Coping with frost

For the second year in a row Canterbury has suffered a devastating “advection” frost. Devastating because it kills off all tender shoots even several meters above the ground, including flowers. Last year it was October 19, htis year November 9th.

Richard L. Snyder, Extension Biometeorologist University of California, Atmospheric Science describes advection frost in an article on the “Principles of Frost Protection”:

Advection Frost

An advection frost occurs when cold air blows into an area to replace warmer air that was present before the weather change. It is associated with moderate to strong winds, no temperature inversion, and low humidity. Often temperatures will drop below 32^°F (0^°F) and stay there all day. Advection frosts are difficult to protect against, but fortunately they are rare in California fruit growing regions.

Another helpful explanation that includes reference to the affect of terrain (like snow on the Port Hills or foot hills draining down onto the plains) can be found at “The Weather Doctor”.  The way they put it is:

Whereas frost masses move across continents under the push of global air currents, flood frosts fall downslope under the pull of gravity — their cold air heavier than the surface air undercutting the lighter, warmer air below. Flood frosts form at high elevation and flood down hillsides and valleys, forming frigid pools in depressions and low terrain. Unlike the frost masses, flood frosts usually whisper as they roll down the hills and valleys at night, stirring dead leaves in passing and blackening low-lying vegetation with their touch.

Flood frost is a form of atmospheric motion known as katabatic flow.

Katabatic Frost

We have put up more information about preventing frost damage on the NZWIG website.  There are some links to other material, and there is an edited version of a useful 1971 article from the DSIR by E.W. Hewitt.

Actually it seems that there is not much any of us could have done to prevent major damage from the advection frosts but there are some helpful ideas for less severe events.

Zinc Foliar Spray?

Zinc Foliar sprays Help..

Our Zi levels in our (01Feb-sampled) leaf samples have gradually fallen at ~ 5ppm per year from 30ppm in 2006 to 20ppm in 2008 so we have decided to act.  We are keen to try foliar spray and intend to mix with mankocide (so no ‘spraying cost’) and spray in Nov or Dec.

The best guidance we currently have is http://walnutresearch.ucdavis.edu/1993/1993_196.pdf and this seems a little dated (1993).

Has anybody tried to elevate Zi levels with foliar sprays.. did it work (what product/rate etc)?  Were there any ‘issues’.. phytotoxic effects?

Any data, information, knowledge or wisdom out there?

[message relayed here on behalf of Clive]

Where to get Diameter tape measure

Thanks to Heather North who has passed on this link to where we can buy Diameter Tapes [http://www.geosystems.co.nz/Category/67,11,57/Diameter-Tapes.aspx].  This is the best (most efficient and accurate) tool for measuring the growth of our trees.

The tape gives you a diameter measurement rather than the circumference.  Remember, we are measuring trees at 600mm above ground level.  Use the webform to send in your data so we can add it to the benchmark project.

Graeme

Measure that girth!

The benchmarking project has had a real boost by contracting Ivan Barnett to liaise with orchardists and carry out some field work.

May is the month for measuring trunk diameters. All orchardists can do this, and the more that do the better. By comparing the growth of trunk diameter per year with other orchards through the benchmark project each orchardist can gauge how effective their management is at promoting tree health and growth. This helps each of us develop best management and learn what walnut trees respond to.

To contribute data to the project orchardists should randomly select 25 trees of a particular cultivar and age from a given block, note these trees for future reference, and measure the trunk diameter at about 600 mm above ground level. For smaller trees the easiest way is to use a vernier caliper (see the photo) available for a few dollars at hardware shops. Plastic calipers are ideal as they are less likely to damage the tree bark. For larger trees use a tape measure (such as a dress-makers tape) and record the circumference in millimeters. We then convert the circumference measurement into diameter (mulitply by 7 and divide by 22).

Measurements should be recorded in millimeters (no decimal places). Orchardists can then find the average for their block by adding all the diameters and dividing by the number of trees.

Perhaps the easiest way to add your data to the research project is to simply enter it directly on the webpage: www.walnuts.org.nz/benchmarkdata.html – alternatively it can be recorded on paper and sent to Ivan Barnett, 5a Waterholes Road, Springston, Christchurch. Please include your name, location, block sampled, cultivar type and tree age.

