Best Management Practices
for the Noxious Weeds of
Mesa County

Jude Sirota
Mesa County Horticulture Pest and Weed Inspector
Tri River Area
CSU Cooperative Extension
Grand Junction, Colorado


General Rules

1) KNOW YOUR WEEDS! Identification is the first step in forming a weed management plan.

2) Early detection is always the best defense against noxious weeds. Treat intensely when a new or small patch is found.

3) Understand the biology of the weed to identify the best management practices.

4) Know which growth stage to implement control measures so that control is most effective. For example, once a biennial or annual has gone to seed, it is too late to do anything about it. Spraying a perennial in the rosette stage is a waste of chemicals as the root system will send up new shoots.

5) Use weed free seed, hay, forage, and mulch.

6) Reseed site with competitive species. Grasses are often recommended so that broadleaf herbicides can be used to spot treat broadleaf weeds.

7) When tilling, till only in the weed patch so roots and seeds do not get spread. Always clean equipment and machinery after working in a weed patch to prevent spread.

8) Many biological control agents are available for control of large weed patches. This is a long-term process and not recommended for small patches. Biological control never provides 100% control and must be incorporated with other methods for successful management.

9) Weed management is a long term process and hence a long term commitment to the land. Weed seeds last 5-50 years in the soil and pieces of root as small as 1/2 inch can start a new plant and a new infestation.

10) Drought causes plants to shut down their growth process. Spraying weeds during dry periods is not recommended because effectiveness diminishes greatly. Treat after rainfall IF the weed is still in the proper stage for effective control.

11) Not all herbicides work equally on all weeds nor can every herbicide be used in every situation. Noxious weeds, in particular, are often not controlled successfully with products available at nurseries, garden shops and other retail markets. Read the label, and consult weed manuals and experts for the most effective chemical to use.

12) Developing a weed management plan depends on how much time, money, and land a person has. If someone wants to do non-chemical control, they will not need a lot of money, but they will need a lot of time and energy. If they want fast action, herbicides can be the most efficient use of money and time, but not always. Annual weeds may be as effectively controlled with tillage or hoeing as with spraying if done properly and at the right time.

ANNUALS and BIENNIALS

Target: prevent seed production
1) Hand grubbing (pulling), hoeing, tillage, cultivation in rosette stage and before flowering or seed maturity.
2) Chop roots below soil level.
3) Herbicide treatment in rosette or bolting stage, before flowering.
4) Mow biennials after bolting stage and before seed set; mowing annuals may not prevent the plants from flowering.

 

PERENNIALS

Target: deplete nutrient reserves in root system, prevent seed production
1) Allow plants to expend as much energy from root system as possible; do not treat when first emerging in spring but allow to grow to bud/bloom stage.
2) Herbicide treatment at bud to bloom stage or in the fall. In the fall plants draw nutrients into the roots for winter storage. Herbicides will be drawn down to the roots more efficiently at this time. If the weed patch has been there a long time, another season of seed production is not as important as getting the herbicide into the root system. Spraying in the fall will kill the following year's shoots, which are being formed on the roots at this time.
3) Mowing usually is not recommended because the plants will flower anyway; seed production may be reduced, however. Many studies have shown that mowing perennials and spraying the regrowth is not as effective as spraying without mowing. Effect of mowing is species dependent so know what weed you are working with and consult the experts.
4) Tillage may or may not be effective. Most perennial roots can sprout from pieces only one half to one inch long. Clean machinery thoroughly before leaving the weed patch.
5) Hand pulling is generally not recommended for perennial species unless you know the plants are seedlings and not established plants. Hand pulling can be effective on small patches but is very labor intensive because it must be done repeatedly.

 


Control recommendations for species on the Mesa County Noxious Weed List

Dyer's woad (Isatis tinctoria): Winter annual/biennial/short-lived perennial; hand grubbing at early flowering stage, herbicides

Houndstongue (Cynoglossum officinale): Biennial; reseed disturbed sites with fast growing grasses, physical removal of plants at flowering or early seed formation, herbicides at pre-bud or rosette stage

Knapweed, diffuse (Centaurea diffusa): Annual/short-lived perennial; seed head flies, herbicides at rosette stage, tillage in rosette stage

Knapweed, Russian (Acroptilon [Centaurea] repens): Perennial; reseeding disturbed sites with fast growing grasses, herbicide in fall (Curtail recommended), allelopathic - tillage necessary

Knapweed, Spotted (Centaurea maculosa): Biennial/short-live perennial; herbicides at rosette stage, seed head flies

Leafy Spurge (Euphorbia esula): Perennial with high seed production; mowing before seed set followed by fall herbicide application, sheep or goat grazing followed by fall herbicide application, many species of flea beetles available

Oxeye Daisy (Chrysanthemum leucanthemum): Perennial; weed free wildflower mixes; buy Shasta daisy instead; herbicide application at early flowering

Purple Loosestrife (Lythrum salicaria): Perennial with extremely high seed production; early detection and removal, remove flower heads in late summer, hand grubbing in small patches, apply aquatic labeled 2,4-D before flowering, Rodeo in mid-late summer

Tamarisk or salt cedar (Tamarix ramosissima and T. parviflora): Perennial shrub; burning is not recommended; repeated or historic flooding of bottomlands to prevent seedling establishment; hand pulling seedlings; spray herbicides on basal portion of stems of young, smooth barked plants, cut larger plants and treat cut stumps within 30 minutes with concentrated herbicide plus an adjuvant (remove all stems from site after cutting - they will resprout if in contact with soil); shade intolerant - promote growth of native riparian species that will shade out the tamarisk; beetles and mealy bug biological controls not available on Colorado River drainage at this time.

