Evaluating Corn to Determine Harvest Priorities

During harvest time, the question of harvest order may not always be straightforward. While weather, equipment, and other factors always come into play, plant health is an important aspect to consider.

To get an idea of what fields to go for first, we probably all begin with planting date and comparative relative maturity (CRM), sometimes referred to as days-to-maturity. CRM gives us a sense of which corn to check for harvest maturity first, and it also tells us how many fields might be ready at the same time. This is a great starting point because it also lets us know which corn will become vulnerable to late-season diseases and extreme weather events the soonest. Fields planted early and/or with a short CRM will typically mature first, after which they will no longer be protected by many chemical and structural defenses that a plant uses to prevent disease when alive. At this stage, plants are more susceptible to breakdown by pathogens and opportunistic fungi that simply take advantage of dead tissue.

The other bit of information to recall is hybrid selection. This choice that was made almost a year prior now comes into play when traits like stalk strength, resistance to disease, husk cover, and ear orientation are considered. Standability can be affected by anything that robs the plant of its ability to maintain good stalk structure beyond its maturity, for example, nutrient deficiencies, drought, root and stalk rots, and foliar diseases that prevent photosynthesis during grain fill. When growers choose hybrids with high breeder ratings for stalk and foliar disease resistance, stalk strength, and drought tolerance, they select traits that will keep plants upright longer into harvest season.

Ear disease resistance and physiological traits should also be considered.  Ear rots are a serious threat to yield and grain quality as they may affect test weight and be associated with mycotoxins. Even if the ears are free of mold approaching maturity, ear tips that are exposed from the husk because of hybrid physiology or insect damage will be more susceptible to fungal infection as harvest wears on. Similarly, ears that naturally turn downward upon maturity will shed water more readily than those that stay upright and provide a less conducive environment for fungi to grow.

Scout to gather real-time information regarding your crop's longevity

Standability

Using a W or X pattern across the field, push the middle of stalks over about 30-45 degrees from upright. If more than 10 percent of the stalks you test do not spring back to vertical, this field is at risk of lodging in a weather event and should be prioritized for a careful harvest when possible. This becomes even more critical if the ears are big and well-filled since this will make the plant top-heavy.

To help determine the cause of stalk issues, pull up several affected plants and some healthy ones and examine the roots and stalk interiors (split with a knife). Plants infected by a root rot pathogen may show weak or very few roots, while those with a stalk rot disease may display discoloration of the inner tissue and crown. Plants that experienced drought or severe foliar disease may show a cannibalized pith inside the stalk.

Ear integrity

Moving in the pattern described above, check the ears of your plants for health. Any mold growth at the tip or interior of the ear should be noted. Prioritize fields with existing ear molds and those with exposed ear tips, insect damage, or upright ears.