Organic Weed Control: Many Little Hammers!

How can you control weeds without using herbicides? This is a fundamental question on farms considering the switch to organic, and one of the biggest challenges for the organic farmer.

Have a plan. Integrated weed management involves using "many little hammers" to control weeds. There is no one control tool, but many different strategies that work together to manage weeds to a level where they do not impact yield. Weed control does not have to be perfect.

Crop Rotation

The use of different crops reduces the buildup of weeds that flourish in specific crops. Organic farmers have found that growing continuous soybeans does not work. Annual weed populations build up in a crop that offers low levels of crop competition. Cereal and forage crops are much more competitive to reduce many of the row crop weeds.

Cover Crops

Using cover crops to fill in the after harvest periods helps to smother out weeds that may grow on bare soil. Weed seeds germinate and wither from competition, reducing the seed bank. Late season weeds are not allowed to replenish the seed bank. Some cover crops such as rye produce allelopathic chemicals that impede the growth of weeds.

Compost

Non-composted manure can have weed seeds and higher levels of available nitrogen that stimulates the germination of weeds. On organic farms only composted manure is used in the spring planting season.

Clean Seed

One of the best ways to get new weeds is to buy them from other farmers with the seed and then plant them in your own field. When using your own seed always clean it at a reputable seed-cleaning establishment. That seed in the bin may look clean...... but it isn't!

Planting Date

Planting cereals early allows a cool season spring crop to get ahead of the weeds. Delayed planting of warm season crops such as beans allows for an extra spring tillage to kill one flush of weeds and helps the crop to emerge quickly to establish a quick crop canopy.

Varieties

Studies have shown that cereal varieties with less erect leaves (more parallel to the ground)Decrease weed growth. Some have suggested broader leaf types. These principles of less erect plant types and dense leaf canopies apply to all crops. Select varieties that are able to quickly establish a dense canopy, to reduce the light getting through to the weeds at the soil surface.

Row Width and Plant Population

The trick is to get a good stand of healthy plants as quickly as possible and with narrower row widths the crop canopy fills in quickly. On organic farms this has to be balanced with wide rows enough for inter-row cultivation.

Harrowing or Rotary Hoeing

Most crops can withstand light harrowing or rotary hoeing both before and after emergence. Care should be taken at emergence, and depending on the crop and the implement, avoid this time period. Seeding rates should be about 10-15% higher to allow for some plant loss when using these implements. Success is best when done before the weeds emerge, with each pass killing 40-60% of the non-emerged weeds. Frequently growers will combine passes to harrow/hoe twice over in opposite directions to enhance the weed control. Weeds rooted deeper than 2-3 cm are tough to kill. These techniques are not appropriate for crops planted less than 2 cm.

Inter-Row Cultivation

The number of passes depends on the need. Use overlapping shovel arrangements that can cover the full width of the inter-row area. The first pass should go as close to the plants in the row as possible, without pruning roots or injuring plants. Throw some soil in the row to cover weeds, but be careful not to cover crop plants. In some cases you may wish to use fenders or shields to keep the dirt from landing on the crop plants. On the second pass, use more speed to throw more dirt into the crop row to aggressively cover weeds while protecting plants. Never cultivate too deep or when the soil is wet enough to create large clods or curls that rise up from the shovels.

New Weeds

Scout during the summer. Walk through fields to manually control problem weeds. When necessary change the crop rotation to enhance the control of these special weed challenges.

Sanitation

Clean combines and tillage equipment on a regular basis. Inspect field boundaries for potential sources of weeds that do not need to spread into your field. Stop weeds before they spread.

None of these strategies are really new. Most of them were learned from our grandparents in the 60's. It was usually followed by a comment from my grandmother that "one year of seeding means 7 years of weeding". Hopefully, all the little hammers will work well for you!