becomes systemic in the seedling and blocks water -conducting 

 vessels. 



UPDATE ON THE SOUTHERN CORN LEAF BLIGHT 



To date, the southern corn leaf blight has been found only in Dade and Palm Beach 

 Counties in southern Florida. Cold weather and lack of rainfall have prevented a 

 build-up of the disease. In northern Florida, only normal (N) cytoplasm is planted. 

 All sweet corn is sprayed with fungicides. 



The weekly Dixie Early Warning Service report, received May 10, shows no blight in 

 South Carolina, North Carolina, Texas, or Alabama. In Mississippi and Kentucky, 

 there were only traces in volunteer fields and on indicator plantings. 



Helminthosporium maydis , race T, appears to have overwintered in Illinois and sur- 

 rounding states in the Corn Belt primarily on corn debris left above ground after 

 last year's harvest. Where erosion control is not a problem, making a clean plow- 

 down is a reasonable precaution. 



No H. maydis spores (conidia) have been caught in spore traps at Dixon Springs or 

 Urbana-Champaign during the past two weeks (as of May 12) . 



AERIAL REMOTE -SENSING FOR SOUTHERN CORN LEAF BLIGHT IN ILLINOIS 



Several commercial companies plan to offer farmers infrared and color photographs 

 of their fields (at a considerable cost) , in an attempt to detect the presence of 

 southern corn leaf blight (SCLB) . However, in terms of disease control, the science 

 of aerial remote -sensing is still in the observation phase, not the applied phase. 

 Ground observers are still needed to correlate the aerial photographs. Only corn 



