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As corn nears maturity, stalk integrity can be reduced by several factors. Stalk strength is naturally reduced by cannibalization, which occurs when nutrients are moved from the stalk to kernels during the grain fill process. This can cause disintegration of the stalk pith cells and impact the amount of lignin in the rind cell walls, which may lead to physiological stalk lodging. Additionally, stalk rots and secondary pathogens can diminish stalk quality (Figures 1 and 2). Wetter than normal conditions can lead to an increase in stalk rot and diseases. High winds can cause corn plants to lodge in fields where a crop has not yet been harvested. Heavy rains, wind, and hail can also knock down healthy corn plants. Stalk cannibalization can result in significant lodging when combined with stalk rot infection and high winds (Figure 3).
Figure 1. Healthy outer corn stalk on left, versus anthracnose infected stalk on right.
Figure 2. Outer corn stalk symptomology of diplodia.
Fields with considerable lodging can be a challenge to harvest efficiently. Harvest losses in down corn may be 10 to 15% even when care is taken during harvesting. Most harvest losses occur at the gathering unit with most of the total machine loss caused by corn never getting into the combine. Downed corn is also at greater risk of poor drydown and other kernel problems. Lodged corn will be more likely to have molds or kernel sprouting if ears are in contact with the ground. The combination of variable grain moisture, possible kernel molds and kernel sprouting can increase the challenges of successfully storing the grain.
Figure 3. Fall stalk lodging due to cannibalization and stalk rots.
Start by inspecting fields to identify where corn is down and where it is standing. Check fields for stalk strength with the grab test. Grab the corn stalks at shoulder height, pull or push about 18 inches off center and release. If the corn stalks remain upright, stalk strength is good. If not, stalk strength is weaker. Also, determine the grain moisture in the fields. Knowing the percent of corn that is down and the grain moisture in each field can help determine harvest order. Take into consideration that upright corn, depending on stalk strength, is also at risk of lodging. Fields with down corn may take three or four times longer to harvest than fields of upright corn. It can be challenging to decide when to harvest the downed corn and the upright corn.
Lodged corn can delay harvest. Harvesting as many of the downed ears as possible requires slow going and patience. The issue becomes how to operate the combine to gather up the most ears.
Fields with considerable lodging can reduce harvest efficiency. The following are some harvesting tips to protect yield potential: