The question of at what scale herbicide use becomes necessary is a good
We farm 1100 acres organically and we know that there are succesful
organic farms that are much larger than ours. This is really more
dependent on management than it is on scale. Done properly, organic weed
control costs no more than chemicals do, if you figure the true cost of
production . When you add to the comparison the large savings from not
using insecticides and the avoided cost of chemical nitrogen, the
economic justification for using chemicals also weakens. The use of
chemicals becomes necessary especially if farmers don't use a good
rotation and a balanced fertility program. The problem is that most
farms are too specialized and don't grow a healthy mix of crops. The
markets and government programs punish farmers if they don't put most of
their acres into a very small number of crops (corn, soybeans, wheat).
Livestock has all but disappeared from grain farms. At the same time,
far removed from where they could actually be of benefit, nutrients from
manure are polluting land around animal factories.
Successful non-chemical weed control MUST be based first and foremost on
cultural weed control. We have a long article in the June 2000 issue of
Acres USA on the concept of cultural weed control, but we will summarize
it here briefly. We strongly urge anyone interested to read further
about this topic in Acres and comment/contribute their suggestions to us
or to Sanet.
Cultural weed control is defined as a combination of management practices
that give the crop an advantage over the weeds. While chemicals often
hurt both the weed and the crop, as well as the soil, cultural practices
actually benefit the crop and soil, increase yield, and make any
follow-up mechanical weed control methods much easier. This is
especially critical if you had bad weather for optimal mechanical weed
control. We are able to control weeds on our farm very well using
relatively few trips over the fields - often only one pass with the row
cultivator and 2 trips with a weeder (coil tine or Lely).
It is critical that a farmer must not rely exclusively on mechnical weed
control - that approach is either doomed to failure or can become
extremely expensive. By using cultural practices, the farmer has a
surprising amount of control over the weed populations and their vigor.
It is exactly the lack of appropriate cultural weed control on
conventional farms that has made weeds such a menace, requiring stronger
and more expensive herbicides. It is therefore very important to note
that cultural weed control should not just be viewed as 'an organic
thing'. Any farmer, organic or not, can reduce their weed pressure and
improve their crops by incorporating these ideas into their management.
What does cultural weed control include?
1. Crop Competition
Since a vigorously croping crop is less likely to be adversely affected
by weed competition, any practice that promotes the health and vigor of
the crop plants will reduce weed pressure. It is imperative to create
conditions wehre the intended crop can establish dominance quickly.
Using high quality seed, a well adjusted planter, well adapted varieties,
optimal soil fertility, good soil drainage and tilth, and proper soil
preparation will usually result in rapid vigorous crop growth.
2. Soil Fertility and Condition
It is important to rely on the biological activity of the soil as the
main source of fertility and of favorable soil physical structure. An
active and diverse soil microbial population is the key to growing
healthy high yielding organic crops. Successful organic fertility
management should primarily feed the soil microbial life in a long term
manner, rather than simply feeding the plants. Soil organic matter,
especially material that is actively decomposing, is a tremendous source
of plant nutrients and water holding capacity. Soil tests can be very
useful, but only if the results are interpreted correctly. Careful
attention to the calcium:magnesium ratio will often reduce weed problems
and enhance crop plant growth. One common mistake made by many famers is
the improper application of manure or poorly finished compost for soil
fertility. When such materials are used, this tends to throw off the
balance of certain soil nutrients and soil microbial life, and can
actually increase weed growth.
3. Crop Rotation
Civerse crop rotations that encompass the entire farm and that are
planned a number of years in advance are essential to build a healthy
sustainable organic system and to break pest cycles. In general, it is
best to alternate legumes with grasses, spring planted crops with fall
planted crops, row crops with close planted crops, and heavy feeders with
light feeders. Careful use of cover crops when the ground would be bare
adds organic matter, releases nutrients, improves soil microbial
diversity and prevents erosion.
One way that crops compete with each other is by releasing chemical
substances that inhibit the growth of other plants. Alleopathic crops
include barley, rye, annual ryegrass, buckwehat, oats, sorghum,
sudan-sorghum, wheat and sunflower.
5. Variety Selection
Careful selection of crop varieties is essential to limit weeds and
pathogen problems, and to satisfy market demands. Any crop variety that
is able to quickly shade the soil between the rows and is able to grow
more rapidly than the weeds will have an advantage. Disease resistant
crops may also be of great advantage.
The use of clean seed, mowing weeds around the edges of the fields or
after harvest to prevent weeds from going to seed, and thoroughly
composting manure to kill weed seeds can greatly reduce difficult weed
populations. It is possible to hand eradicate small localized outbreaks
of new weeds, even on a large farm. Other factors would include
cleaning machinery used in weedy fields, and the establishment of
hedgerows to limit wind blown seeds.
7. Deep shading crops
By blocking sunlight from hitting the soil, a crop can effectively
smother weed seedlings as they start to grow. Alfalfa, clover, and
grasses are particularly good at shading, as are corn, sorghum and
barley. Old German research showed that hemp was by far the best crop
available for deep shading. Unfortunately growing this crop in the
United States may attract 2 legged pests from the DEA.
8. Orientation of Rows
Small grains have been shown to have less pressure if they are planted
east-west, since that way the sun is not shining down the rows and the
ground is more shaded.
9. Mismatching the lifecycle of the crop to the lifecycle of problem weeds
For example, wild garlic comes up in the fall when you plant winter
grains and matures at the same time - this makes garlic a particularly
troublesome weed in these grains. Planting spring grains and row crops
in fields infested with wild garlic or wild onion will reduce the
Many of these practices are ones that good farmers probably do - or at
least should do - regardless of whether they fully understand why they
are doing them. As we gain a better understanding of cultural weed
control, it becomes evident that many of the worst weed problems on
conventional farms are actually the result of the farming system.
Chemicals tend to facilitate poorer cultural practices on farms. Round
Up Ready crops especially seem to make poor management practices
possible, but that doesn't necessarily result in the highest quality or
highest yielding crops.
We try to see weed problems, especially specific localized ones, as a
report on the condition of the soil and the lack of success of our
management practices. Weeds can often teach us many things. For
example, when we corrected a zinc deficiency on our farm, milkweed and
hemp dogbane disappeared. If we see foxtail and other summer grasses
coming in, this indicates a decline in soil tilth - usually around here
due to too much magnesium. We've noticed that our quackgrass has
virtually disappeared as our land was converted to organic management -
isn't it ironic when we stopped using Round Up, our quackgrass went away?
Hope this adds some perspective to the discussion. Klaas and Mary-Howell
Martens (New York)
To Unsubscribe: Email firstname.lastname@example.org with the command
"unsubscribe sanet-mg". If you receive the digest format, use the command
To Subscribe to Digest: Email email@example.com with the command
All messages to sanet-mg are archived at:
This archive was generated by hypermail 2b29 : Mon Jul 03 2000 - 12:00:38 EDT