Thistle, Bull (Cirsium vulgare): Biennial; weevils and gall flies, grazing by goats and horses, hand grubbing, tillage or herbicides in rosette stage, repeated mowing at bolting stage

Thistle, Canada (Cirsium arvense): Perennial with high seed production; reseeding with competitive plants necessary, mowing every 2 weeks over 3 growing seasons, mowing followed by fall herbicide application, beetles, herbicides in late summer or fall

Thistle, Musk (Carduus nutans): Biennial; tillage or hand grubbing in the rosette stage, mowing at bolting or early flowering, seed head and rosette weevils, leaf feeding beetles, herbicides in rosette stage

Thistle, Plumeless (Carduus acanthoides): Winter annual/biennial; herbicides, tillage or hand grubbing in rosette stage, mowing during bolting to early flowering stage, seed head weevils

Thistle, Scotch (Onopordum acanthium): Biennial; tillage, hand grubbing, herbicides in rosette stage, mowing at bolting stage

Toadflax, Dalmation (Linaria dalmatica): Perennial with high seed production; hand pulling in small infestations, repeated cultivation for several years, herbicides in early flowering stage, caterpillars

Toadflax, Yellow (Linaria vulgaris): Perennial; repeated cultivation twice a year for 2 years during bud stage, mowing 2-3 times per year at bud stage followed by reseeding, repeated application of herbicides during early flowering

Whitetop (Cardaria draba): Perennial with high of seed production; herbicides during bud stage or early flowering

Yellow Starthistle (Centaurea solstitialis): Annual; seeds germinate over a 2-3 month period, weed free hay and seed, weevils and gall flies, repeated cultivation of rosettes, early grazing by sheep, goats and cattle, repeated herbicide application to seedlings or rosettes

Noxious Weed Biology
Species Type* Jan Feb March April May June July Aug Sept Oct Nov Dec
Dyer's Woad-1st year B, P, WA rosettes --> --> --> flowering --> seed set --> germination-rosettes -->
Dyer's Woad-2nd year B, P, WA rosettes --> bolting flowering --> seed set --> -->
Houndstongue B rosettes --> prebud flowering - seed set germination --> --> -->
Knapweed, Diffuse B, A --> --> rosettes --> bolt flowering seed set --> germination -->
Knapweed, Russian C P emerges --> flowering --> --> regrowth -->
Knapweed, Spotted P   germination   bolt flowering seed set --> germination
Leafy Spurge C P growth bracts-flowering seed set --> regrowth -->
Oxeye Daisy P growth --> --> flowering - seed set --> -->
Puncturevine A emerge flowering and seed set continuous
Purple Loosestrife P growth --> --> flowering and seed set continuous -->
Tamarisk* P semi-dormancy --> leaves emerge flowering & seed set growth flowering & seed set senescence & semi-dormancy
Thistle, Bull - 1st yr B germination   rosettes --> --> --> --> --> --> -->
Thistle, Bull - 2nd yr B --> --> --> --> bolting flowering seed set--> --> --> rosettes
Thistle, Canada P rosettes --> --> flowering seed set regrowth -->
Thistle, Musk - 1st yr B germination rosettes --> --> --> --> --> -->
Thistle, Musk - 2nd yr B rosettes --> --> --> bolt flowering seed set -->
Thistle, Plumeless WA, B rosettes --> --> --> flowering seed set --> --> germination - rosettes
Thistle, Scotch B rosettes --> --> --> --> bolting flowering - seed set germination - rosettes
Toadflax, Dalmatian P growth   flowering - seed set
Toadflax, Yellow P growth bud stage --> flowering - seed set --> -->
Whitetop C P emergence flowering --> seed set regrowth --> --> -->
Yellow Starthistle A --> --> --> --> bolting flowering - seed set --> germination -->
A = annual; WA = winter annual; B = biennial; P = perennial; CP = creeping perennial
Shaded areas indicate best control timing.
*Tamarisk control can be done at any time of year, but is easier when leaves are absent and weather is cooler.

 

Colorado State University, U.S. Department of Agriculture and Delta, Mesa, Montrose & Ouray Counties cooperating. Cooperative Extension programs are available to all without discrimination. No endorsement of products is intended nor is criticism of products mentioned.


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