Winter Not Cold Enough For Kiwifruit
Media Release 26 July, 2002
Mild winter bad for kiwifruit
Warm winters are great, but not if you are a kiwifruit grower. Kiwifruit require winter chilling to maintain a commercial yield and HortResearch scientists are warning that this winter is just not cold enough.
In mid July they were concerned that bud break on Hayward kiwifruit will be late, not until early October in Te Puke and Kerikeri, and the number of flowers will be low, similar to spring 1998.
Predicting a bud break date is always uncertain because it means predicting the weather and although HortResearch scientists are really good even they have some limits. However they have developed a computer programme that uses current and historical temperature data and then makes a "most likely" prediction.
The average monthly temperatures work well as an indicator of bud break even though it is related to a complicated temperature index and that includes warm spring temperatures. For Hayward kiwifruit growing between the Nelson region and Kerikeri, the number of flowers is best predicted by measuring chilling through the winter months.
One thing that is known for sure is that the number of king flowers per winter bud increases as temperature decreases i.e. the colder the better.
HiCane (hydrogen cyanamide) can help to break dormancy. It has been shown to increase the number of flowers per bud by 0.3 at cool sites, and 0.6 at warm sites. For example in the Bay of Plenty and Kerikeri the increase using Hi Cane is equivalent to lowering winter temperature by about 1oC. HiCane does not completely compensate for poor winter chilling.
Hort16A or ZESPRI GOLD Kiwifruit breaks bud earlier than Hayward and therefore require warm temperatures earlier in spring. Hort16A needs cool weather in May and June.
Check the HortResearch web site www.hortnet.co.nz/news/2002/n4404.htm for regular updates of the latest predictions.