(submitted photo/Ministry of Agriculture)

By Alice McFarlane

Frost Damage

Assessing frost damage

May 30, 2019 | 4:19 PM

If you were in an area that had frost recently, you may need to scout your fields to assess any damage.

That’s because the extent of crop damage caused by frost depends on the crop, temperature, length of exposure time, humidity levels and how long the crop takes to reach freezing temperature.

Ministry of Agriculture Crops Extension Specialist Kim Stonehouse said newly emerged canola at the cotyledon stage can be very susceptible to spring frosts.

“Most canola crops can withstand a temperature down to -4 Celsius but it kind of depends on how well they have hardened up before the frost so it’s adjusted to it,” Stonehouse said. “If it’s quick like what we had, they can get damaged a fair amount even at -4 C.”

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“The frost tends to burn the leaves and basically what happens is when the water in the plant crystalizes, it expands and it causes the cell walls to rupture and the fluid will leak out of the cells and you’ll see them look a little watery in appearance,” Stonehouse said. “This will disrupt the plant’s growth and in extreme conditions will kill the plant.”

(submitted photo/Ministry of Agriculture)

Frost is very hard to predict in terms of damage potential in the crop as there are many factors that affect the tolerance. Stonehouse urged farmers to be patient.

“When you’re evaluating it’s usually best to wait 24 to 48 hours after the frost to see the initial symptoms on the plant to see what it looks like but it could take a week to 10 days to get the full extent of the damage,” Stonehouse said. “The reason we suggest to wait is any crop that’s out there now has better potential for yield then anything you’re going to seed later. If the frost didn’t do so much damage that it actually killed the plant, it’s better off that those plants continue to grow rather than working them up and reseeding it.”

For cereals, the growing point is below the ground until the five-leaf stage. This protects the plant from severe frost injury in the spring. The plants may lose above ground leaf matter but will regrow from below ground.

Flax is quite sensitive to frost when it is coming out of the ground. Temperatures that reach -2 C can injure flax up to the two-leaf stage. As flax grows it becomes more tolerant to frost, Stonehouse said. After the two-leaf stage, flax can withstand temperatures down to -7 C and even slightly lower if the plants have been hardened.

The growing points of peas and lentils remain below ground during early development. The above ground material may be severely injured by frost but new growth will start again from the nodes within a few days.

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alice.mcfarlane@jpbg.ca

On Twitter: @AliceMcF