1. Noxious Weed Ecology
© J. Mohler

2. Why should I care about weeds?
1 spotted knapweed plant = 300 flower heads = 140,000 seeds = densities of up to 2 million plants per acres
Spotted knapweed roots are involved in chemical warfare. The roots exude a substance called catechin, which acts as an herbicide to inhibit competition from other plant species.

3. Invasive Weed Spread Weed Annual Spread Reduced Grazing Canada Thistle
10%
42%
Leafy Spurge
12%
59%
Spotted Knapweed
24%
80%
Source: Living on the Land v. 1, UNCE/WSARE

4. Weeds Impact Wildlife Reduce wildlife forage
Alter thermal and escape cover
Change water flow and availability to wildlife
Elk lose productive winter & spring ranges, resulting in a decline in numbers and a marked change in distribution patterns
In some cases, noxious weeds increase soil surface runoff and sedimentation into streams, a process many scientists believe is the beginning of desertification.
source:

5. What are noxious weeds? Plants species that are deemed to be invasive
and possess the capacity to negatively impact
the state's natural vegetation communities
and agricultural lands. 
Noxious Weeds are defined in state law as exotic species which may render land unfit for agriculture, forestry, livestock, wildlife, or other beneficial uses or that may harm native plant communities and are determined by Rule of the Montana Department of Agriculture (MDA) under the provisions of the Montana County Weed Control Act. 
Individual counties may further designate species as Noxious Weeds in their respective jurisdictions. 

7. Noxious vs Nuisance Weed
Oxeye Daisy Dandelion

8. The three D’s of noxious weeds
Damaging to the economy or environment
Difficult to control
Tend to Dominate a site
Image: MSU Extension Bulletin 134

9. How do weeds ensure their success?
Competitive - grow well in spite of interference from other plants
Adaptable - to changing conditions
Persistent
-will return year after year
-reproduce vigorously
-spread seeds effectively
© J. Mohler

10. Phases of Invasion: Introduction, Colonization, Naturalization
Prevention
Eradication
Containment
Restoration

11. Gallatin-Big Sky Weed Committee
Step 1 - Identification
Montana Weed Control Association
Gallatin-Big Sky Weed Committee
Houndstounge

12. Step 2 - Understand Weed Biology
Annual
One season for all stages of development
Produce foliage, flower seeds, then die
Biennials
Require two seasons for completion of life cycle
First year: develop roots and low-growing leaves
Second year: flowers, sets seed and matures
Examples are houndstounge & musk thistle
Perennials
Live more than two years
Will produce foliage, seed, and reach maturity year after year
Examples are leafy spurge and Canada thistle
Musk Thistle
Canada Thistle

13. Reproduction Annuals & biennials Seed Seed Bank Perennials
Reproduce by seed and roots
Canada thistle - Creeping horizontal roots sprout new plants and can reach more than nineteen feet in one season. These roots can also go as deep as twenty two feet.
Creeping roots of Canada Thistle

14. Seed Production & Seed Bank
One spotted knapweed plant can produce up to 140,000 seeds, and seeds have been shown to remain viable in the soil for up to 8 years
Seed Bank = the store of seeds in the soil
Proportion of viable seed in seed bank decreases with decreased disturbance frequency
Seed predation: by birds, rodents, insects, worms, microbes
Denmark: 600 year old seeds were found in a monastery.
11 seeds germinated!

15. How do weeds spread? Natural means wind water animals Mechanical means
irrigation
harrowing & spreading manure
construction/fill dirt
vehicles
tillage
contaminated seed or feed
ornamental plants
© J. Mohler
Dalmation toadflax was planted in the gardens around Mammoth in YNP for table flower arrangements. It quickly escaped cultivation and aggressively reproduced in the surrounding area.

16. Disturbance
Disturbances open up habitat that is suitable for pioneer species by making available light, water, nutrients or bare soil that theses species require.
Natural = hurricanes, fires, floods, pests, & diseases
Man made = building roads, construction, grazing, etc.

17. Step 3: Understand Weed Management
Prevention is the first line of defense to keep weeds from occurring or increasing.
Eradication is the removal of weeds from an area so they will not recur unless reintroduced.
Control reduces a weed population to a manageable level
Noxious weed reality check – in general, it takes several years of repeated management to reduce or eliminate the population.

18. Preventing Invasion & Spread of Weeds
Minimize soil disturbance and bare ground
Don’t overgraze pastures
Avoid driving in weed infested areas
Don’t transport flowering plants that you cannot identify
Pull small patches before seed is formed
Collect burs / seeds that stick you to & your dog and throw away!
Carefully remove weeds that have flowered – cut and bag flowers & seeds!

19. Eradication
Removal of all weeds of a given species from an area so they will not recur unless reintroduced
Must deplete seed bank of viable weed seeds by controlling all seedlings
Requires yearly management for multiple years
Must revegetate the area with competitive vegetation
The best time to control weeds is in the first growing season, when they are all “annuals”.

