Cold Weather and Corn
By Greg Stewart, OMAFRA Corn Specialist

Corn planting was completed very rapidly this spring and for the most part the crop is off to a good start. Generally corn plants are ahead of normal in terms of growth and development. This fact may cause corn producers some anxious nights if weather patterns produce the risk of frost. There is very little that can be done to minimize the potential problem but here are some management factors that do increase the risk of frost damage to corn should temperatures fall:

1. Inter-row cultivation
2. Side dressing nitrogen (where soil is disturbed)
3. Herbicide applications
4. Presence of weeds
5. High levels of previous crop residue

If the forecast calls for a risk of frost farmers may elect to delay inter-row cultivation, nitrogen Side dressing or herbicide applications until warmer temperatures return. If corn does receive frost damage it will generally have very little effect on the crop providing the growing point of the corn plant is still below the soil surface. This is the case until the young plant reaches roughly the 6th leaf stage. On more advanced plants/and or where damage is more severe stalks will need to be split to see if the growing point has been damaged. However, this procedure will require some patience! It probably takes 3-5 days following a frost to accurately determine the degree of damage, to verify the presence of healthy growing points (yellowish-white in colour and firm) or to see new leaf growth.

In some cases frozen leaf tissue, which bleaches to a straw colour several days after freezing, also develops a "knot" which may restrict expansion of the undamaged tissue lower in the whorl. Often it appears that clipping these knots by mowing the field aids in the plants recovery. Tests conducted on frosted corn fields over the years have arrived at the conclusion that clipping appeared to help the fields "green-up" but that unclipped sections of the same fields often recovered as quickly and yielded as much or more than the clipped sections.

Decisions regarding the severity of frost damage, the need to replant, or the advantages to mowing the damaged corn should not be done in haste or without due regard for the young corn plants ability to recover.

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