This project tested the idea that using sterile soil amendments might serve as an effective alternative soil fumigant to methyl bromide in strawberry production. It had two objectives:
1. Measure plant yield under the alternate fumigants (number of daughter plants produced)
2. Detect the presence of nematodes and Phytophthora cactorum (phytophthora) under each treatment
Use of methyl bromide as a soil fumigant for nursery strawberry production is scheduled to be phased out in 2005. Current practices of producing strawberry nursery plants depend on methyl bromide, both as a cultural practice and as a regulatory requirement for commercial production. The high cost of fumigants, their impending loss and the availability of two sterile soil amendments – cogeneration ash from an electricity-generating facility fired by pine wood and mint residue from a peppermint distillation facility – gave rise for optimism.
The experiment was conducted in the Fall River Valley of Eastern Shasta County, Calif., near McArthur at an elevation of 3,300 feet. The soil was Pittville sandy loam, commonly used in strawberry nursery production. Six treatments were begun Oct. 31, 2000, each replicated five times. The cultivar Diamonte was planted according to commercial practices.
Neither amendment proved effective, eliminating them as potential substitutes for methyl bromide.
At midseason, plants in the fumigated soil had the most leaves and runners, followed by unfumigated soil. The third best treatment was 50% mint residue and 50% unfumigated soil, followed by all treatments containing the ash. Harvest yields showed similar results
Assays for nematode were all negative. One replication of one treatment (50-50 mint-unfumigated soil) showed phytophthora. And the fumigated plots had fewer weeds, although that may have been because the more vigorous strawberry plants out competed the weeds.
Given the requirement that transplants be free of nematode and phytophthora, the results show that the only acceptable treatment is fumigation.
The project team wondered why such a promising trial failed to produce beneficial results. The soil mixtures used were high in organic matter and had a relatively high pH. Although the plots were designed to be well drained, the amended plots tended toward anaerobic conditions after irrigation because of slow drainage. Different water management may have reduced plant death and increased daughter plant yields, the researchers said.
Even so, it would be hard to overcome the differences in plant response: The fumigated plots had 26% more leaves and 42% more runners than the amended plots. More importantly, however, given that phytophthora was detected in one of the amended plots, and no level of the disease is tolerable in strawberry nursery plants, any improvement in leaf and runner yield would be irrelevant.
The primary benefit of this study is that cogenerations ash and mint residue can be eliminated as potential fumigation substitutes for methyl bromide in the production of nursery strawberry plants.
FARMER ADOPTION AND DIRECT IMPACT
Given the dependency on methyl bromide as a soil fumigant, at a cost of $1,800 per acre, and the availability of the wood and mint byproducts, local producers were disappointed with the test results.
FUTURE RECOMMENDATIONS OR NEW HYPOTHESES
Looking ahead, the project team sees no further need for additional projects with these soil amendments.
DISSEMINATION OF FINDINGS
Some preliminary data were used for written testimony given to the U.S. Environmental Protection Agency in hearings related to methyl bromide during the summer of 2001. Because the trial’s outcome has little significance to the industry, no further outreach with the results is planned.
The main producer involved was project coordinator Allen Albaugh, a partner in Fall River Nursery.