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US: Less is more when it comes to raspberry fumigantIt turns out that less maybe more when it comes to raspberry fumigation, according to Washington Sate University.
Raspberry growers typically use broadcast fumigation to deal with root lesion nematodes and root rot, but increasing EPA restrictions inspired horticulturist, Thomas Walters, to seek alternatives.
Bed fumigation apparatus, used in WSU research trials, reduced fumigant use and buffer zones, and resulted in fewer nematodes and larger raspberry plants.
Raspberry plants required certain soils, which makes usual rotation techniques ineffective, meaning that once pests and disease get a hold they multiply and become entrenched. Every five to eight years plants are usually removed, the soil is fumigated and planting is began anew.
New EPA Environmental Protection Agency regulations require a buffer zone for two days after fumigation. The size of the buffer zone depends on the field size, the fumigant, and associated rate used and other factors, but it can easily be 600 feet or more. With many raspberry fields in close proximity to houses, this approach is no longer practical.
To more selectively apply fumigant, Walters borrowed a concept from California strawberry growers, and adapted a bed fumigation apparatus. This multi-stage tractor-drawn tool uses a shank to cut the soil. Fumigant is injected into the soil through a hose behind the shank. The apparatus then shapes the three-foot wide bed and pulls a fumigant-resistant plastic tarp over it. Raspberry rows are spaced 10 feet apart, with no fumigation in the alleyways.
Because the new process uses only one third as much fumigant as broadcast fumigation, the statutory buffer zone drops to 25 feet, making the process much more neighbor-friendly. However, the expense of the tarp makes the cost about the same as broadcast fumigation. The biggest drawback of bed fumigation is that it requires more planning to be sure the beds are properly placed for irrigation.
Since the study began in 2010 results have been promising. The raspberries are growing at least as well as those cultivated with broadcast fumigation. Soil tests show 10 times more nematodes in the broadcast fumigated pots in fact and are smaller than those under trial.
Publication date: 6/8/2012
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