The information on restrictions against planting alfalfa (or many
other rotation crops, cover crops and grasses/legumes) probably was in
reference to imidazolinone or sulfonylurea resistant corn or beans
varieties. These products typically have a 12 month or more crop rotation
restriction, in some cases, much more (see below).
Some major soybean herbicides by class associated with GMOs and some
of the crop-rotation or plant-back restrictions are briefly reviewed below.
Soybean herbicide percent acres treated data are from USDA/NASS, for 1997.
Plant back, crop rotation restrictions are from pages 143 to 168, section on
soybeans, in "Weed Control Manual," Meister publication, Vol. 31, 1998.
Sulfonylureas
Chlorimuron-ethyl (Classic), 13% national soybean acres treated. Plant back
depends on soil Ph and region, have to see the label, but is surely 12 to 24
months or longer for most crops.
Sulfentrazone+chlorimuron-ethyl (Authority), new product, market-share
unknown. Canola, beets, 30 months. Alfalfa, sorghum, 42 months. (Recall
one reason the low doses work is because of the chemical' persistence;
persistence=longer plant back restrictions, and more undiagnosed (and
diagnosed) crop injury when, for one reason or another, herbicide residues
in the soil take longer to break down than "normal").
Sulfentrazone (Cover). New product. Alfalfa, 12 months. Many other crops
12-18 months, and rest, 30 months.
Imidazolinone
Imazaquin (Scepter), 13% acres treated. Most crops, 18 months (include
alfalfa). Sugar beets, 24 months.
Imazethapyr (Pursuit), 38% acres treated (average rate of only 0.05 pounds
a.i. per acre). Potatoes, 26 months. Sweet corn, 18 months. All other
crops 40 months after application. (So much for cover crops, small grain
rotations, alfalfa, etc, on 1/3 of soybean acres).
Clomazone (Command). 5% acres treated. No crop rotation until 16 months
after planting in Northern U.S., 12 months elsewhere.
Clearly, some herbicide tolerant plant varieties are going to cause
some serious localized problems. Application rates tend to be a bit higher,
and repeat applications are much more common in herbicide tolerant programs.
One reason -- herbicide/GMO-seed companies are, in effect, guaranteeing
"satisfactory" weed control, and give growers the chemical needed for later
season resprays. These extend the crop rotation restrictions, but more
worrisome, can lead to runoff following an early summer thunderstorm.
Imagine what a little of these herbicides will do to that nice new grassed
waterway, or grass filter strip, half or 3/4 paid for with public dollars,
as runoff flows over the newly established grass stand. Also, expanded use
of these technologies will lead to more problems among neighbors when either
drift, runoff, or volatization (and drift) lead to herbicide injury in
nearby fields.
chuck
Charles Benbrook 208-263-5236 (voice)
Benbrook Consulting Services 208-263-7342 (fax)
5085 Upper Pack River Road benbrook@hillnet.com [e-mail]
Sandpoint, Idaho 83864 http://www.pmac.net
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