One of the biggest challenges for growing chickpeas is weed control. Unlike cereal and oilseed crops, pulse crops are generally not competitive with weeds and are highly susceptible to yield loss (20 to 40%) as a result of weed competition.
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 preventative measures, cultural measures, and effective use of herbicides.
Selecting a field that has weeds that may be controlled culturally or with herbicides registered for use in chickpeas, is important when planning chickpea 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
Chickpeas 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 chickpea fields.
Maintain Accurate records of herbicide use
Keep accurate up-to-date records monitoring residual herbicides on all fields as even reduced rates of residual herbicides can cause serious injury to the crop up to two years following application.
Cultural Measures
Common Groundsel
CROP ROTATION
Diverse crop rotations provide good competition to weeds and allow for a wide range of herbicide options.
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.
Proper seeding rates/management will help produce a healthy, vigorous, uniform crop, for better competition with weeds and easier herbicide timing.
Higher seeding rates can increase crop competitiveness against weeds and reduce maturity. However, an increase in crop canopy may lead to higher disease levels.
Tillage
Tillage may have a beneficial effect for control of some weeds while having the opposite effect on others.
Tillage is a tool to reduce kochia populations. Burial of kochia seed to at least one centimetre or deeper can result in reduced germination, or death of the germinated seed prior to emergence.
Farmers should consider limiting spring tillage as part of an integrated weed management program for cleavers.
Rod-Weeding
Rod-weeding five to seven days after seeding provides excellent weed control without herbicide use, and good tolerance, however, you must seed chickpeas 2.75 inches 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, to permit effective rooting and stand establishment.
Post-Emergence Harrowing
Post-emergent harrowing of chickpeas is not recommended as it can spread disease and cause severe mechanical crop injury.
Effective Use of Herbicides
Blue Burr, Photo Credit: Alaska Department of Agriculture
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.
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
Clean the sprayer thoroughly – Watch for other broadleaf herbicide residues in the sprayer tank – thoroughly clean the sprayer before spraying a chickpea field.
Herbicide testing indicates that chickpeas are especially sensitive and can be damaged easily by some herbicides registered for other crops, such as the control of broadleaf weeds in lentils or peas.
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.
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
The best way to check a weed’s identity is to compare weeds using a weed seedling identification guide. Various references include:
During periods of crop stress (heat, drought, frost, or after land rolling) the ability of chickpea 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 with broadleaf herbicides.
Follow the growth stage of the crop, rather than spraying by the calendar. Apply herbicides based on the label instructions.
Node staging – not the height of the plant – determines time of spraying. With chickpea plants, the best results, are at the one to three above ground node stages, and the weeds are small.
Chickpea injury is more severe at advanced growth stages.
If weeds have emerged, apply herbicides at early crop stages. This will improve weed control, reduce competition from the weeds, and usually reduces herbicide injury.
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.
SEPARATE APPLICATIONS OF HERBICIDE ON THE SAME FIELD
Separate applications of herbicides on the same field may give better weed control at a lower cost under the following conditions:
Grassy weeds are well established but broadleaf weeds have not emerged: in some years, cold spring conditions and low soil temperatures result in rapid growth of grassy weeds (like wild oats) but slower growth of broadleaf weeds.
Grassy weeds occur mostly in patches: patch spraying with a grassy weed control chemical in a second pass will be more economical than using a tank mix over the entire field.
Weed populations vary throughout the field: more economical weed control can be achieved by varying the rates of either the grassy or broadleaf herbicide – this result would not be possible with a tank mix.
RISKS OF SPLIT APPLICATIONS
Most post-emergent herbicides are applied in the two to six-node stage, which only allows for a two-week window to complete all herbicide applications.
In years with rainy or windy weather, the second herbicide may be applied too late and increase the risk of crop injury and reduce weed control.
Split applications may cost more.
Delayed herbicide applications are usually less effective, and a late application may be after substantial yield losses from weeds have already occurred.
MANAGING HERBICIDE RESISTANT WEEDS
Herbicide choice should take into account herbicide rotation to slow the development of resistant weeds. Resistant weeds are troublesome in chickpeas simply because they are a less competitive crop and there are limited herbicide options.
A few examples of herbicide-resistant weeds that are particularly troublesome for pulse growers include:
Rotating herbicide groups away from Group 1 and 2 products, especially in rotational years where chickpeas are not grown, can help prevent or manage resistant weeds.
Resistance can build with each application and applications do not have to be consecutive year after year. With high risk herbicides in Groups 1 and 2, the longer you can rotate away from these chemistries, the better the resistance.
On average if a grower has applied Group 1 or Group 2 herbicides more than 10 times in a field, there is a high risk of resistance developing among one or more weed species.
Research indicates that alternating between two modes of action for wild oat control will double the number of years for resistance build-up, and alternating with a third mode of action will increase the time of resistance build-up to four times as long as for a single mode of action for wild oat control.
Use integrated control methods through the rotation, such as higher seeding rates, promoting quick crop emergence, and using herbicides only when economic thresholds are reached.
Preventing kochia from setting viable seed for one or two years greatly reduces kochia populations in a field because the seed is short lived in the soil.
Timing of Herbicide Application
Green Foxtail, Photo Credit: Western Producer
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.
WEED CONTROL THE YEAR BEFORE
Weed management for chickpea crops should also be considered in the fall prior to growing chickpeas.
Crop choice the year prior to growing chickpea may allow the use of an herbicide to control a troublesome weed that has no herbicide available for in-crop control in the chickpea crop. Herbicide options in chickpea are much more limited than most other crops.
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 herbicide application for control of winter annuals is critical.
Control perennial weeds through using fall tillage or a pre-harvest glyphosate product the year before chickpea, 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.
A spring herbicide application, either pre-seed or pre-emergent herbicide (PEH) is recommended and are used extensively by experienced chickpea growers.
This provides early season weed control and may provide control of weeds for which no in-crop control is available.
Chickpea is slower to emerge, especially the larger seeded kabuli types, so a wider window between seeding and emergence allows more time if a post-seed/pre-emergent glyphosate application is planned.
With good growing conditions and shallower seeding, emergence can be quicker than expected so timing must be watched closely. Seedlings can be damaged as early as soil cracking as they are emerging and many come into contact with glyphosate.
In a direct seeding system, a spring burn-off application of glyphosate may provide effective weed control – delayed seeding to allow spring weed growth may result in high flower blast and lower yields.
SAME YEAR – IN CROP
POST-EMERGENT WEEK CONTROL
Follow the growth stage of the crop, rather than spraying by the calendar. Apply herbicides based on the label instructions.
Best performance is achieved when chickpea plants are at the one to three above ground node stages, and the weeds are small.
Chickpea injury is more severe at advanced growth stages.
Some leaf scorch will almost always be evident after application, but plant recover quickly if they are small.
If weeds have emerged, apply herbicides at early crop stages. This will improve weed control, reduce competition from the weeds, and usually reduces herbicide injury.
Timing for effective herbicide application is critical, not only with respect to the growth stage of the chickpea plant but for the weeds as well – in general, the smaller and younger the weed, the better the control achieved.
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.
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.
Chickpeas: Plants have yellowed, the pods have matured, and seeds have changed colour and detached themselves from the pods (pod rattle stage).
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.
