Stalk rots in corn

The distribution and prevalence of stalk rot diseases vary from year to year. However, the diseases are present in most years even though it may be at low levels. The majority of stalk rot damage in Ontario is caused by three fungi, Anthracnose, Gibberella and Fusarium. However, Diplodia and Pythium have also been observed.

Although these fungi cause different symptoms, their ultimate effect on the corn plant is the same. They reduce grain fill, stalk integrity, and accelerate senescence. The severity of this damage increases when the crop is under stress.

Scouting

The Push Test:

Randomly select 20 plants from 5 different areas of the field
Push the top portion of the plant 6-8 inches to the side
If the plant becomes lodged, it has a stalk rot
Record the number of lodged plants

The Pinch Test:

Randomly select 20 plants from 5 different areas of the field
Remove the lower leaves and pinch the stalk just above the brace roots
If the stalk easily collapses, it has a stalk rot
Record the number of rotted stalks

If 10-15% of the plants are lodged or rotted, harvest the crop early. The cost of extra drying will be offset by less corn being left out in the field.

Management Strategies

At this time of year, the only thing a grower can do to minimize yield loss from stalk rots is to harvest infected fields prior to healthier fields. The following management tactics can be used to assist in preventing stalk rots from developing in the future:

Plant hybrids that have good resistance or tolerance to leaf diseases and stalk rots
Manage insects such as European corn borer
Control weeds
Plant appropriate populations for the soil type/hybrid
Balanced N and K fertility program
Crop rotation
Tillage of crop residue

Disease	External stalk symptom	Internal stalk symptom	Environment
Gibberella	Small black spots, easy to scrape off	Shredded with a pink to red colour pith	Warm, wet weather during & after pollination
Fusarium	Light brown to black lesions near the nodes	White to salmon pink fungal growth	Warm, dry weather, stresses after pollination
Diplodia	Small black spots, hard to remove	Disintegrated pith	Warm, wet weather 2-3 weeks after pollination
Anthracnose	Large, shiny, dark brown to black streaks	Discoloured black and rotted pith	Any stress following pollination
Pythium	No visible signs	A “wet rot” at the base of the stalk	Wet weather