Nightmare in Tilling Fieldsa Horror
for Weed Pests
Tilling farm fields in the dark may be a nightmarenot for farmers, but
for weeds. U.S. Department of Agriculture research in Rosemount, Minnesota,
shows nighttime tillage can cut some weed problems in half.
"We're talking about working in absolute darkness," says weed
scientist Douglas D. Buhler of USDA's Agricultural Research Service.
"Certain weed species have light requirements to break dormancy. Just a
brief exposure to a little light from tractors or possibly a full moon may
trigger weed seeds to sprout like they do in daylight."
However, he says, "Some initial research reports coming from Europe
have shown remarkable reductions in weed populations when tillage was done at
night. If nighttime tillage also works here, it has the potential to reduce
reliance on chemicals in weed management."
With daylight tillage, according to Buhler, light penetrates the soil as it
is being turned, breaking the dormancy of buried weed seeds. Tilling the soil
in the absence of light reduces this occurrenceat least with certain
types of weeds.
So, last year, Buhler and ARS technician Keith A. Kohler borrowed U.S.
military-issue night goggles and drove a tractor and tillage rig in total
darkness around some Rosemount cornfields.
"Night vision was good enough to perform between-the-row cultivation,
and that's an area we are exploring in current research," Buhler says. He
and Kohler are based at the ARS National Soil Tilth Laboratory in Ames, Iowa.
During their studies, Buhler and Kohler documented the effect of night
tillage on the emergence of 13 annual weed species. It was the first time so
many types of weeds had been tested using night tillage.
"Farmers often work at night out of necessity. Now they may have a
method to improve weed control at the same time," Buhler says.
"I get more done after 6 p.m. than I do before," says Iowa farmer
Doug Alert, who lives in Hampton, about 60 miles from Ames. He had read
articles about night tilling in European journals and was curious to try it on
his 400-acre farm.
Alert believes that farmers would cultivate their fields at night if they
could be convinced that the practice would cut weed emergence 50 percent or
more without using herbicide. He says he only uses chemicals "on an
as-needed basis, spending about $5 to $7 per acre for them. Most farmers use
$20 to $30 worth per acre."
According to Buhler, interest in night tillage has come from sustainable and
organic farmers who want to use less chemicals. But he adds, "night
tilling isn't the answer to everyone's weed problems. Obviously, farmers would
need to change the timing of their work schedule during the planting and
growing season. It would also be important for them to understand the
susceptibility of the weed species in their fields."
One interested farmer, Dick Thompson in Boone, Iowa, has worked for several
years with ARS scientists at the Ames lab to better manage his 300-acre farm.
[See "Alternative vs. Conventional Farming," Agricultural
Research, October 1989, pp.4-7.]
But Thompson cautions, "Any system to control weeds must be
practical." For instance, he does not believe that ridge planting in
darkness is feasible.
Of another approach, he says, "We built a cover attachment for our
planter to exclude light so we can plant during daylight and still gain the
benefits of tilling at night."
Last year, he tried tilling at night. This year, that field is planted to
corn with no herbicide applied to control weeds. "We did some day and
night tillage to cultivate fields," Thompson says. "I'm anxious to
see which system works better."
Detailed data on emergence of a wide range of weed species is
critical to assessing the effect of night tillage on weeds. Here, agronomist
Doug Buhler and Iowa State University student Amy Beatty count emerging weeds.
Buhler says, "Our research showed enough promise that we tried it again
Data from the second year of field tests is substantiating initial findings.
Most small-seeded broadleaf species in the study (common lambsquarters, common
ragweed, black nightshade, pigweed, smartweed, and wild mustard) again emerged
less after tilling during darkness.
"We have seen reductions in weed emergence as great as 80
percent," says Buhler, "but generally reductions are 50 to 60
"Usually, farmers till before planting to stimulate weed growth. They
later knock out those weeds come up by tilling or with herbicide or both,"
Night tillage postpones or prevents some weed emergence, causing seeds left
buried to become less viable and more prone to attack by soil microbes. If
fewer weeds appear, that means fewer tractor trips and reduced herbicide use.
While results have been encouraging, large-seeded weeds like velvet-leaf and
cocklebur still sprouted after night tilling. In addition, annual grass species
were not affected.
Weeds included in the study were:
- Annual grass speciesbarn yard grass and green, yellow, and giant
- Large-seeded broadleaf weedscocklebur, giant ragweed, and
- Small-seeded broadleaf weedslambsquarters, ragweed, wild mustard,
nightshade, smartweed, and pigweed.
These are some of the most troublesome weeds infesting corn and soybean
fields in the Midwest.
Buhler tilled at night between 11 p.m. and midnight. For comparison, he did
daytime tillage and applied the herbicide Roundup between 2 and 4 p.m. An
evaluation of the two methods was made by counting weeds that came up 15, 30,
and 50 days after tillage.
Buhler says many farming operations, such as planting and cultivating corn,
can be trickyeven in daylight, let alone at night. But, by combining the
night-vision goggles with precision farming tools such as a cultivator
row-tracking system, night tilling becomes technically feasible.
Farmer Thompson, who has never tried night-vision goggles, doesn't think the
goggles are the only or best answer for working at night. He has instead
equipped a tractor with a set of lights that shine only out in front of the
vehicle, allowing him to see while preventing light from reaching the soil
during the tillage operation.
Additional research is needed, says Buhler, to determine the light
sensitivity of various weed speciesas well as the effects of tillage
depth, tillage implements, and other factors like crop planting date on the
effectiveness of night tillage.
"We also need to understand how different tillage implements
redistribute weed seeds, so as to minimize the number of seeds that are brought
to the soil surface," says Buhler. "Seeds moved to the surface at
night would be exposed to light the following morning, reducing the
effectiveness of the night tillage." By Hank Becker, ARS.
Soil Tilth Laboratory, 2150 Pammel Drive, Ames, IA 50011; phone (515)
294-5723, fax (515) 294-8125.
"Nightmare in Tilling Fieldsa Horror for Weed
Pests" was published in the
December 1995 issue
of Agricultural Research magazine.