Adventures in Finger-weeding

Researcher: Andy Hammermeister

Weed control is a big challenge facing organic farmers. Along with using clean seed, most organic farmers have adopted good tillage and rotation practices to get ahead of their weeds. At Brookside we have a diverse group of experiments leading to a wide variety of weed challenges. As we expand our research program at Brookside we've opened more land, and finger-weeding became an important tool for managing annual broadleaf weeds. We have finger-weeded potatoes, peas, mixed crops, flax, wheat, and barley. We are a bit 'green' when it comes to finger-weeding, but thought we would share what we have learned (and welcome any advice).

I've been told that "timing is everything" when finger-weeding. But what is the right time? Do you base it on your crop stage, weed stage, or soil conditions? A loose moist seed bed with sunny and dry conditions works best for killing weeds. We have found that a pre-emergent finger-weeding can be very effective. We finger-weeded the soybean crop when the shoot was a good inch below the soil surface and the weeds were at the cotyledon emergence stage. At this stage the weeds are extremely susceptible, but barely visible (you can't see them from your tractor seat). We had 83% weed control with one pass of the Lely finger-weeder and 91% control with two passes.

After much debate we decided to finger weed potatoes. We finger weeded our potatoes twice, once when they were just sprouting (weeds at cotyledon stage) and again when 2 or 3 leaves had emerged (weeds at 1-2 leaf stage). Most of the finger-weeder pressure was on the hills; we were not worried about poor control between rows because those weeds would be controlled at hilling. With a single pre-emergent pass we had 83% weed control, with pre and post-emergent passes there was 87% control. With more control of weeds and no damage to the potato with the pre-emergent pass, it is recommended to repeat it at least once or twice. A second post-emergent pass provided negligible benefit (additional 2% weed control) with minimal damage to the potato crop.

We finger-weeded our peas just after they emerged; the weeds were at the cotyledon stage. We had 92% weed control with a one pass of the Lely weeder, with only 3% damage to the pea crop.

Flax is known to be a difficult crop to finger weed and so the weeder was set to be less aggressive. We found that if finger-weeded too early the flax plants (2.5 - 3 cm tall) were buried and couldn't recover (34% losses, 57% weed control). Too late (flax 10 cm tall) and the weeds (at the 3 leaf pair stage) are too big to get effective control (7% flax loss, 34% weed control). We had the best luck finger-weeding when the flax was 5 cm tall (9% flax loss, 54% control).

In summary, finger weeding strategies vary by crop and soil conditions, however, whatever you can do to get the crop growing ahead of the weeds will not only make finger weeding more effective but will give your crop an advantage. To get the upper hand here is what we are trying:

• till just prior to planting
• use a seeder with an in row packer as opposed to pulling a general packer behind the seeder; only packing the rows results in firm soil around plant, loose soil around weeds
• do pre-emergent passes if possible (the longer you wait the firmer the soil will be and the more aggressive your weeder will need to be)
• don't let the weeds get beyond the 4-leaf stage (cotyledon pair + 2 pair of true leaves)
• on potato hills, do at least 2 pre-emergent passes; the tines spread out on the hill and therefore are less effective with one pass.