August 25, 2017

Management of Diplodia Stalk and Ear Rots in Corn​

 

Key Points

  • Diplodia stalk and ear rot is usually most severe when corn follows corn and when wet weather occurs after silking.
  • Diplodia ear rot can reduce the quality of the grain and stalk rot can result in lodging.
  • Though you can't do much about Diplodia stalk and ear rot this season, you can plan now for proactive management next season.

What To Watch For

 
Figure 1. Diplodia infected ear and stalk.

Diplodia ear rot

Diplodia ear rot is usually most severe in corn-on-corn rotations and when wet weather occurs within the first few weeks after silking. Corn products vary in their level of susceptibility to Diplodia ear rot; however, any product can be infected under extremely favorable conditions. You may first notice prematurely bleached or straw colored husks that stand out against the green foliage of the rest of the plant (Figure 2). When pulling the husks back, the ear will have a whitish mold forming between the kernel rows, usually starting at the base of the ear and progressing toward the tip (Figure 1). Black specks (fungal spore-producing structures) can also be found on the husks, cobs, and kernels. If the infection becomes severe, entire ears will turn gray to brown and completely rot.

Diplodia stalk rot

Diplodia stalk rot is favored by warm, wet weather after pollination. Corn plants that have experienced other stresses, such as disease or insect injury, may be more susceptible to Diplodia stalk rot. Corn-on-corn and reduced tillage systems may also increase the incidence of stalk rot. You may not notice stalk rot symptoms until several weeks after silking. Infected plants may begin to die prematurely and take on a grayish-green cast similar to frost injury. Lower stalk internodes may turn brown to straw colored and feel spongy, dry, and can be easily crushed. The internal pith tissues become disintegrated (Figure 1). You may also notice fungal spore-producing structures on the lower stalk surface (Figure 3).

Impact On Your Crop

 
Figure 2. Bleached husks from Diplodia ear rot.

Ears infected with Diplodia are lightweight and subject to breakage and losses during harvest. Diplodia is not known to produce mycotoxins, but will result in feed with lower nutritional value. Grain quality will also be reduced in plants that die prematurely and/or lodge from stalk rot, and harvesting them is more difficult.

Tips To Manage

 
Figure 3. Fungal spore-producing structures.

Begin scouting your fields for stalk rot when corn reaches the dough through denting stage. Especially monitor those fields that have been heavily affected by foliar diseases, as these fields will be more susceptible to stalk rots.

Evaluate stalk quality on 10 plants in a row at several locations throughout your fields by either pinching the lower internodes between your thumb and finger to see if the stalk collapses, or by pushing each stalk to a 45 degree angle to see if it breaks. If stalk quality has been compromised in more than 10% of stalks, then harvest that field early.1

While there isn't much you can do this season to manage Diplodia ear and stalk rots, proactive strategies can help manage these diseases in future seasons.

  • The fungus that causes Diplodia stalk and ear rot only infects corn and survives only on corn debris; therefore, tillage to bury infected corn residue will speed decomposition of the fungus and crop rotation with a crop other than corn can help reduce the inoculum load by the time corn is planted again.
  • Reduce moisture, nutrient, insect, and disease stresses during the growing season to maintain stalk integrity.
  • Plant corn products with greater levels of tolerance to Diplodia stalk and ear rots and with good standability ratings.
  • Plant at proper populations to decrease plant stress.
  • If you plant continuous corn, consider rotating corn genetics.
  • Plant products with insect protection traits to help minimize damage from stalk boring insects and protect ears from ear feeding insects that may compromise husk coverage.
  • Apply fungicides when foliar diseases are present at high levels to help minimize stalk cannibalization during grain fill.

Grain Drying

Proper drying and storage of grain are important when Diplodia ear rot is present.
  • Harvest early to prevent further spread of ear rot if weather conditions have been favorable or if stalk lodging is a concern. 
  • Allow corn to dry in the field to 23 to 25% moisture and dry grain to 13 to 14% moisture prior to storage.2 
  • Store grain at cool temperatures between 36 and 44°F after drying.
  • Limit storage to cold weather and do not store through the next summer.
  • Check grain periodically for temperature, wet spots, and insects. 
  • Clean the bins thoroughly before storing.
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Sources:

Sources: 1 Bissonnette, S. 2000. Diplodia ear and stalk rot. The Bulletin. University of Illinois. http://bulletin.ipm.illinois.edu/. 2 Lipps, P., Dorrance, A., and Mills, D. 2004. Corn disease management in Ohio. The Ohio State University Extension. Bulletin 802. http://ohioline.osu.edu/. Other sources: Diplodia stalk rot. Field crop diseases. University of Illinois. http://cropdisease.cropsci.illinois.edu/corn/Diplodiastalkrot.html. Grabow, B. Diplodia stalk and ear rot. Kansas State University Department of Plant Pathology. http://www.plantpath.kstate.edu/. Web sources verified 8/1/16. 130816014103