Identification and Management of Stalk and Ear Rots

Stalk and ear rots can lead to reduced grain quality, stalk lodging, and premature plant death, all of which can impact yield potential. In addition, some ear-infecting fungi produce mycotoxins that are harmful if fed to livestock. In-season management options are often limited but proactive management practices can help reduce stalk rot and ear rot issues in future crops.

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In general, stalk and ear 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. Ear rots generally occur when the husk, silks, or kernels are damaged such as from insect or bird feeding, wind or hail, and frost. Ear rots can directly damage kernels and some ear rot fungi produce mycotoxins that are harmful if fed to livestock.

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Identification of Stalk and Ear Rots

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Figure 1

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

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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.

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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.

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Figure 2

Figure 2. (A) Fusarium ear rot, (B) Fusarium ear rot with starburst patterning, (C) Aspergillus ear rot, (D) Gibberella ear rot progressing from the tip to the base of the ear, (E) Diplodia ear rot begins at the base and progresses toward the tip of the ear.

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Fusarium ear rot. A white to pink mold can be seen scattered across the ear and/or kernels, which may have a starburst pattern (Figure 2A, B). Fusarium ear rot produces a mycotoxin called fumonisin that is harmful to livestock.

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Aspergillus ear rot. A powdery gray-green or light green mold initially develops at the tip of the ear and may progress down the ear (Figure 2C). This fungus produces a very dangerous mycotoxin called aflatoxin which is harmful to humans and animals if consumed and has very stringent action levels.

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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.

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Gibberella ear rot. A pink to reddish mold begins at the tip of the ear and progresses toward the base (Figure 2D). Two mycotoxins are produced by this fungus, vomitoxin and zearalenone, which are harmful when fed to animals.

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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).

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Diplodia ear rot. The base of the husk will have a premature tan or bleached appearance. Infected ears develop a white to gray mold that grows between the kernels beginning at the base of the ear and progressing toward the tip (Figure 2E). Pycnidia, similar to those seen with the stalk rot, can also be found on the husks, cobs, and kernels.

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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.

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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).

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Scouting for Stalk and Ear Rots

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Push or Pinch Test. Scout fields periodically after pollination to check for stalk and ear 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 check ears for signs of infection by peeling back the husks and observing the ears. Also, 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.

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If more than10% of the stalks in a field are rotted or prone to lodging and/or significant levels of ear rots exists, 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 and diseased grain.

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Management Options

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

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  • Choose corn products with greater levels of resistance to stalk and ear rots and with good standability ratings. Refer to agSeedSelect.com for seed product ratings.
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  • 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 (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.
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Minimizing stress during the growing season can help maintain stalk quality and minimize the effect of stalk and ear rots.

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  • Plant products with insect protection traits to minimize damage from stalk boring insects and to protect ears from ear feeding insects that may compromise husk coverage.
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  • Apply fungicides when foliar diseases are present at high levels to help maintain healthy photosynthetic leaf area and minimize stalk cannibalization during grain fill.
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  • Plant products with different relative maturities and/or different growing degree day requirements to flowering so that the entire crop does not flower during peak environmental conditions for ear rot infection.
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  • Use recommended planting populations to decrease plant stress as higher plant populations can lead to thinner stalks.
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  • Maintain balanced soil fertility, especially nitrogen and potassium, to prevent nutrient deficiencies which can lead to stalk cannibalization.
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Grain Drying

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Proper drying and storage of grain are important when ear rot diseases are present to prevent further mold growth that can reduce grain quality and lead to deductions.

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  • Harvest early if necessary or allow corn to dry in the field to 23 to 25% moisture and dry grain to 13 to 14% moisture as soon as possible after harvest.
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  • Store grain at cool temperatures between 36 and 44 °F with adequate aeration after drying and do not store through the next summer.
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  • Store diseased grain separate from healthy grain.
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  • Check grain periodically for temperature, wet spots, and insects.