Lecture 9 - Assessing Weed Infestations Flashcards
how do you assess weed infestations
weed surveys/counts
purpose of weed surveys/count
produce a broad scale to fine scale map of weed populations and distributions
founder effect
small number of starting population causes specific phenotype to form patches
weeds occur in ________, which can effect management and surveys
patches
purpose of broad area assessment
- assess weed invasion
- marketing
- agriculture policy
- resistance monitoring
purpose of small area assessments (by field)
- weed thresholds
- resistance monitoring
- weed patch spraying
- weed invasion
- herbicide selection and timing
why use broad scale weed surveys
- document at one time
- document over time (shift or new species)
- predict upcoming weed problems
who uses weed surveys
- provincial weed specialists
- weed researchers
- chemical companies
when are surveys conducted and why
they are conducted in mid-July AFTER the farmer has used control measures. It is to measure the residual weed population and detect weeds that avoid management
ecoregions are areas of similar:
- climate
- natural vegetation
- soils
- land use
frequency
% of fields in which it occurs
field uniformity
% of quadrats in which it occurs
field density
average number of weeds
challenges with a weed survey
density (scale, time, patchiness
relative cover (scale, consistency)
contemporary/modern surveys
provides a snapshot of weeds
constraints of a contemporary/modern survey
- only major agricultural crops considered
- only small portion of each field surveys
- some mistakes in identification possible
- weeds are counted but give not indication of size
general principles of weeds
- many weeds are generalists are are spread across canada
- some weeds are more restricted in occurrence but are locally abundant
- shifts in in weed populations and abundance have occured
linkage between cleavers and canola (why are cleavers seen most of where canola is)
they have similar seeds
patch
a continuous infestation in which the neighboring cells of a sampling grid contain seedling densities greater than 0
origin of patches
- invasion events
- weed escapes
why are weeds patchy
-intrinsic demographic effect (founder effect, limited seed dispersal
- edaphic factors (soil type, salinity)
- management (cultivation, harvest)
- interactions between organisms (allelopathy, selective grazing)
why patchiness important
large potential savings in herbicide use through precision agriculture
what are sampling techniques influenced by
- intended end use
- target species
- farming system
- amount of detail needed for end product
3 different sampling techniques
- discrete area sampling
- continuous area sampling
- co-ordinate mapping of individuals
