"Eutypa" A.K.A. Grapevine Trunk Disease

Twenty years ago it was believed that dead arms and diebacks were cause by a single organism- Eutypa lata. It is now known that many fungi all cause the same symptoms and eventually kill the vine. The management of these diseases is the same.

The organisms responsible for trunk disease live in the vineyard year-round. Winter rain causes spores to be released. These spores enter the vine through unhealed pruning wounds eventually killing the vine and shortening the vineyards productive life by decades in some instances.


Practices to Prevent Infections

Delayed pruning
When the weather is cold, pruning wounds heal slowly leaving them open to infection. In December and January a pruning wound requires 2-3 weeks to heal. In February 1-2 weeks is required. Pruning wounds can heal in as little as 1-2 days. The later in the year a vine is pruned, the less likely it is to be infected by a trunk disease pathogen.
Double pruning
Since it is rarely practical to prune an entire vineyard in March, double pruning can help. Double pruning or “pre-pruning” removes the bulk of the dormant cane material mechanically or by hand. By leaving 12”-15” of cane behind after the first pruning pass any infections that occur will be removed during the second finishing pass by hand. Double pruning also speeds up the finishing pass as workers do not have to handle all of the pruning wood. This method is only practical for cordon trained, spur pruned vines.

Protectants include fungicides and pruning wound sealants. Sealants can be applied by hand with a brush, sprayed directly on the wound with a spray bottle, or applied with a traditional spray rig. Two poplar products are B-Lock and VitiSeal. Sealants should be applied the same day the pruning cuts are made if at all possible.
The two most commonly used fungicides are Topsin M (thiophanate-methyl) and Rally (myclobutanil). These products should be sprayed on the vines as soon as possible after the pruning cuts are made. Having some fungicide on the wound while it is healing will help protect vine from infection at that point.

Avoid Rain
Avoid pruning during or right before rain. The rain induces the fungi to sporulate. If a vine is pruned right before this sporulation it is very likely the vine will become infected because the wounds have not had a chance to heal.
Many growers have pruning programs with similar characteristics to make the execution of these practices workable. 
1. Pre-prune the vineyard by machine in December/January.
2. Final prune by hand in January/February/ March.
3. Send the pruning crews back down the row painting the cuts they made or have a smaller crew follow behind painting wounds.
4. Spray some combination of Topsin-M, Rally, and/or VitiSeal from a spray rig in the afternoon or evening after the pruning crew has finished for the day. Adjust nozzles to spray directly on the spurs and cordons.