Crop Scene Investigation - 17 Solved: Bruce's dilemma - to replant or not?

Thursday, April 2, 2009

by SHAWN BRENNEMAN

We had already established that frost was the root of Bruce's problem. His corn plants were brown and wilted as a result of the temperature dipping to around -3 C for several hours. The tricky question Bruce faced was whether or not to replant.

There are a number of factors we had to weigh, including plant survival, loss of yield due to both potential lower stand and later planting date. After weighing all of these and looking closely at the plants, I advised him not to replant. And, indeed, after several days his crop outgrew its frost symptoms. The damaged leaves were replaced with new leaves within a week.

The healthy growing point was the clue that the plant was only experiencing superficial damage and that it would pull through. The growing point is usually protected below ground until the plants reach the five-leaf stage. If it appears healthy and is white to light yellow in colour several days after frost, full plant recovery is likely.

When frost kills leaf tissue, it's not surprising that growers like Bruce worry about whether or not the crop will recover. In fact, removal or death of leaf tissue above the growing point has only a small effect on corn growth and yield at these early stages.
Bruce's neighbour got anxious seeing the frost-damaged plants and quickly replanted. His efforts resulted in 20 less bushels/acre in the fall compared to Bruce, who left his stand. This yield loss is a direct result of the later planting date.

Bruce's neighbour also incurred the expense of purchasing more seed and extra planting costs. This goes to show that it pays to wait a day and call someone with agronomic expertise and diagnostic tools to decide the best course of action.

The question of replanting doesn't have a standard answer, because it depends on the stage of the plant at the time of the frost. If the frost occurred a week or two later, it might have killed off the growing point of the plant and Bruce's neighbour's efforts would have paid off. 

When you take advantage of early planting, frost damage isn't something you can avoid, but there are some management factors which increase the risk of damage if temperatures fall. This includes inter-row cultivation, side dressing nitrogen (where soil is disturbed), herbicide applications, presence of weeds and high levels of previous crop residue.

If you make crop management decisions with these risk factors in mind, you can reduce your chances of frost damage and the tough question of replanting. Congratulations to Amy Vandendool, Port Lambton, ON for her correct answer. BF

Shawn Brenneman, CCA, is a Sales and Agronomy Manager for NK® Brand, Syngenta Seeds. He is based near Tillsonburg.