University of Manitoba: Natural Systems Agriculture: In-Crop Tillage for Weed Control
University of Manitoba Faculty of Agricultural and Food Sciences Department of Plant Science

In-Crop Tillage
for Weed Control


Rotary hoe.

In-crop tillage attempts to selectively kill weeds, while not killing the crop. Untimely rains sometimes reduce opportunities for pre-emergence harrowing, increasing the need for such early season in-crop weed control tactics. Some organic farmers make extensive use of in-crop tillage, while others choose not to use in-crop tillage.

In-crop tillage is typically performed during the early part of the season, during the critical period for weed control.

There has been little research to compare crops ability to withstand in-crop weed control tillage. Estimates of crop tolerance to in-crop harrowing is presented in the table below.

  Crop Type
(resistance to in-crop tillage decreases from left to right)
Pea and Chickpea Sunflower Lentil Wheat and Barley Oat Flax and Canola
Estimated % of crop plant loss Less than 20% Less than 20% 30% 30% 30% 60 to 90%

The best type of equipment for in-crop tillage depends on soil conditions, equipment availability and weed problems. Most farmers own a light-duty spring tine harrow, and luckily this implement can be used for most in-crop weed control operations.

Research in Saskatchewan has compared Phoenix and tine harrows for effectiveness of in-crop weed control in peas.

Results showed that both implement types produced similar results and that optimum setting for each machine was critical to its success in selective weed control. It was recommended that tine harrows be angled back 45 degrees while the phoenix harrow be run at a 45 degree angle across the field (Frick and Johnson, 2002).

Lambsquarter uprooted by in-crop tillage.
Lely Harrow.

Farmers also modify existing equipment to suit their needs. An example of a newer idea for in-crop weed control is the Samurai weed eater:

Harrow for in-crop, post-emergence weed control.

"A farmer from Hokkaido, Japan gave Jeff this idea. He and the Institute farm crew built a simple metal frame to extend behind the rotary hoe, carrying tire chains that drag the entire tilled surface, rolling small weeds onto the surface, where they shrivel in the sunlight. The whole set up cost a couple a hundred bucks to build, and definitely improves the weed control before seedlings emerge."

Jeff Moyer, Rodale Institute

Seeding Cover Crops With In-Crop Tillage

Air seeder for legumes mounted on tine harrows.

The time of in-crop tillage provides an opportunity to seed cover crops. This practice is better suited to wetter areas where moisture is more predictable. The advantage of establishing the cover crop at this time (eg., 2 to 4 leaf stage of cereal) is less competition to the main crop. Some farmers have equipped their weeding harrows with air-seeding units that apply cover crop seed (eg., red clover, sweetclover or annual ryegrass) in front of the harrows.

Combing Crops

In long-term organic farming systems in Europe, researchers have observed an increased number of climbing weeds (similar to vetches and buckwheat). These researchers have been using tine harrows late in the growing season to "comb" the climbing weeds out of the crops. Does it work? Yes, it works well enough to suppress the weeds that reduce their interference in the harvest operation.


  • Consider soil type, stage of weeds, and crop type before deciding to use in-crop tillage for weed control.

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This page created August 2004.