Cause Several fungal leaf spots and leaf blights affect corn. The more important ones in the Pacific Northwest include Northern Corn Leaf Blight (teleomorph: Setosphaeria turcica; anamorph: Exserohilum turcicum, = Helminthosporium turcicum, = Bipolaris turcica, = Drechslera turcica), Northern Corn Leaf Spot (formerly known as Helminthosporium leaf spot) (teleomorph: Cochliobolus carbonum; anamorph: Bipolaris zeicola, = Helminthosporium carbonum, = Drechslera zeicola), and Gray Leaf Spot (Cercospora sorghi var. maydis and C. zeae-maydis). Usually these diseases have not had great economic significance in the Pacific Northwest. The fungi overwinter on infected plant debris, and winds can move spores long distances. Moderate temperatures and high humidity favor the disease. Other grass species are affected.
Symptoms In each of these diseases, the symptoms are long circular to elliptical, grayish green or tan lesions. In moist weather, concentric dark rings may be observed in the lesions. Lower leaves are affected first, and the disease moves up the plant. The plant's premature death resembles frost or drought injury.
Cultural control
- Plant resistant varieties and hybrids if available. The most tolerant hybrids are late maturing.
- Manage irrigation to avoid long periods of high relative humidity in the canopy.
- Practice crop rotation.
- Burying infected plant debris can minimize disease.
Chemical control
- Cueva at 0.5 to 2 gal/100 gal water on 7- to 10-day intervals. Not a good stand-alone product. May be applied on the day of harvest. 4-hr reentry. O
- Demethylation-inhibiting (DMI) Fungicides (Group 3) are labeled for use.
- Tilt at 2 to 4 fl oz/A on 7- to 14-day intervals. Do not apply within 30 days (field corn forage, grain and stover) and 14 days (sweet corn ears and forage) of harvest. 12-hr reentry.
- Dithane F-45 Rainshield (Group M3) at 1.2 quarts/A on 4- to 7-day intervals, for leaf blight only. Preharvest interval is 7 days for sweet corn and 40 days for field corn. Do not feed treated forage to livestock. 24-hr reentry.
- Strobilurin fungicides (Group 11) are labeled for use. Do not make more than one (1) application of a Group 11 fungicide before alternating to a labeled fungicide with a different mode of action.
- Headline at 6 to 9 fl oz/A prior to disease development on 7- to 14-day intervals. Preharvest interval is 7 days. 12-hr reentry except if hand detasseling or hand harvesting, for which the reentry interval is 7 days.
- Quadris Flowable at 6 to 15.5 fl oz/A on 7- to 14-day intervals. Preharvest interval is 7 days. 4-hr reentry.
- Vertisan (Group 7) at 10 to 24 fl oz/A on 7- to 14-day intervals. Do not make more than two (2) sequential applications before alternating to a labeled fungicide with a different mode of action. Preharvest interval is 7 days for grain and stover; 0 days for forage. 12-hr reentry.
- Premixes of fungicides are available for use.
- Elatus (Group 7 + 11) at 5 to 7.3 oz/A for sweet corn for two (2) applications at least 14 days apart. Preharvest interval is 7 days. 12-hr reentry.
- Miravis Neo (Group 7 + 3 + 11) at 13.7 fl oz/A. Early application (V4-V8); late application when disease first appears or at VT or R1. May be re-applied 7- to 14-days later. Do not apply more than two (2) sequential applications. Preharvest interval is 30 days for field corn and popcorn; 14 day PHI for sweet corn. 12-hr reentry.
- Quilt (Group 11 + 3) at 7 to 14 fl oz/A or Quilt Xcel (Group 11 + 3) at 10.5 to 14 fl oz/A on 14-day intervals. Preharvest interval of Quilt is 14 days for sweet corn and 30 days for field corn. Preharvest interval of Quilt Xcel is 14 days. 12-hr reentry.
- Stratego (Group 3 + 11) at 10 fl oz/A for sweet corn or 10 to 12 fl oz for field corn and popcorn on 7- to 10-day intervals. Do not apply within 14 days of harvest for sweet corn and 30 days of harvest for field corn or forage. 12-hr reentry.