How do you check for frost damage?

• When: Inspect crops when they are between ear-emergence and grain-fill, after the temperature drops below 2°C (screen temperature). Damage is usually most evident 7−10 days after a suspected frost event.
• Where: Examine the crop in more susceptible lower parts of the landscape first and if the crop is
  damaged proceed to higher ground.
• How: Walk through the crop and examine a whole plant every 10−20 paces.

If the head has not emerged from the boot, check that the developing head has not been damaged. You will need to carefully dissect the plant from the top down to find the head of the plant inside the leaf sheaths. If the crop has flowered, open the florets to check if the grain is developing.

After a frost event, tag a few heads with tape and note the stage of development. Return a week later to determine if head/grain development and grain filling is continuing. To check for stem frost, remove the leaf sheath from around the stem from the flag leaf to the roots checking for a pale to white ring, shrunken or wrinkled/blistered appearance.

This podcast with Ben Biddulph could help you identify frost damage.

Identifying Frost Damage video

What does frost damage look like?

The nature of frost damage depends upon the plant development stage at which the frost occurs.

• Grain: Frosted grain at the milk stage is white eventually turning brown with a crimped appearance. It is usually spongy and when squeezed it doesn’t release a milky dough substance. Frosted grain at the dough stage is shrivelled and creased along the long axis, like a pair of pliers has crimped the grain in the middle.
• Flowering: Frosted anthers are white turning a dull brown colour, ovaries turn a dull brown and are spongy when squeezed. They begin to shrivel as no grain is developed. Also the head will be underdeveloped and/or have bleached florets.
• Stem: Pale green to white ring on the peduncle (the stem below the head), or between the internodes which can lead to a crimped, cracked/blistered appearance with a rough texture. The damaged area may turn white/brown and the head/stem may bend over.

These guides to identify frost in canola and pulses as well as cereals may help.

Stages of frost damage

1. Cold or chilling damage occurs when plants are exposed to temperatures less than 10°C down to -2°C. If the changes in temperature are sudden the plant is unable to increase the fluidity of membranes (largely made of fats) at the lower temperature and this compromises cellular and plant energy balances. If this occurs at critical stages in reproductive development this can cause a few or all of the florets to abort during pollen development. The damage is not related to the formation of ice within plant tissue, although it may appear to be.
2. Desiccation from ice formation occurs at temperatures from 0 to -2°C. When plants are exposed to freezing temperatures during a white frost the dew initially freezes on the outside of the plant, but then the ice nucleation can move within the leaf through cracks in the leaf cuticle and stomata. The water inside the leaf then starts to freeze. Initially the water around the cells freezes but it also then draws out the water from inside the cells and dehydrates the cells. The cells themselves may not necessarily freeze or have ice form inside them. This process won’t necessarily kill the cells as long as the dehydration and desiccation don’t go too far. When the ice thaws these cells can re-hydrate and recover but can still suffer from dessication.
3. Freezing damage is the final stage of frost damage. It occurs when there is rapid ice nucleation and ice crystals form. The ice crystals physically rupture cell walls and membranes within the cells causing physical damage to the cells. Freezing damage is generally not reversible, but can be limited to specific tissues within the plants, for example stem nodes, individual florets or individual tillers.

Is stem frost damage as bad as flowering frost damage?

Stem damage may not be as bad as flowering frost damage, provided there are viable grains and mild weather conditions during grain filling. The stem structure is similar to a bunch of straws where water and nutrients travel to the head/grains. Not all straws may be affected, allowing water and nutrients to still reach the head/grains. Dye can be used as an indicator of how much damage has occurred. To demonstrate this, cut a plant at the base and place outside in a mixture of water and food dye for 24 hours. The ease of which the dye travels up the stem will give you an indication of damage.

Normally it’s the xylem (capillary tubes which transport water) that are the issue, (the phloem which transports the sugars can rebuild), if it is hot or water stressed, the heads can lose ability to maintain evaporative cooling because of restricted water flow and can over heat. This can result in white bleached heads after a hot day. Lodging of cereals can also be an issue if windy conditions occur during late grain filling stages.

Stem frost damage late in grain filling can be confused with root diseases such as, crown rot, rhizoctonia or septoria. To determine the cause of damage, remove the leaf sheath from around the stem from crown to peduncle to check for a pale to white ring, shrunken or wrinkled appearance.

Do all crops respond the same to frost?

All winter grain and oilseed crops are susceptible to frost. It is therefore important to consider less susceptible crop species for frost-prone paddocks. The order of susceptibility for cereals is (most to least); durum, triticale, wheat, barley, cereal rye and oats. Wheat is more susceptible then barley at flowering, but barley is as or more susceptible during grain fill.

Field peas are the most frost susceptible pulse crop followed by faba beans and lupins. Canola is susceptible to frost, with the most sensitive time from late flowering (90%) to the clear watery stage (about 60%). However due to its indeterminate nature canola has a good capacity to recover from frost, given a favourable finish.

Canola is an expensive crop so careful consideration needs to be made for frost prone paddocks. Grain and oaten hay crops are the least susceptible to frost. Oats are less susceptible to frost during the reproductive stage than other cereals and as hay production requires biomass, reproductive frost damage will not reduce yield and may in fact improve the quality of the product through the mobilisation of sugars. Pasture rotations are also lower risk enterprises.

Read the Managing frost risk tips and tactics fact sheet for more information.