Frost: How, Why & What To Do About It

There’s nothing more gut-wrenching than seeing your year’s work wiped out in one night thanks to frost damage. No one wants to hear it, but…
October 8, 2018News & Advice Back to All

There’s nothing more gut-wrenching than seeing your year’s work wiped out in one night thanks to frost damage.

No one wants to hear it, but frosts are continuing to occur and cause damage in our area. Consciously or not, we’ve learnt to become wary of clear, cold and calm nights in spring.

Especially in our Mid North areas, it seems like frosts are becoming more frequent, and continually hitting our best-looking crops. We’re not going to discuss why frosts seem to be occurring more frequently (we’ll leave that to the climate experts.) But, we do know of a few hypotheses about why frosts have been so damaging to crops.

One theory is that the crops we are growing are more prominent and have better canopy closure. We’re sowing with high seeding rates, high nitrogen and thus have bigger canopies with higher yield potentials. It is thought that these denser canopies shade the soil, reducing the sun’s abilities to heat up the soil during the day. Therefore, the soil’s ability to act as a heat bank to buffer the frost is reduced and therefore it will be cooler and drop to lower temperatures overnight.

Other hypotheses suggest that with the drier, warmer years we’ve experienced, crops are developing sooner than intended and flowering during much higher frost risk periods. Drier years generally mean more sun, more warmth, and quicker crop growth. Thus, plants are going to head and flowering earlier in frost prone periods even though we’re planting at what we think is the right time. So, as the average growing season conditions warm up, the growing season shortens. GRDC estimates that the plant growth stage moves forward by seven days for every 1ºC of warming.* When combined with earlier or dry sowing, it means flowering or grain fill is being brought back into the period of higher frost risk.
Another result of drier conditions is the impact of frosts is often more severe due to the lack of soil and plant moisture. It may seem contradictory, but drier soils will cool more rapidly than moist soils, and plants that are holding less moisture will freeze more quickly.


So, what can you do?

You’ve had a frost. So what do you look for and how will it affect your crop.

If you do suspect your crops endured a frost, the best time to check is 5-10 days after the event. Start by looking for damage in the lowest parts of the paddock. Examine a whole plant every 20-30 paces, and peel back the leaves and look for stem damage, and for damage to the developing head. If the crop is past growth stage 51 (head emergence) open the florets on the head to check that the grain is developing.

Stem Frost:

As crops will mature at different rates, and sowing times vary, frosts can hit during entirely different growth stages. When your crop is between growth stages 31-49 (stem elongation – booting), you could receive a stem frost. This is where water that has settled inside the leaf sheath has frozen, which will then cause damage to the peduncle or the internodes of the stem. This damage stops water and nutrients from being transported past these points and therefore can result in either head loss, or severe head damage and death of the primary tiller, causing re-tillering along with being more prone to lodging. The damage will be shown as discoloured or bleached flattened peduncle or felt by the stem having a rough texture. See our pictures for examples.


Head Frost:

A head frost can occur at flowering, grain development, dough development, and harvest, all having different effects. During flowering, a frost event can cause sterilization of the spikelet, as it can affect the pollen, ovary or both, which will stop grains from being developed. Frost damage during grain & dough development will affect the forming grain, and it could become crimped and shrunken.

head frost and stem frost.jpg

Dealing with Frosts: You’ve suffered frost damage, so what are your options?

We have 4 main suggestions depending on your situation.

Firstly, harvest the grain.
Depending on the amount of damage and the growth stage of the crop when the frost hit, some plants will be able to recover and compensate for yield loss. If there are sufficient soil moisture and nutrients available, some recovery is possible. If grain prices are up, as they currently are, this could be your best option. But check if it is viable by estimating yield potential. Yield potential can be estimated by working out the what the yield potential was before frost, let’s say 4t/ha. Then, check the number of heads not affected, for example, let’s say 6/10 heads will set grain normally. Our new yield potential will be 4t/ha multiplied by 0.60 (6/10 heads) = 2.4 t/ha. Also, remember that frost-affected grain can still be sold for suitable livestock feed. With reasonable prices, and shortages around our dry country next year, this could still be a viable option.

Our second option is to cut for hay or silage.
This can be a tricky one. You will need to consider the demand and opportunity for marketing hay, as well as the potential on-farm storage and use of hay from the frosted crop. You’ll also need to consider likely costs and returns from haymaking. If pulse crops are unlikely to recover they can be used for good quality fodder. There is not the same urgency to cut pulses as quickly as cereals, as the feed quality doesn’t decline as rapidly after a frost. If there is also a lack of soil moisture, it may bring on leaf drop, and that will influence the timing of cutting. This delay in cutting also gives a better indication of the severity of the frost and grain yield is better known. (We’ve included an excellent fact sheet by the GRDC on our online news for those who are interested – regarding failed crops and hay options.)

The third option is grazing.
Of course, this depends if you have the livestock, but crops will supply good feed for the animals. Hayfreezing is an option that could work out cheaper than cutting and then feeding back to livestock.

Finally, our last option would be to green or brown manure the crop.
This is done by ploughing in the green crop, or spraying out any remaining crop and weed, and returning the organic matter and nutrients to the soil. Even though it won’t provide a return for this year, it will be an investment in next years crop, as it will help manage crop residues and improve soil fertility and structure.

Avoiding Frosts: Is it possible?

Unfortunately, we can’t control the weather. We have to work with it or around it. The best we can currently do to avoid frost is to pick our sowing dates to try to fit flowering windows around desired dates. This can be done by picking varieties that have different maturing times or flowering periods or choosing varieties that are less susceptible to damage by frosts.
Just remember that we have to play the long game with mother nature in farming. Frosts cause a lot of pain, but there are always options, and there is still next year.