A three year study in the Broadwater District of NSW by NSW Sugar Milling Co-perative Ltd, C S I R O , NSW Dept Agriculture and Sugar Research & Development Corporation

What is Frost Damage?
Frost damage occurs when freezing ruptures plant cells (which are the basic building block of plants). The most significant type of damage to the plant is death of the growing point (otherwise known as the heart). Other common forms of damage are leaf burn, and death of the eyes down the cane stalk.

During a frost, death of the growing point begins to occur at temperatures below -2.0^oC. However, the extent of death will be affected by both the minimum temperature reached, the length of time spent at frosting temperatures and the previous hardening of the crop by exposure to mild frosts.

The Overcoat Effect
Although frost damage to the growing point begins at -2^oC, a well developed, complete leaf canopy acts like an overcoat, keeping the cold air above the canopy from seeping down to the growing point. In such cases, a headland temperature of around -3.5^oC is required before the growing point reaches -2.^oC

Managing Cane to Reduce Frost Damage
The goal is to ensure that in moderate and mild frost years damage to the crop is minimised.

Some suggestions are:

• Select varieties with an erect habit.
• Avoid sprawling in vigorous varieties by reducing fertiliser application and by delaying some of the fertiliser application until after the first winter.
• Laser grade for water and cold air drainage.
• Use irrigation (if available) to ensure a complete canopy by winter.
• Grow some high CCS varieties such as Q124 that can be harvested at one-year if frosting occurs.
• Select varieties with some frost resistance such as Q141, BN78-8031.
  

Improving Frost Resistance on New Varieties
There are two means of improving frost resistance of new varieties.

Improve Frost Avoidance - improve the overcoat.

Improve Frost Tolerance - the capacity of the cane plant to survive freezing.

Management and seasonal influences play a larger role in frost avoidance than the difference between varieties. It is therefore not efficient to target avoidance factors i.e. crop canopy etc in a breeding program. However, 50% of the later stages of the NSW variety improvement program are sited in frost prone areas and there is therefore a significant amount of natural selection for avoidance and tolerance factors.

Frost damage in the Broadwater Mill area in 1993.
Photo taken one month after frost occurred.