Unit 3 KA3 Flashcards
Monoculture
Huge numbers of a single species of crop plant grown over a wide area to improve efficiency.
Monocultures are vulnerable to attacks by diseases or insect pests, which can spread rapidly.
Weed
Any plant growing where it is not wanted.
Competes with the crop for light, nutrients and water, reducing productivity.
May release chemical inhibitors into the soil, act as hosts for crop pests and diseases and contaminate crops with their seeds.
Annual weeds
Complete their life cycle in one year.
Grow and produce flowers rapidly, produce large numbers of seeds that can remain dormant in the soil for a long time.
eg. poppies, Arabidopsis (Thale cress - model organism)
Perennial weeds
Live for several years, becoming dormant in the winter and re-growing in the spring.
Compete with crops as they are already established in the habitat.
Have food storage organs such as deep tap roots. eg. dandelions
Reproduce vegetatively (asexually) using runners eg. buttercups, or rhizomes (underground stems) eg couch grass
Invertebrate pests
Invertebrates are animals without backbones.
Invertebrate pests include insects, especially larval stages of butterflies (caterpillars) and aphids; molluscs (slugs and snails) and nematode worms.
Leaf damage by pests
Caterpillars and molluscs eat leaves, reducing photosynthesis and therefore production of sugars for growth and starch storage.
Effect of aphids (greenfly)
Pierce the phloem to suck out the sucrose, reducing productivity and transmitting viruses.
Effect of nematodes
Attack roots and tubers, laying eggs inside them.
They damage crops and make them unmarketable, due to their appearance.
Plant diseases
Caused by pathogens such as fungi, viruses and bacteria.
They are carried in the soil, are airborne or are transmitted by insect pests such as aphids.
They reduce crop yield and productivity, make products less marketable due to their appearance and reduce storage life.
eg. potato blight, apple scab
Cultural control - definition
Use of traditional methods to controlling pests and diseases.
Usually preventative and involve planning.
Ploughing
Turning over the top layers of the soil to bury weeds.
Timing of sowing and weeding
Allows crops to outcompete weeds.
Removal of alternative hosts and crop residues
Reduces habitats for pests and sources of fungal spores.
Cover crops
Example - clover (N-fixer)
Used to enrich the soils and prevent weeds from becoming established.
Good for pollinators.
Crop rotation
Growing crops in a different location each year to break pest lifecycles.
Pesticides
Chemicals used to control pests and diseases.
Include herbicides, pesticides and fungicides.
Selective herbicides
Used to kill broad leaved weeds that compete with grass and cereal crops (narrow leaved).
Similar to plant hormones and work by over-stimulating growth so that the weeds exhaust their food reserves and die.
Non-toxic and biodegradable.
Contact herbicides
Non-selective.
Kill all green plant tissue that they come into contact with rapidly.
Biodegradable with short-lived effects.
Do not affect underground storage organs.
Systemic herbicides
Absorbed by weeds and transported internally to other parts via the phloem.
Act slowly, but are more effective as they reach roots and underground storage organs.
Other pesticides
Chemicals used to kill invertebrate pests - insecticides, mollluscicides and nematocides.
(The term also refers to herbicides and fungicides)
Contact pesticides
Kill the pest when it is sprayed, and remain as a protective layer on the crop plant, as a poisonous residue.
Systemic pesticides
Absorbed by the plant and are transported to all parts via the phloem.
When the plant is attacked (eg. when the phloem is pierced by an aphid) the toxin is ingested, killing the pest.
Fungicides
Pesticides that kill fungal parasites on crop plants, eg. potato blight.
Contact fungicides
Sprayed onto the crop before the spores land, as a protective layer.
Spores are killed as they germinate.
Easily washed off, so repeat applications needed.
