If you just experienced a frost event, there are several things to consider when assessing the damage. Before deciding on a course of action, think about the weather before and after the frost, your field’s soil conditions, the growth stage of the plant, the amount of damage, and your options for re-seeding.
Consider the weather before and after the frost
- If warm temperatures suddenly drop below zero, crop injury is more likely.
- If the weather is cool leading up to a frost, there is less likely to be injury as plants will already be hardened off.
- If temperatures are below zero at night and then rise to be very warm during the day, it can be shocking to the plant and could cause injury. The length of time that the temperature remains below zero is important; if the thermometer just drops down for a short amount of time, it’s typically not as damaging as if the temperature was below zero for a few hours.
Understand how soil conditions can impact the severity of the frost injury
- Soil that has a lot of trash won’t warm up as fast as a bare soil, as trash prevents the sun from hitting the soil directly. Bare soil, however, holds the sun’s heat creating a layer of warm air above the plants, making them less likely to get hit by freezing temperatures.
- A field that is bare but sandy compared to a field that is bare but black is more likely to get hit by damaging frost as it doesn’t hold as much heat.
- Good soil moisture helps the soil retain daytime heat and can also help buffer the soil from the cool night temperatures.
Assess the growth stage of the crop
- Canola plants are less tolerant to frost as their growing point is above ground.
- Canola plants at the cotyledon stage are less tolerant than plants with 2-3 leaves.
- Wait at least three to seven days before assessing frost injury. How long you should wait depends on conditions; the better the weather, the sooner you will know. The plant can look black and shriveled, but may start to re-grow if there is a growing point that isn’t dead.
Calculate the survivors
- Measure how many plants per square foot are left. Canola plants are very “plastic”, that is, they are very good at growing according to the space they are given.
- The ideal number of plants per foot square for a canola crop is 7-10 but a plant stand of two plants per square foot can still lead to a decent crop, as long as weeds are effectively managed. This is why seeding rates are targeted for denser plant stands so some plants can be lost and you can still have a viable crop.
Make a final decision
No doubt you will be wondering whether or not to re-seed when your field has been affected by frost. As discussed, assessing the soil conditions, the time of year, as well as frost damage will be necessary to help you make this decision.
- In mid to late May, there can be enough time and sufficient soil moisture to make re-seeding a good choice.
- If you are making this decision in June and there aren’t the same moisture conditions as in May, it might not be a good idea to re-seed. At this point you are less likely to get rain to help with the germination and the risk of not having enough time for the crop to mature is high.
- If you have crop insurance, they will make the final call; if they say don’t re-seed and you do, it won’t be covered.
- Don’t forget to check the re-seed programs that each seed company has and their procedures for reporting frost injury.
Remember – when the “f” word – frost - impacts your crop, remain calm. Taking the time to assess the situation will pay off later. Wait three to seven days, check plant stands and finally, see if it is viable to re-seed another crop, considering the soil conditions and date.
For help with assessing a frost damage situation or for more information on this topic, contact your local Cargill Agronomist, we’re here to help.