Corn Stalk Rots

Stalk rots can lead to reduced grain quality, stalk lodging, and premature plant death, all of which can impact yield potential. In-season management options are often limited but proactive management practices can help reduce stalk rot issues in future crops

In general, stalk rots occur late in the season. Stalk rots are favored by late-season stresses such as an excess or lack of moisture, a nutrient deficiency, excessively cloudy weather, and invasive injury to the leaves, stalks, or roots by insect feeding, foliar diseases, wind, or hail. Compromised stalks may lodge and/or produce ears with a reduced kernel size and weight due to a limited ability to transport sugars to the developing grain.

 

Figure 1. (A) Anthracnose stalk rot, (B) Fusarium stalk rot, (C) Gibberella stalk rot, (D) Diplodia stalk rot, and (E) Charcoal rot.

Identification of Stalk Rots

Anthracnose stalk rot. The surface of the lower stalk will have a shiny appearance with black blotches or streaks, especially on lower internodes (Figure 1A). Internal stalk tissue may become dark and soft. Lodging typically occurs higher on the stalk than with other stalk rots.

Fusarium stalk rot. Infection commonly leads to premature dry down and rotting of roots, crown, and lower internodes. A white fungal growth may sometimes be seen on the outside of the stalk and a whitish-pink to salmon discoloration may be visible inside the stalk. Disintegration of internal stalk tissues begins at the nodes (Figure 1B). Visible fungal reproductive structures are lacking.

Gibberella stalk rot. Affected plants may wilt and leaves turn a dull gray-green color. The lower stalk becomes straw colored and pith tissue disintegrates, leaving only vascular strands intact. The inside of a rotted stalk will have a pink to red discoloration (Figure 1C). Small, dark fungal bodies called perithecia form on the surface of the lower stalk that can be easily scraped off.

Diplodia stalk rot. Lower internodes become straw-brown, spongy, and dry. Pith tissue disintegrates leaving only vascular strands intact. A white fungal growth may appear on the stalk surface. Tiny, dark fungal structures called pycnidia embedded in the outer stalk tissue are difficult to scrape off (Figure 1D).

Charcoal rot. Symptoms begin with the upper leaves drying out and stems may eventually become shredded. Tiny, black fungal structures called sclerotia are produced inside the stalk, which give the appearance of charcoal dust (Figure 1E).

Physiological stalk lodging. When under stress, corn plants will remobilize sugars from the stalks to fill the kernels, resulting in reduced carbohydrate content in the stalks, which can weaken them. This process is referred to as stalk cannibalization and is especially common when foliar diseases have substantially reduced photosynthetic leaf area, leaving the plant with a limited ability to produce sugars. The weakened stalks are more susceptible to colonization by fungi and to toppling over due to their own weight (physiological stalk lodging).

Scouting for Stalk Rots

Push or Pinch Test. Scout fields periodically after pollination to check for stalk rots. Different corn products and fields with different management practices (irrigated vs. dryland, fungicide treated vs. untreated, etc.) should be evaluated separately. Walk a zigzag pattern through the field and test stalk firmness by squeezing or pinching each stalk at one of the lowest nodes above the brace roots. Healthy stalks are firm and cannot be compressed. If a stalk feels soft, it is likely prone to lodging. A second method for determining potential stalk lodging is to push each stalk about 5 to 8 inches from upright (approximately a 45° angle) and note whether the plant springs back, remains tilted, or breaks. Check at least 10 plants in each of several locations in the field.

If more than 10% of the stalks in a field are rotted or prone to lodging, consider scheduling the field for early harvest. In severe instances, it may be more economical to harvest early and dry the grain post-harvest. Combine adjustments can help improve the efficiency of harvesting lodged corn.​

Management Options

In-season options for managing stalk rots are limited and fungicides are not labeled for their control, but proactive practices can help manage stalk rots in future crops.

Choose corn products with greater levels of resistance to stalk rots and with good standability ratings. Refer to agSeedSelect.com for seed product ratings.

Reduce the levels of inoculum in the field with crop rotation or tillage that buries infected residue. Note that when the disease is widespread or present in neighboring fields, inoculum may still be carried in from these areas. Also, some of these diseases affect other crops (i.e. Fusarium can also affect sorghum, wheat, barley, oat, and rye). It is important to know the causal agent of the disease and understand its host range when making crop rotation and tillage decisions.

Minimizing stress during the growing season can help maintain stalk quality and minimize the effect of stalk rots.

Plant products with insect protection traits to minimize damage from stalk boring insects.

When foliar diseases are present at high levels, apply fungicides to help maintain healthy photosynthetic leaf area and minimize stalk cannibalization during grain fill.

Use recommended planting populations to decrease plant stress as higher plant populations can lead to thinner stalks.

Maintain balanced soil fertility, especially nitrogen and potassium, to prevent nutrient deficiencies that can lead to stalk cannibalization.​​

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