Hemmy's field focus - Maize frost damage

Earlier sowing and recent cold weather have led to reports of frost damage to maize crops on some farms. While maize crops can tolerate temperatures around 0^oC, anything below freezing will cause crop leaves to wilt and die.

The extent of frost damage to young maize plants is linked to the temperature and growth stage of the plant.

Field topography has a significant impact on frost damage – expect to see more damage in depressions and valleys.

While the risks to above-ground leaf damage can be serious, yield penalty will be minimal if the growing point of the plant is not frozen. The growing point of the plant typically remains below ground – and therefore is protected – until about growth stage five, where the maize plant has five fully developed leaves, with the sixth leaf visible but not fully emerged.

However, if sub-zero temperatures struck and crops became frosted at growth stage six and onwards, plants would be unlikely to survive, even if the conditions were experienced for only a couple of hours.

Darkening of leaves – Within the first 24 hours after the frost, maize plants will take on a darkened, almost black appearance. Affected plant tissue then quickly turn brown (within 24 hours). Some lower plant parts may remain intact and stay green.

Allow three to five days before assessing the impact of frost on crops. New growth will usually be detectable, with recovery more rapid on warm days and significantly slower if temperatures remain cool. When the leaves of larger plants are frozen, they can form a tightly twisted whorl that is difficult for the emerging leaves to penetrate.

If the growing point was above ground (6 leaf+ stage) when sub-zero temperatures occurred, dissect plants and examine the growing point. A green growing point is a good indication that the plant will survive, whilst a discoloured / brown growing point may indicate death of the plant.