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Weed control in field productionDr. James Altland

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Nursery weed management

• Field production– Seeds in soil

– Each crop planted back is same soil

– Weed control should be preventative

– Several postemergence options

• Container production– Bark is weed-free

– Each new crop planted in fresh bark

– Weed control must be preventative

– No postemergence herbicides.

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Redroot pigweed• Seed survive for more than 30 years

– Soil surface or buried

• Seed can be wind dispersed– Small size

• Plants produce up to 100,000 seed– 13,860 with no fertilizer– Over 34,600 when fertilized

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Field bindweed• Convolvulus arvensis• Seeds persist in soil for 60 years• Roots grow to a depth of 30 feet.

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Field weed control

• Start clean………..stay clean

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Field weed control

1. Field preparation

2. Prevent weed establishment– Most important step– Sanitation– Cultural practices– Preemergence herbicides

3. Control (kill) escape weeds

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Field preparation

1. Spray with broad-spectrum post herbicide– Wait 2 weeks

2. Till weeds under– Wait 3 weeks– Apply soil amendments?

3. Till field again, final prep

4. Plant nursery crops

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Notice the tractor on the far left that is doing the final tillage in preparation for planting. Following immediately behind is the tractor in the center of the image that is doing the planting. These plants are being installed in a soil free of emerged weeds. This is ideal for application of preemergence herbicides.

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Perennial weeds

• Tillage can be used to eradicate perennial weeds

• Probably will take at least 2 years– Tilling every 3 weeks

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Example: Yellow nutsedge (Cyperus esculentus) requires at least 2 years of intensive tillage to eradicate it from the field. That means disking or plowing the field to a depth of 12 inches every 3 weeks over the course of 2 years (only during the growing season).

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Example: Wild garlic (Allium vineale) requires 3 to 6 years of tillage during winter months (probably not possible in Oregon) to eradicate.

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Field preparation

• Goal is to reduce weed populations– Complete eradication is impossible

• Excessive tillage is damaging to soil structure

• Limit the number of tillage passes (plow, disk, roto-till, etc.) to a minimum.

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Weed prevention• Sanitation

– Clean tillage equipment– Control non-crop area weeds– Physical barriers

• Cultural practices– Tillage – Fertilization– Irrigation

• Preemergence herbicides

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Sanitation

• Clean tillage equipment– Prevent spread of perennial weeds

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Sanitation

• Control weeds in non-crop areas

Grassed water ways and drainage ditches are ideal for preventing erosion and soil loss. However, they must be maintained weed free so they don’t become a source of weeds in the production site.

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Sanitation

• Physical barriers– Prevent wind-blown seed– Thistles, groundsel, fireweeds

• Seed dispersed during growing season– Use fast growing deciduous plans (poplar)

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Example: common groundsel (Senecio vulgaris) seed are wind dispersed.

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Example: Canada thistle (Cirsium arvense) seed are wind dispersed.

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Cultural practices

• Fertilization– Band apply fertilizers– Do not broadcast apply

Nitrogen

• Weeds grow poorly in absence of nitrogen

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Cultural practices

• Irrigation– Switch to drip irrigation if possible

• Drip irrigation– Faster growing crops– More uniform crops– Less labor– Less water– Less money– FEWER WEEDS!

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This is a field that was just irrigated with sub-surface drip tape.

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Overhead irrigation is obviously more conducive to weed growth.

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Cultural practices – Tilling

• Tilling– Low/no chemical input– Prevents soil from crusting– Looks good– No weed resistance

• Repeated tilling– Damages soil structure– Degrades soil aggregates– Accelerates organic matter degradation– Leaves soil prone to erosion

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Tillage is the primary dispersal mechanism for perennial weeds. Top: horsetail (Equisetum arvense)Bottom left: field bindweed (Convolvulus arvensis)Bottom right: yellow nutsedge (Cyperus esculentus)

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Tillage

• If perennial weeds are present– Flag area– Do NOT till – Eradicate with post herbicides– Wait 30 days for regrowth– Spray again– Excavate if necessary

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Clean cultivation

• 100% vegetation control

• Herbicides within rows

• Till between rows

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Clean cultivation

• Disadvantages– Reduces soil organic matter– Destroys soil structure– Degrades soil aggregates– Soil compaction– Allows for erosion

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Living mulch

• Cover crop growing between rows of nursery stock

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Many nurseries use a crop of ‘Poco’ barley planted between the tree rows during the winter to prevent soil erosion.

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Living mulches

• Disadvantages– They can compete with nursery crops– Cover crops can attract unwanted pests– Seeds can become weed problem– They require maintenance– Many don’t look very good.

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Living mulch• Advantages

– Reduced soil erosion and runoff

– Increases soil organic matter

– Increase soil aggregates– Reduces soil compaction– Suppresses weeds– Improves percolation– Reduces temperature

fluctuations in soil

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The same crop with or without a living mulch.

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Living mulches

• Characteristics of a good living mulch– Small or low growing– Requires minimal maintenance (mowing)– Minimal competitor for nutrients and water– Forms dense cover for weed suppression– Not attractive to pests or wildlife

• Clover attracts deer• Turf attracts Japanese beetles in some areas

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Preemergence herbicides

• Herbicide selection

• Application timing

• Maintain the chemical barrier

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Plant uptake

• Most seed germinate in the top 1 inch of soil.

• Herbicide placement should occur where seeds will germinate and begin growing.

• Application of herbicide followed by incorporation with water is necessary for proper placement.

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Preemergence herbicides

• Will not kill weeds present at time of application– Exception is spray-applied Goal and SureGuard

• Even small weeds have roots large enough to escape effect of pre herbicides.

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Notice the relatively large root system compared to the small shoot system. This weed will survive most preemergence herbicide applications because its root system is well below the chemical barrier created by the herbicide.

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Preemergence herbicides

• Do not prevent seed from germinating

• Do not kill dormant seeds

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Herbicide timing

• First application – February-March– Irrigate newly plant crops to settle soil– Apply preemergence herbicide to soil– Incorporate the herbicide with ½ inch of

irrigation

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Herbicide timing

• Second application– Early summer (May) – Reinforce herbicides applied earlier– Control emerging summer annuals– Be careful of herbicides on tender foliage

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Herbicide timing

• Third application– Late summer (September) – Winter annual weed control– Can provide weed control through next spring

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Maintain the chemical barrier

• Incorporate the herbicide

• Reduce unnecessary traffic

• Reduce excessive irrigation

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Reduce traffic

Foot and vehicular traffic over treated areas will disrupt the chemical barrier and allow weeds to grow.

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Incorporate the herbicide

• Most abused aspect of weed control

• Incorporate immediately after application– Herbicides degrade on soil surface

• Incorporate with irrigation if possible

• Do NOT incorporate with drip irrigation!!!

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Field weed control

• Controlling escape weeds

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Controlling escape weeds

• Herbicides– Glyphosate and paraquat most commonly used

– Spot spray only

– Broadcast applications are dangerous around valuable nursery crops.

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Controlling escape weeds

• Cultivation– Used extensively for weed control between tree

rows.– Negative consequences on soil structure and

health.

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Controlling escape weeds

• Hoeing– Safe– Labor intensive– Inefficient– Very expensive!

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Summary

• Field preparation

• Weed prevention

• Weed eradication

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Website

• http://oregonstate.edu/dept/nursery-weeds/