The 2016 corn crop for most areas of Illinois is setting up to be one of the largest in history. High yielding crops cause a lot of nutrient strain on the plant as it attempts to fill ears to their maximum potential. When plants run short of available nutrients from the soil, translocation starts to take place leaving the lower portions of the plant open for late season integrity issues either from cannibalization, stalk diseases or both.
Stalk rots are common in the Midwest and are in every field to some extent. Identifying the specific type of stalk rot is easier during early stages of development, but becomes more difficult late in the season. Regardless of which stalk rot pathogen causes the primary infection, the end result is the same: yield loss due to lodging or premature plant death.
|ANTHRACNOSE STALK ROT||Black shiny lesions or streaks on outer stalk; tan internal discoloration; may also cause top dieback||High temps and extended periods of cloudy weather; prolonged humid conditions|
|CHARCOAL ROT||Black sclerotia scattered throughout vascular tissue; gray internal discoloration||High soil temp and low soil moisture during grain fill|
|DIPLODIA STALK ROT||Dark brown lesions extending either direction from the nodes; small black specks on the lower internodes of the outer stalk; tan internal discoloration||Dry conditions early and warm wet conditions following silking|
|FUSARIUM STALK ROT||Whitish pink to salmon internal discoloration; nodes on outer stalk may appear white||Dry conditions early and warm wet conditions following silking|
|GIBERELLA STALK ROT||Pink to red internal discoloration; dark streaks on lower internodes; some black specks that can be scraped away||Dry conditions early and warm wet conditions following silking|
|PYTHIUM||Decay of the first internode above soil; soft brown and water-soaked; twists and falls over; foul odor||Warm wet conditions|
As with any disease, the disease triangle needs to be completed. Severity of stalk rots depends on the amount of inoculum present, a susceptible host, and environmental conditions that favor disease establishment. Stalk rot inoculum occurs naturally in the soil and on plant residue for a large number of pathogen species. Many stalk rots enter the plant through wounded stalks or through the roots. Stalk rot pathogens move into the roots and up through the stalk if root health is compromised by excessive heat, extended dry weather, prolonged saturated conditions, root disease pathogens, or insect damage. Anything that interferes with plant health, and subsequent photosynthesis during grain fill, will cause the plant to cannibalize stalk tissue to meet needs of the developing ear. Cannibalization makes the plants more susceptible to stalk rot establishment
Stalk rots are becoming more apparent in this year’s crop. Fields at high risk include those with large kernel set at pollination followed by dry conditions after pollination, fields showing N deficiency, root lodged fields, fields with leaf disease, and fields that were saturated. Inspect fields for stalk rots by pinching stalks six inches above the soil, splitting stalks and looking for shredded, discolored, internal tissue or by scouting for prematurely dead plants. If stalk rot symptoms are found, a revamp of your harvest schedule may be necessary. Consult your seed representative or agronomist to help identify and develop a harvest strategy.