Management of Allium White Rot

Project Overview

Project Type: Farmer
Funds awarded in 2011: $8,301.00
Projected End Date: 12/31/2012
Region: Northeast
State: Maine
Project Leader:
Amy LeBlanc
Whitehill Farm

Annual Reports


  • Vegetables: garlic, leeks, onions


  • Crop Production: crop rotation, cover crops
  • Education and Training: extension, on-farm/ranch research
  • Pest Management: biorational pesticides, eradication, sanitation
  • Production Systems: organic agriculture
  • Soil Management: organic matter, soil analysis

    Proposal summary:

    The devastating fungus Allium White Rot (Sclerotium cepivorum) has arrived in Maine, and if left unchecked, will pose serious problems for both conventional and organic farmers. When this fungus arrives on a farm, by whatever means, the result is the same: total loss of crop in the affected area and the necessity of taking that land completely out of Allium production. Most of the garlic grown in Maine is grown on small farms, both organic and conventional, and the crop represents a significant percentage of farm income. To date there have been no East Coast studies targeting control or management of this fungus. After reading reports of early studies of a new technique, I propose to begin an aggressive program of biostimulation. This technique introduces an Allium stimulant into the soil to trick the disease into germinating, with no actual plant host, thus reducing the dormant fungal population. As a part of this program we are also developing strict sanitation protocols to prevent unintentional spreading of the sclerotia, and will rogue out any alliums that pop up (due to being missed while harvesting in prior years). I propose to test a biostimulation program, over the course of at least two years, with the goal of gaining management and/or control of Allium White Rot, in a 4 year rotation, in an infected certified organic operation. Biostimulation is a process where a product containing the chemical exudates necessary to stimulate pathogen germination is applied, and without actual plant presence, the completion of the life cycle is thwarted. The biostimulants that I propose to use are garlic juice, prepared on-farm, and ground up green garlic plant material (frozen on-farm, from previously harvested healthy plants). With four full replications, one of each treatment and a control, we will be able to compare pre- and post-treatment assays of the presence of the fungal sclerotia in the soil. The data will allow us to begin development of a management plan that can be shared with New England farmers and gardeners. The project will last longer than one year, but with assays of the fungal sclerotia present both before and after the each year of treatments, it will be possible to streamline subsequent treatments, and eventually to achieve a level of infection that is manageable. Presentation of the results of our first, and subsequent years research, will be made through the University of Maine Cooperative Extension newsletters, at MOFGA and NOFA events, in the newsletters of both organizations, and at our farm during Open Farm Day.

    Project objectives from proposal:

    Since Allium White Rot is so persistent, and biostimulation is not guaranteed to make a 100% clean sweep with one application, this project will last more than one year. The initial season should indicate which of the 2 treatment methods works the best, and subsequently I am prepared to treat my growing beds for at least 4 more years, in rhythm with my normal crop rotation.

    In the early spring of 2011 I will need an assay of dormant sclerotia in each plot to determine a baseline. At the end of the first growing season each plot will by assayed again to indicate initial efficacy. A second assay after winter (to ensure dormancy, in early spring 2012) will more accurately show remaining dormant sclerotia.

    Assays will be performed at Nematodes, Inc., in Selma, CA. This lab is recommended by Bruce Watt, Ph.D., University of Maine, and by Robert Ehn, of the California Garlic and Onion Research Board. The lab protocol is very specific about sampling depth, timing, storage, and shipping, and the methods used to ascertain levels of viable sclerotia.

    I’ll then commit the time and effort to biostimulate the beds repeatedly, both in the early spring and during the growing season, for 4 years. In year 5 of the rotation (2015) garlic will be growing in the plots and we will have a final assessment of the program.

    One pertinent aspect of our farm is our hill. We have moved to wooden sided raised beds because of the slope, primarily to prevent erosion. The original pathogen was “planted” (via seed garlic purchased from an out of state source) in the fall of 2004, in a bed at the top of the slope (C2). In July of 2005 we identified the disease, and in an attempt to isolate it, planted the bed to a perennial herb crop. It has been undisturbed, at least by tools or tilling, since then.

    We will prepare the beds with known pathogen for treatments by dividing each bed into three plots, separated by deep wooden barriers. Two plots of each bed will be treated with a biostimulant, and one plot will be left untreated as a control.

    We’ll use two biostimulant treatments: garlic juice, and ground green garlic plant material (frozen from last season). The products will be worked into the soil of the designated plots, to a depth of 6-8”, and then watered in. We’ll then plant normal crops – other than alliums – in the beds. Any volunteers, missed from the previous season, will be rogued out as the season progresses. Dr. Crowe suggested that we apply a second treatment of garlic juice and plant material, via irrigation, in mid-season.

    The first treatment will be applied in the early spring when soil temperatures have gone above 50 degrees Fahrenheit. This should occur in late April or early May, well before our regular planting season. We’ll use soil thermometers to monitor soil temps prior to treatments. Then at the regular planting time, in late May, we will plant crops in the beds. We’ll follow our regular rotation pattern for the spring planting and in subsequent years. The second treatment will be applied in late August with irrigation water as was recommended by Dr. Crowe.

    Garlic juice will be prepared on-farm using a juicer, and will be applied, with water, at a minimum rate of 1 part to 1000, using an agitating sprayer. The recommended amount of product will be mixed in water, on a plot-by-plot basis, and sprayed onto the soil. The soil will then be hand cultivated, as if in preparation for planting, to a depth of 6-8”. The cultivation needs to be done immediately in order to limit loss of the allium exudates due to the their volatile nature.

    Applying green plant material will be done similarly on a plot-by-plot basis. We’ll use the material we have stored in the freezer (harvested from about 1,200 healthy plants in 2010, ground and frozen immediately after harvest). We’ll thaw and measure, dividing the available material by volume, and then spread a thick layer of material on each plot. Cultivation will take place immediately, to a depth of 6-8 inches.

    At the end of the first growing season we’ll collect soil samples to submit for assay from each of the 18 plots. And in the following spring (2012), when dormancy is ensured, we’ll collect and submit a second set of soil samples. This spring assay (2012) will provide a baseline for the second year program which will proceed along similar lines, with the same 18 plots, treatments, sanitation and roguing. Soil samples will be taken after the second growing season and the following spring (2013) for assay and analysis of results.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.