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Faba Bean – Weed Control

Summary

Cow Cockle, Photo Credit: The Western Producer

Good weed control is essential for optimum faba bean production. Faba bean is a poor competitor with weeds especially in the seedling stage – in research plots, faba bean seed yield was reduced by as much as 85% when wild oat levels were high.

Challenges include:

  • the development of herbicide resistance in weed populations
  • limited options for herbicides on the market
  • chemistries not registered solely for pulses due to its small global market.

For all of these reasons, it is important to take an integrated approach to weed control which combines cultural measures, preventative measures, and effective use of herbicides.

The major weeds of concern in faba bean crops are Canada thistle and perennial sow thistle. Other significant weeds include cow cockle, round leaf mallow, blue burr, cleavers, and wild tomato.

Preventative Measures

Blue Burr, Photo Credit: Alaska Department of Agriculture

Knowing your field’s weed history

 
  • Selecting a field that has weeds that may be controlled culturally or with herbicides registered for use in faba bean is important when planning faba bean production. 
  • Avoid fields with known infestations of perennial weeds such as Canada thistle or sow thistle, biennial and/or Group 2 resistant weeds such as cleavers, kochia, wild mustard and smartweed.

Choose clean fields, free of herbicide residues
  • Faba beans can be damaged easily by herbicides registered for other crops, or soil residues of some herbicides used in previous years.
  • Care should also be taken to avoid drift of herbicides from other fields onto faba bean fields.

Maintain Accurate records of herbicide use
  • Keep accurate up-to-date records monitoring residual herbicides on all fields.
  • Faba beans are highly susceptible to herbicide residues both from pre-seeding burn off as well as weed control used in the previous two crops. Learn more about Robyne Bowness Research.

Cultural Measures

Round Leaf Mallow, Photo Credit: Province of Manitoba

Crop Rotation
  • Grow a rotational crop that provides good competition to weeds, allows for a wide range of herbicide options, and is easy to control as a volunteer in the following pea crop.
  • Crop rotation goes beyond disease considerations and weed control (including volunteer crops). Crop rotation can influence both the faba bean crop and the crop(s) following faba bean.
  • Good weed control in faba bean requires a long-term strategy involving the entire crop rotation.

SANITATION
  • Good sanitation practices, such as cleaning harvest and seeding equipment to avoid spreading weed seeds between fields.

Seed/

Seeding Rates
  • Choose a clean, healthy seed.
  • Seed early. Faba bean plants are more competitive with annual weeds if they emerge rapidly and cover the soil surface before the weeds emerge.
  • Proper seeding rates/management will help produce a healthy, vigorous, uniform crop, for better competition with weeds and easier herbicide timing.
  • Make the crop more competitive (ex. higher seeding rates, appropriate fertility levels) to help choke out weeds and help reduce the reliance on herbicides.
  • Careful selection of a clean seedbed.
  • Delayed seeding should be avoided as it greatly reduces faba bean yields due to late maturity.

Tillage
  • Appropriate tillage weed control in previous year.
  • Inclusion of a shallow tillage operation in problem areas prior to seeding.
  • Spring tillage, even minor tillage, significantly increases the burial and resulting germination of false cleavers and catchweed bedstraw. However, growers should limit spring tillage as part of an integrated weed management program.
  • Tillage may have a beneficial effect for control of some weeds while having the opposite effect on others.
  • Increased tillage favours stinkweed, wild oats and chickweed.
  • Other weeds – such as bluegrass, clover, groundsel, and smartweed – germinate better under reduced tillage.
  • Tillage may be a tool to reduce kochia populations. Kochia appears well adapted to no-till with germination beginning at 50 cumulative growing degree days (well before other common weed species). Burial of kochia seed to at least 1 cm or deeper can result in reduced germination or death of the germinated seed prior to emergence.
  • Tillage to bury kochia seed should not be overlooked as a part of an integrated weed strategy for kochia control. However, this has limited value where minimum or no-till is practiced.

Rod-Weeding
  • Rod-weeding five to seven days after seeding provides excellent weed control without herbicide use, and good tolerance to faba beans, however faba beans must be seeded 2.75 to 3 inches deep. Tillage 10 to 12 days prior to seeding helps stimulate weed growth for control with the rod-weeder.

