1. Weed Control
Plant Science 280
Mr. Gomes

2. Weed Ecology The growth and adaptations of weeds!
How do people play a role where the practice of agriculture is life
Adaptive properties that that enable weeds to do well under certain conditions
There is a strong human influence on the ecological relationships of weeds

3. Weeds in Ag Most Ag weeds are specialists to disturbed soils
People have played a huge role in the propagation of specialty weeds
Rangelands, forests, and other native sites don’t offer the nutrient rich climate
Why do most of our weeds come from Europe and not Asia???

4. The Ideal Weed (Baker 1974) Germinated in many environments
Great longevity of seed
Rapid growth through vegetative phase to anthesis
Continuous seed production
Self compatible
When cross pollinated, unspecialized visitors or wind used
Very High seed output
Tolerant
Has adaptations for long and short distance dispersal
Vigorous vegetative reproduction or regeneration from fragments
Plant not easily drawn from the ground
Ability to compete by special means

5. Humans on Weed Ecology
Settlers came to US Great Plains and PNW to inhabit and develop agriculture
They cleared roads, but brought Downy Brome
It flourished in two human created ecosystems in the West
Winter Wheat
Rangeland
Currently it invades roughly 100 million acres
Agriculture created the environment, Humans aided the dispersal
Humans are the only species that can change Ecology

6. Weed Ecology at it’s Roots
Early cultivars of staple grains really started the change
Green Revolution in 1960’s with wheat and rice… changes in maturity
Desirable plant traits changed weed types
Shorter, stiffer strawed, higher grain, nutrient demand
Weeds started to adapt and evolve

7. Understanding These adaptations is crucial to long term planning
Herbicides are not the smoking gun
Increased control on basic manufacturers through legislature and fear
Poor regulatory and stewardship
Therefore understanding how the weed crop ecosystem crucial

8. Shifting towards Ecologically based Weed Management
1.) Highly susceptible weeds replaced by species more difficult to control
2.) Herbicide resistance to chemistry’s and their families
3.) Weeds in monocultural ag that are not easily solved by current techniques.
4.) New weed problems occurring in reduced and minimum tillage systems
5.) Economic factors!!!
6.)Environmental costs (Johnson grass/half life)

9. Three Factors Driving This Ecology
Climate
Light, temp, H2O, wind, humidity,
Soil
Soil H2O, temp, pH, fert, fert source, cropping system
Biota (living organisms)
Mirror seed size to crop, plant look, life cycle, maturity, germ, ripening

14. Driving Factor for these Adaptations
COMPETITION!!!!!!!!!!!!!!!
Nutrients
Water
Light

15. Nutrients N-P-K…The primary plant nutrients
Weeds require the same basic nutrients
Demand requirements changes
Misconception that weeds require vastly more or less nutrients
Timing of that need is the issue
Faster and often times more efficient

16. Water The single limiting factor in crop production
In corn, every day of wilt stress can mean 5-8 % yield loss
Reduction in turgor pressure and lodging
Gallons needed to produce 1 lb of dry matter
Affects on arid or drought stricken regions/time

17. Light Unlike nutrients and water, light cannot be stored
Use it or lose it
Quicker growth
Broader, or higher reaching leaves
Tall versus prostrate
Nightshade in tomatoes
Light variation
Yellow nutsedge and corn by population

19. Characteristics of Competitiveness
Rapid expansion of tall canopy
Horizontal leaves under overcast conditions and slanting leaves under sunny conditions
Large Leaves
C4 photosynthetic pathway and low leaf transmission of light
Leaves forming a mosaic leaf arrangement
A climbing, twining habit
High allocation of dry matter
Rapid stem extension in response to shading

20. Weed Density and Crop Loss
direct correlation
Increased weed density, reduced crop loss