NORTHERN PLAINS: There are several conditions that can lead a corn field to fall victim to stalk rot, some of which are easier to manage than others.
To compensate for reduced nutrient uptake, plants tend to cannibalize their roots and stalks for needed nutrients to fill the ear later in the season. This gives soil-borne stalk rots ideal conditions to infect the roots and, ultimately, the stalks. Weather events such as hail and soil conditions affect this, while leaf diseases such as gray leaf spot, leaf blights and corn rust can all exasperate it. Areas with the most stress will see the biggest problems. European corn borer, along with other tissue-damaging insects, also can add to the problem. One of the largest contributors, meanwhile, is late-season nitrogen deficiencies (prevalent throughout South Dakota this fall).
Factors affecting stalk rot development
Any circumstance or group of circumstances that weaken the plant (root, stalk or leaf) and reduce photosynthesis within the plant can lead to stalk rot infection. Here are some of the common contributors:
- Insect pressure – European or Southwestern corn borer, corn rootworm, etc.
- Leaf diseases – especially grey leaf spot, but also many others
- Hail damage
- Saturated soils
- Herbicide damage
- Low soil potassium levels and high nitrogen levels
- Nutrient deficiencies
How to spot it
Scouting for stalk rots should be done at or before harvest. There are two common methods: the pinch test (the hard way) and the push test (the easy way).
The pinch test is done by squeezing the lower internodes of the corn stalk and checking for pith deterioration. If the stalk is easily compressed between the thumb and forefinger, stalk rot may be present. The push test consists of pushing the stalk at ear height five to ten inches from vertical. If the stalk breaks between the ear and the lowest node, stalk rot is likely present. You may also want to split some stalks to look at the stage of pith disintegration, discoloration and other symptoms that aid in the identification of the disease present.
Make sure you check several areas in the field and enough plants to be confident in your findings. Five locations with 20 plants per location should be sufficient. Observing 25 percent or better of the plants with stalk rot is an indication that early harvest is warranted.
The first symptom you may see is discoloration of the plants, not unlike frost damage. Plants die prematurely and early development of these diseases may lead to poor grain fill and chaffy ears. The lower stalk may turn tan to dark brown, and the pith disintegrates. Stalks may break, lodge or drop ears, leading to harvest loss. You may see several symptoms in one plant, which is relatively common.
It is more important to identify stalk rot, not the specific strain, as the disease management for all strains is the same. Visual symptoms can be confusing, inconsistent and nonexistent, so send a sample to the South Dakota State University Plant Clinic to have a specific pathogen identified.
What can I do?
- Scout your fields
- Prioritize fields for harvest based on disease prevalence
- Harvest early – don’t wait for diseased fields to field dry
- Test soil, then fertilize to optimum levels
- Till, which can reduce disease inoculum and remove compaction
- Select hybrids with robust roots, sturdy stalks and a foliar disease package
- Control insects, especially European and Southwestern corn borer
- Control weeds EARLY
- Plant at suggested populations for hybrid and soil type
- Rotate your crops
- Balance soil fertility with regard to potassium and nitrogen
- Consider use of fungicides
Reported from Chamberlain, S.D.