VALLADOLID, Spain, May 12 (UPI) -- Spanish scientists say the search for alternatives to ozone-depleting agricultural pesticides might be a more complex task than originally thought.

A widely used odorless, colorless gas -- methyl bromide -- was introduced during the 1980s to control weeds and increase fruit yields. But in 2000 it was classified an ozone-depleting substance, and in 2005 it was banned in the United States and the European Union.

Since then the Agrarian Technological Institute of Castile and Leon in Valladolid, Spain, has been studying new methods of weed-control in strawberry nurseries participating in Spain's Methyl Bromide Alternatives Project.

The researchers discovered several alternative chemicals consistently controlled weeds, but were less consistent in terms of plant yields. They also found some barrier films increased the performance and consistency of alternative pesticides, but environmental factors caused inconsistencies in weed-control at high-elevation nurseries.

"Replacements for methyl bromide will require more than one fumigant component, as well as a higher level of management of pest populations … during rotational crop production," said lead researcher Eva García-Mendez. Also, she, she said, EU restrictions may require the use of non-chemical alternatives in the near future.

The research was reported in the February issue of HortScience.