1. Weeds and their importance

2. What are weeds? Plants growing where they are not wanted
Plants out of place
Plants whose virtues have yet to be discovered
Is this a limited definition?
Questions
Is there a difference between a volunteer potato plant in a patch of lettuce and an invasive, persistent, noxious plant species like field bindweed (Convolvulus arvensis L.)?

3. Noxious weeds What makes a weed ‘noxious’?
A noxious weed is defined by Montana Law (MCA ) as, “any exotic plant species established or that may be introduced in the state that may render land unfit for agriculture, forestry, livestock, wildlife, or other beneficial uses or that may harm native plant communities.” 
Any unwanted non-native plant with potential impact serious to the extent that it has been declared by the state of Montana that landowners must enter into an approved management program to keep it from spreading.

4. Montana has 32 state-listed noxious weed species
A weed gains ‘noxious’ status through rule-making authority by the Montana Department of Agriculture, as a district noxious weed by a county weed board, and/or following public notice of intent and a public hearing regarding the status of a weed.
If a weed is designated as a statewide noxious weed by rule of the Department of Agriculture, that weed must be considered noxious in every county of the state. 

5. How are noxious weeds classified in Montana?
State designated noxious weeds are categorized into five different levels or Priorities.
These levels are classified as priorities 1A, 1B, 2A, 2B and 3. 
This ranking system is based on the management techniques used to control the species as well as their presence and population density. 
In Montana, there is only one species of noxious weed listed under Priority 1A, and currently this plant, yellow starthistle, is not present in the state. 
Under each Priority listing there is a brief description of what is to be done if the species listed under that Priority is found.  Also listed under each Priority heading are the species including their scientific name.   

6. What are weeds? Plants growing where they are not wanted
Plants out of place
Plants whose virtues have yet to be discovered
Is this a limited definition?
Questions
Is there a difference between a volunteer potato plant in a patch of lettuce and an invasive, persistent, noxious plant species like field bindweed (Convolvulus arvensis L.)?
Are there certain characteristics that a weed possesses that set it apart from other plant species?

7. Ideal Characteristics of Weeds
Discussion
What makes a weed successful?
Germination requirements fulfilled in many environments
Discontinuous germination and great seed longevity
Rapid growth through vegetative phase to flowering
Continuous seed production
Self-compatibility
Cross-pollination by unspecialized visitors or wind
Very high seed output

8. Ideal Characteristics of Weeds cont’d
Production of some seed in variable environmental conditions
Adaptations for short and long-distance seed dispersal
If a perennial, vigorous vegetative reproduction or regeneration from fragments
If a perennial, brittleness, so as not to be pulled from the ground easily
Ability to compete interspecifically by special means
Rosette, choking growth, allelochemicals

9. The Bottom Line
Weeds are successful because they have special biological features that allow them to:
Harm other plants
Survive in a variety of environments
Produce abundant, long-lived seeds
Grow and spread rapidly
Can we come up with a better definition for a ‘weed’?
Weeds are plants that interfere with the growth of desirable plants and are unusually persistent.
They damage cropping systems, natural systems, and human activities, and are therefore undesirable.

10. The Impacts of Weeds Crop impacts Loss of yield Loss of quality
12% of crop loss in the US
$32 billion annually
85% of cropland receives an annual application of herbicide
$6.6 billion annually in chemical control
Doesn’t include the cost of herbicide application, tillage, hand-weeding
Can also have indirect impacts by limiting other resources (e.g., water)
Loss of quality
Weeds contaminate harvested crops
Objectionable odors
Wild garlic in wheat, mustards in dairy feed can ruin milk
Crop spoilage from moisture
Staining of crop or edible seeds

11. The Impacts of Weeds Crop Impacts
Increase processing required for harvested crops
Added expense
Loss of value
Can’t be used as certified seed
May be docked at the grain elevator due to presence of weed seeds
Limit management choices
Crop selection
Limited by life cycle of weeds present, herbicide compatibility/carry-over
Tillage options

12. The Impacts of Weeds Crop Impacts Harbor non-beneficial pests
Overwinter in crop debris and underground root systems
Rodents in no-till crops
Interfere with harvesting
Slows hand-harvesting
Vines and thicker-stalked weeds wrap around cylinders of mechanical harvesters
Wear on machinery
Necessitates the use of desiccants
Increase transportation costs

13. The Impact of Weeds Human Impacts Livestock impacts Allergies/rashes
Weed pollen (from ragweed and perennial grasses) affects more that 45 million Americans
Poison ivy/poison oak
Fires
Obstructions
Poor aesthetics for homeowners
Livestock impacts
Poisonous plants in rangeland
Tall larkspur, locoweed, lupine, halogeton, leafy spurge
Milk sickness, abortion, death
Reduced value of rangeland

14. Downy brome/cheatgrass Eurasian watermilfoil
Invasive Species
Many crop weeds are native, but many others are introduced
As many as 73% of weed species in crops are non-native
Invasive species are:
1) non-native to the ecosystem under consideration
2) species whose introduction causes or is likely to cause economic, environmental, or human health problems
Better known invasive species in the US:
Leafy spurge (Euphorbia esula)
Purple loosestrife (Lythrum salicarid)
Yellow starthistle (Centaurea solstitialis)
Giant reed (Arundo donax)
Downy brome/cheatgrass
(Bromus tectorum)
Saltcedar (Tamarix spp.)
Spotted knapweed
(Centaurea maculosa)
Eurasian watermilfoil
(Myriophyllum spicatum)

15. Questions!
Cropland weeds allow farmers to choose from a multitude of crop management options. True or False.
In Montana, a noxious weed is considered to be “any ________ plant species established or that may be introduced in the state that may render land unfit for agriculture, forestry, livestock, wildlife, etc.”
Native
Exotic
Non-invasive
Undesirable
Name one characteristic that helps weed species increase their success, and explain why it makes them successful.

16. Common lambsquarter Scientific name: Chenopodium album
Family: Amaranthaceae (aka the Goosefoot family)
Life cycle: Annual
Where found: Cropland
Physical description:
Seed: shiny black
Cotyledon: linear to bluntly lanceolate
True leaves ovate to lanceolate
Alternate arrangement
Have a mealy/powdery coating on underside of leaf
Newest leaves of seeding often tinged pink/purple
Stems pink or purple, often striped at maturity
Upright growth habit
Interesting facts:
Latin name describes plant
Chen=goose, podium=foot refers to shape of true leaves
album=white, refers to whitish coloration imparted by the mealy coating

17. Redroot pigweed Scientific name: Amaranthus retroflexus
Family: Amaranthaceae
Life cycle: Annual
Where found: Cropland
Physical description:
Seed: shiny black
Cotyledon: linear to lanceolate, reddish undersides
First true leaves ovate, slightly notched at tip
Subsequent true leaves ovate to lanceolate, small bristle at leaf tip
Alternate leaf arrangement
Leaves feature prominent veins
Upright growth habit
Interesting facts:
Thick, red taproot
Inflorescence is characterized by the presence presence of spiny green bracts