The Crush - January 2021 - 2

FEATURE STORY
equipment and tools should be maintained to produce clean cuts.
Mechanical pruning sometimes creates more " ragged " cuts that
do not callus well and leave more surface area for spore infection.
Recommended preventative practices are delayed or late
pruning, applications of pruning wound protectants and double
pruning. In California, pruning wounds are susceptible to
infection by fungal spores during the rainy season in December
and January. Delayed pruning, in February or March, can
significantly reduce susceptibility, as fewer spores may be
present, and pruning wounds can heal faster as vine sap flow
and seasonal growth begin.
Delayed pruning can be most cost effective as it requires no
additional cost to implement. But due to labor availability
and scheduling, especially with hand pruning, not all growers
can wait until February or March. Growers with mechanized
operations may be better positioned to use late pruning. Double
pruning involves two passes: one in December or January, often
with a mechanical hedger or pre-pruner, and a second pass in
March as the final cut to remove the section below the pruning
wound that may have been infected after the first pass.
Pruned and infected plant material should be removed promptly
to prevent development of GTD fungi fruiting structures in the
vineyard that produce spores.
PRUNING WOUND PROTECTANTS
Eskalen's research and recommendations focus on pruning
wound protection. Although total disease control is difficult
because of the large number of wounds on a grapevine and the
period of wound susceptibility, Eskalen said, " Pruning wounds
are the main entry point, and protecting wounds is essential
to preventing and reducing infection from GTD pathogens. "
He also advises protecting vine wounds resulting from other
viticultural operations, such as mechanical harvest.
Timing of pruning and applications of wound protectants in
relation to rain events can reduce infection risk by performing
these tasks during prolonged dry weather. The efficacies of
different pruning wound protectants can vary based on timing,
weather conditions and the fungal species present. More than
one application is commonly needed during the susceptible time
period, and combinations of protectants can increase efficacy.
Some protectants can be applied with conventional spraying
equipment - both tractor and hand application tools.
Eskalen's research lab conducted trials in 2019 and 2020 and
posted reports: Evaluation of Biological and Chemical Pruning
Wound Protectants Against Selected Fungi Associated with
Grapevine Trunk Diseases. These trials specifically evaluated
efficacies of protectants against E. lata and N. parvum. Three
2020 trials were conducted in Elk Grove, Delano and Davis.
More information is available at the Eskalen lab webpage, with

2 JANUARY 2021

Example of a clean cut. Pruning wounds are susceptible to infection by fungal
spores during the rainy season in December and January.

specific data from recent trials. Based on trials, Eskalen listed
the following available protectant options, and promising
experimental protectants, that show good results to date.
*	BIOCONTROLS: Bio-Tam, containing two Trichoderma species
(Isagro USA). Serenade, a Bacillus subtilis strain (Bayer Crop
Science). Vintec, a Trichoderma strain to control Esca from
Bi-PA was recently registered by the U.S. EPA but is still
experimental in California. Crab Life Powder, a blend of crab
and lobster shell powder containing chitin, is an experimental
protectant showing good results. GCM, another promising
experimental protectant, contains the gelatinase and chitinase
producing Bacillus velezensis.
* CHEMICAL FUNGICIDES: Topsin-M + Rally (Corteva) and
Luna Sensation and Luna Experience (Bayer Crop Science).
* SEALANTS: VitiSeal, a co-polymer emulsion with natural plant
oils (VitiSeal International). Spur Shield, a natural resin barrier
(Miller Chemical & Fertilizer). EMP Barrier is an experimental
co-polymer emulsion that has shown good results in
combination with VitiSeal.
Eskalen began research in 2019 funded by the American Vineyard
Foundation to collect and identify naturally occurring and
potentially beneficial microorganisms in grapevines from 20
vineyards in 10 counties in California. Cordon, trunk and root
tissue were taken from vines using nondestructive methods to
isolate, analyze and study endophytic bacterial communities
between healthy and diseased vines showing trunk disease
symptoms. Bacterial isolates from several genera, including
the genus Bacillus, are being tested in greenhouse and field
trials to evaluate those exerting the highest percentages of
inhibition against important GTD pathogens. Trials are also being
conducted at commercial grapevine nurseries with chemical and
biological products using a vacuum chamber to infiltrate the
fungicides into dormant cuttings prior to grafting.
" Naturally occurring bacteria live in plant tissue without causing
any damage, and some can secrete secondary metabolites that
inhibit harmful GTD microorganisms, " Eskalen said. He added,
" There is no single pesticide we can apply to address all GTD
pathogens. We are trying to come up with a biocontrol system so
the vine can have a defense from multiple pathogens. "
https://www.ucanr.edu/sites/eskalenlab/Fruit_Crop_Fungicide_Trials/
The Crush - January 2021

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