March 2022 - 11

Image 3. Severe spur damage on a muscadine vine in Clarksville, Arizona, in May 2021
following temperatures of (-) 15° F on Feb. 16, 2021. Photo: Margaret Worthington
ground, including 'Carlos' and 'Noble,'
following temperatures of -20° F during
February 2021 at the University of
Arkansas Campus research farm, 90 miles
northwest of Clarksville in Fayetteville,
Arkansas (Image 6).
Previously, 'Carlos' has been listed
as " moderately cold hardy " in several
muscadine production guides. 'Carlos'
may not have been listed in the most cold
hardy category because of its tendency
to break bud early, which puts it at risk
for spring freeze or frost injury. In 2007,
'Carlos' experienced severe spring frost
injury and major crop losses in Eastern
North Carolina because it broke bud in
March and temperatures reached as low
as 25° F on April 9. Other cultivars that
broke bud later survived the April 9
freeze in Eastern North Carolina with
little impact, and in the cooler Piedmont
area of North Carolina, 'Carlos' went
on to produce a full crop that year
because it had not yet broken bud. Early
bud break has never been an issue for
'Carlos' production in Arkansas. In fact,
temperatures reached 28° F on April 22,
2021, at the University of Arkansas Fruit
Research Station, approximately a week
past the usual " frost free date. " Many
blackberries and peaches planted at the
station experienced severe spring freeze
damage, but all muscadines, including
'Carlos,' were still dormant at that date
and escaped injury.
In nearby Altus, where much of the
Arkansas wine industry is concentrated,
temperatures reached -8° F. John Post
of Post Winery stated that the temperatures
resulted in minimal damage to their
'Carlos' and 'Noble' crops, but
considerable plant losses to 'Sugargate' on
young vines.
" We lost about 25% of the 'Noble'
plants, but less than 1% of the 'Carlos,' "
said Post.
Previous observations of higher spur
cane damage on 'Noble' relative to 'Carlos'
reemphasize the superior cold hardiness
of 'Carlos' for production in the northern
muscadine growing range.
Winter cold hardiness is not solely
cultivar dependent, but is also influenced
by the stage of crop dormancy. As plants
break dormancy, they lose cold hardiness.
Crops that are fully dormant and that
have been previously exposed to freezing
temperatures are likely to be more cold
hardy than crops exposed to extreme
Image 6. 'Carlos' muscadine vine in
Fayetteville, Arizona, with severe cold
damage that had no bud break in May
2021 and has been killed to the ground
following temperatures of -20° on Feb. 16,
2021. Photo: Margaret Worthington
The Arkansas Fruit Breeding
Program has taken this cold event as
an opportunity to advance processing
and fresh market breeding selections
that survived the cold event with little
damage and make new crosses among
cold-hardy material. It is hoped that these
efforts will result in the release of new
muscadine cultivars that are well-adapted
for production in areas that frequently
experience temperatures below 10° F,
including Arkansas, North Carolina,
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fluctuations in temperatures from warm
to cold. Prior to the extreme cold event
in February 2021 in Arkansas, there had
been consistent temperatures at or near
freezing for several days before and after
the coldest temperatures occurred on
February 16. This combined with the late
winter occurrence of the event meant
that all the muscadine vines were still
completely dormant when the sub-zero
temperatures occurred.
Of course, good plant health also
contributes to better plant tolerance to
extreme conditions.
The University of Arkansas muscadine
breeding program aims to select
muscadine cultivars with good winter
hardiness. While 'Carlos' and 'Noble'
survived the extreme cold temperatures
of Feb. 2021 with little damage, all
of the fresh-market cultivars used as
commercial checks of parents in the
breeding program suffered severe injury
and about 85% of the 5,000 seedling vines
planted at the Fruit Research Station were
killed to the ground.
Image 4. Muscadine vine with shoot collapse
due to injury to the vascular tissue in June
2021 in Clarksville, Arizona, following
temperatures of (-)15° F on Feb. 16, 2021.
Photo: Margaret Worthington
Image 5. View of 'Carlos' crop in
August 2021 following temperatures
of (-)15° F on Feb. 16, 2021, in
Clarksville, Arizona.
Photo: Amanda McWhirt
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FGN | MARCH 2022 | 11
2/17/22 11:51 AM

March 2022

Table of Contents for the Digital Edition of March 2022

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