- Vegetables: garlic, leeks, onions
- Education and Training: on-farm/ranch research
- Production Systems: organic agriculture
Producing a quality garlic crop organically in Maine is increasingly more difficult as diseases rarely seen before (Garlic Bloat Nematode and Garlic Rust) are becoming all too common. Allium White Rot (AWR), the deadliest and most persistent of all, is present in at least three areas of the state. AWR, caused by the fungus Sclerotium cepivorum, is the most devastating fungus most farmers and gardeners will ever encounter. AWR threatens the profitability of Maine farms, particularly those with small acreage. When AWR arrives on a farm, the result is certain: total loss of crop and the need to take the affected land out of garlic production, potentially forever. In 2011 we received a SARE Farmer Grant to begin a study of biostimulation as a potential management tool for AWR. Our project was designed to be concurrent with a 4-year rotation, with the intention of evaluating biostimulation as a viable way for small organic farmers to manage AWR. After two seasons and assays of the pathogen it is clear that we have made some progress. In order to complete the 4-year rotation intention and iron out some variables (not apparent in 2011), it will be necessary to continue the project for another two full growing seasons. In the spring of 2015 we will submit the final lab samples and plant an allium crop in all of the beds. We will then be able to make an analysis of biostimulation as an AWR management tool. Presentation of results will be made through UMaine Cooperative Extension newsletters to growers, MOFGA, NOFA, and at various conferences.
Project objectives from proposal:
Allium White Rot (AWR) is a persistent and destructive disease, with a dormant lifespan of up to 25 years. The dormant sclerotia (resting fruiting bodies) are typically scattered throughout the soil at an average depth of 8” making it very difficult to have an accurate assessment of the degree of infestation with any single test. As there is no guarantee that samples can be taken at the exact same spot or exact same depth for successive tests the testing needs to be repeated over a longer time, preferably several growing seasons. This will improve the accuracy of the results.
When winter temperatures in Maine put the AWR sclerotia into dormancy, it is possible to assay the amount of infection. The test results literally report the number of viable sclerotia in the sample. When the soil warms in the spring, to between 50 and 55 degrees, samples can be taken. After digging – in many places scattered over each plot (in a grid pattern typical of standard soil testing methods) – the samples from each section are thoroughly mixed, separately bagged, and allowed to dry for about 2 weeks. Drying reduces shipping costs and does not affect the sclerotia. Assays of dormant sclerotia have been completed at Nematodes, Inc., in Selma, CA, a laboratory highly recommended by Dr. Fred Crowe.
Allicin, the organo-sulfur compound that gives garlic and other alliums their typical odor, is present in all parts of the plant. Exudates from the roots of an allium plant will stimulate the sclerotia to awaken, infect the plants and carry out their life cycle, producing more sclerotia. Biostimulants work by providing the exudates without the presence of a live host plant, resulting in death of the sclerotia.
In the spring of 2011, 6 beds were prepped, divided, and biostimulant applications were planned with a fully randomized pattern, including control plots. The beds are separated in two different gardens, providing replication. This pattern was designed by Rick Kersbergen, Crop Specialist, UMaine Cooperative Extension. A vital part of this project was developing a strict sanitation protocol to prevent further spreading of the AWR sclerotia. The sclerotia are very easily moved by volunteer plants, on shoes, tools, plant supports, in compost, by rainwater. All volunteer plants were systematically rogued/removed. When working in a bed, hands and tools are
cleaned before moving on to a new section. In the fall all plant supports and tools are cleaned. The wash water is disposed of in a deep hole off site.
In May of 2011 we collected and submitted soil samples for an initial baseline assay of the amount of sclerotia present in the soil of all of the beds/sections. We then did the first years biostimulation: in 6 sections we applied garlic juice, diluted in water to a minimum of 1 part juice to 1000 parts water, and in 6 sections dug in a 2” deep layer of ground green garlic material ground and frozen after the previous years healthy harvest. The 6 control sections received no treatment. All 6 beds were then planted to non-allium crops respecting our crop rotation plan.
In the spring of 2012 we again collected and submitted soil samples, applied the biostimulants according to the original plan, and planted non-allium crops.
We will continue to document the Allium White Rot (AWR) project with a diary (cultivation, soil samples, applications and amounts, planting, harvesting, clean up, etc) and photo journal. By the spring of 2013 we will be able to make a preliminary assessment of results using the baseline, 2nd, and 3rd AWR assays. The 3rd assay will be done and available at the end of the first grant period, in the spring of 2013,at that time we will be able to draw initial conclusions.
Using the laboratory results from our first two years of treatments, we will be able to refine and implement the biostimulation plan for 2013/14 and 2014/15. The anticipated margin of error has been amply demonstrated by the first post-treatment soil test, and with that in mind we will be extremely consistent with our sampling technique and biostimulant applications. We will also follow Dr. Crowe’s current recommendation to apply a second spray, after cultivating, when applying the garlic juice.
In June or July 2015 we will receive the results of the last soil test. At that time we’ll be able to chart the progress of the project, beginning with the 2011 baseline AWR sclerotia assay and compiling the four subsequent test results. We’ll be able to show which of the biostimulant applications – garlic juice or green plant material – is more effective, as well as the overall effectiveness of biostimulation.
In the spring of 2015, as the ultimate test of the project, we will plant spring onions and storage onions in all of the bed sections. These crops will act as additional biostimulants and therefore also provide a bioassay of any remaining sclerotia. The immediate goal will be to remove the spring onions as a viable crop. The crop will show that, if there are any residual sclerotia present, the crop can be removed before it is infected.
In August of 2015, when the storage onions are harvested, we will have a physical demonstration of the efficacy of this program. We will send the harvested plants to Dr. Johnson and to Bruce Watt, University of Maine Plant Disease Diagnostician, for analysis and to confirm that they are or are not disease free.
Project Continuation Methods
Starting in early June of 2013 we will resume the process of applying biostimulant treatments, following our original plan.
We will continue to use garlic juice, mixed with water with a minimum of 1 part juice to 1000 parts water. According to Dr. Crowe’s current recommendations, a concentration where the odor of the garlic is strong will be fine. We will mix 4 tablespoons of garlic juice into a 4-gallon agitating sprayer. We’ll use the open nozzle of the sprayer to apply a steady stream of juice/water, while another person digs, turns over, and cultivates the bed until the soil is saturated. Per Dr. Crowe’s current recommendation, we will then spray the surface again to ensure that soil brought up from 8-10” is saturated. We will use ground green garlic plant material from the 2012 healthy crop as the second treatment. We will apply a 2” layer of the green material to the bed section, digging and turning the soil to a depth of about 8-10”, incorporating it thoroughly.
We will then plant the beds to crops other than alliums, respecting our regular 4-year crop rotation. This process will be repeated in 2014. During the growing season, harvest, and cleanup we will continue to follow our sanitation protocol, cleaning all tools, wheelbarrows, hands, plant supports, and shoes when moving from bed to bed. We will take soil samples and send them for tests in the spring of both 2014 and 2015. At that time we’ll have test results reflecting 4 years of biostimulant applications and will be able to chart and analyze results.
As a final demonstration, in 2015 we will plant a mixed crop of spring onions and storage onions in all the beds. The spring onions will serve as a further biostimulant and will provide a bioassay. The goal will be to harvest the spring onions before any remaining sclerotia can infect them. The storage onions will then serve to indicate any remaining infection and will be tested by Dr. Steve Johnson and the UMaine Plant Pathology laboratory for the
presence of AWR.