Harrowing
  • Harrowing between seeding and emergence of the crop can control newly emerged weed seedlings and remove weeds that escaped previous tillage operations.
  • Harrowing should be avoided during crop emergence and for several days afterwards due to excessive damage of the seedlings.

Post-Emergence Harrowing
  • Post-emergence harrowing has been researched at Agriculture and Agri-Food Canada. A higher seeding rate should be used to offset the plant losses due to harrowing. Post-emergent harrowing should be done under warm, dry conditions to improve weed control and to prevent the spread of diseases.
  • Post-emergent harrowing can occur once faba bean seedlings are 2 to 6 in. (5 to 15 cm) high
  • Tine harrows are most effective when used crosswise to the direction of seeding and at a ground speed of 6 km/h (4 mph) or less.
  • Harrowing can increase the risk and spread of disease
  • Harrow on a dry, sunny day when plants are somewhat wilted.

Effective Use of Herbicides

Canada Thistle

Herbicides are effective tools for the control of weeds. These chemicals are capable of killing some kinds of plants (weeds) without injury to other kinds (crops).

To determine which herbicide is best suited for your needs, refer to Alberta Blue Book (Crop Protection Manual). This manual provides a comprehensive and up-to-date guide for the selection and application of chemicals to protect your crop. Always follow label recommendations and check product labels carefully. Your most up-to-date label information is available on the manufacturer’s website links on the product label.

Because faba bean does not provide a competitive canopy early in the season, weed growth will be greater and more visible in an emerged faba bean crop.

The decision to spray or not to spray should be based on economics. If the potential yield loss is greater than the cost of the chemical and application, then you should spray. Prior to spraying, producers should evaluate the sensitivity of the surrounding environment and avoid spray drift.

SPRAYER
  • Thoroughly clean the sprayer before spraying a faba bean field.  Faba bean can be easily damaged by herbicides registered for other crops.
  • Ensure your sprayer is functioning properly (leaks, plugs, pressure gauge, etc.) and choose appropriate nozzles for the situation.
  • Maximize sprayer efficiency – ensure the herbicide hits the target, water volume is adequate, nozzles provide good coverage, and travel speed is reasonable enough to ensure a good spray pattern.
  • Resource:  Sprayers101

CROP SCOUTING
  • Crop scouting and anticipating in-crop weeds are key components of a successful weed control program. 
  • Perennial weeds are best controlled pre-harvest in the previous crop. Fields should be inspected again before freeze-up, first thing in the spring as this is an ideal time to control winter annuals.
  • The next weed inspection should be just prior to planting to time pre-seed burn-off.
  • Fields should be inspected again upon crop emergence to establish the frequency and distribution of weed species and to determine appropriate herbicide products for post-emergent weed control.
  • One to two weeks after applying an herbicide, scout for both weed control symptoms and crop injury symptoms. If the weeds are not completely dead, look for symptoms of herbicide activity such as yellowing, purpling, twisting, cupping, or bleaching. Timely post-spray audits may leave enough time to perform a rescue treatment if necessary.

KNOW YOUR WEEDS

ALLOW FOR CROP STRESS
  • During periods of crop stress (heat, drought, frost, or after land rolling) the ability of the pea crop to tolerate herbicide application may be reduced. Crop injury can be reduced by waiting approximately four days after the crop stress occurs before applying herbicide, by maintaining water volumes at label recommendations, and by applying the product in the evening.
  • Correct application of herbicides: To minimize crop stress, use higher water volumes of 15 gallon/acre (70 litre/acre) with broadleaf herbicides.
  • Resource:  Application of Herbicides Under Stressful Conditions 

NODE STAGING
  • Follow the growth stage of the crop, rather than spraying by the calendar. Apply herbicides based on the label instructions.
  • Application stages on labels may refer to leaf, node, or above ground node stages.
  • Most recommendations are at the one to six above-ground node, others include any 80-day, 60-day, and 30-day pre harvest interval.

