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Control of Select Weeds on Pastures and Hay Land In Saskatchewan

Weed infestations within forage stands can have a direct impact on pasture and hayland forage yield and quality.

Prevention is always the first and most important line of defense for weed control.

An effective weed control program prior to seeding is an important start in controlling weeds. Once established, maintaining a competitive forage stand with proper soil fertility and rest periods will minimize weed growth and help prevent new weeds from invading. Below you will find information about chemical and cultural control of several common pasture and hay land weeds including:

  • absinthe;
  • pasture sage;
  • field bindweed;
  • canada thistle;
  • dandelion;
  • leafy spurge; and
  • scentless chamomile.

Absinthe (Artemisia absinthium)

Best time for chemical control

Chemical control measures should be made in late June, prior to flowering. Second applications of herbicide may be necessary later in the season when plants have six to 10 inches (15 to 25 cm) of new growth. More than one season of application may be required to achieve full control. Manage for a competitive forage stand in combination with chemical control.

Recommended herbicides

See the current edition of the Saskatchewan Guide to Crop Protection for the most up-to-date chemical recommendations and registrations.

Recommended cultural method

Absinthe is a perennial that spreads primarily by seed. Seed, spread may be minimized by mowing, as buds are emerging. Absinthe can also spread very slowly, through expansion of the crown. When fractured by a disturbance, the crown may also reproduce a new plant from transplanted pieces. Managing for a competitive forage stand should help reduce the spread of this weed.

Pasture Sage (Artemisia frigida)

Best time for chemical control

Apply herbicide to the foliage of actively growing plants. Avoid spraying these plants under adverse growing conditions. Pasture sage is a perennial that forms a grayish mat of leaves first, and forms numerous spindly stems by flowering time. It typically forms cluster-like flowers around August.

Recommended herbicides

Refer to the label or the Saskatchewan Guide to Crop Protection for the most up to date herbicide recommendations and registrations.

Research has shown that infested domestic forage stands treated with a combination of a balanced fertilizer blend and 2, 4-D LV Ester has dramatically enhanced results. The 2, 4-D suppresses the pasture sage, while the fertilizer promotes the recovery of the forage species. Manage for a competitive forage stand in combination with chemical control.

Recommended cultural method

Pasture sage is known as an "opportunistic" species and an infestation often indicates excessive grazing pressure. Best results come from maintaining a healthy forage stand by utilizing proper grazing management that minimizes overgrazing. Applying manure or fertilizer on tame forage stands will assist in forage recovery.

Deferred grazing may be required to allow native or tame species recovery.

Field Bindweed (Convolvulus arvensis)

Best time for chemical control

Generally, most herbicide applications should be made from the late bud stage up to the full flowering stage and early seed-set (June to August),.  Be sure to check the label as different herbicides have a different recommendation for timing.

Recommended herbicides

There are many herbicides currently registered for application to field bindweed that will only provide top growth control.

For control of the perennial root:

  • Picloram (Tordon 22K);
  • Dicamba (Banvel II/Oracle, DyVel DSp); and
  • Triclopyr (Remedy).

For additional information, refer to the current edition of the Saskatchewan Guide to Crop Protection. Manage for a competitive forage stand in combination with chemical control.

Recommended cultural method

Field Bindweed is a deep rooted creeping perennial reproducing by both seed and rootstock. Preventing an infestation is important, since seeds have been reported to survive for up to 50 years in the soil. Bindweed can store two years of carbohydrate energy in its roots, so a multi-year integrated plan is needed.

Sheep are known to graze field bindweed and help keep it in check.

The biological control agent Aceria malherbae, a European gall-forming mite that attacks the growing points of the plant works well initially. The mite needs to be reintroduced over time in some locations as initial numbers decline. Manage for a competitive forage stand.

Canada Thistle (Cirsium arvense)

 
Best time for chemical control

Research has shown that fall herbicide applications work the best. Sugar movement is primarily root-ward when daylight length is less than 15 hours. This allows some systemic herbicides to move with sugars to the root where efficacy is increased.

Best efficacy is observed when herbicides are applied during times when the plant is weak - in short supply of stored energy - or when the plant is replenishing its root reserves.

Flowering can occur from July to September.

Recommended herbicides

Canada thistle has a number of herbicide registrations for control. Refer to the Saskatchewan Guide to Crop Protection for products and type of control. Some products will only give top growth suppression while others give season long control with some root kill.

Most of these herbicides will provide better results when applied later in the season as days shorten and buds are formed on the Canada thistle. Manage for a competitive forage stand in combination with chemical control.

Recommended cultural method

Canada thistle is a perennial that reproduces by seed and rootstock. Alfalfa, brome, or alfalfa/brome mixtures are able to supply good competition to help control Canada thistle, and continual top growth removal weakens root reserves.