We will focus a little more on this at the AGM in June.

NZWIG AGM Notice

New Zealand Walnut Industry Group: Annual General Meeting
(up-dated)

Sunday 15 June, 2008

11am – Demonstration and presentation on benchmarking.

Learn how easily you can contribute to this important project.
Presenter: Graeme Nicholas.

Location: Frank and Margaret Brenmuhl’s property 129 Station Road, Aylesbury

Turn right onto Station Road (at Aylesbury corner) off the Main West Coast Road (as you’re heading away from Christchurch).

12.30pm – BYO lunch at West Melton Hall.A chance to talk to others in the industry.

1.00pm – Annual General Meeting

Decision on importation of walnut cultivars
Presenter: Clive Marsh Chair NZWIG Research Committee
AGM
Reports from committees
Report from Chair of NZWIG
Election of officers
General AGM business.

Tissue Culture

For those interested in finding out a little more about tissue culture (to be discussed at the forth-coming AGM as a way of introducing new cultivars to NZ). There is a useful introductory article with pictures here on the Texas A & M University website. It starts:

Tissue culture (often called micropropagation) is a special type of asexual propagation where a very small piece of tissue (shoot apex, leaf section, or even an individual cell) is excised (cut-out) and placed in sterile (aseptic) culture in a test tube, petri dish or tissue culture container containing a special culture medium.

Click here to find out more.

A warning on root rot

Probably the greatest threat to the survival of walnut trees is a root rot, probably a phytophthora fungus.  It is not unusual for orchardists on heavier soils to lose a few trees.  We had a reminder recently that even older trees are vulnerable.  It appears that several trees in the Lincoln University trial block may be suffering from root rot.  They are still alive, but may not survive.  We have lost trees to this disease in that block before.  It is a reminder not to over irrigate.  Walnuts do not like wet feet.  In our anxiety to maximise growth and influenced, perhaps, by so many dairy and cropping farmers pouring water on throughout the summer we can easily be tempted to over do the water.

Graeme

Benchmarking – estimating yield

The benchmarking project enters a new phase over this year. We are keen to get data on the ultimate benchmark, how productive our trees are being. There are two ways of knowing how good our management of our orchards is. For younger trees the most effective measurement is trunk diameter (we measure it at 600mm above the ground). For older trees we are interested in the production of nuts at harvest. Some orchardists have been keeping records of production for years, now we are going to systematically collect yield data into the benchmarking project so we can establish what production might be expected for particular cultivars of particular age.

This year we trialled a way of estimating the final crop by counting measured parts of sample trees in January. Now we need to find out what yield actually came from those trees and so we can work out how good our estimation method was.

Currently our benchmark coordinator, Ivan Barnett is working with the selected orchards on yield, and he is preparing orchardists for the benchmarking event this year – measuring trunk diameters, in May-June.

Ivan will be contacting a range of orchardists to see if they are willing to be involved.  If you are interested, contact Ivan (033295986).

Graeme

A place to enquire and discuss

We have added a new page to Chatzone. It is designed to encourage walnut related discussion, questions and interaction in an open forum. Check it out. You will see the tab at the top of the page, Discussion. You may have a response to someone’s question, or a question or observation of your own.

Blight Counting – 2008

The NZWIG Newsletter is out. It contains this article about blight counting this year.

Blight researchers have been out checking the prevalence of our most significant management challenge. TreeCropper reports that NZ Tree Crops Association members recording blight levels in Waikato found that Shannon was by far the most blight resistant of seven varieties they tested. The walnuts were on Nick Empson’s organic property at Pirongia.

The group found Serr to be the most prone to blight, though in a low blight season it could easily out produce the other varieties.

In Canterbury, members of NZWIG’s research team did their annual mid-January assessment and found a very significant difference in the incidence of blight on Rex and Meyric with Rex averaging less than 20 per cent and Meyric more than 40 per cent. The team had to accept a smaller sample this year because a severe frost in mid-October cut production and there were fewer orchards with enough walnuts to count. The project’s coordinator Graeme Nicholas says they counted the incidence of blight and estimated the potential yield, but need to go back to calibrate the actual yield at harvest time.

You can find the whole newsletter, and past issues, on the main NZWIG website, here.