Producing 85 percent of the nation’s strawberries, California growers urgently need alternatives to methyl bromide fumigation if they are to maintain yields. Methyl bromide has been phased out for all but critical uses because it depletes ozone in the upper atmosphere.

UC scientists now report that use of totally impermeable film in strawberry fields can improve the effectiveness of a widely used methyl bromide alternative known as 1,3-D (1,3, dichloropropene). Use of the film reduces the amount of 1,3-D needed to maintain yields, while lowering field emissions overall.

The strawberry industry is highly dependent on soil fumigation to control pests and maintain high yields. The methyl bromide alternative, 1,3-D, can be used only in certain quantities, due to air quality concerns.

In a recent trial, totally impermeable film (TIF) was laid out over Salinas fields to prevent the fumigant from leaking. The new film was compared with the standard film used by growers. Fumigant concentrations under TIF were 46 to 54 percent higher than under standard film, and the higher concentrations were correlated with higher strawberry yields and better weed control. Scientists report these findings in detail in the October–December 2011 electronic edition of the University of California’s California Agriculture journal.

Impermeable films have three benefits, according to lead author Steven Fennimore, UC Cooperative Extension specialist and weed scientist in UC Davis Department of Plant Sciences. The films trap the fumigant in the soil for a longer time and thereby increase its effectiveness; they reduce fumigant emissions, which after reacting with nitrogen oxides, can convert to ground-level ozone; and they reduce the amount of fumigant needed for effective pest control.

Emissions are a chief concern. Methyl bromide, a widely used fumigant in combination with chloropicrin, has been phased out since 2005 because it is an ozone-depleting substance targeted by the Montreal Protocol (a global treaty to control ozone depletion) and the U.S. Clean Air Act. However, it is still being used in some California strawberry fields under a critical-use exemption. Restrictions on the use of 1,3-D to 90,250 pounds per 36-square-mile township (called the township cap) leave few other options for growers in key strawberry production areas near densely populated areas.

Comparing TIF with standard film, and methyl bromide plus chloropicrin with varying amounts of 1,3-D plus chloropicrin, the scientists rated the effectiveness of TIF. The results, writes Fennimore, suggest that to achieve fruit yield and weed control similar to methyl bromide and chloropicrin, 33 percent less 1,3-D plus chloropicrin is needed under TIF than standard films.

TIF may ease some of the burdens of fumigant regulations on end-users, as well as ease concerns of the general public about exposure to fumigants, he concludes.

The entire October–December 2011 issue, and the electronic edition, can be viewed and downloaded at http://californiaagriculture.ucanr.org.

California Agriculture is the University of California’s peer-reviewed journal of research in agricultural, human and natural resources. For a free subscription, visit http://californiaagriculture.ucanr.org or email calag@ucdavis.edu.

Writers/editors: To request a hard copy of the journal, email crllopez@ucdavis.edu.