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Ontario Grain Farmer Magazine is the flagship publication of Grain Farmers of Ontario and a source of information for our province’s grain farmers. 

The replant decision


IN ANY GIVEN year, tens of thousands of acres of corn and soybeans might be replanted in Ontario. Farmers do everything they can to make sure all is done correctly at planting time, but frost, flooding, or disease and insect attacks in the days afterward are always a possibility. At that point, growers find themselves in a situation where the option to replant must be seriously considered.




“There are a lot of factors involved and it is always a field-by-field decision,” says Doug Alderman, National Sales Manager at PRIDE Seeds and a Certified Crop Advisor. “I have walked thousands of acres over the years and each situation is a little different. The crop, the weather, the soil conditions have to be looked at carefully every time.”

Alderman says, in the end, farmers (and also perhaps their agronomists) must do their best to weigh all the factors and make that call – to replant or to leave the field as is.

The question of whether the stand is adequate or whether it is likely worth it to replant is complex. ‘Likely’ is an important word to focus on, because there are no guarantees.

Leaving the field as-is may be more cost-effective than replanting in terms of things like additional weed management. In addition, a replanted stand may turn out to be far from perfect. It is a well-established fact that yield potential begins to decline the later in the season that a crop is planted.

“A lot of times the first plant is the best plant,” says Alderman. “And even though things can look bad early on in a field, it is possible that an ‘acceptable’ stand may generate nearly maximum yield potential.” Replanting only part of a field is another option. 
Alderman says that in general terms with all crops, the decision of whether or not to replant comes down to field conditions. “After a flood, for example, with ponding of water, you can’t get into the field until it’s dried up, and then you have to see if the seedling could get through that crust,” he says. “So sometimes you’re not looking at an emerged stand but what is happening in the ground with the seedling, and if there is rot or a crust, no emergence will happen.”

With frost, the ability to bounce back depends on the growth stage, Alderman notes. “Insects can also play a big role in germination and emergence. For example, wireworm is more prevalent in cool, damper soils,” he says. “The longer the seed lays there, the longer it is exposed.”

In Ontario, soybeans may be more prone to poor stand establishment than corn. Through their online resources, the Ontario Ministry of Agriculture and Food (OMAF) advises farmers to take their time in assessing a poor soybean stand, since more seedlings are likely to come up. Even fields where there has been 50 percent plant reduction do not need replanting “if plant loss is uniform and the stand is healthy.”

A LOOK AT 2014
This year, we had a “good old-fashioned winter,” Alderman notes. “We’ve had lots of snow cover across Ontario and Quebec and it’s been colder than normal. This means both good and bad things. On the positive side, the cold temperatures should give us less insect pressure and all the snow will give us lots of soil moisture. We may see, however, that fields are wet well into the spring and all the ice on the Great Lakes will mean it will take longer before we see warmer soil temperatures.”

Alderman thinks that due to the cooler and damper soils that are likely to come around planting time, fungicide seed treatments will likely play an important role this year in aiding plant survival.

If you do decide to replant, the initial poor stand must be removed, or it will interfere with yield for the replanted crop. OMAF notes that the ‘graminicide’ herbicides control emerged volunteer corn and annual grassy weeds but offer no residual weed control, and are therefore a good option for killing poor corn stands prior to replanting.


“You do everything you can the right way, the first time around,” Alderman concludes. “Farmers know very well that they only have one real shot at planting. When you have good soil conditions and a good forecast, you plant. To get stand consistency, you set up your planter properly, plant at the right speed and depth, and make sure you have good seed-to-soil contact. The rest is up to Mother Nature. No one can control whether there will be a flood or frost days after planting. Patience is a virtue, but you have to know when to pull the trigger as well.”

The Ontario Corn Replant Calculator was developed by Greg Stewart, Corn Specialist with the Ontario Ministry of Agriculture and Food, and Dr. Dave Hooker and Ken Janovicek both of the Plant Agriculture Department at the University of Guelph. This tool allows growers to input original planting date, potential replant date, seed costs, replanting costs and crop insurance factors to determine if replanting is the most profitable choice.  Visit the website:

The Pioneer corn replant calculator is based on a long-standing chart developed by Dr. Emerson Nafziger of the University of Illinois. It illustrates the effects of planting date and plant population of grain yield for the central Corn Belt, taking into account the current shift to higher populations. Visit the website:

The mobile app of the University of Illinois Corn Replant Calculator developed by Dennis Bowman and Emerson Nafziger is available here: csrec/eb260/category_154.html. •

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