As winter is all but finished, well at least in theory, how was it?
There is some concern that in places we had a dry autumn and have not yet fully recharged the soil over winter. In autumn the trees stack away the reserves they will need come spring; stonefruit trees wake up naked – no leaves, so all the early growth comes from reserves stored in the buds. Have a good look as bloom starts, as scummy flowers may not pollinate as well as big healthy flowers.
The primary determinate is the amount of winter chilling received. Our deciduous trees need a certain amount to wake up happy in the spring. Different species and different varieties have different requirements (see table below). When investigating new plantings, it is a good idea to know what its chilling requirements are, especially in more northern climes.
Chill requirements
|
Fruit type |
Chill hours |
|
Almond |
500-600 |
|
Apple |
400-1000 (low chill varieties are less) |
|
Apricot |
500-600 |
|
Blackberry |
200-500 |
|
Blueberry |
800 (northern) |
|
Cherry |
700-800 |
|
Chestnut |
400-500 |
|
Citrus |
0 |
|
Currant |
800-1000 |
|
European pear |
600-800 |
|
European plum |
800-900 |
|
Fig |
100-200 |
|
Filbert |
800 |
|
Gooseberry |
800-1000 |
|
Grape |
100+ |
|
Japanese pear |
400-500 |
|
Japanese plum |
300-500 |
|
Kiwifruit |
600-800 |
From gathering some information from the Summerfruit NZ portal and doing a comparison, it seems like we have had a reasonably good season. If your closest station is not on the list below, have a look on the portal. There have been fewer chill units in Hawke’s Bay and Marlborough than average, but nothing significant. Compare that to the warm winter of 2016. Central Otago picked up a few more chill units than average, again nothing too significant. Bernie Attfield has commented that there has been plenty of fog about at various times which fits in with increased chilling.
Look on the Summerfruit NZ portal under Tools/Climate summary tools/Weather history/Chill units calculator where the information can be found. If you do not have a portal log in, please contact the Summerfruit NZ office by emailing anna@summerfruitnz.co.nz or richard@summefruitnz.co.nz
Richardson chill units
|
Region |
Five year average |
2019 |
2018 |
2017 |
2016 |
2015 |
|
Bay View |
1102 |
1017 |
1142 |
1350 |
931 |
1069 |
|
Twyford |
1152 |
1110 |
1208 |
1400 |
870 |
1174 |
|
Longlands |
1172 |
1164 |
1194 |
1363 |
972 |
1167 |
|
Renwick |
1423 |
1369 |
1523 |
1641 |
1344 |
1236 |
|
Cromwell |
1496 |
1508 |
1549 |
1584 |
1435 |
1404 |
|
Clyde |
1374 |
1445 |
1395 |
1399 |
1327 |
1304 |
|
Roxburgh |
1750 |
1862 |
1835 |
1846 |
1530 |
1678 |
I have presented the data above as Richardson chill units, which seems to be the most appropriate model for us in the temperate climate of New Zealand. Other models are used in other parts of the world, for instance hours under 7.2˚C (45˚F), so be a little careful that you are comparing like with like. The best chilling occurs at 4˚C.
It’s interesting to see that in some seasons Marlborough can pick up as many chill units as Central Otago, and then behave more like Hawke’s Bay with heat unit accumulation.
Rainfall March to July
|
Bay View |
4 of 5 lower than the 15-year average, and the high one, June was 3% up |
|
Twyford |
4 of 5 lower than the 15-year average, and the high one, June was 54% up |
|
Longlands |
4 of 5 lower than the 15-year average, and the high one, June was 8% up |
|
Renwick |
3 wetter and 2 drier years than the last 13 years, with a dry June |
|
Cromwell |
2 wetter, 1 on average and 1 drier than the last 14 years. July figures missing |
|
Clyde |
4 wetter and 1 drier than the last 15 years |
|
Roxburgh |
3 wetter and 2 drier than the last 15 years |
Diving back into the portal, we can have a look and see what is happening with diseases with regards to temperature and rainfall. At this stage we have models to help predict leaf rust, leaf curl and brown rot. Now that we have bloom and a few leaves, I have had a look and compared the same regions as above to see what has happened in the past few days, and what we are anticipating in the next few days.
Leaf curl (this week)
|
Bay View |
primary infection likely on August 17, and another of 3 insufficient duration |
|
Twyford |
primary infection likely on August 17, 4 insufficient duration, and more to come |
|
Longlands |
primary infection likely on August 17, 4 insufficient duration, and 3 more coming |
|
Renwick |
primary infection likely on August 17, 4 insufficient duration, and 3 more coming |
|
Cromwell |
2 insufficient events and 2 more coming |
|
Clyde |
1 insufficient primary infection period and another insufficient coming |
|
Roxburgh |
3 insufficient periods and 2 more coming |
Leaf rust (number of infection periods this week)
|
Bay View |
3 marginal and 1 light infection periods |
|
Twyford |
3 marginal and 1 light infection periods |
|
Longlands |
1 marginal and 2 light infection periods |
|
Renwick |
1 marginal and 2 light infection periods |
|
Cromwell |
1 marginal and 1 marginal predicted period |
|
Clyde |
1 marginal and 1 marginal predicted period |
|
Roxburgh |
1 light infection period |
Brown rot (this week)
|
Bay View |
2 marginal periods |
|
Twyford |
moderate period with another coming |
|
Longlands |
1 moderate infection |
|
Renwick |
a marginal and a severe period |
|
Cromwell |
nothing |
|
Clyde |
nothing |
|
Roxburgh |
nothing |
Of course, none of this is of great importance if there is no suitable host for the disease to infect. So here we go again thinking of the disease triangle. To get infection we need:
- the right weather conditions,
- the disease present, and
- a suitable host.
Dr Elmer and others have been strongly suggesting that orchard hygiene is one of our better tools. If you were to drag all the wood and fruit/stones into the grassed area and smash it into little bits that would be a great start to gaining season long control. And we could do with a good one!
This article is made possible by your commodity levy.