Corn Leaf Diseases Looking for Attention
Albert Tenuta and Greg Stewart, OMAFRA

Agriculture and Agri-Food Canada in Ottawa (Lana Reid and Xiaoyang Zhu) in conjunction with OMAFRA in Ridgetown (Albert Tenuta and Cheryl Van Herk) have recently completed an annual seed corn and field corn survey of the province. Although the samples continue to be processed, field observations show Northern Leaf Blight (NLB) is the most prevalent disease in southern Ontario (over 70% of fields). The most common leaf diseases in southern Ontario were Northern Leaf Blight, gray leaf spot, anthracnose leaf blight, common rust and Stewart’s Wilt. Of particular interest to Eastern Ontario field corn producers was finding gray leaf spot in the Renfrew and Ottawa- Carleton areas. AAFC (Ottawa) is testing corn samples from Kingston to Ottawa that displayed typical Stewart’s Wilt symptoms. Correct identification is important since many commercially available hybrids are resistant or tolerant to many of these diseases but at varying degrees. Therefore select hybrids based on which diseases are present in your field or developing in your area.

Northern Leaf Blight
Northern Leaf Blight has long (2–15 cm), elliptical, grayish-green or tan streaks which often begins on the lower leaves. As the disease develops, individual lesions may join, forming large blighted areas. In some cases the entire leaves may become blighted or “burned.” Losses due to Northern Leaf Blight are most severe when the leaves above the ear are infected at or slightly after pollination. Northern Leaf Blight susceptibility has increased in many commercial corn hybrids over the past few years which has lead to the disease increasing in the province.
F1-01 Gray Leaf Spot Symptoms
Gray Leaf Spot has very unique light tan coloured rectangular lesions (2–7 cm long) which often begin on the lower leaves. The lesions are narrow and run parallel to the leaf veins giving the rectangular shape. As the lesions mature, they become gray and join - killing or blighting entire leaves. Gray Leaf Spot, although first found in Ontario in 2001, continues to increase in the province.
Stewart’s Bacterial Wilt
Stewart’s Wilt symptoms can be confused with Northern Leaf Blight. Leaf lesions are pale green to yellow streaks with irregular or wavy margins that run parallel to the veins (may run the full length of the leaf). Infected leaves eventually become dry and brown. Often corn flea beetle–feeding tracks are visible within the lesions. Premature leaf death can result in reduced yield and an increase in stalk rots since weakened plants are more susceptible to stalk rots or storms.

The disease survey was supported in part by the Seed Corn Growers of Ontario, the Canada-Ontario Research and Development (CORD IV) Program, administered by the Agriculture Adaptation Council (AAC). CORD IV funding was provided by Agriculture and Agri-Food Canada and the Ontario Ministry of Agriculture, Food and Rural Affairs under the Canada-Ontario Agricultural Safety Net Management Agreement.

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