Working together to strengthen and support noxious weed management efforts in Montana.

Manual Weed Control

Hand Pulling

Pulling Spotted Knapweed - photo credit Diana EricsonIf you do not have a large infestation of noxious weeds, hand pulling may be a viable option, however, this technique can involve a great deal of labor and time. Noxious weeds can be-pulled in small patches (1/4 acre or less) with the exception of Canada thistle, leafy spurge, and perennial pepperweed and/or other rhizomatous rooted plants. Breaking up the soil can cause further infestations, so care must be taken to minimize impacts on soil and make sure that all equipment and clothes are inspected for weed seed before moving into or out of the site. Annuals and noxious weeds with tap roots, such as spotted knapweed and houndstongue, are more effectively controlled with hand pulling. Perennial plants and those noxious weeds with extensive and/or rhizomatous root systems, such as leafy spurge or Russian knapweed, are not as effectively controlled with this method. When pulling weeds, it is highly advisable to wear gloves as some plants can cause moderate to severe skin irritation. Knapweed, for instance, contains toxins that can cause irritation to the skin. The key to hand pulling is to remove as much root as possible with minimal soil disturbance. With many noxious weeds, any parts of roots left behind can still be viable and sprout. The best method of disposing weeds after pulling is to put them in plastic garbage bags and take them to your landfill. Regarding concerns over spreading weeds at the landfill site, these bags are buried deep, the biological break-down process inhibits growth, and if they do manage to survive these first two components, weeds will be contained in a local site which most county weed districts monitor.

Mowing

Mowing reduces seed production in some plants. It is most effective on annuals before they flower and set seed, but timing and frequency of mowing varies with each species. It has been shown that mowing can increase seed production in diffuse knapweed, while spotted knapweed can show a seed decrease when mowed in the flowering stage. However, in some species, re-sprouting occurs quickly and in large volume. Spotted knapweed has the ability to shorten its height and flower and set seed at lower levels after extended mowing. As a part of an integrated weed control program, mowing will remove large amounts of vegetation which will then allow for more effective herbicide treatments. Remember after mowing, that it is important to gather up noxious weed flowers and seeds to prevent further infestations. Again, the best method of disposal is to bag weeds up in plastic bags and dispose of them at your landfill.

Some noxious weeds will respond to this method of treatment in that mowing reduces seed production, but it will not control the plants and can further spread infestation through dispersal of seed or plant parts.

Cultivation & Other Mechanical Methods

Tilling, disking, plowing, or the use other equipment to create a soil disturbance is generally limited to cropland and pasture situations. Mechanical control can be effective against -rooted biennials and perennials such as diffuse & spotted Knapweed, but small fragments of some species, particularly those perennials with rhizomes, can often re-sprout following tillage. Some rhizomatous noxious weeds, such as leafy spurge or Russian knapweed, are not effectively controlled by mechanical alone. Mechanical control should be completed before seeds develop and are shed onto the soil. The best control is achieved when the soil remains dry so that remaining plant fragments dry out instead of  re-growing.  Mechanical methods may be used to stimulate seed germination and should be followed by additional mechanical disturbance or herbicide application to control emerged seedlings.  Mechanical control is not recommended in erosion-prone areas.

If mechanical methods are your preferred choice of control, the weeds should be managed prior to flowering. Re-vegetation should be a component when using this method.  Planting competitive vegetation, using smother crops, and crop rotation are most often suited to cropland agriculture.  When dealing with noxious weeds in non-cropland settings, it is important to maintain the native or desirable vegetation in a healthy condition to allow adequate competition once the weeds have been controlled.

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