Over the last few weeks, we have received samples with at least four different types of ear rots – Diplodia, Gibberella, Fusarium, and Trichoderma. Of these, Diplodia ear rot seems to be the most prevalent. Ear rots differ from each other in terms of the damage they cause (their symptoms), the toxins they produce, and the specific conditions under which they develop.
Foliar diseases, especially Gray Leaf Spot (GLS), are beginning to show up in some corn fields. This is not at all surprising, given that the crop was planted relatively late and it has been wet and humid in some areas. GLS is favored by humid conditions, particularly if temperatures are between 70 and 90 F. Foliar diseases of corn are generally a concern when they develop early and progress up the plant before grain fill is complete. This is especially true when the hybrid is susceptible. In most years, GLS and NCLB usually develop late or remain restricted to the lower leaves.
Corn seedlings often turn yellow (due to low nitrogen uptake and/or limited chlorophyll synthesis) or purple (reduced root development and/or increased anthocyanin production) under cool, wet conditions. Some hybrids are more likely to increase anthocyanin (purple pigment) content when plants are cool. Yellowing or purpling of corn plants at this stage of development generally has little or no effect on later crop performance or yield potential.
With corn now beyond the R4 growth state in most fields, there is really nothing you can do about southern rust in terms of fungicide application. However, correct diagnosis of this disease is still very important from the standpoint of identifying the hybrids that were most severely affected. Although our growing conditions generally do not favor this disease and we may go for another several years without seeing as much southern rust as we did in 2017, we still need to identify those highly susceptible hybrids.
Both southern and common rust have been confirmed in multiple corn fields across the state, but as is usually the case in Ohio, the latter is much more wide-spread than the former, and most of the affected fields are in the southern half of the state. Southern rust is characterized by the presence of small, circular, light orangish pustules predominantly on the upper surface of the leaves, whereas common rust produces larger, more elongated, and darker (cinnamon-brown) pustules on both leaf surfaces.
Abnormal Ear Diagnosis Poster, ACE-1. Farmers frequently encounter abnormal corn ears in their fields when the crop has experienced a major stress, such as drought, temperature extremes, disease, insect injury, or misapplied chemicals. These abnormalities often affect yield and grain quality adversely. In this poster, ten abnormal corn ears with distinct symptoms and causes are highlighted.
Corn Disease Management in Ohio, Bulletin 804. Five to 15 percent of Ohio's corn crop is lost to disease each year, amounting to nearly $100 million in lost farm income. Corn diseases include seedling diseases, leaf blights, stalk rots, ear and kernel rots, and viruses. This bulletin describes the disease symptoms, provides color images, gives the environmental factors favoring the disease, the method of transmission and infection, and management options for the major diseases affecting corn in Ohio.
to be the most prevalent. Ear rots differ from each other in terms of the damage they cause (their symptoms), the toxins they produce, and the specific conditions under which they develop.
