Weeds Flashcards
What is crop productivity reduced by?
weeds
pests
diseases
How can we ensure the greatest yield of crop?
Tightly control, weeds pests and fungal infections
Why are weeds bad?
They can compete with crop plants for resources and reduce yield
What are the two main groups of weeds?
Perennial weeds
annual weeds
Properties of perennial weeds
-Live for several years
-become dormant in winter-time
-grow again in the spring
-storage organs
-vegetative reproduction
Properties of annuals weeds
Complete there entire life-cycle in one year
-high seed output
-short life cycle
-rapid growth
-long-term seed viability
Are most pests of plants invertebrate or vertebrate? +examples
invertebrate
such as insects, nematode worms and molluscs
Effects of invertebrate pests
-they DESTROY LEAVES
-this reduces the plant’s ability to carry out PHOTOSYNTHESIS and therefore their ability to PRODUCE SUGAR
-this causes a reduction in VIGOUR and YIELD OF CROP
What are plant diseases caused by? and what are the 3 types?
what are they often carried by?
pathogens
-fungi
-bacteria
-viruses
These diseases are often carried by invertebrate vectors (carriers
What are the 2 ways in which weeds, pests and disease controlled?
by cultural means
by chemical means
cultural methods of crop protection
1-ploughing
2-weeding
3-crop rotation
Chemical means of crop protection
pesticides
including:
-herbicides to kill weeds
-fungicides to control fungal disease
-insecticides to kill pests
-molluscicides to kill mollusc pests
-nematicides to kill nematode worms
What are pesticides?
chemicals which are applied to crop plants to protect them from damage
What 2 types of pesticides are there?
systemic and selective
What are systemic pesticides?
systemic insecticides, molluscicides and nematicides spread through the vascular system and kill pests feeding on plants
what are systemic herbicides
-applied to **kill weeds*
-They are absorbed into the plant’s transport system and quickly spread through the vascular system of the plant
-This has a lethal effect on the leaves and the roots of the plant so avoids regrowth of the weeds
What are selective herbicides?
-they mimic the action if plant regrowth hormones
-they work by being absorbed through the leaves
-this speeds up the metabolism of plants to the extent that they use up their food reserves and die
-selective herbicides have a greater effect on certain plant species (broad leaved weeds)
What do farmer’s often apply fungicides based off of?
disease forecasts
This is a preventative method
and is more effective than treating crops which are already diseased
What issues can the use of pesticides lead to?
-Toxicity to non-target species
-persistence in the environment , bioaccumulation or biomagnification in food chains
-producing resistant populations of pests
What is bioaccumulation?
A build-up of chemicals in an organism
What is biomagnification?
An increase in the concentration of a chemical moving between tropic levels
What is biological control?
The control of a pest population through the introduction of one of its natural ‘enemies)
What types of biological controls are there?
A predator
A parasite
A pathogen of the pest
What is the main advantage of using a biological control?
No chemicals are used which may persist in the environment
Problems with biological control
The control organism may become an invasive species, parasite, prey or be a pathogen of another species
What is Integrated pest management (IPM)
IPM uses a combination of chemical, biological and cultural control to improve yield
What is the main aim of IPM
to reduce chemical use and only use chemicals which do not persist and reduce pests to levels which allow biological control methods to take over
