Published in Fall 2024
By: Todd Anderson, OSU Extension Service Small Farms Program
Recognizing a “lost cause” and removing a loved tree or berry patch is emotional no matter how necessary you may know it is. This was going to be a PSA style article on Raspberry Bushy Dwarf Virus (RBDV), a common raspberry disease affecting home gardeners and small farmers in our region, and I will touch on it, but an affected grower’s response to my recommendations inspired reflection on how difficult removing something you cared for can be. I had recommended to “kill the patch and replant elsewhere”, they then told me “my heart sank when I read your email”.
1. Blueberry Shock Infected Blueberry Plant Photo credit: Field Guide British Columbia Blueberry
Recently I had to face my own realization that despite knowing the risk, I was avoiding removing a diseased plant. I was in denial that one of my blueberry plants had Blueberry Shock Virus (BSV), a growing issue in our region that spreads through pollen and unsanitized pruning equipment. It took a colleague visiting and pointing out what I already suspected for me to finally remove the plant. This heartbroken grower and my stubborn self are not alone. At our Small Farm Program pruning workshop in February the most common questions were related to saving unproductive and possibly diseased trees. Homeowners unwilling to remove clearly diseased and dangerous trees are not uncommon.
Keeping diseased plant material around is a poor sanitation practice. When you take stewardship of anything living, be it plant or animal, you also take responsibility for the wellbeing and safety of those around you. Diseased plants are not only your problem. Biology doesn’t care about property boundaries, and depending on how a disease is spread, that sick tree you are holding on to can spread to a disease throughout your orchard and to those of your neighbors, including farmers who depend on crops for their livelihood. If you suspect a disease, it is your responsibility to take measures to prevent its spread.
Some proactive steps would be following good sanitation practices, such as sanitizing tools between plants, pruning out diseased branches, appropriately disposing of diseased material, and planting or replanting disease resistant varieties. Best practices differ depending on the disease, and this article cannot cover every crop disease present in our region. We have numerous Extension resources on identifying what you are experiencing and your best management plan. See a list of resources included with this article.
Both Raspberry Bushy Dwarf Virus (RBDV) and Blueberry Shock Virus (BSV) are species-specific pollen spread viruses, meaning they respectively affect raspberries and blueberries exclusively. RBDV greatly weakens and kills off the raspberry plants, reducing the vigor of new growth as you can see in the pictures resulting in sickly and dying plants despite otherwise good care. BSV feels more insidious, most of the blueberry plants will recover, but the infected plants will continue to spread the virus to surrounding plantings and neighbors. The best general recommendation for RBDV is to kill off the planting and to avoid planting raspberries in that spot for a few years, then pick a new spot that has not had raspberries before and plant with new plants from a reputable nursery (disease free plants). When selecting the new location try to avoid spots that have had tomatoes, peppers, eggplant, potato, or blackberries in recent years just to avoid other diseases that can spread between these plants. We have a publication that goes much deeper into best practices. For BSV a similar recommendation is to remove infected plants and rotate into cover crops or other plants that do not share similar diseases for at least three years. This rotation is in consideration of other diseases present and to ensure leftover blueberry plants are not flowering and spreading the virus into a new planting.
2 & 3. Examples of Raspberry Bushy Dwarf Virus Photo credit: Bernadine Strik
Unproductive fruit bushes, patches, and trees occur for a variety of reasons, often being improperly pruned or unpruned for a couple seasons. When planning how you will approach this issue, your personal goals and needs are important considerations. For instance, in the home garden, you may have an old plum tree with no visible disease that may be generally unproductive, but provides valuable shade and enjoyment. Poor yields may not be a reason to fire up the chainsaw and wood chipper.
On the flip side, in a commercial operation, if the tree is unproductive and it will take too much effort to bring it back into production, replacement and removal is often the recommendation which even commercial growers struggle with. When I was working at the California Polytechnic State University San Luis Obispo orchards, my boss talked about why ultra high density avocado orchards often didn’t perform as planned outside of the research orchards. Ultra high density avocado orchards were developed to make the most of often small properties in Coastal Central and Southern California, areas with some of the most expensive land and water in the country. To be financially viable, avocado orchards needed to maximize water and space efficiency. In an Ultra High Density Orchard trees are planted extremely close together and full production is reached very quickly, helping to speed the return on investment. After a few years of production the trees are thinned, removing every other tree to allow for the remaining to continue to grow.
The problem was, the thinning process has growers cut down and mulch productive trees loaded with valuable fruit. Growers would often push off the thinning until the trees have grown to a point where the trees shade each other, reducing the orchard’s yield permanently and making thinning more difficult and even cost prohibitive. These growers are experienced and often very good at making business decisions to have stayed in the game this long, but it can still be very hard for them to remove trees even when it is the best course of action.
To have and protect our farms and gardens, we need to know when to remove a plant, even if we are emotionally attached to it. If you suspect a disease, try to narrow down the cause and act accordingly. Ask for help, this helps us keep tabs of growing problems so we can address them and keep the community aware. Often disease testing itself is cost prohibitive for the home gardener, there is that saying “When in doubt, cut it out”, and as a general rule, it is best to remove anything diseased even if you don’t have the confirmed diagnosis. Get your best diagnosis within your means and act accordingly. Most bacterial and fungal diseases can be pruned out, while viral pathogens often require the plant be removed. When it comes to unproductive plantings with no visible signs of disease, know your goals and your capacity. If you are growing for your household you have much greater flexibility than if you see your plants as part of a business venture. Like most hard decisions in life, being honest with yourself is the most important step.
Resources
Growing Raspberries & Disease Issues - https://extension.oregonstate.edu/catalog/ec-1306-growing-raspberries-your-home-garden#common-problems
Blueberry Virus Management - https://extension.oregonstate.edu/catalog/em-9518-managing-blueberry-viruses-pacific-northwest
Blueberry Field Guide - https://fieldguide.bcblueberry.com/blueberry-shock-virus/
OSU Plant Diseases - https://extension.oregonstate.edu/pests-weeds-diseases/plant-diseases
OSU Plant Clinic - https://bpp.oregonstate.edu/plant-clinic
Pruning Mature Trees - https://extension.oregonstate.edu/ask-extension/featured/pruning-mature-fruit-trees
Ask Extension - https://extension.oregonstate.edu/ask-extension