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| Wednesday, January 03, 2007 |
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Frequently Asked Questions - Control of Select Weeds on Pastures and Hay Land in Saskatchewan Absinthe (Artemisia absinthium) To get an answer to your own question, click here
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 additional new growth. More than one season may be required to achieve full control. Recommended herbicides: 2, 4-D LV Ester and Banvel II are both registered for use in pastures that have no legumes. 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. Since Absinthe reproduces entirely by seed, spread may be minimized by mowing, as buds are emerging. Otherwise, Absinthe spreads very slowly, vegetatively, through expansion of the crown. When fractured by a disturbance, the crown may also reproduce a new plant from transplanted pieces. Competitive grasses may 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: 2, 4-D LV Ester and Banvel II are registered to control pasture sage in non-legume pastures. Tordon 22 K is also registered. 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. Recommended cultural method: Pasture sage is known as an “opportunistic” species in pastures. High infestations are usually the result of open soil, as a result of improper grazing techniques. Best results come from maintaining a healthy forage stand. This can be achieved by utilizing proper grazing management that allows forage species to recover periodically so they may compete with this opportunist. Applying manure or synthetic fertilizer will assist in the recovery of domestic forage species, but deferred grazing for up to four years may be required to allow native species to recover.
Field Bindweed (Convolvulus arvensis) Best time for chemical control:
Generally, most herbicide applications should be made somewhere around the late bud stage up to the full flowering stage (June to August), and slightly beyond the flowering stage. Different herbicides have a different recommendation for timing. Be sure to check the label. Recommended herbicides: There are many herbicides currently registered for application to field bindweed that will only provide top growth control. Picloram (Tordon 22K), dicamba (Banvel II/Oracle, DyVel DSp) and triclopyr (Remedy) based herbicides provide control of the perennial root. For additional information, check the current edition of the Saskatchewan Guide to Crop Protection. Recommended cultural method: This is a deep rooted creeping perennial reproducing by both seed and rootstock. Prevention 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, then declines in numbers, and needs to be reintroduced over time in some locations.
Canada Thistle (Cirsium arvense)Best time for chemical control:
Research has shown that results are better with fall herbicide applications to control this weed. Sugar movement is primarily rootward when daylight length is less than 15 hours, allowing some systemic herbicides to move with sugars to the root where efficacy is increased. Best results are observed when herbicides are applied during times when the plant is weak (when it is in short supply of stored energy) or when the plant is replenishing its root reserves. Herbicide efficacy is enhanced during this time. Flowering can occur from July to September. Recommended herbicides: Canada thistle has a number of herbicide registrations for control (see Saskatchewan Guide to Crop Protection), but generally those containing glyphosate (Roundup, Vantage, Touchdown, etc.) or clopyralid (Lontrel, Curtail M, etc.) are considered the most effective. Most of these herbicides will provide better results when applied during short days. 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.
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. Applications of herbicide in the spring are 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. Research by Alberta Agriculture Food 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 renovating old alfalfa stands. 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, therefore maintaining a competitive stand of forage will prevent dandelion from becoming established. Dandelion presence in alfalfa is a good indicator of a need to renovate alfalfa stands. Alfalfa populations will naturally thin over time, due to self inhibition, and as a result, dandelion will move into gaps 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 infestations of leafy spurge should be treated without delay in order to attempt eradication and prevent spread. 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 as 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. 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) to be effective with repeated applications, over a period of three to four years. Herbicides such as 2,4-D and MCPA only provide control of the top-growth of leafy spurge, or control of seedlings, and require frequent applications just to prevent seed production. This plant is impossible to control with a single treatment of any herbicide. Recommended cultural method: Leafy spurge is a perennial that spreads by seeds or from underground rootstock. Leafy spurge is best managed using an integrated control strategy that includes several non-conflicting approaches. These methods may include: biological (beetles), sheep and goat grazing; fire; and seeding of competitive grasses in conjunction with herbicide treatments, to contain established stands. 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.
Scentless Chamomile (Matricaria perforata) Best time for chemical control:
Herbicides should be applied to scentless chamomile while in the vegetative stage of growth and while actively growing. Most herbicides registered to control scentless chamomile are to be applied between the two and four leaf stage. 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. Larger plants become increasingly more difficult to control. Recommended herbicides: Scentless chamomile is tolerant to 2,4-D and MCPA. Herbicides containing metsulfuron methyl (Ally, Escort), clopyralid (Lontrel, Curtail M, etc.) or bromoxynil (including mixes of bromoxynil and either MCPA or 2,4-D) are active on scentless chamomile. Metsulfuron and clopyralid are for use in grass forages only. Bromoxynil may be used when scentless chamomile plants are up to the four leaf stage in alfalfa seedlings, to assist with establishment. Velpar used in established alfalfa for seed production controls the seedlings of scentless chamomile. Recommended cultural method: Scentless chamomile may 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 will 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, and being spread further along the direction of travel as debris is ejected from the mower. Most weeds are often best dealt with prior to seeding or re-seeding land to a forage crop. Forage crops will establish much easier in the absence of these problematic weeds, and production levels will be much greater. Once established, competitive forage crops provide the best defense against the invasion of problem plants. More information can be found at these Internet websites: Scentless Chamomile, Biology and
Management Acknowledgements: Dale Risula, SAF, Integrated Cropping Management Systems Specialist | ||||||
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