Trunk Disease Management for Eastern Grape Growning Regions

We often discuss about diseases on green tissues such as downy mildew. Do some of disease pathogen capable of infecting woody tissues?  Yes, they do. Some of the examples are: Botryosphaeria canker (as shown on the picture above), Petri disease (aka Esca, leaf symptoms pictured below), Crown Gall, and Eutypa dieback. In addition, some of the other pathogens such as Phomopsis are also capable of infecting woody tissues.  These diseases typically cause damages to the infected vines in a long timespan. Thus, the infection today may not cause any obvious damage until a few years from now. Moreover, these pathogens act more like a “silent killer” and can shorten the life of the vine by 5-10 years. Thus, the prevention of these diseases will benefit you in a long run. On the other hand, if you have younger vines (up to 5 years or so), these diseases can progress rapidly and cause a decline of the infected vine within a year or two. Since these pathogens limit the movement of water and nutrients by infecting xylem and phloem, typical symptoms of these diseases are discoloration of leaves and shoots. 

So, how these pathogens infect grape vines? Since grape has a thick bark, there will be very low probability of these pathogens infecting healthy bark tissues, invade through cortex, phloem, cambium, and xylem tissues.  Instead, they are more likely to start an infection from exposed woody tissue, such as injury on trunk, or as you guessed, pruning wounds.

The common questions I have been asked are about chemical management strategies.  Pruning wound treatment has been discussed in different places and with different contexts. In California where Eutypa dieback is a big issue, they tested a wound paste with boron.  They used Biopaste, which was not a product in the US, but now we have a product called B-Lock (Nutrient Technologies, CA).  These pastes protect wounds from the infection by Eutypa and Esca. In Australia and New Zealand, they have tested a product called Garrison, which seems to work as well. However, Eutypa is relatively a minor problem in VA. The survey of wood canker diseases by Dr. Phillipe Rolshausen (one of the authors of the article above) in 2008 could not find a positive Eutypa case from VA samples.

In addition to the paste, there are two fungicide treatments that have been registered.  One is Topsin-M which has a special local use label for VA, and the other is Rally, which has a supplemental label for pruning wound application. These will be applied as a paint-on or as a spray.  Please see the labels for detailed rate and application information. One of potential advantages of Topsin-M is that it works well against Botryosphaeria that is very common in VA. If you decided to use these materials, you need to obtain the labels.  Please click the links above where you can find the label for special local use for Topsin-M and supplemental label for Rally.  You need to have these labels prior to the application.  Please note that Topsin-M has a 2-day REI. 

(Note:  I am interested in setting up demonstration plots for these paste and fungicide treatments, so, please contact me if you are interested in participating in it.)

The other regular wound paints, such as latex paints, are also used commonly (which does not require a registration), but the general consensus among growers (not only grape but also other crops) are that the paints are not very effective. Another alternative method that has been discussed is a fungicide application as you would during the regular season, but we do not have any materials registered for such use. Moreover, it seems that the efficacy of the spray is not consistent and does not last very long.

Therefore, my recommendation is that we need to go back to the basic, the use of the cultural practice. The fungi and bacteria that cause diseases on grape require a certain temperature range and more importantly, a wet surface. Thus, if the pruning wound is dry, there will be fewer chances for the pathogens to infect the tissue. The rain will also initiate the pathogens to release spores, so, it is very important to avoid rain.  Please check the weather forecast before pruning and make sure you will get sunny days to ensure the wounds will be dried out in a few hours, and there will be enough time for wound to heal. You may also want to avoid pruning during the late afternoon because once the night falls, temperature drops and relative humidity increases, then wounds will not dry out for an entire night until the sun comes up.

It depends on other factors such as labor and your time, but if you can afford, you may want to pay attention to the timing of pruning.  In CA, they recommend growers to wait as late as possible because under cool weather, pruning wounds take more time to heal. It may take up to two weeks under low temperature range (40’s), and about one week in mild temperature (50’s).  The same principals probably apply to us.  We have much colder winter than CA, and I would not expect pathogens to be active in snow.  However, it will take longer for wounds to heal.

The other consideration is to practice double pruning, which is also listed in the article above.  The idea is to do pruning in two passes where the first pass in winter or early spring to conduct rough pruning and then the second pass in late spring to do final pruning. It has several advantages.  First, you do not need to spend long time under very cold winter weather to perfect your pruning. Second, it takes less time when you do final pruning because you do not have to move long shoots from the wires in the second run. Plus, third, even if the first pruning wounds take time to heal and infected, the second pruning will get rid of infected tissues.

Make sure your pruning equipment is clean. Your old trunk may be infected with the pathogens, and they may have already produced spores that can be transferred from one vine to another. I understand that it will be very time consuming, but what you can do is make a 10% Clorox solution (10:90 Clorox:water solution) in a bucket, and dip your equipment between vines for 1-2 minutes. Or get 70% alcohol (rubbing alcohol) and spray onto the pruner.  It is probably not practical to do it all the time, but you can do it after pruning heavily infected vines and/or after each row or section.

We also recommend keeping vineyard clean of debris.  Many wood canker pathogens can survive on dead tissues, especially Bot. canker.  Thus, it is ideal to remove pruned woods out from your vineyard to be composted (FYI, it will take a long time to compost woody tissue), or to be burned.  The other option is to bring pruned woods to the row-middles and run them over with a bushhog or mower. Hopefully, it will speed up the rate of decomposition.  If you make a big cut, say from re-training of a cordon, it would be the best to remove the old cordon out from your vineyard.  There will be no benefit from keeping the old dead tissues in your vineyard.

Pruning surface shape and orientation are also important, especially when you make a big cut. If you make it flat and level, it can hold water. Thus, it is recommended to make a slant surface so that if there is rain, water will not stay on the surface.

Last, but not least, I would like to mention about Phomopsis cane and leaf spot.  The pathogen of this disease infects canes in previous years, and produces spores on it during following growing seasons.  Thus, if you have infected canes nearby new shoots, it will make it easier for the pathogen to infect it, especially when the new shoot is coming beneath the old infected cane because spores drips down from the old wound with rain.  So, please pay attention to the relative orientation and distance between old and new shoots. Also, it gives you another reason not to keep dead old shoots on your vines. Many people have asked me about a dormant application of fungicide against Phomopsis.  It works, but it costs a lot, is harsh on equipment, and its efficacy is not that great. Therefore, unless if you had a recent outbreak of Phomopsis, the best management approach is to tighten in-season mancozeb application schedule to protect new shoots when shoots are about 1-inch long.

So in summary:
1.     The first line of defense is cultural practice

a.     Keep pruning wounds dry

b.     Double pruning

c.     Wait for warm weather for the final pruning

d.     Keep vineyard floor clean
e.      Consider pruning surface angle and orientation (esp. for a big cut)

f.     Sanitize pruning equipment, if possible

2.     Chemical management is also available

a.     Topsin-M or Rally for Bot canker and Esca (special labels are required)

b.     B-Lock paste which contains boron (known to work against Eutypa and Esca)

                                               i.     These options can come in handy especially when you make a big cut

c.     “Dreft” with 30% aqueous suspension (wt/vol) showed efficacy against Eutypa; however, we do not have a data on common trunkd diseases in VA such as Botryosphaeria canker

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