Do We Need to Sterilize Pruners?  
Jay W. Pscheidt, Ph.D.                                                                     


Professor of Botany and Plant Pathology and Extension Plant Pathology Specialist, Oregon State University                

In late May 2015, José Úrbez-Torres, Research Plant Pathologist, Pacific Agri-Food Research Centre, Summerland, Canada visited Oregon. Dr. Úrbez-Torres’ research focuses on identifying and managing grapevine trunk diseases. Trunk pathogens infect grapevines through injuries and wounds; even those made annually during dormant season pruning,. Prevention is the key to manage these diseases. Many growers came away from his seminar believing that sanitation of pruners was required.
Dr. Úrbez-Torres explained that it was a misunderstanding and that he was not recommending or promoting this practice. He did outline some recent research from Spain (Agustí-Brisach et al 2015) that showed that many of these trunk pathogens could be detected on pruning shears and could be transmitted to healthy vines through pruning, but the devil is in the details. The research group used a very sensitive technique (nested PCR) to find specific pathogens on the pruning shears. The technique can detect extremely small amounts of DNA that may represent a few pathogen propagules (such as live or dead fungal spores or mycelia). So, yes, the pathogens (alive or dead) can be found on shears after pruning an infected vineyard, but in very small numbers.
 
The research group in Spain also placed a huge amount of spores or mycelial fragments (ten thousand to a million) on pruning shears to see if just cutting a healthy vine with contaminated shears could transmit them to the wound. So, yes, at these high levels, pruning shears can transmit these trunk pathogens (with a frequency below 50% at the highest inoculum level). These inoculum levels, however, are far above would be found in a normal, practical situation. Given this information, Dr. Úrbez-Torres says the risk of transmission via pruning shears is “insignificant.”
 
I know there are those of you who are risk-adverse and will want to clean your pruning shears. If you choose to do this, here are some practical suggestions that will make this task both effective and efficient. First, you must start with clean and sharp shears. Cuts made with sharp shears heal much more quickly. Sharpen shears at every worker rest break. Most crews already bring sharpening tools since it is so much less tiring pruning all day with a sharp shears.
Disinfesting shears can be done with a wide variety of solutions but the key is starting with a clean pruning shear and using long contact times. Think soaking rather than dipping. I recommend you carry at least two sets of shears, one to soak and one to use while the other soaks. When you need to change the shears after every (insert your own tolerance statement) vine, row, section, vineyard, etc. place the used shear to soak in the disinfestant and pick up the one that has been soaking and continue pruning.
Although the bleach solution (10% Clorox – 1 part bleach to 9 parts water) that Dr. Torres mentioned is very quick and effective to oxidize pathogen propagules, it also oxidizes your shears – they rust! You can use other solutions as long as you soak for the duration mentioned above. This includes various alcohols (70% ethanol or isopropanol-rubbing alcohol), peroxides (OxiDate or ZeroTol), or quaternary ammonia (KleenGrow or Physan 20). Many of these products have labels to follow but other general cleaning solutions may also be useful. Change the solution frequently – each break, day, etc.
Managing grapevine trunk diseases will require more tactics such as a wound protectant after pruning. These tactics can be found at:
 
Bottom Line: No, you don’t need to sterilize or disinfest your pruning shears.
Reference: Agustí-Brisach, C., León, M., Garcia-Jimenez, J. and Armengol, J. 2015. Detection of Grapevine Fungal Trunk Pathogens on Pruning Shears and Evaluation of Their Potential for Spread of Infection. Plant Disease 99:976-981.

The sky is falling!

(Well, maybe not.)

Jay W. Pscheidt, Ph.D.
Professor of Botany and Plant Pathology and Extension Plant Pathology Specialist, Oregon State University

The new Compendium of Grape Diseases, Disorders and Pests (Wilcox et al 2015) points out the multitude of problems that can beset grapes. Oregon’s grape industry has done well to avoid many of these troubles using geographic isolation, unique climate conditions and planting stock quarantines. Grapes are still susceptible to all these problems, which could arrive and cause havoc on any growing season. When one of these problems does come along, we may sound a lot like “Chicken Little” declaring that the sky is falling. Several disease issues have fallen onto our doorstep that need to be discussed. Although some are very serious and not unexpected, all can be dealt with. These issues include Xylella, sterilizing pruners, fungicide resistance and climate change, which we will address throughout the season.

Xylella

In October, 2015, the presence of the bacterium Xylella fastidiosa was confirmed by the Oregon Department of Agriculture (ODA) in several pear trees growing in the field germplasm collection at the USDA Repository in Corvallis. Grape growers may be alarmed knowing that Pierce’s Disease is caused by Xylella fastidiosa subsp. fastidiosa. Pierce’s Disease has been a high-profile and rapidly increasing disease in California and other southern states but has not been known to be in the Pacific Northwest. At this time, the preliminary DNA sequence data suggests the bacterium on pear is X. fastidiosa subsp. multiplex, which can cause a chronic leaf-scorching disease in many different species of woody landscape shrubs and shade trees, including oak, elm, and other trees – but not grape. (Whooh!)

There are still a ton of questions that need to be answered in the coming months and years about this find. Keep half an ear open on this problem.

Why don’t find Pierce’s Disease in the Pacific Northwest? Our climate may be too cold for the pathogen to survive. Infected grapevines do not retain the pathogen after a cold dormant season typical of continental climates. Also the majority of leaf hoppers (xylem feeding insects that vector the bacterium) found in PNW surveys are Western grape leafhopper which are not efficient vectors of Xylella. The Blue-green sharpshooter will vector Xylella and has been found in the Willamette Valley, Columbia Gorge, Medford and Milton-Freewater areas of Oregon. This leafhopper is usually found in surrounding vegetation but less in vineyards. The glassy winged sharpshooter, a very efficient vector, has not been found in or around Oregon vineyards nor is it abundant in the PNW.

If you are still worried, you can keep an eye out for various symptoms. Pierce’s Disease first appears as water stress in midsummer and gradually gets worse. Leaves become slightly yellow or red along margins in white and red varieties, respectively, and eventually leaf margins dry or die in concentric zones. Fruit clusters shrivel or raisin. Dried leaves fall, leaving the petiole attached to the cane. Wood on new canes matures irregularly, producing patches of green, surrounded by mature brown bark. ‘Pinot Noir’ and ‘Cabernet Sauvignon’ have highly regular zones of progressive marginal discoloration and drying on blades. Unfortunately, any other problem that blocks, inhibits or limits water from getting to the leaves will produce similar symptoms. Fungal cankers, damaged trunks, girdling roots, gopher damage, herbicide injury and root rots also can produce similar symptoms.

Bottom Line: Finding Xylella on pears in Oregon is not, at this time, a worry for grape growers.

Reference: Wilcox, W. F., Gubler, W. D. and Uyemoto, J. K. 2015. Compendium of grape diseases, disorders, and pests. Second edition. St. Paul, MN: APS Press.