Crop and variety choice
Select appropriate crops
Crop selection is an important factor to consider for frost-prone paddocks. Crops grown for hay are harvested for biomass and avoid grain loss from frost. Pasture rotations are a lower risk enterprise and oats are the most frost tolerant crop during the reproductive stage. Barley is more tolerant than wheat at flowering, but it is not known if barley and wheat have different frost tolerance during grain fill. Canola is an expensive crop to risk on frost-prone paddocks due to high input costs.
Fine tuning variety selection
No wheat or barley varieties are tolerant to frost. Consider using wheat and barley varieties that have lower susceptibility to frost during flowering to manage frost risk of the cropping program while maximising yield potential. There is no point selecting less susceptible varieties for the whole cropping program if there is an opportunity cost of lower yield without frost.
Preliminary ranking information for current wheat and barley varieties for susceptibility to reproductive frost is available from the National Variety Trial website (www.nvtonline.com.au). A new variety should be managed based on how known varieties of similar ranking are currently managed.
NVT data could be useful to help guide your selection.
This frost susceptibility rankings video could also help inform crop and variety selection.
Targeting optimal flowering windows to reduce your risk
All wheat varieties are susceptible to frost however their risk profile during flowering can differ. The frost performance values provided on the National Variety Trial website give an indication of a varieties risk to frost damage during flowering. Variety choice and time of sowing is a major driver of variation in yield and is still the most reliable way of reducing yield losses from frost. To minimise the impact of frost, first select varieties adapted to your region and then match to the appropriate sowing time to ensure the optimum flowering period. Sowing the correct variety early can lengthen the growing season and deliver increased yields. However, when sowing early, it is critical to choose a variety that flowers during the optimum flowering window (refer to DPIRD’s Flower Power or local agronomic material).
Consider using multiple varieties (with different flowering times) to target flowering throughout the optimal flowering period for your location to minimise the impact of frost. This can decrease the impact of sporadic frosts that occur within the optimal flowering window in some years.
Spreading flowering times
When sowing crops in frost risk areas, a good tactic is to ensure the flowering window of the cropping program is spread widely. This can be done by using more than one variety and manipulating sowing date and varieties with different phenology drivers so crops flower over a wide window throughout the season. It should be noted that flowering later than the frost may result in lower yields in seasons with hot, dry finishes due to heat and moisture stress.
Staging sowing dates over a 3–6week period is recommended. If sowing just one variety, this would provide a wide flowering window. If sowing more than one variety: sow winter wheat first; then a long season spring wheat or a daylength sensitive wheat; then an early maturing wheat last; the whole wheat program is set to flower over a two week period, potentially exposing it to more frost risk but maximising the yield potential in the absence of frost. Even with this strategy in place it is possible to have more than one frost event that causes damage. Flowering over a wide window will probably mean that some crop will be frosted but the aim is to reduce extensive loss.
Sowing at the start of a variety’s preferred window will achieve higher yields at the same cost as sowing late. Sowing time remains a major driver of yield in all crops with the primary objective to achieve a balance between crops flowering after the risk of frost has passed but before the onset of heat stress. The loss of yield from sowing late to avoid frost risk is often outweighed by the gains from sowing on time to reduce heat and moisture stress in spring.
To minimise frost risk there needs to be a mix of sowing dates, crop types and maturity types to be able to incorporate frost avoidance strategies into the cropping system. In years of severe frost, regardless of which strategy is adopted it may be difficult to prevent damage. Trials have found that blending a short season variety with a long season variety is an effective strategy. However the same effect can be achieved by sowing one paddock with one variety and the other with another variety to spread risks.
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