Methyl bromide substitutes screened

After evaluations of vine growth and nematode counts this winter, “micro-plots” planted with single Cabernet Sauvignon grape vines will show how various compounds — some old, some more recent — measure up to methyl bromide for control of nematodes.

This growing season the trials at the University of California's Kearney Agricultural Center at Parlier have been screening more than a dozen compounds as potential replacements for the widely used fumigant.

Blamed, along with other compounds, for ozone-depletion in the atmosphere, methyl bromide is due to be phased out of commercial agricultural use by Jan. 1, 2005, except for quarantine and other special applications, in the U.S. and other developed countries.

At a recent grape day, UC, Riverside nematologist Mike McKenry said, “During the winter of 2000 only two products exhibited significant activity against root knot nematode. Studies like this require two full years of evaluation before it is appropriate to indicate winners and losers.”

However, he said, some materials in the trial indicated methods worthy of tests in adjacent micro-plots for the 2001-2002 season.

The major thrust of his experiments is to find new methods to deliver alternative, post-plant nematicides to areas of the vineyard where the microscopic worms cause the greatest harm, rather than treating an entire block of vines.

“To do this we have to use nematicidal agents having reduced mammalian toxicity. A number of products are sold as nematicidal but have not been evaluated against standard nematicide comparisons,” he said.

First step

He went on to say the first step in the process is to compare performance of various nematicidal agents against nematodes that parasitize the outside of vine roots as well as others that live inside the roots. The micro-plots, upright sections of PVC drainage pipe about 18-inches in diameter, are best suited for such trials.

The vines of Cabernet Sauvignon, which is particularly susceptible to root knot nematode, were planted in June of 1999 in sandy and sandy-loam soils infested with that species, as well as citrus, root lesion, and dagger nematodes. The various treatments began the following May.

“These young vines are producing new roots about 10 months out of the year and the soil is warm enough for root knot nematode to penetrate new root tips about seven months of each year,” he explained.

In comments about the alternatives he is applying in the trials, McKenry said, “We are observing products that are nematicidal but move properly in one soil texture but not another. There are products that stimulate vine growth (and presumably root growth) but are not nematicidal. There are also products that are phytotoxic but when the rates are reduced the nematicidal control also may decline.”

Products in the study include: Nemacur, Enzone, DiTera, urea, lignosulfonate, AGI 9100 chitosan, Oxycom, fosthiazate, Cordon, Admire, Agri 50, Agroneem, and humic acid.

Treatments were made to vines in three gallons of water through May 2001 and in four-gallon applications, to take compounds deeper in the soil, in June 2001 and afterward.

e-mail: [email protected]

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