-6- 



Here are some points to keep in mind before spraying to protect against southern 

 corn leaf blight: 



1. Maturity of corn when the blight hits . Corn that has reached the early dough 

 stage before the blight hits is likely to produce satisfactorily if fungicides 

 are not applied. Corn that is in the early tassel stage when 10 or more lesions 

 appear on the upper leaves will benefit most from fungicide sprays. 



Fungicides will only protect corn plants against new infections. The chemicals 

 will not kill fungus growth already in the plants. 



2. Weather pattern . Warm (60 to 80° F.) and humid weather with frequent showers 

 favors the rapid development and spread of race T of the southern corn leaf blight 

 fungus. Warmer temperatures enhance the development and spread of race 0. If con- 

 ditions are favorable and lesions increase rapidly in both size and number, spraying 

 may start earlier. Read and listen to reports from county Extension advisers and 

 plant pathologists to keep up-to-date on blight in your area. Fields should be 

 checked at least once a week. 



3. Type of cytoplasm planted . As a general rule, do not spray normal -cytoplasm 

 corn. The only exception would be if the hybrid is susceptible to northern corn 

 leaf blight and this disease should build up. Closely examine susceptible, T- 

 cytoplasm fields. Give them priority if southern corn leaf blight builds up and 

 spraying seems to be necessary. Fields planted with less-susceptible T hybrids 

 and blended seed would come next in the order of priority. 



4. Availability of spray- application equipment and fungicides . Check with custom 

 applicators using ground or aerial equipment, chemical salesmen, and county Exten- 

 sion advisers in your area on the availability and cost of the materials and equip- 

 ment that would be needed for spraying. 



The U. of I. plant pathologists say that Dithane M-45 and Manzate 200- -two fungi- 

 cides suggested for blight protection- -cost about 90 cents a pound. A pound and 

 a half of material is needed for each acre to be sprayed. After adding about 5 

 cents an acre for the appropriate spreader- sticker applied with the fungicide, 

 the cost of materials for one treatment comes to about $1.40 per acre. 



The specialists say that spray should be applied every 7 to 10 days. Three or 

 four sprays may be needed between the early tassel and early dough stages under 

 Illinois growing conditions. 



The total cost for three sprays --applied at the proper intervals, and including 

 the cost of application- -should be from $10 to $15 per acre. It may be possible 

 to stretch the spray interval during periods of hot, dry weather. 



Remember that corn plants sprayed with zineb cannot be used for silage, and that 

 the grain from these plants cannot be fed. Maneb and Polyram--two other blight 

 fungicides --are cleared for use on sweet corn only. Cit-cop, a liquid copper 

 fungicide, provided good control in Iowa last year. 



SPECIAL MEETING ANNOUNCEMENTS 



Corn Rootworm Insecticide Demonstration Plots 



We will examine the roots and count the number of worms per plant, for different 

 insecticides applied at planting time. This will give you a chance to see the 

 results of the various insecticide applications side by side in the same field. 



