Weed Management

Here’s the outline and photos from the presentation on weed management I gave at the North Willamette Horticultural Society Meeting yesterday. The outline is rough so if you have questions let me know.

Wednesday, January 16, 2008

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Discussion Outline

- Where I’ve developed this system

- Rotations and Cover Crops

- Stale Bedding

- Crop Spacing

- Irrigation

- Mechanical Tools

terminology note - I use cultivations to roughly mean weeding

Sauvie Island Organics

- 18 acres - 10 cultivated

- growing a very diverse range of annual vegetables, cut flowers and culinary herbs

- Planting almost every week from February into October

- Irrigating from late April into October

- Cultivating every month of the year

- Harvesting April through February

Rotations

Crops that build weed pressure vs. crops that reduce pressure

Examples: corn and winter squash build pressure, lettuce and salad mix reduce pressure

Irrigation overlaps between blocks

Examples: potato field irrigation overlaps with corn field’s early cover or bare fallow, not the crop

Cover Crops and Bare Fallows

How I’ve used cover crops

Summer Covers

sudan needs to be mowed to keep weed seed production down

buckwheat is fast enough to force mowing before weed seed production

Cool season covers of cereal rye, vetch, bell beans, red clover and crimson clover

a good stand will smother most weeds, but some survive and may make seeds

timing of seeding and fast germination and establishment is important

Leaving harvested crop to mature in low weed pressure situations

examples: salad mix, kale, corn stalks

benefits: reduced tillage, seeding costs and good wildlife habitat

How I use bare fallows (clean cultivation with a disk or spader)

benefits: reduced weed seed bank, cleans trash for finer seed bed, preserves moisture

drawbacks: oxidizes organic matter, potential for wind and water erosion, potential for leaching with rain, combined above factors cause compaction and loss of soil structure.

Stale Bedding

Four weeks before planting:

Flail and deep spade in cover crop

Maybe one more disking after a few weeks to work in more trash or to knock down weeds

Allows trash to break down

Germinates weed seeds

Week of Planting

Drop spread soil amendments

Final shallow spading

Mark bed with cultivating tractor for proper spacing

plant or direct seed

Crop Spacing

3-2-1 flexible system

Tight spacing - advantages:

reduces tillage energy, cultivation passes and hand weeding

reduces space to irrigate

canopy fills out and prevents late weed competition

canopy cover reduces wind and water erosion potential

Disadvantages

tight working quarters for people and tractors

possible small reduction in yield or size

Irrigation

Drip for wider spaced crops and crops that are in for extended periods reduces weed germination significantly - especially when combined with dust mulching

Overhead for tightly spaced crops - needs to be coordinated with cultivation

less frequent overhead irrigation helps crops root more deeply and limits weed seed germination

Basics of Mechanical Cultivation

Make sure that things are spaced right by marking plantings with the cultivating tractor before planting - setting wheel tracks helps with later guidance

Cultivations are most effective when weeds are in the thread stage!

weeds are constantly germinating on about a 5-9 day cycle so we cultivate 1x per week.

when weeds are at thread stage they are barely visible so we cultivate when the field looks bare

Cultivation has other benefits:

reduces further weed seed germination by dust mulching

improves air and water infiltration

Cultivations continue until the crop is too tall to fit over

We expect to hand weed at least once but the tractor cultivation delays the need and make the hand weeding much faster

My strategy is to not let weeds go to seed whenever possible - this does greatly reduce weed pressure after a few years. This also means paying attention to late weeds in the field - even if they aren’t going to effect this year’s yield.