HERBICIDE TANK MIXES
  • Tank mixes, or herbicide products offering both broadleaf and grassy weed control, should be applied when either weed group is nearing its maximum growth stage for good control.
  • Never use unregistered mixes or ‘cocktails’ in a crop – this may result in reduced or no herbicide activity, poor weed control and severe injury to the crop.
  • Surfactants can affect both weed control and crop safety – the use of an incorrect surfactant is very risky.
  • All adjuvants are not equal – producers changing adjuvants, or even altering adjuvant rates in the herbicide or tank mix, should expect variable results in weed control.

Timing of Herbicide Application

Timing of herbicide application is very important. Earlier herbicide application means weeds are well-exposed, are smaller (generally weeds are easier to control at a younger stage), and the crop is less susceptible to injury.

Perennial Sow Thistle, Photo Credit: South Dakota University, Department of Agriculture

Weed Control the Year Before

 
  • Weed management should also be considered in the fall prior to growing faba beans.
  • Controlling winter annual weeds – their growth habits make them difficult to control. Winter annuals germinate in the fall and overwinter as rosettes, producing seed the following year. If these weeds are allowed to bolt the following year, prior to herbicide application, control becomes nearly impossible. Therefore, timing of the herbicide application for control of winter annuals is critical. 
  • Fall application of pre-emergent, soil incorporated herbicide is recommended as it provides a more uniform distribution of herbicide for improved weed control and crop tolerance; conserves soil moisture by reducing spring tillage operations; and allows for earlier seeding in most years.
  • Control perennial weeds through using fall tillage or a pre-harvest glyphosate product the year before faba bean, and apply when weeds are actively growing under proper temperature, good moisture and bright light.

SPRING PRE-SEED AND

PRE-EMERGENT WEED CONTROL 

 
  • Spray early to remove weed competition. Weeds tend to be more susceptible (and faba bean more tolerant) at the early growth stages
  • Several herbicides are registered for use on faba bean to control most of the common weed problems.
  • Faba beans are poor competitors with weeds, especially during the seedling stage. In research plots in Alberta, yield was reduced as much as 85% when wild oats were high.  However, time of weed removal studies have not been conducted on the Prairies for faba bean.
  • A spring herbicide application, either pre-seed or pre-emergent herbicide (PEH), is recommended as faba beans are relatively poor competitors, especially early in the growing season. This provides early season weed control and may provide control of weeds for which no in-crop control is available. 
  • Broadleaf and grassy weed products for faba bean are recommended prior to seeding or prior to emergence.

SAME YEAR – IN CROP

 

POST-EMERGENT WEED CONTROL

 
  • Apply a post-emergent herbicide at the earliest crop stage listed on the herbicide label. 
  • To maximize yield potential, spray once most grassy weeds have germinated.
  • Spraying early will minimize crop damage. Drop injury due to late herbicide application is a common problem.
  • Follow the growth stage of the crop, rather than spraying by the calendar. Apply herbicides based on the label instructions, most herbicides are applied between the one to six-node stage.
  • With more use of direct seeding, farmers have seen shifts in weed communities. Weeds traditionally controlled by cultivation – such as winter annuals and perennials – are increasing. Both winter annuals and perennials are poorly controlled by in-crop herbicides.
  • Perennial weeds increase and become more visible under direct seeding while wild oat and green foxtail populations tend to decrease after continuous direct seeding.
  • Timing for effective herbicide application is critical, not only with respect to the growth stage of the plant but for the weeds as well – in general, the smaller and younger the weed, the better the control achieved.

PRE-HARVEST WEED CONTROL 
  • A pre-harvest application of glyphosate effectively controls perennial weeds.
  • Appropriate application stage is when the crop is at physiological maturity (30% seed moisture or less).  Know the proper staging for harvest aid products and ensure the entire area being sprayed is at the recommended stage.
  • Faba bean plants are fairly mature with leaves drying down and stems green to brown in colour, pods are filled, and lower 80% of bottom pods are than or black in colour.

POST HARVEST WEED CONTROL

 
  • A fall application of an herbicide from mid-October to freeze-up is critical to control winter annuals – these can be tough to control in the spring, especially if allowed to grow past bolting stage.
  • See resource below.

RESOURCES

 Links