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Helminthosporium turcicum Lesion Numbers Related to Numbers of Trapped Spores and Fungicide Sprays. Richard D. Berger, Associate Plant Pathologist, University of Florida, Institute of Food and Agricultural Sciences, Agricultural Research and Education Center, Belle Glade 33430; Phytopathology 63:930-933. Accepted for publication 4 February 1973. DOI: 10.1094/Phyto-63-930.

Helminthosporium turcicum lesion numbers were directly related to numbers of trap-monitored spores collected 7 days previously. Aerial sprays of maneb (manganese ethylenebisdithiocarbamate) effectively controlled northern leaf blight on sweet corn, when applied on days of peak spore occurrences. Sprays applied the day before significant spore deposition were largely ineffective because infection took place on unprotected leaf tissue emerging from the whorl. Sprays applied 24 hr after spore deposition were ineffective in control. There were few new infections after tasseling on the sprayed corn despite high spore numbers and most disease increase then came from enlarging lesions. An understanding of corn plant growth characteristics was valuable in determining the importance of whorl infection, new lesion appearance, disease progress, and control.