Weed Test 2 Flashcards
Interference
interaction among species involving both competition and allelopathy
Competition
plants compete with one another for resource in short supply
Allelopathy
inhibition of one plant by another through the release of selective toxic metabolic by-products into the environment
Intraspecific interference
interference between plants of the same species
Interspecific interference
interference between plants of different species
Damage/competitive threshold
the weed population at which a negative crop yield response is detected
Economic threshold
the weed population at which the cost of control is equal to the crop value increase from control
Optimum economic threshold
economic threshold plus input of weed seed production on long term economics of weed management decisions
Period threshold
implies that there are times during the growing season in which weeds are more or less damaging than other times
Action/aesthetic threshold
point at which some control action is initiated and usually includes economic considerations along with other less tangible factors such as aesthetics, risk aversion, or sociological pressures
Resistance
acquired ability of a weed population to survive a herbicide application that was previously known to control the population
Tolerance
ability of a species to survive and reproduce after herbicide treatment
Cross Resistance
resistant to two or more herbicide families with SAME mode of action
single resistance mechanism
Multiple Resistance
resistant to two or more herbicides with different modes of action
may be result of two or more different resistance mechanisms
Dominant weeds dependent on
how long and how land has been used agriculturally
nature of the widely dispersed weeds in the region
method of reproduction
competitiveness and density of weed seed per unit area or volume of soil
Characteristics associated with competitive plants
shoot and root characteristics
Shoot characteristics associated with competitive plants
rapid expansion of canopy
overcast conditions: horizontal leaves or
sunny: slanted leaves
large leaves
c4 photosynthetic pathway
and low leaf light transmission
mosaic leaf arrangement for best light interception
climbing habit
high allocation of dry matter to build tall stem
rapid extension in response to shading
Root characteristics associated with competitive plants
early and fast root penetration of a large soil area
high root density/soil volume
high root-shoot ratio
high root length per root weight
high proportion of actively growing roots
long and abundant root hairs
high uptake potential for nutrients and water
Factors influencing competitiveness
variation between species and competing crop
variation in cultivars
variation in competitiveness between weeds of same genus
row spacing influence on weed competition
planting date
duration of a crop
geographic region
level of interference
Critical weed-free period
- a longer critical period means crop is less competitive or the weed is more competitive than the crop
- rainfall and planting date influence critical period
- beginning of critical period influenced more by differences in weed densities and environmental factors
- initiation of weed control based upon crop development stage and susceptible weed stage so better term is critical period of weed control
Environmental parameters involved in weed competition
no competition as long as essential requirements are in excess
2 categories of environmental factors and plant responses:
consumable environmental resources
non-consumable environmental conditions
Consumable environmental resources
water nutrients light CO2 O2 plant response: an increase through a resource-limited phase to saturation level where another factor becomes limiting
Non-consumable environmental conditions
temperature
soil properties
other factors that affect plant growth
Weed density and yield loss depends on
crop grown weed species present duration of competitor climate impact of weed seed production on future cropping system
true allelopathy
toxic compounds that are released directly into the environment by the plant
functional allelopathy
compounds that are released into the environment but before toxic. Must be transformed by microorganisms
auto-allelopathy
plant secretes a substance which inhibits the germination of other seed from the same species
below-ground root competition
individual compete for space, water, and nutrients which all differ in distribution, mobility, molecular size, and other aspects
above-ground competition
individuals normally compete only for light and space
Competition for consumable environmental resources
competition for water nutrients lights CO2 O2
2 types allergenic plants
plants that produce skin eruption as result of bodily contact
plants affect respiratory tract through inhalation such as pollen
FIFRA
federal insecticide fungicide and rodenticide act 1947
requires pesticides to be registered with the epa
classified general or restricted
requires applicators be certified for use of restricted
penalties for pesticide negligence or
requires pesticides be used as label states except sections 18 or 24c amendments
pesticide labels
legal document that is federal law includes: identifying information precautionary statements hazards to humans and domestic animals environmental hazards physical or chemical hazards directions for use
herbicide labels
herbicide is a type of pesticide used to kill weeds
2 classifications:
general use pesticides
restricted use
general use pesticide
no unreasonable adverse effects on environment
safe to apply
restricted use pesticide
sold only to trained and certified applicators
restriction due to drift, environmental, or toxicity concerns
directions for use
mixing instructions spraying instructions calibration information application directions (by region/crop, method of application, weeds controlled, rates by soil texture or weed stage, tank mix combinations)
types of label registration
section 3
section 5
section 24c
section 18
section 3
main registration of a product label
every product has this
section 5
allows for field testing of a pesticide currently under development
(only good for short period, have to reapply every 1-2 years)
section 24c
state in special need of federally registered product that will provide control
company must apply for this label
limited amount of acres can be used
section 18
emergency crisis of invasive species requiring unregistered pesticide (very limited area/short time)
grower groups, extension specialists etc apply (not companies)
Signal words
danger- highly toxic, category 1
warning- moderately toxic, category 2
caution- slightly toxic, category 3,4
ways pesticides enter the body
orally- mouth
dermal- eyes and skin
inhalation- lungs
prevention of pesticide exposure
wear appropriate pesticide protective equipment that is waterproof or chemical resistant
types of PPE
body covering head covering shoes/boots gloves respirator/mask NIOSH/MSHA approved eye protection
herbicide selectivity
differences in response of plant species to a given herbicide
rate of herbicide required to kill one species is safe on another species
factors affecting selectivity
physical- influence contact between herbicides and plant surfaces
biological- caused by differences among plants
physiological- caused by the different ways plants function
herbicide resistant weeds in arkansas
annual ryegrass common ragweed palmer amaranth johnsongrass pigweed
causes of herbicide resistance
monocultural cropping- planting same crop over and over
using same herbicide consecutively or different herbicides with same mode of action
often occurs in reduced cultivation practices
management strategies to prevent or delay herbicide resistance
crop and herbicide rotation
herbicide combinations
rotation of herbicide modes of action
tillage