20. Control
Mechanical controls
Biological controls
Chemical controls

21. Mechanical Treatments
Cultivation/tillage
Hoeing
Burning
Hand-pulling – always wear gloves & bag those weeds!! Best for tap rooted plants.
Mowing

22. Mowing weeds
Weeds can adapt to mowing…and even be encouraged to spread!!! Canada thistle & leafy spurge send up more tillers, spotted knapweed adapts by spreading low to the ground.
The best time to mow is just before the target weed reaches the flowering stage (reduces seed production & seed bank)
If already gone to seed, you may be spreading the weed seeds around!
A combination of mowing and spraying can be a good 1-2 punch!
Don’t mow lower than 3-4 inches, as you’ll set your grasses back

23. Biological Treatments
Biological control is the use of one organism to suppress another
More effective in combination with other treatment
Can reduce herbicide use
Goal is not total elimination, just to lower general equilibrium
Remember: the weed is their food, so bio controls goal is not to eliminate the weed!
Slower acting control
Great for areas where spraying is not an option: wetlands, riparian areas, steep slopes
Photos: Living on the Land v.1, UNCE/WSARE

24. Chemical Treatments Wear protective clothing: Eye protection
Long sleeve shirt
Chemical resistant gloves
Long pants
Rubber boots
Always read & follow the label
Select the correct herbicide for the weed species you have!!
Understand when& where to apply herbicides
Correctly apply herbicide through calibration
Mix & handle herbicides property
Safely store & dispose of herbicides

25. To be effective, a herbicide application must have:
Proper placement – appropriate dose, proper calibration
Even distribution – depends on nozzle shape & size, nozzle position, pressure
Proper timing – apply when weeds are most susceptible (bolting stage or time of active growth)

26. Caution!! Herbicide Carryover
Herbicides can persist in hay, manure, compost, & grass clippings.
These herbicides eventually break down through exposure to sunlight, soil microbes, heat, and moisture.
Depending on the situation, the herbicides can be deactivated in as few as 30 days, but some field reports indicate that breakdown can take as long as three to five years.
Herbicide carryover can kill your garden!

27. © J. Mohler
A healthy stand of desirable / native vegetation is your best defense against weeds!! The mark of a healthy landscape is species diversity - grasses, forbs, shrubs, trees

28. Native Plants
Once established, native plants are easy to maintain because they are adapted to Montana temperatures, rainfall patterns, and soil conditions.
They resist local pests and disease.
Native plants reduce soil erosion, build soil structure, and absorb rainfall.
Native plants are preferred by native birds and wildlife for food & shelter.
© J. Mohler

30. Xeriscape
It integrates the principals of several conservation initiatives such as:
Reduces water, energy, and chemical usage
Reduces maintenance (cost & time)
Wildlife habitat enhancement
Invasive weed management
Promoting native plants

31. Landscaping with native plants
Many resources available online
Montana Native Plant Society
– on “Weed ID & Control” page

32. Canada thistle (Cirsium arvense)
Asteraceae (Sunflower family)
Colony-forming perennial
Reproduces vegetatively by rhizomatous roots or by seeds
Leaves are spine-tipped and wavy
Flowers are both male and female on separate plants

33. Hoary alyssum (Berteroa incana)
Brassicaceae (Mustard family)
Annual, biennial, or short-lived perennial forb
Tap root
Reproduces from seeds
Plants first form a basal rosette or leaves, followed by an upright, central stem 1-3 feet tall
“Hoary” comes from rough hairs on stems, leaves, & fruit
Numerous white flowers with four deeply divided or notched petals
Toxic to horses

34. Houndstongue (Cynoglossum officinale)
Boraginaceae (Borage family)
Biennial forb with a tap root
Reproduces by seeds/burr-like nutlets
Velvety leaves lack teeth or lobes – rough to the touch
Flowers have five reddish-purple petals
Toxic to horses

35. Musk thistle (Carduus nutans)
Asteraceae (Sunflower family)
Biennial, perennial forb
 Flower heads droop on the stem when fully developed, giving musk thistle its other common name, “nodding thistle.” 
 Seeds are carried on the wind with the aid of a pappus of fine bristles. The seeds may remain viable in the soil for as long as a decade. 

36. Spotted knapweed (Centaurea maculosa)
Asteraceae (Sunflower family)
Short lived perennial, sometimes biennial
Flowers are pinkish-purple, one per stemmed branch, ~300 per plant
Floral bracts are tipped with dark comb-like fringe
Deep taproots help this plant compete for water and other essential nutrients
Secondary compounds may cause allergic reactions in some people

37. Oxeye daisy (Chrysanthemum leucanthemum)
Asteraceae (Sunflower family)
Showy perennial herb
Reproduces by seed or vegetatively by rhizomes
Leaves have rounded teeth, widest at the tip
Flowers consist of white ray flowers (long petals) and yellow disk flowers (center of the flower head).
Shasta Daisey on left, Oxeye daisy on right

38. Yellow toadflax (Linaria vulgaria)
Scrophulariaceae (Figwort family)
Perennial
Reproduces by seeds and underground rootstalks
Leaves are pale green, numerous, narrow, pointed at both ends
Flowers are 1” long with bearded orange throat

39. Review Identify weeds correctly
Create a management plan that takes into account the biology and ecology of the property
Promoting healthy/competitive vegetation
Use all the tools in the weed management tool box!
© J. Mohler

40. Review Properly use herbicides
Select based on the noxious weeds present
Calibration – a must for proper application
Apply at the right time
Follow the label – it’s the law
If you don’t know – get help!!!

41. Adaptive Management
Successful weed management requires constant vigilance!
Successful weed eradication requires yearly
treatment for many years.

42. Help Available Gallatin-Big Sky Weed Committee
Click on “Weed ID & Control” page for info on pet safety, how to calibrate a sprayer, herbicide carryover, “cheat” sheets for each noxious weed species, etc.
Gallatin County Weed District
- Cost share
- Sprayer rental
- Property inspections
- Enforcement & compliance
Montana Weed Control Association

44. Acknowledgements
Adapted with permission from Living on the Land: Stewardship for Small Acreages, copyright 2001 University of Nevada Cooperative Extension/WSARE, UNCE CM-03-07
Additional sources:
Montana Weed Control Association
Montana's Statewide Noxious Weed Awareness and Education Campaign
Center for Invasive Plant Management
Montana State University Department of Animal & Range Sciences
Colorado State University’s Guide to Poisonous Plants