Crazy top has been showing up in a number of Illinois cornfields in the past few weeks. This disease appears to be fairly common in some areas due to the wet weather and flooding that occurred this spring. Crazy top is different from most corn diseases in the effect it has on the plants and the type and mode of infection of the pathogen.|
The initial symptoms of crazy top are excessive tillering, rolling, and twisting of upper leaves. The tassel proliferates in part or completely until it may resemble a tight bunch of leafy structures (this is the origin of the name "crazy top"). In addition, ear shoots may become elongated, and stunting and chlorotic striping of leaves may occur.
Crazy top symptoms on corn.
The type of pathogen and the way it impacts the plant are unlike most corn pathogens. Plants are infected either soon after planting or up to the four- to five-leaf stage. Crazy top is caused by the downy mildew called Scleroph-thora macrospora. This pathogen is closely related to the "water molds" such as Pythium and Phytophthora. All of these pathogens require saturated soil or flooded conditions for 1 to 2 days to initiate infection with their swimming zoospores. This is the reason why crazy top is typically seen in low areas of fields. After infection, the pathogen grows inside the tissues and seems to focus its growth on the meristematic tissue, where it disrupts growing points in the infected plants.
Fortunately, crazy top is usually more of a curiosity than a severe disease and tends to cause significant losses only in scattered patchy areas. This disease is best managed by improving field drainage or by avoiding low, wet areas in fields. Rotation may be helpful if care is taken to keep rotational fields free of grassy weeds, because the crazy top pathogen can infect a wide range of different grass species.--Dean Malvick