Effects of Fumigant Alternatives to Methyl Bromide on Pest Control in Open Field Nursery Production of Perennial Fruit and Nut Plants

Authors: Schneider, Sally; Hanson, Bradley

Submitted to: HortTechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/20/2009
Publication Date: 9/1/2009
Citation: Schneider, S.M. and B.D. Hanson. Effects of Fumigant Alternatives to Methyl Bromide on Pest Control in Open Field Nursery Production of Perennial Fruit and Nut Plants. 2009. HortTechnol. 19:526-532.

Interpretive Summary: California producers of perennial crop planting stock such as fruit and nut plants must meet stringent regulations to ensure that the nursery stock is free of economically important nematodes. Currently, these growers depend upon preplant fumigation with methyl bromide to meet this requirement. Because methyl bromide is being phased out due to its deleterious effect on stratospheric ozone, alternative fumigants and application techniques are needed by this industry. The research reported in this paper was conducted to test pest control efficacy and crop safety with several currently available alternative fumigants as well as a new active ingredient material in a fruit and nut plant nursery. Fumigant treatments were applied in the fall with traditional shank-injection equipment and a variety of tree, vine, and cane berry nursery stock was planted the following spring. No fall treatment with any fumigant caused injury to the spring-planted nursery stock. Several alternative chemicals provided statistically similar control of nematodes, pathogens, and weeds as the methyl bromide treatment; however, only methyl bromide reduced nematode populations below detection limits. Untarped fumigant treatments generally did not provide adequate pest control for perennial crop nurseries. Combinations of iodomethane and chloropicrin provided similar pest control to the only currently registered methyl bromide alternative although usually not as good as methyl bromide.

Technical Abstract: Producers of deciduous fruit and nut trees and vines rely on preplant fumigation to meet regulatory requirements designed to ensure nematode free planting stock. In the past, preplant treatments with methyl bromide or high rates of 1,3-dichloropropene were the preferred treatments. However, the phase out of methyl bromide due to environmental concerns and evolving regulations on the use of 1,3-dichloropropene has increased the need for effective and economical alternative fumigation treatments in open field nursery production. A field trial was conducted in a commercial nursery to test weed and nematode control with several tarped and untarped preplant applications of 1,3-dichloropropene, chloropicrin, and iodomethane in comparison to methyl bromide. Crop safety and nematode infestation was evaluated on a wide range of tree, vine, and berry nursery stock. No fall fumigation treatment in this study caused measurable injury to spring planted nursery stock. There were few statistical differences between methyl bromide and the other fumigation treatments in crop establishment, crop quality, or nematode populations at planting five months after treatment although some untarped treatments had detectable levels of the root-knot nematode. At grape and berry harvest after the first growing season, few statistical differences were noted in nematode populations isolated from roots; however, only methyl bromide had non-detectable nematode levels in all varieties. The highest nematode levels were usually found in untarped iodomethane:chloropicrin and untarped chloropicrin plots. At tree harvest 26 months after fumigation, root-knot nematodes were isolated from the roots of highly susceptible tree varieties in several iodomethane:chloropicrin treatments and in chloropicrin alone plots. Untarped applications did not provide commercially acceptable control of weeds or root-knot nematode in this trial. Tarped applications of 30:70 and 50:50 iodomethane:chloropicrin provided nematode control similar to 1,3-dichloropropene although not as good as methyl bromide. Iodomethane:chloropicrin combinations have been registered in other states and should be considered for use in California perennial crop nurseries as an alternative to methyl bromide.