Research conducted by USDA's Forest Service, combined with the efforts of cooperators and the insight of nursery managers, could help develop integrated pest management programs that will be needed when methyl bromide is no longer available.

The impending loss of this chemical and the major concerns expressed by various commodity groups, including ornamental and forest nurseries, have underscored the heavy reliance on methyl bromide to provide broad-spectrum control for pest problems.

"The potential loss of methyl bromide has emphasized the need for a better understanding of the pest problems that affect forest tree nursery production in the United States and for the development of alternative strategies to prevent and control these problems," says Jerry Sesco, the Forest Service (FS) deputy chief for research.

Many nursery managers presently rely on routine fumigation with methyl bromide because of its broad-spectrum ability to control diseases, nematodes, insects, and weeds that can affect seedling production and quality, according to Sesco. A basic lack of understanding of how pest problems develop, uncertainty about the potential impactof certain pests on seedling production, and an inability to prevent and control pests through alternative practices essentially mean that fumigation is currently the nursery manager's best "Insurance policy" against potential problems.

"We're aggressively seeking to develop better integrated pest management programs that will provide nursery managers with the necessary information to manage complex pest problems through alternative chemical, cultural, physical, and biological cotrol practices," Sesco reports. "Our goal is to provide nursery managers with the best information possible to manage potential pests."

To accomplish this, the Forest Service is supporting research efforts at its laboratories in Athens, GA, and St. Paul, MN. In addition to the Forest Service's State and Private Forestry and National Forest System, cooperators include USDA's Agricultural Research Service, State natural resources agencies, universities, and commercial and industrial nurseries. Research collaborators are investigating alternative pest management practices and collecting information that will be used in developing integrated pest management (IPM) programs. Research efforts include collecting information on factors that influence pest outbreaks and developing alternative pest management strategies to prevent and control losses.

"Our strategy has been to focus on developing both short- and long-term IPM systems," says Stephen W. Fraedrich. An FS plant pathologist at the Southern Forest Experiment Station in Athens, GA, he and colleague L. David Dwinell are working with plant pathologists Jennifer Juzwik and Cynthia M. Ocamb, who are located at the FS North Central Forest Experiment Station in St. Paul, MN.

"In the short term, it is imperative that IPM systems are developed which will minimize or prevent the disruption to U.S. forest tree nursery operations because of the loss of methyl bromide," Fraedrich says. "Therefore, we're placing greater emphasis on the use and application of other soil fumigants as well as other pesticides for these short-term systems. However, because of increasing public attention to environmental and health issues, there are likely to be increasing challenges to using other chemicals in the future. For the longer term, we're working to develop cultural, physical, and biological pest management strategies as well as a better understanding of precisely when specific chemicals are needed."

In St. Paul, Juzwik and colleagues have refined application methodology of the chemical dazomet, enhancing its efficacy for field soil sterilization and control of root diseases in conifer seedlings.

"Root diseases caused by fungi such as Cylindrocladium spp., Fusarum spp. and Pythium spp. are a major problem facing forest nurseries," explains Juzwik. "In trials in the North Central States we've found dazomet as effective as methyl bromide in controlling root diseases, with no harmful effects on seedling quality." She and colleagues will work with Fraedrich and Dwinell from the Athens lab to refine techniques for use of dazomet in southern nurseries beginning this fall.

Researchers at the St. Paul station have extensively screened potential biological control agents to suppress the pathogenic soilborne fungi.

"Preliminary studies showed that applying selected bacteria, along with ectomycorrhizal fungi, protects containerized seedlings against various Fusarium fungi," Juzwik says. "We're also conducting bareroot nursery field trials with these same antagonistic, beneficial microorganisms."

Scientists at the Athens lab are studying seedborne fungi and their possible role in disease development in nurseries. Seed orchard and cone harvesting conditions are being studied because they may influence the establishment of pathogenic fungi with seeds. They're also evaluating the efficacy of a nonpathogenic bacterium, Burkholderia cepacia, that is reportedly antagonistic to some plant pathogenic fungi.

At both locations, FS scientists are examining ways to disinfest the surface of seeds with chemicals such as hydrogen peroxide as well as investigating potential biocontrol agents to suppress seedborne pathogens.

Efforts are also under way at both locations to determine the underlying causes of disease development. "Studies done in Georgia show that seedling quality was increased in some nursery beds by fumigation," explains Fraedrich. "But in other beds, we've observed no differences in seedling quality in fumigated and nonfumigated treatments. We want to know why certain fields remain productive without fumigation, while seedling quality is reduced and mortality increased in other nonfumigated fields."

The impact of fungi and nematodes on seedling production is of particular interest, he says.

"In the North Central States, soil-water management is critical in controlling root diseases," reports Juzwik. "Maintaining optimal soil moisture is a key factor in minimizing Fusarium losses in both fumigated and nonfumigated nursery beds."

"We have also examined the effect of bare-fallowing, which can control disease losses in the Pacific Northwest nurseries," she continues. "But we have found that this practice is not effective for the control of root diseases in the North Central States."

Future research efforts by the Forest Service will include assessments of

• soil solarization
  
  
• the impact of cover crops and organic amendments on soilborne pests such as nematodes and pathogenic fungi
  
  
• efficacy studies of other possible chemicals
  
  
• factors that influence the development of pest problems
  
  
• various combinations of chemical, cultural, physical, and biological pest control strategies.