Milkweed seeds? Corn meal extract? These are just two of the possible alternatives to methyl bromide for soil fumigation mentioned by Wesley Kline of Rutgers at the Mid-Atlantic Vegetable Growers Convention.
Fumigation of soil is a way to control weeds, nematodes, soil insects, and soil-borne diseases. But the most widely used chemical for fumigation, methyl bromide, will be phased out by 2005. So scientists across the country are scrambling to find alternatives.
Two alternatives already exist. Metam-sodium (Busan, Nemasol or Vapam), for example, is currently the most widely used fumigant in New Jersey. “Metam-sodium is our recommended material, and is preferred by our growers,” commented Kline.
New Jersey growers do a lot of fumigating because farms there are smaller – typically about 65 acres - and every acre is intensively farmed, planted with two or three crops a year. Even in winter, fields are planted to overwintered crops of leeks, spinach, green onions, and Swiss chard.
With such intensive farming, proper rotations can be impossible.
“Some growers grow crucifers after crucifers after crucifers,” said Kline. “There’s a history of soil-borne diseases. Vapam can be put through the drip system, or we can inject it with equipment. In the field, we seal it in by cultipacking. It’s used quite heavily in greenhouses because we still have a number of growers who are planting directly in the soil, and they fumigate in the fall,” he said.
Telone is another currently available alternative to methyl bromide, although there are restrictions on its use in California, due to air quality concerns, and it does not give as good of weed control as Vapam. Some Telone is currently being used in southern New Jersey. Telone is injected with equipment, which the company brings to you. Currently it comes from North Carolina.
It’s becoming more and more of a factor in the fumigation market in our area. With all fumigants, you need to prepare the soil. Get the debris under and broken down before fumigating. The soil needs adequate moisture— at least field capacity, according to Kline. The soil temperature at a six-inch depth should be 50° to 80°.
Fumigate two to three weeks before time to plant. At two weeks, you’re really pressing your luck though. You could get phytotoxicity problems.
But if you’re fumigating late and you have to get in to plant, you can work up your soil with tillage equipment set as shallowly as possible to let the remaining gases escape, making planting safe. Kline offers this caution: “Don’t go too deep with your tillage equipment. Set it as shallowly as possible, or you can bring up unfumigated soil.”
The number one product not yet available to growers that is being looked at as an alternative to methyl bromide is methyl iodide, which has an activity similar to methyl bromide.
However, it is not yet labeled or available commercially, and at present it is l0 to l4 times the price of methyl bromide. “The IR-4 program is working very aggressively on this product,” said Kline. “But we could be looking at four to five years before it could be registered, and until it’s mass-produced, the price would be prohibitive for most growers.”
Another possible alternative to methyl bromide down the road is Basamid, a granular product similar to Vapam. “I used Basamid in Central America,” said Kline, “and it does work quite well. You must get it under the soil, and make sure the soil is sealed, or you won’t get the gassing effect. However, it is not labeled for vegetables now.”
Plant Pro 45, another possible alternative, is an Iodine-based material with control very similar to methyl bromide, except that it is not as good for weed control. It is also not currently labeled for vegetables in the U.S. Fosthiadzate, an organophosphate, has been used in Europe for several years on tomatoes, but it is not currently labeled in the U.S. (Tillam is currently labeled and available for tomatoes, but is not available for peppers and some other crops.)
“Turning to non-chemical alternatives to fumigation, solarization does look like it will have a place in fall production,” said Kline. Solarization must be done when the sun’s heat is at its most intense.
Work in New Jersey on solarization has been done in greenhouses.
“With our work,” said Kline, “we use thin l.5 mil plastic, and solarize six to eight weeks. Florida and California have been doing work outside. First they prepare the soil for planting. It needs to be level. Then they irrigate it to field capacity. Without good moisture, you don’t get a good effect. Then they actually roll out huge rolls of plastic, covering the whole field, and seal the edges.”
In Florida, they have also been solarizing prepared beds, thereby cutting costs. Before they plant in the solarized soil of the beds, they paint the plastic white so as not to burn plants.
“I believe,” said Kline, “that there is a place for solarization in fall production of tomatoes and peppers in the northeast. It will control weeds. It will even control nutsedge. But certain weeds like purslane escape. So you’d need some herbicide under the plastic for your fall crops.”
Some precautions: the plastic must be in tight contact with the soil. That’s how you get the transfer of heat through the plastic into the soil. Second, you have to have a good seal on the sides of the beds. Any opening allows heat to escape, and then you don’t get the control you need.
Also, you must use UV inhibited plastic. Otherwise the extreme heat just under the plastic breaks it down, making it crumble. Temperatures of l20&Mac251; F control nematodes, l30 kills botrytis, and l50 kills most bacteria, worms, and slugs. It takes very high temperatures to kill weed seeds.
“In our work with peppers,” said Kline, “at a one-inch depth, we got l42&Mac251; with clear plastic, and l45 with black plastic. In most of the work that’s been done, if you can get ll3-l20 at a l0 to l2 inch depth, you’re getting pretty good control of a lot of pathogens. We have a couple growers doing this commercially now, putting clear or black plastic on the soil surface, and they’re very happy with the results.”
Then there are the ground-up milkweed seeds. “Preliminary work in Washington state has been able to show control of nematodes, and in Illinois, they have been able to show control of the European corn borer.”
“Cornmeal extract has been worked with in Florida,” he continued, and there’s a commercial product available now. Personally, I’ve not seen it used, but some of the data looks pretty good.” There’s a lot of work being done around the country on compost, either manure-based or as a green manure. “It seems to have some potential for control,” said Kline. There’s good work being done at Cornell on commercial farms, where compost is being applied on large acreages. The only question is in finding the volume of compost necessary. And the effect is not instantaneous as it is with chemicals.
It takes time. Cover crops and green manures also show promise in a number of studies in suppressing weeds, nematodes, and disease organisms. Studies in Ontario have focused on pearl millet to control nematodes in a rotation crop. Researchers in California and Florida have gotten pretty good control with sun hemp, a legume, getting a nitrogen effect plus disease and weed suppression.
Work has been ongoing at Rutgers, in New York, and in the Midwest on Sudangrass. It definitely has been shown to suppress weeds, and some work shows it also suppresses disease and nematodes, in addition to giving 22 tons to the acre of biomass to cut and turn under.
A cover crop of white mustard, according to studies at Cornell, releases a chemical similar to Vapam as it decomposes, after being incorporated and sealed by cultipacking. Plant in July and incorporate in late September.
Another alternative can be as simple as the use of clean equipment. “If you have a field you know is infested, clean your equipment when going from that field to another,” advises Kline.
“To cut the necessity for fumigation, a cultural control is to rotate your crops as much as possible, as I tell my growers,” he said. “Also, know why you are fumigating. Do you have a real problem, or is it a perceived problem?”
“The solution to the problem posed by the loss of methyl bromide will eventually probably be a combination of chemical and cultural controls. What they’re doing in Florida right now is solarization combined with low levels.
