ble knowledge, a large portion of the handbook is devoted to
registered uses of herbicides, crop desiccants, and some plant growth regulators. In all cases, authors have
made every effort to list only registered herbicides and to ensure that the information conforms with product
labels and company recommendations.
Intended Users: The handbook may be useful to producers, company field representatives, commercial
spray applicators, consultants, and herbicide dealers. The editor of each section is listed. Feel free to call them
or your state weed Extension specialist, if you have questions.
Revision and Availability: The handbook is revised every 2 years and is available from the Bulletin rooms at
Montana State University (406-994-3273), Utah State University (435-797-2251) and the University of
Wyoming (307-766-2115).
Caution!
The information provided in this handbook is not intended to be a
complete guide to herbicide use.
Before using any chemical, you should thoroughly read the label. The recommendation on the manufacturers
label, when followed, can prevent many problems arising from incorrect use of a chemical.
This information is supplied with the understanding that no discrimination is intended and no endorsement is
implied by the University Cooperative Extension Service. Trade names (brand names) are used in this handbook.
The authors have assembled the most reliable information available to them at time of publication. Due to
constantly changing laws and regulations, the authors assume no liability for the recommendations. Any use of
a pesticide contrary to instructions on the label is not legal or recommended.
Weed Management Suggestions Weed Prevention
Weed prevention means a land manager prevents the introduction of weed seed or vegetative propagules onto
the land. This requires vigilance and the ability to identify weed seeds, seedlings, and mature plants. After a
weed is introduced to a piece of land WEED ERADICATION is nearly impossible, and the endless process
of WEED MANAGEMENT begins.
One of the most important aspects of weed management is the development of a multi-tactic program to
control weeds. This approach, known as Integrated Weed Management (IWM), reduces the chances of
a weed to adapt to any particular control technique. For example, the increased reliance in herbicides with the
same mode of action has resulted in weeds that are resistant to those herbicides (see Section IV. Herbicide
Resistant Weeds). Also, the continuous production of certain crops provides weeds a chance to adapt to the
particular environment associated with that crop. IWM takes advantage of cultural, mechanical and chemical ii
weed control strategies in the best possible way with the goal of maintaining weed densities at manageable
levels while preventing shifts in weed populations to more difficult-to-control weeds.
Combining as many of the following practices as possible will allow you to design an IWM program: Avoid weed establishment; eliminate individual survivors. Establish competitive crops that will choke out weeds. Identify and map weed infestations. Keep records over years. Recognize and eliminate new weeds before they multiply and establish. Control vegetation and seed sources around the field or site. Comply with or become involved in establishing county/state weed laws and noxious weed control
programs. Employ sanitary procedures; prevent weed spread:

Clean equipment between sites or infestations. Examine nursery plants, seed, and imported soil or media. Use Certified Seed. Screen irrigation water that comes from surface storage through canals.
Cultural Practices of an IWM Program
Crop Rotation, defined as the alternation of different crops in a systematic sequence on the same land, is one
of the most important components of an IWM program. Weeds thrive in crops having similar environmental
requirements as their own. Moreover, management practices designed to benefits certain crops may also
benefit the growth of specific weeds. For example, winter annual weeds such as downy brome or jointed
goatgrass are commonly found in winter wheat fields as they share similar environmental requirements. Crop
rotation helps managing weeds because the different environmental conditions created by different crops within
a rotation disrupt weed germination and growth cycles. Also, the wide variety of management options associated
with each crop (tillage, planting dates, herbicide rotation, etc.) creates multiple stresses on weeds.
Know the weed spectrum
in a field then select the crops according to their ability to compete with those
weeds. Rotate crops to disrupt weed life cycles or suppress weeds in a competitive crop before planting a less
competitive crop.
Plant competitive crops
instead of fallowing to improve soils and weed management. Research with Indianhead
lentils and other annual legumes appears to be promising fallow substitutes. Also, alfalfa reduces the ability of
annual weeds to grow, however it favors growth of perennial weeds. Sudangrass, perennial grasses and tame
buckwheat, grown in dense stands, provide intense competition against weeds. Consider legumes to supplement soil nitrogen requirements. Consider specific varieties of cereals with natural plant toxins (allelopathy); vegetation must remain
uniform on the soil surface; either perennial or large-seeded crops can be planted through undisturbed
mulch. Consider crops such as oats or spring barley that winter kill after vigorous fall growth. This avoids or
reduces the need for controls the following spring.
Alter planting dates to encourage maximum early crop growth or delay planting until the first flush of weeds
is controlled. iii
Modify placement and time of application of fertilizer, especially nitrogen. Band or spot fertilizer below crop seed to reduce its availability to surface-germinating weeds. Time the application of fertilizer using side-dressing for maximum crop growth or to minimize weed
development.
Develop crop canopy to shade weeds and suppress weed germination. Select crops or varieties that form a canopy quickly. Space plants in equidistant (triangular) arrangements and vary density depending on crop management
constraints or harvest requirements. Interplant crops in space and time (consider mechanical limitations in commercial plantings).
Manage an appropriate living mulch (grass or legume) between perennial crop rows.
Improve pasture management by reseeding and/or fertilizing to reduce weed infestation (weeds are
usually a symptom of poor management).
Apply Mulch Organic mulches such as straw may reduce available N when decomposing, but it could be infested
with weed seed. Sawdust can be used but you must avoid vertebrate pests by maintaining a mulch-free circle around
trees. Also, perennial weeds can become a serious problem under mulch. Use bark mulch, black plastic or landscaping fabric which excludes light and therefore controls most
annual weeds. Avoid clear plastic mulch because it acts like a greenhouse and produces poor weed control. There are wavelength-selective plastics that can help in weed and pest management.
Mechanical Weed Control
Mechanical weed control involves the physical destruction of a weed. Techniques involve HAND PULLING
or HAND HOEING which are practical for small infestations. MOWING is often used; but by far, the most
common practice of mechanical control includes TILLAGE. Advantages of tillage include: Elimination of weed debris Controll of annual weeds Suppression of perennial weeds Tillage methods include plowing, rototilling, disking, and harrowing. Weed control implements include
sweeps, rolling cultivators, finger weeders, push hoes, rotary hoes, etc.
Other Cultural Methods of Weed Control
Flaming is a technique that can be useful but it requires a physical difference or separation between crops and
weeds, or crop protection with a hooded row cover or protein foaming agents.
Proper water management, such as the use of drip irrigation or uniform irrigation, can eliminate certain
weeds. iv
Stale seedbeds involve a delay in planting after seedbed preparation to control the first flush of weeds before
seeding.
Biological Weed Control
Biological control involves the use of natural enemies, such as predators, parasitoids, competitors, or pathogens
to control pest insects, weeds, or diseases to levels lower than they would otherwise be. There are three main
methods of biological control: conservation, introduction, or augmentation. Human activities can greatly influence
the extent to which natural enemies are able to suppress pests. Conservation Biological Control is defined
as any biological control practice designed to protect and maintain populations of existing natural enemies.
This approach is particularly useful in agroecosystems where management practices such as cultivation, pesticide
applications, and harvest disrupt the life cycle of the beneficial organisms. Introduction or Classical Biological
Control refers to the importation of foreign natural enemies to control previously introduced, or native, pests.
Finally, Augmentation Biological Control involves control practices intended to increase the number or
effectiveness of existing natural enemies. This approach is commonly used in cases where natural enemies are
missing (greenhouses) or late to arrive at new plantings (some row crops), or simply too scarce to provide
control.
Many of our worst weeds originated in foreign countries and biological control practices can help us to maintain
them below threshold levels. These newly introduced plants, free from the natural enemies found in