Challenges and limitations to methyl bromide alternatives
A number of technical and regulatory challenges limit the adoption of methyl bromide alternatives by the perennial crop nursery industry.
- Few alternatives available (with both Federal and State registration)
- Few alternatives meet California nursery certification requirements
- Current or pending regulations on available alternatives due to environmental quality or human health concerns
- Concerns over control of secondary (non-quarantine) pests
First, there are simply very few fumigant or non-fumigant nematicides available. In the US, only a handful of fumigants are registered including: methyl bromide, 1,3-dichloropropene, chloropicrin, dimethyl disulfide (DMDS), methyl iodide, and the methyl isothiocyanate generating compounds. Of these compounds, DMDS is not currently registered in California and has had only limited testing in nurseries. Methyl iodide (iodomethane) was recently registered in California; however, the available 50:50 mixture with chloropicrin has also had limited testing in the state.
Most of the methyl bromide alternative fumigants are heavily regulated due to concerns about human safety (workers, bystanders, neighboring populations) and environmental quality related to emission of volatile organic compounds (VOC). These concerns have led to a constantly changing regulatory environment related to buffer zones, required field preparation requirements, available compounds, and rate limitations on a field and air basin level. Industry uncertainty about current and pending regulations presents a continuing challenge in California.
Finally, although fumigation in the perennial crop nursery industry is driven by nematode certification, there are serious concerns that the level of secondary pest control provided by methyl bromide will not be matched by the alternatives. Weed control is generally not as reliable with many of the alternatives (reviewed by Hanson and Shrestha 2006). Although weeds can be addressed to a large extent with tillage, handweeding, and herbicides, there will certainly be economic impacts. More importantly perhaps, many nursery producers are also very concerned about the consequences of soil-borne diseases that are currently controlled with methyl bromide or methyl bromide:chloropicrin combinations. Reliance on alternatives with narrower pest control spectrums may result in problems with new diseases or the resurrection of old disease problems.