Is A Fungicide Needed For Developing Corn Diseases?

Figure 3: A. Eyespot on corn leaf. B. Corn leaf held against the light to reveal eyespot halo around the lesions.

Eyespot

Eyespot is another common corn disease that sometimes can reach yield-reducing levels on susceptible hybrids. Initial symptoms start as small translucent circular lesions with yellow halo surrounding the lesions (Figure 3A). Later, lesions expand and have tan centers surrounded by brown ring with a narrow yellow halo. The halo is clearer when the leaf is held against the light (Figure 3B). The lesions can coalesce to form larger lesions especially on maturing corn leaves. This disease is caused by the fungal pathogen, Kabatiella zeae, which survives on corn residue and is splashed onto leaves by rainfall.

Fungicide Strategy

The question often asked is, “Is a fungicide application needed for the diseases developing in corn at this time?”

The disease pressure currently being observed in corn fields is low to necessitate a fungicide. However, this could change based on the susceptibility of the hybrid planted, the weather conditions (frequent rains), and agronomic practices such as corn on corn. Diseases such as gray leaf spot and northern corn leaf blight that develop later in the season can also show up. Research shows chances of return on fungicide investment are higher when diseases are present (>5% severity on ear leaf and leaves above). Research also shows that VT-R2 (tasseling/blister) is the best fungicide timing and gives better returns on investment. Growers are encouraged to scout their fields and also consider the factors mentioned above to decide if a fungicide will be needed. If a fungicide is decided upon, a number of fungicides effective against corn diseases are available in the publication, “Fungicide Efficacy for Control of Corn Diseases.” The fungicide efficacy table is produced by the Corn Pathology Working Group, in the Central region, of which SDSU has contributed data.