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27 Cards in this Set

  • Front
  • Back
What is weed competition?
how long weeds and crop can grow together before there is damage
What is interference?
competition + other factors that impair the crop
What are the increasing factors that determine the amount of competition?
light, water, nutrients, space
8-10 weeks
How long does this crop need to be weed-free to have max yield?
There is a big loss in yield
What happens if you wait 6 weeks to spray herbicide?
between weeks 2-4
When is the crop the most sensitive?
field corn b/c it only needs to be weed-free for 4 weeks to have no effect on yield
What crop is the most competitive and why?
The longer a weed is in competition, the larger % yield reduction
Interpret this table.
yield decreases the longer a weed in the field
Interpret this table.
What factors affect weed/crop interference?
Time of weed/crop emergence
Growth form
Weed Density
How does the time of weed/crop emergence affect interference?
1) the plant that emerges first gains the advantage
2) affected competition is greatest when plants are young
3) late season weeds has a quality and nutrient (P & K) issue
How does growth form affect interference?
Root- tap vs fibrous
Height- prostrate vs tall
Leaf area
Which is more competitive- tall plants that grow fast or prostrate and spindly?
fast growing tall plants
Yield decreases as weed density increases
Explain how weed density affects the crop.
May not need to spray if there isn't many weeds in the field and not much yield loss
Explain why this information may be important to a grower.
What is the physiological basis of competition above ground? What can increase this competition?
weeds that take the most light away will be more competitive
Factors: bigger leaf area, lie flat, vining habit, lower light compensation point
What is the physiological basis of competition below ground? What can increase this competition?
Early and rapid root penetration
Factors: high root density, distribution of roots (fibrous vs. tap), nutrients- N, P, K
When is water an issue during competition?
when it is under irrigation and limiting during fruit/seed development
What ways can manipulating the crop gain competitiveness?
1) Row spacing- narrow rows allow for quicker canopy of crop
2) Fertilizer placement- in the row
3) Drip irrigation
4) Breeding
What are some mechanisms of interference?
1) Crop quality
2) Harvest losses
3) Interference with other pest control methods, spray deposition
4) Hand harvesting
5) Staining on cotton
What is allelopathy?
chemical interference of one plant with another, produces toxin that deters germination or growth of neighboring plant
What is allelopathy influenced by?
Growth of allelopathic plant
Growth of affected plant
Breakdown rate of residue containing toxin
What can allelopathy occur from?
Leaching of residues
Decomposition of plant residues
What is the effect of black walnut on bermudagrass?
kept it from growing in it drip due to its allelopathic effect
What is parasitism?
one plant physically interferring with growth and development of another plant; physical attachment
Give some examples of parasitic weeds?
dodder, mistletoe, witchweed
What are some characteristics of parasitic plants?
occurs in flowering plants
receives all or partial requirements from host
fully photosynthetic or non-photosynthetic
attaches via haustoria
special adaptations such as sticky seeds, exploding seed pods, host excreted stimulant