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Now that we are about a month away from the devastating spring frosts, it is possible to get a better feel for what the effect has been and also the likely implications for this year's crop outturn.
In addition to the frosts there have also been some fairly cool periods during apple flowering, which appears to have adversely affected fruitset. Flowering of some varieties has been delayed too.
The most severe frost on 5 October 2002 occurred prior to fruitset in most apples, but after fruitset in summerfruit, so there are severe losses of summerfruit whereas apples have not been badly affected. Frost tender crops such as kiwifruit and grapes were also severely damaged, reflecting the difference in frost tolerance among these crops.
Temperate crops such as apples will tolerate temperatures down to about -2.50C during the pre-fruitset period and have the ability to compensate for any fruit or flower loss by heavier fruitset than normal on the later flower, which was much less vulnerable to frost injury because of its much lower susceptibility to frost injury at the time of the frost. Temperate crops which were post-fruitset do not have later flower coming through to compensate for the frost loss.
The frosts and the cool spring will have a marked effect on this season's fruit supply.
Volumes of summerfruit will be markedly reduced. Early flowering summerfruit varieties were advanced in development because of the warm winter, and particularly warm August temperatures. These varieties are expected to ripen earlier than normal. Mid and later flowering varieties struck cold weather and this will delay their development. We should, therefore, see a longer summerfruit marketing season than normal and this always helps prices because lower peak sales volumes occur.
The apple season will be generally later, and also more spread out. Many apple blocks this year were treated with dormancy breakers. Where good frost protection was used, or the locations did not get killing frosts there has been good set of the early flower, so here the full benefit of the earlier flowering will be captured. Even so, cool October weather will have delayed development of this fruit.
Where frost damage occurred, most of the crop is being carried on later flowering lateral bud of one year wood. This class of fruit is usually 7 to 10 days later than the stronger early flower fruit and also smaller.
For Hawke's Bay, this year we estimate that the flowering period for non-dormancy treated Royal Gala was about 14 days behind last year, and one of the latest flowering seasons we have seen for this variety. This suggests that the main picks of this variety may not come on stream until early March.
At this stage, Braeburn appears to be the only apple variety suffering significant crop loss from the frosts. It has not stood up a well as other varieties to frost injury.
Russet and Fruit Shape
Typical frost ring russet expression is already showing up on early flowering Royal Gala blocks which were hit by the frost. We have also seen some on Pacific Beauty.
Braeburn is not showing a lot of russet, or frost cracking, but is showing quite a lot of distortion at the calyx end of the fruit, so we can expect real problems this year with fruit shape and particularly squat fruit.
In frosty areas, many fruit are showing skin bleaching and a reddish discolouration in the calyx end. We have often seen this symptom in the past on Braeburn and believe that it masks out once the blush colour comes through.
It is too early to determine what affect the frosts will have on russet levels in the general crop. Retained early flower fruit are already showing frost russet rings where they have been damaged by frost. On the positive side, apparently undamaged fruit around them is looking very clean at this stage.
Effectiveness of Frost Protection Systems
As usual, well-designed overhead sprinkler systems gave full protection to even the most frost-tender crops such as kiwifruit.
Under tree sprinklers were effective on large areas for temperate crops such as apples. In the long frost on 5 October, when unprotected temperatures outside the irrigated area dropped down to below -20C, our company measured temperatures around -10C where3 under tree sprinklers were being used. This lift was enough to prevent damage in the relatively frost tolerant temperate fruit crops.
Windmills and helicopters were also effective for the temperate pipfruit and summerfruit crops, but apparently less effective for frost sensitive crops such as kiwifruit and grapes where there was little or no warm air inversion layer to draw on.
In the case of apples, the effective area covered by windmills was somewhat reduced with severe frost injury occurring beyond their influence. In these types of frosts, windmills need to be supported by an additional heat source such a strategically placed oil burners.
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