1. Crop rotation, cover crops and
ecological weed management
Assist.Prof.Dr. Boonthida
Kositsup
Department of Botany
Faculty of Science
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3. Definition of a weed
• A weed is an undesired
plant out of place
– Water hyacinth in a
aquatic garden
: not a weed
– Water hyacinth clogging
canals
: a weed
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4. What is a Weed?
• A plant that is growing where it is not wanted
Roberts et al. 1982. Weed Control Handbook
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5. What is a Weed?
• A plant that is successful in colonizing disturb,
and maintaining their abundance under
conditions of repeated disturbances
MohlerC., 2001. Ecological Management of Agricultural Weeds
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6. Disturbance
• An event that disrupts ecosystem, community
or population structure
• Changes resources, substrate availability or
the physical environment
Pickett and White, 1985
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8. Why Do We Have Weeds?
BECAUSE WE CREATE THE ENVIROMENTS
WHERE WEEDS THRIVE (go, develop or be
successful)!
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9. What management practices contribute to
weed problems?
• Poor soil management
• Excessive use of manure
• Poor crop rotations using crops with similar
seasonal growth patterns which have similar
weed species associated with them.
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10. Weed Management
• Goal
Manage cropping systems (not just weeds!) so
that the resources made available through
disturbances are captured by crop and not by
weeds
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11. What are some conventional
treatments used to control weeds?
• Physical removal
– The use of agricultural tools such as hoe to
physically remove weeds
• Chemical suppression
– Herbicide application is not favored in ecological
farming
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12. What are some basic principles for
ecological weed control?
• Create a diverse ecosystem. Use as many
species and types of plants as possible
• Use a good crop rotation
• Don’t over fertilize your soil with manure or
fertilizers as this will leave too much fertility
on the soil for weeds
• Use clean seed (free of weeds)
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13. Crop Rotation
“Rotation of crops, when accompanied
by care in the use of pure seed, is the
most effective means yet devised for
keeping land free of weeds.”
Leighty (1938)
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14. Crop rotation
• is the practice of growing a
series of dissimilar types of
crops in the same area in
sequential seasons.
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15. Crop rotation: two considerations
3.Vary the seasonality of planting
Varying crop seasonality and management practices
prevent any one species from getting out of
control
5.Vary crops allow you to vary management
practices
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16. How does crop rotation help control
weeds?
• Breaks weed multiplication cycles, as certain
weeds are associated with certain crops.
• Maintain soils fertility which helps crop
growth.
• Crops that have different season growth
patterns compete for weed space on the field,
as weeds have different growth cycles.
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17. Cover crops
are crops whose main purpose is to benefit the
soil, to manage soil fertility, but is not intended to
be harvested for feed or sale.
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18. What is a cover crop?
A crop whose main purpose is to benefit the
soil or other crops in one or more ways, but is
not intended to be harvested for feed or sale.
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19. Cover crops
• Plants that are grown for various ecological
benefits other than as a cash crop (a crop that
is grown mainly to be sold).
• They may be grown in rotations during
periods when cash crops (main crops) are not
grown.
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20. Advantages of cover crops
• Cover crops can also improve soil quality by
increasing soil organic matter.
Increased soil organic matter enhances
soil structure, as well as the water and
nutrient holding of soil.
• Weed suppression
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