Organic Weed Control
Spring Cover Crop
Summer Cover Crop
Fall Cover Crop
Inter-cropping
Critical Period of Interference
Cultivation
Animals
Minor Weed Control Principles

Spring Cover Crop:

In the spring, plant as early as possible before weeds start to grow. This will prevent weeds from ever getting started. Use genetics that are bred for cold weather. If you cannot plant your actual crop early, plant a thick cover crop early. Extremely early cover crops are flax, turnip, and peas. Flax and peas can be mowed before planting your actual crop using no-till methods.

USDA - Cover Crops
SARE Managing Cover Crops Profitably
NRCS - Cover crops and termination method
Cornell - cover crops for vegetables
eOrganic - large scale mulching in very cold climates

Summer Cover Crop:

After crops have been harvested in late spring or early summer, grow a summer cover crop for mulch roll down before the fall crop is planted. Great care must be used in selecting cover crops for the summer, since not all cover crops are easily terminated in the early fall. Black eyed peas, fenugreek, etc. are good summer covers.

North Carolina State - killing summer cover crops
North Carolina State - mechanically killing cover crops

Fall Cover Crop:

In the fall, after harvesting a summer crop, grow a cover crop for later mulching in place the next spring. In warm climates, you can wait for the fall cover crop to mature next spring before direct seeding your actual crop. In cold climates, you may need to transplant instead of direct seeding.

Winter Annuals - Keith & Dale
eOrganic - winter killed cover crops
Cornell - cover crop trials
Bradford Research - cover crop trials

Inter-cropping:

After your actual crop has come up and the mulch is starting to deteriorate, plant a living mulch between the rows before weeds get a chance to grow. If possible, push the remaining mulch against the crop. Avoid even shallow cultivation as it also severely disrupts the mycorrhizal network.

Most inter-cropping field trials have had very mixed success and even more so for no-till. Mainly because even legumes will compete for nitrogen until it is used up before they fix new nitrogen.

Rick Clark - no-till
NCBI - fenugreek, vetch, etc.; good intercropping since low N uptake
Midmore Farms - intercropping wheat and flax or oats and peas.
Helen Atthowe - living mulch examples
AEA - flax intercropped with legume
Gabe Brown - decrease herbicide use by increasing cover diversity
Intercropping in Africa - push-pull
Veganic Permaculture
SARE - inter-cropping trials
Montana State - inter-cropping trials
Clover with broccoli
SARE - Crimson Clover
SARE - berseem
Missouri State - berseem clover
Archive Univ Cal Berkeley - berseem clover
Intercrop study with corn
College of Tropical Agriculture - Broccoli with clover
Crop Science - wait to intercrop
Vermont Extension - interseeding

Critical Period of Interference:

The only time that weeds critically affect yield for most crops is within the first few weeks after planting (Critical Period of Interference). But this depends on the weed type, crop type, and bio-diversity levels.

University of Florida
Hasanuzzaman
Iowa State
Science Daily

Cultivation:

You may still need to shallow till occasionally. But if you have a good crop rotation, then you can time it for when you need to harvest root crops and disturb the soil anyway.

Weed em and Reap
ATTRA weed management
Manitoba Gov. - weed management in organic crop systems
SARE - Steel in the Field

Animals:

During the growing season, use Chinese weeder geese to control grass weeds. Portable fencing may be necessary to keep them out of the grain crops. In the fall, after harvest, turn animals out on the stubble to suppress weeds and speed crop residue decomposition. Hogs can be used to dig up roots. Allow animals to graze between orchard rows. Mob grazing and diversity work the best to control weeds in pastures. The use of animals may require some extra measures to prevent contamination such as never using antibiotics on your animals, using dung beetles, using poultry and hogs to disrupt manure, encouraging fly parasites, never harvesting off the orchard floor, etc.

According to the CDC, EColi is essential for human digestion and most EColi are beneficial. Our focus should be to stop the excessive use of antibiotics, not the removal of animals from agriculture.

CDC - most EColi are harmless
EFAO News
University of Idaho

Minor Weed Control Principles:

Weed seeds die more quickly with no-till

USDA NRCS - weed seeds die quicker with no-till

Cover crops may need to be rolled at an angle different from the original row planting. Get a seeder that can handle a thick mulch.

Plant row crops dense enough to quickly form a canopy, but not so thick that it reduces yield. This will allow the crop to outcompete weeds.

Plant early maturing and cold tolerant varieties. This will allow an early planting and reduce the window for the critical period of interference. It will also allow more time to plant a follwing cover crop.

Pile wood chips for several months to allow at least some partial decomposition before using them as mulch in the orchard or garden. Keep the pile fungal by using slow cold decomposition. Layer with air circulation pipes across the pile. Never use fresh wood chips directly on the soil as mulch since they will rob nitrogen from the orchard as they start decomposing. Once old mulch is built up, then use chop and drop without composting.

Most weeds need to be cut only after fully blooming and before seeding to kill them by cutting. If they are cut before fully blooming, they will only keep trying to bloom.

Not all weeds are bad. For example, some weeds can be allowed to grow along side brassica to support mycorrhizal fungus for the next crop.

Joseph A. Cocannouer

Some plants and materials are allelopathic and can be used to advantage: barley, rye, wheat, oats, brassica, sunflower, sweet potato, tobacco, walnut shells, and sunflower shells.

Books which provide some guidance:

Weeds and What They Tell Us by EhrenFried Pfeiffer
Weeds, Control Without Poisons by Charles Walters