Identifying Frost in Broadacre Crops on your Farm
Spring is in full swing throughout the Wimmera and Western Districts of Victoria. With that also brings the thought of the dreaded F word - Frost. With dryer then average springs in recent years frost has become a major problem for grain production in cereal, canola and pulse crops. Although frost is no certain to occur this spring it is better to be prepared and understand our options, rather than sticking our heads in the sand and hoping for the best. Growers and agronomists alike need to work closely and be proactive in the event of a frost to ensure the correct management decisions are made. This starts with being able to correctly identify frost damage in crops.
Identifying frost in cereals, canola and pulses
Wheat is extremely susceptible to frost. The most critical time for frost in wheat is flowering (GS 60-69). A frost event during this time can cause sterilisation of the spikelet preventing grain development in that floret. To identify frost at flowering, peel back both the glume and then the lemma. This will reveal the anthers and other reproductive structures. If damage has occurred at this stage, the anthers will be distorted and appear a dullish brown colour.
Photo 1. Left shows a healthy wheat head with no frost damage. Right shows frost damage with anthers that appear discoloured and banana shaped. Image source; GRDC
Grain development (GS 70-79) is another critical time for frost. Healthy, unfrosted grain will show a cloudy milk texture. In contrast, frosted grain will contain a much clearer liquid. Frost during dough development (GS 80-89) can result in distorted and crippled grain. There may be some grains in the head affected and others not, it all depends on the severity of the frost. Late frosts in wheat (after GS 90) usually result in shrivelled grain. This can reduce grain viability, which will impact germination for following seasons.
Barley is less susceptible to frost than wheat. This is because flowering generally occurs whilst the head is still inside the boot. This helps protect the critical reproductive components of the head, nonetheless, frost damage can still occur. Frost in barley is easily
identifiable in the field by holding the head up against the sun you can clearly see whether or not there is grain fill.
Photo 2. Frosting of barley with undeveloped grain (Left) and frosting of spikelet in oats (Right). Image source; Department of Agriculture and Food Western Australia.
Oats are even less susceptible to frost than Barley. However, damage can still be seen after a particularly severe frost. The most damaging frosting in oats usually occurs when the panicle is emerging. The downward hanging structure of the oat florets allows for solid protection against frost. However, in the event of a bad frost look for white shrivelled panicles on oat heads (photo 2).
Canola can be quite sensitive to frost. Due to the large flowering window, canola can have damage to flowers, pods and seeds all at the same time. Frosted flowers will appear burnt and will abort their reproductive process. Look for discoloured flowers, that fail to set a pod. Poor pod set and pod fill can also occur, distorted and blistered pods are a key symptom that frost damage has occurred at this stage. Severe frosts can damage developing seed which turns a mushy green-brown that dries to a small black or brown speck (photo 3).
Photo 3. Frost affected seeds in pod in the earlier stage (left) and right frost affected seeds at later stage. Image source; Department of Primary Industries and Regional Development.
Faba Beans are usually quite tolerant of frost. This is due to their thick pod that provides an insulating effect, protecting the seed from the outside environment. They can be delicate during flowering and early pod set. Look for burnt off flowers, however keep in mind that faba bean flowers dry out and turn black naturally as they ripen. Fortunately, faba beans have the ability to compensate for frosting to flowers, but only if there is sufficient soil moisture. Developing pods can appear burnt and shrivelled and which usually transfers to aborted seed within the pod.
What to do after experiencing a frost?
The most important thing after experiencing a frost is to not panic. It is imperative that you wait 5-7 days after a frost to accurately determine the severity and overall damage that has been caused. Timely decisions will have to be made if there has been a frost, but there is no need to make any irrational judgements. It is a good idea to check crops after experiencing night time air temperatures of two degrees or less, when received in combination with a frost. Check your most frost prone areas first, keeping in mind that frost can occur sporadically with high variability of damage on both the plant and throughout different sections of the crop.
If there is frost damage evident, some tough decisions may need to be made. Cutting frosted crops for hay is a way growers can reduce the economic loss of a frost. There are calculations and number of factors that need to be considered, and these can vary greatly between crop types. These may include:
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Damage to the crop (e.g. 25%) and potential grain yield.
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Current grain and hay prices.
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Crop biomass.
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Contracting costs.
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Weather conditions and contractor availability.
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Access to markets.
What are ways to mitigate the effect of frost?
Unfortunately, 100% protection against frosts is not possible, however there are a number of techniques we can utilise to help reduce the damage caused to farm businesses.
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Identify frost prone paddocks, e.g. topography
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Consider crop selection.
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Diversification of sowing times.
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Plant more than one variety (e.g. winter and spring wheats)
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Consider grazing cereals to manipulate flowering times.
Please consult with your Western AG agronomist first if you think you have experienced a frost on your farm. For any further information in relation to frost identification as always contact your local Western AG agronomist to discuss today.