Allium white rot biostimulation project-Part 2
The overall goal of our ongoing project is to continue biostimulation in the selected raised “SARE” beds at Whitehill Farm, using on-farm materials, to reduce the presence of the fungus Allium White Rot (AWR). We hope to be able to demonstrate a management strategy, working within the normal 4-year rotation recommended for organic farms, that will allow allium production on a farm that is coping with AWR.
AWR attacks all members of the allium family (onions, leeks, garlic, etc) and when it matures produces tiny (the size of poppy seeds) hard fruiting bodies called sclerotia. If AWR is established in farm/garden soil it has a dormancy period of up to 25 years and cannot be removed or controlled with any method that is approved for organic production. Biostimulation is a method of awakening the dormant sclerotia without the presence of actual plant material. Without host plants the sclerotia then die, thus reducing the amount of the pathogen.
I continue to check in with Dave Fuller – my University of Maine Cooperative Extension agent – as he and Dr. Steve Johnson, also at UMaine, are working on another garlic project. Their project is long term, working to develop production of certified disease free seed garlic. When the opportunity arises I bring Dr. Johnson up to date. Dr. Fred Crowe, Emeritus, Oregon State University, continues to be a great source of information and support. We have had periodic phone conferences where I bring him up to date on my project and he makes any recommendations he feels could be of help.
2013 and 2014 were years where we continued the applications of biostimulants, obtaining annual lab reports, and planting non-allium crops in the “SARE” beds. All our activities proceeded as in previous years.
-In the spring, when the soil warms enough to be worked, we take the soil samples. This is conveniently the time that we can do the preparation for planting crops for the year.
-Non-allium crops are planted, mulched, side-dressed, and harvested later in the summer and early fall.
-In the fall the beds are cleaned and mulched for the winter.
We are using two forms of biostimulation, garlic juice applied with water and ground up plant material from the previous years crop. Both biostimulants are applied and thoroughly dug into the soil. Each raised bed is divided into three sections, with wooden partitions, and the biostimulants are applied using the same pattern that we used for applications during our previous Farmer Grant: one section receives the garlic juice, one the green material, and one receives nothing, as a control.
Our main activity continues to be maintaining sanitation protocols. When working in the “SARE” beds every hand and tool is washed between sections. Every weed is destroyed or composted in place. Work is done on dry days to limit moving soil with boots, and when necessary we add boot washing to the regimen.
This coming spring (May of 2015) we will plant test crops in all sections of the “SARE” beds. The crops will be a mix of spring onions (scallions), which will be removed early in the growing season, and storage onions, which will come out in mid/late August. We’ll plant the two crops in an alternating pattern, like a checkerboard, evenly across all the sections.
Our expectations include: that many if not all of the storage onions will be infected in the control sections; that there will be spot infections in the treated sections; it may be possible to get a clean crop of spring onions in many of the sections.
Spring onions may in fact prove to be a biostimulant crop in and of themselves. And, given the short growing time for them, we hope to show that it is possible to have them out before they are infected.
Each spring we are taking soil samples from all the beds and sending them to Nematodes, Inc., a lab that performs an assay of the AWR sclerotia in each sample. Comparing the initial three lab reports we saw a significant drop in the number of sclerotia in all the treated sections.
In the spring of 2014 we again took the samples and sent them to the lab. The results show that in most of the treated beds there continues to be a reduction in sclerotia. However in five of the beds the results are inconsistent as there is an slight increase in the number of sclerotia (literally single sclerotia detected and one germinated).
From this I can make two interesting initial assessments: one, that the sampling difficulty continues to be demonstrated; and two, that the majority of the sections showing the increase are sections being treated with garlic juice.
Please see the attached chart and comments sheet.
Soil sampling is usually done by taking samples from several places in the plot, using a grid pattern, and mixing these to create the final sample for analysis. The difficulty we are experiencing is that we cannot be sure of getting a fair sample that is truly random. Even though we are digging in different places each time, and being sure to dig to a depth of between 8 and 10 inches, catching a fair sample of the tiny sclerotia is difficult. It is our hope that, with five sets of lab results, the variations will be averaged out and we can reach some conclusions.
Perhaps the hardest thing that happened this year was the loss of two more beds despite our care with sanitation. Apparently sclerotia were moved somehow (by rain, tools, hands, etc), and alliums were definitely infected with AWR. One bed (Cassie) was affected only in spots, but because of its location we destroyed it (removed the soil to a safe place for disposal, including several inches below grade, and burned the wooden sides), replaced the soil and grassed it over. The second bed (A7) was also affected in spots and we decided that it too needs to be destroyed. That will happen this coming spring (May of 2015). A third bed (D11) was affected in only one spot and we removed that plant, the adjacent plants, and the soil to a depth of 15″ (following Dr. Crowe’s and Dr. Johnson’s recommendations). That bed was refilled with clean soil. Since there will be no allium crop there for four years, we will do a biostimulation program there in the interim.
Impacts and Contributions/Outcomes
Even though we will not be able to draw conclusions for several months, I feel we have made an important and continuing contribution to the gardening community here in Maine. For four years I have been speaking – sometimes formally, more often in conversation – about the dangers of AWR. This is an emerging problem in Maine and most gardeners just don’t know about it. So I am taking, and will continue to take, every opportunity to open or continue this discussion. It is important that every gardener who grows garlic knows how to recognize AWR, how not to SPREAD the problem, and how to ask for help from the University of Maine labs. Most important is understanding how to avoid the problem in the first place.
When we have completed our study our goal is to have some AWR management suggestions for farmers and gardeners. I’ll report our final results in several places: through MOFGA and NOFA; through Adult Ed; at garden club talks; and at Open Farm Day.
UMaine Cooperative Extension
138 Pleasant Street
Farmington, ME 04938-5828
Office Phone: 2077784650