Forest Nursery Management
USDA-ARS, Corvallis (Jerry Weiland, Pathologist and Project Leader; Anne Davis, Bryan Beck, and Duncan Kroese, Laboratory Technicians): Pythium species component and economic analysis
Weyerhaeuser Company (Will Littke, Pathologist, and John Browning, Pathologist): Fusarium species component and site characterizations
OSU Nursery Technology Cooperative (Robin Rose, Director and Marilyn Cherry, Associate Director): Transplant yield and morphology assessments
Washington State University-Mount Vernon NWREC (Tim Miller, Weed Scientist): Weed species component
University of Washington (Anna Leon, Graduate Student and Bob Edmonds, Pathologist and Advisor): Fusarium species component
Trident Agricultural Products (Mike Conway, Vice President and General Manager): Fumigation component
The problem addressed by this project was the need for stable alternatives to pre-plant soil fumigation with methyl bromide (MB) to control seedling damping-off and root rot problems in the forest nursery industry of California, Idaho, Montana, Oregon, and Washington.
Forest nurseries provide tree seedlings used to reforest land that has been harvested or destroyed by fire, diseases, or insects. In the West (California, Idaho, Montana, Oregon, and Washington), approximately 200 million seedlings are produced each year. The production of healthy, vigorous seedlings is (Fig. 1) critical to maintain forest health and productivity.
Tree seedlings are often adversely affected by damping-off and root-rot problems unless a successful soilborne pest management program is in place. Damping-off is a disease caused by soilborne fungi (Cylindrocarpon, Fusarium, and Pythium species) that kills seedlings soon after germination (Fig. 2). Root rot, caused by many of the same fungal species that cause damping-off, affects older seedlings and results in stunting or seedling death (Fig. 3). Competition from weed species also adversely affects seedling health and can severely impact productivity if weeds are not successfully managed (Fig. 4).
Currently, the forest industry uses an integrated pest management (IPM) program to manage soilborne weeds and pathogens. Seeds are initially disinfested before planting and irrigation is carefully monitored to ensure that seedlings receive the correct amount of moisture for growth. Excess water favors many damping-off and root rot pathogens. Therefore, proper irrigation and adequate drainage are essential. Fumigation also plays an important role and can help eliminate soilborne pathogens and weed seeds that are present before planting. Typically, a forest nursery field will be fumigated on a three year rotation. Each field is cropped for two years and then placed in bare fallow during the summer of the third year. After the bare fallow is complete, the field is fumigated in the fall and then planted to seedlings in the spring of the fourth year. The bare fallow practice maintains the field free of vegetation and helps to reduce the number of pathogens in the soil by depleting the food base (root residues) and by providing dry soil conditions, thereby negatively affecting the survival of many pathogens. Periodically, nonfumigant pesticides are also applied to seedling beds to minimize root infection and reduce weed competition.