Fields coming out of two to three years of hay production were found to have significantly lower populations of Canada thistle than nearby fields that were continually cropped with annuals.

Dandelion (Taraxacum officinale)

Best time for chemical control

Similar to Canada thistle, dandelion is most vulnerable to fall applied herbicides before significant leaf tissue is lost due to frost. Herbicide application in the spring is the next alternative, provided they are sprayed prior to the onset of flowering. When the dandelions are dormant in summer, herbicides are essentially ineffective.

Recommended herbicides

Many chemical registrations exist for controlling dandelions at the seedling stage, but fewer chemicals are registered for control of perennial plants. Grazon, XC, Navius, Reclaim II and Restore II will give good control of perennial plants.

Also research by Alberta Agriculture and Rural Development has shown that Ally/Escort applied at three grams/acre in the fall to tolerant grass forage species provides excellent control of dandelion.

Pre-harvest glyphosate is useful to control dandelion when terminating forage stands. Manage for a competitive forage stand in combination with chemical control.

Recommended cultural method

Clipping is ineffective on dandelion since it does not produce an aerial stem other than the flower stalk. Dandelion seeds require light on the soil surface in order to germinate and maintaining a competitive stand of forage will prevent dandelion from becoming established.

Dandelion infestations in alfalfa indicates renovation is necessary. Alfalfa populations will naturally thin over time, due to self inhibition, and dandelions will move into openings in the stand.

Fertilizing domestic grass species will increase competitiveness against dandelion. Deferring harvest (clipping or grazing) of forage crops will help to smother low-growing dandelion, and allow recovery of tired native stands.

Leafy Spurge (Euphorbia esula)

Best time for chemical control

New small leafy spurge infestations should be treated without delay. Since the seed capsules burst when ripe, shooting seeds as far as five metres, it is imperative that the infested area be contained so that surrounding lands are protected from further invasion. Seeds can remain viable up to eight years in the soil.

Controlling established leafy spurge with herbicides alone is a costly and long-term exercise. Apply growth regulator herbicides (Group 4) when leafy spurge is actively growing, and the yellow colour begins to fade from the flower structures in early July.  Seed viability will be reduced if treatments can occur before seeds turn from yellow to brown or grey.

Glyphosate products perform better when applied in September. Remember that in crop applications of glyphosate will kill the forage plants.

Recommended herbicides

Picloram (Tordon 22K) is the most commonly used herbicide on established plants, but is long lived and mobile in more porous soils, resulting in restrictions on its use.

Research from the United States has shown Dicamba (Banvel II/Oracle) or lower rates of Trodon + 24D = Grazon xc plus an adjuvant to be effective with repeated annual  applications, over a period of three to four years. Herbicides such as 2,4-D and MCPA only provide top growth suppression or small seedling control.

Frequent application may be necessary to prevent seed production.

Leafy spurge is impossible to control with a single treatment of any herbicide. Manage for a competitive forage stand in combination with chemical control.

Recommended cultural method

Leafy spurge is a perennial that spreads by seeds and from underground rootstock. Leafy spurge is best managed using an integrated control strategy that includes several non-conflicting approaches. These methods include:

  • biological (beetles);
  • sheep and goat grazing;
  • fire; and
  • managing for a competitive forage stand.

Scentless Chamomile (Matricaria perforata)

Best time for chemical control

Herbicides should be applied to scentless chamomile in the vegetative stage before flowering and while actively growing. Most herbicides registered to control scentless chamomile are to be applied between the two and four leaf stage. Larger plants are more difficult to control.

Since scentless chamomile can be a winter annual, or an annual, it is important to spray these plants at an early stage. Flowers may occur from late May until freeze-up and contain viable seeds once white petals are visible.

Recommended herbicides

See the Guide to Crop Protection for a current selection of herbicide options.

Recommended cultural method

Scentless chamomile can be an annual, biennial, or short lived perennial. Manually picking, bagging, and burning this plant is practiced in some communities.

There are three biological control insect species available to suppress scentless chamomile. Competitive grass forage will suppress the growth of scentless chamomile, but edges of those fields may still be susceptible. Scentless chamomile flowers contain viable seeds, once white petals are obvious.

Mowing or clipping may be conducted prior to this time to reduce seed shed, but scentless chamomile will re-grow from below the cut line and require re-cutting.

The first clipping should be made high, with each subsequent cut lowered slightly so that the final cut of the season is the lowest available for the mower. Mowing while scentless chamomile is in flower can result in wet material containing viable seeds sticking under shrouds. Seeds are then spread further along the direction of travel as debris is ejected from the mower.

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