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Dear Dr. [omitted]; (Revised January 30, 2003)

Your analysis of the current state of methyl-bromide use in strawberries is pretty accurate. Strawberry growers continue to prefer to use Methyl-bromide (M-b) for several reasons: Being a powerful biocide, M-b provides excellent weed and pathogen control across a very broad spectrum of species at a (previously) affordable price. Soil diseases and weeds become largely irrelevant after proper fumigation.

M-b has also been shown to enhance early plant development through some synergistic reaction with chloropicrin, even in the absence of weeds and pathogens. There appears to be a plant growth stimulant affect that can be measured and considered responsible for an increase in early health of the crop. Recenty studies indicate chloropicrin by itself may be mostly responsible for this effect.

M-b is usually applied by one of two methods in California strawberry fields. The first, and most popular, method is called "flat field" fumigation, or simply "flat" fumigation. The ground is prepared for bed-making, irrigated lightly to induce pathogens and weed seeds to become more active or "viable" and thus more susceptible to the penetration of the poison gas. Then the gas applied to the flat, level soil by injection equipment mounted on caterpillar tractors. Simultaneously, the gas is sealed in the soil beneath solid plastic sheeting.

Caterpillar tractors carrying large (1500 LB) pressurized cylinders of gas and rolls of clear plastic tarp (4 mil thick and 12 feet wide) pass across the field and inject M-b about 12 inches deep. Injection shanks are designed to release the gas in a way that prevents it from escaping the soil too rapidly. The plastic tarp unrolls from the rear of the same tractor as gas is applied, and the sides of the tarp are continuously buried to seal the gas beneath it. These tarps are left sealed for at least 6 days to allow gas to dissipate to safe concentrations, then removed and thrown away. The strawberry beds are then made, and new plastic is laid out on top each of the beds.

The other method of fumigation, which I prefer, is called "bed fume" because the beds are made first then the gas is injected into each individual bed (about 64 inches wide). Single bed tarps are stretched across the beds and buried by the same tractor that injects the gas. These beds are then ready for planting after sitting for 6 days and the fumigation tarp remains on the bed and becomes the bed mulch.

Bed fumigation: saves us time over flat fluming because there is no need to re-prepare the soil for bed making after removing the flat fume tarp; saves us money by not having to buy two sets of plastic; saves on gas purchased because we reduce the total volume of soil fumigated by about 15%, and; saves the landfill room by throwing half as much plastic away.

On the down side, bed-fuming leaves 15% of the field (the open furrows) untreated as a potential source for pathogen inoculation of the plants during the season. The open furrows also need to be cultivated, or in some cases hand-weeded, to control weeds. By the way, I budget $650 per acre for hand weeding each season even WITH methyl-bromide fumigation. I think we’ll be up around $850 without M-b.

The fumigation alternative we have adopted in 2002 is called Inline®, and is a combination of Telone II (1,3-dichloropropene) and Chloropicrin (tear gas). It can be injected into existing sub-surface irrigation lines, making it easier to apply than M-b. Inline® has fewer application restrictions, can be used closer to roads and buildings and the cost of the application is somewhat lower than that of M-b. None of that would matter if it didn't work, but it has proven to do as good a job or better than M-b at raising a productive crop.

One drawback to Inline® is that it can only fumigate the part of the soil that gets wet from the irrigation system. Typically, the outer sides, or shoulders, of the raised bed are not wetted by irrigation and therefore are difficult to treat with Inline®.

Chloropicrin has always been used in conjunction with M-b for agricultural use and has good fungicidal properties and some weed control properties. Though not harmless (tear gas), it is not considered a deadly material like M-b. Telone has good nematode control properties, and has proven a valuable tool in treating soil for other crops like grapes and citrus. Its biggest drawback is its history of seeping into groundwater when overused or used improperly.

My assessment of other methyl-bromide alternatives, from a grower perspective: Metam-sodium (Vapam) has been inconsistent in its weed control for many years, is very corrosive and hard to handle, and smells like dead fish blended with nail polish remover -- a real public relations problem anywhere down wind -- and has become very restricted in its use in California as a result;

Selective herbicides have proven to be injurious to young strawberry plants at almost any application rate that will control weeds, though I see a place for some of the shorter-lived materials to fill in weed control gaps when using Inline®;

Plant extracts, especially from corn and broccolli, need to be researched further as some crops have shown good results (one trial of corn gluten meal on bed tops for weed control was interrupted by black birds poking holes in the bed plastic to eat all the meal we applied);

We have always used, and strongly advocate, the use of safe organic amendments and biological additives to manipulate the soil microenvironment in our favor. The theory is that the soil will only physically support a finite population of microorganisms. If you inoculate the soil with large nuM-bers of benign species, the pathogens have no place to live. I am not the expert in this area, but I believe this has helped us raise healthier, more productive crops;

Steam sterilization is still cost prohibitive for large field applications unless you have a cheap natural source of heat such as natural hot springs. It has proven very effective in the nursery and greenhouse industry, however;

Solarizing the soil is effective only where ambient temperatures reach 85 and above for at least several weeks, longer periods being even more effective. Along the coast where most strawberries are grown we simply don't get the temperatures under the plastic necessary to kill weed seeds and pathogens.

I have long advocated the breeding of plant stock with increased vigor and resistance to pathogens. It now seems that several advanced breeding programs have come to the same conclusion that strawberries simply do not have the genetic capability to grow as well without fumigation/sterilization of some sort. This does not rule out the possibility of finding the necessary genetic component in other species and engineering these traits into strawberries...but that opens a whole new can of worms we'll deal with another time.

I hope these observations will add insight into your studies of methyl-bromide. As a practical matter, the impending loss of an important production tool like methyl-bromide ultimately assists me, and other better growers, in competing with less capable growers who depend on methyl-bromide to raise a viable crop. I will continue to use all the resources at my disposal and will prosper. I do not, however, support the manner in which changes in M-b use has been promulgated.

EDITORIAL: M-b was labeled an ozone depleting substancein early the 90's by a committee of scientists sanctioned by the UN, calling for its ban under the Monreal Protocol. Recently, this same UN scientific committee has taken a giant step back and publicly stated they may have overestimated the danger to the ozone presented by manmade Methyl-bromide. This announcement, however, does not appear important enough to reconsider M-b phase-out legislation, nor is it newsworthy enough for publishing in most media, and I find that very provocative.

I ask, "What other changes are we being asked to make under the pretense of scientific fact, when we really don’t know all the relevant information?" I am not a conspiracy theorist by nature, but the "freon-in-air-conditioning" debacle of the 80’s has left me cynical. That is, DuPont financially allied with environmentalists to ban freon use when they were, and are, the only manufacturer of an approved replacement for air conditioning systems.

Was freon dangerous to our environment? Conceding that it was for argument’s sake, are we really comfortable with DuPont’s role in the whole affair? I can’t say how important methyl-bromide is in reducing the ozone layer, or even if the ozone layer grows and shrinks all by itself. But, I do know the loss of methyl-bromide will lead me to buy a whole lot of Dow Chemical’s Inline®.

Best wishes

Dave Peck

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