Harvest is approaching too quickly this fall. Between the dry summer and the spurts of hot weather in August and early September, crop standability is degrading quickly. This blog will go over some potential reasons for standability issues and ways to assess and prioritize fields for harvest.
The crop just ran out of gas
As of last week, the Iowa Drought Monitor placed more than 50% of the state in D2 (severe) or D3 (extreme) drought. While drought effects late in the season are difficult to evaluate as the crop is naturally maturing, Bob Nielsen updated a Purdue University article in 2023 on some of the effects of drought on corn. Late in the season, drought effects are likely to show as faster senescence (death) of leaves and other factors, like premature ear drop. When the crop is rushed to maturity and cannot use soil and photosynthetic resources to adequately finish filling ears, the plant will use all it’s remaining resources– like sugars in the stalk – to finish grain fill. Widespread standability issues in corn this year are likely a sign that the crop simply ran out of resources given the hot, dry conditions.
Crown and stalk rots
Scattered, individual plants in a field turning brown, appearing to have reached physiological maturity likely have crown and/or stalk rot; we often refer to these as “ghost” plants when surrounded by healthier plants (Figure 1). Using a knife to split the plants from the ear down to the crown will provide a diagnosis. Plants with crown rot will, as the name implies, have a discolored, rotted crown (Figure 2). Plants with stalk rot will have shredded, and/or discolored pith in the internodes, and discolored nodes (Figure 3). Pink to red discoloration may indicate Gibberella or Fusarium species as the cause. Dark discoloration could be anthracnose, while peppering (tiny black spherical sclerotia scattered throughout the pith) could be charcoal rot. Although not much can be done to manage the disease now, taking good field notes is important to plan for subsequent years.
Crown and stalk rots compromise standability as infected plants are more prone to lodging. Two simple tests for lodging potential are the ‘push’ and ‘pinch’ tests that you can read more about here. Fields in which more than 10 percent of the plants have compromised stalks should be scheduled for an early harvest.
As a side note, I have also noticed a high prevalence of anthracnose top dieback: random, scattered plants that are dying from the top. Plants with top dieback usually develop stalk rot. If you notice fields with top dieback symptoms, it’s a good idea to scout these for stalk rot too. Note that some hybrids mature from the top down. If this is the case, all the plants in the field will have top dieback, rather than random, scattered plants.
Alison Robertson Professor of Plant Pathology and Microbiology
Dr. Alison Robertson is a professor of plant pathology and microbiology. She provides extension education on the diagnosis and management of corn and soybean diseases. Her research interests include Pythium seedling disease of corn and soybean and Goss's wilt. Dr. Robertson received her bach...
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