Lecture 8 - Predicting Crop Yield Loss Flashcards
economic thresholds
density at which cost of weed control operation equals potential yield loss in the crop
spray when it pays theory
crop yield thresholds for weed species calculated by Cousen’s type models will allow you to make spray decisions
what is economic thresholds based on
- cost of control
- cost of application
- yield of weed free crop
- selling price of crop
- proportion of yield loss
- effectiveness of control measures
_________ economic threshold means less competitive weed
high
steps for calculating and using economic thresholds
- establish crop yield loss thresholds for major weed species
- assess field for weed infestation (scout)
- make spray decision
factors effecting prediction of economic thresholds
- relative time of weed emergence
- critical period of weed control
_______ emerging weeds are most competitive. Why?
earlier. they become taller than crop and capture more resources, making competition asymmetric
critical period of weed control
time period in which crops must be kept “weed free” in order to prevent yield loss
what is the critical period of weed control a function of
- critical weed free period
- critical time of weed removal
what iis the critical weed-free period related to
- weed seed germination
- competitive crop canopy establishment
- weed competitiveness
- crop and weed phenology
- weed and crop characteristics
the critical weed free period is ______ for competitive crops
longer
problems with yield loss prediction
- unreliability of estimates
- model parameter values differ between experiments
- method of infestation assessment
how can loss model predictions be improved
account for variability in model parameters
Kropff and Spitters Model
use relative weed leaf area to measure intensity of infestation (accounts for time of emergence, weed and crop conditions)
why is farmer adoption of economic thresholds poor
it must be specific for each crop and weed, time of emergence, different environments, and consider seed returns
economic optimum thresholds
takes into account the impact of leaving some weeds and is based on weed seed production, longevity, recruitment, predation, future crops, rotations, and price)
problems with economic optimum thresholds
- many different management strategies will give different answers
- based on seed bank and weed population dynamics, which not many know about
