WineGrape Advisory - December 14, 2001
Andy Allen
Extension Associate - Viticulture and Small Fruits
(919) 515-3705
andy_allen@ncsu.edu
Hort Agents and Growers,
I have received some calls from a few growers in the Piedmont recently
concerned with bud-swell due to the unseasonable temperatures and what
can be done about it. The major concern at this time is bud and vine hardiness.
Any freezing or sub-freezing temperatures at this point can lead to some
damage or kill on vines that have swollen buds or even new shoot growth
(reported in Yadkin and Orange Co.). If, however, temperatures decrease
slowly over a period of time, vines should regain their hardiness, although
swollen buds may not become as hardy as they otherwise would have. If
the swollen buds or new growth are just on the tips of canes (where bud
swell typically first occurs in grapevines) and we gradually cool down
so that the rest of the vine regains its hardiness, then bud damage will
not have much impact on next year, since most of this wood will be pruned
off anyway. The chance of impacting next year's growth and crop will be
greater, however, if the swollen buds are also located at the base of
canes (wood that will provide fruiting spurs for next year) or on young
trunks or cordons.
Some of the growers I've spoken with have been advised to spray a 3% solution
of Stylet oil to retard bud swell. I've spoken with Dr. Tony Wolf at VA
Tech (whose program has been doing that work) and with Martie York, the
vineyard manager at Biltmore Estate (one of the sites where the work has
been done) about this and both have said that there are problems associated
with this technique. It has only been done experimentally with backpack
sprayers, ensuring a complete coverage of the vine, and not with tractor-mounted
vineyard sprayers. Delaying of bud-swell has only been successful with
the 3% solution, weaker solutions haven't worked. However, the 3% solution
has itself led to damage through phytotoxicity. Also, according to Dr.
Wolf, the response is very variety-specific. The short answer: It is a
technique with some promise for bud-break delay, but it has its own set
of problems and needs more research before it can be recommended as a
course of action.
Andy Allen
Extension Associate - Viticulture and Small Fruits
North Carolina State University
Campus Box 7609
Raleigh, NC 27695-7609
(919) 515-3705 - Phone
(919) 515-2505 - Fax
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