Successful Christmas tree production begins with preemergence weed control

This information will help you select the best herbicides to ensure you have a healthy stand of trees with maximum growth.

Effective weed control in the years after transplanting Christmas trees is essentialto obtain a good ­­­­­stand of healthy trees and to achieve maximum growth. Poor weed controlduring the years after establishment may result in dead seedlings and reduced growth of the survivors. Inadequate weed control also has adverse indirect effects. It is difficult to spray pesticides and to prune trees in fields full of common milkweed, poison ivy, Canada thistle, hemp dogbane, giant ragweed, common pokeweed, horseweed, horsenettle, and other large or poisonous weeds. For long-term weed control, it is easier to start with a clean field and keep weeds under control than to try to clean up a weedy field after weeds are established. The presence of weed trash in trees at harvest reduces tree value, and may limit markets because of quarantine or noxious weed laws.

Preemergence herbicide application should be the first and most important activity in a season-long weed control program. Growers should formulate a weed control plan that includes residual herbicides and postemergence herbicides with several different modes of action. Most Christmas tree plantings will require mowing, hand-weeding or tillage in addition to herbicides to maintain adequate weed control. After trees are too large for application with a ground sprayer, growers should consider air application or applications with back pack sprayers. Air-blast sprayers do not provide adequate soil coverage and should not be used for preemergence herbicide application.

The following preemergence herbicides are registered for use on Christmas trees. Most herbicide labels list the tree species for which the herbicides can be used. Some labels allow use on other species not listed on the label if growers have tested the herbicide and found it to be safe. Some labels list the major types, e.g., fir, pine, spruce. Please read labels carefully before applying any herbicide.

Abbreviations used

BF       Balsam Fir

DF       Douglas Fir

FF        Fraser Fir

WF      White Fir

GF       Grand Fir

NF       Noble Fir

WP      White Pine

BS       Blue Spruce

NS       Norway Spruce

WS      White Spruce

AP       Austrian Pine

SP        Scotch Pine

PPO     Proto-porphyrinogen oxidase inhibitor

PSII     Photosystem II inhibitor

ALS    Acetolactase Synthase Inhibitor

Aatrex (atrazine) 4L

Species: DF, GF, NF, AP, SP, BS; apply after transplanting or to dormant trees

Rate: 2-4 qt/acre (2-4 lb ai/acre)

When: Apply to new transplants after transplanting; apply to dormant established trees in late fall or early spring.

Weeds Controlled: Most annual broadleaves and grasses for 4 to 6 weeks;   quackgrass

Limitations: Several broadleaf weeds are resistant to atrazine and other PSII inhibitors; atrazine has a short (4-6 weeks) residual life. Atrazine is a safe herbicide for use on new transplants; it may be applied by airplane.

Mode of Action: Photosystem II (PSII) inhibitor.

Princep (simazine) 4L

Species: BF, DF, FF, WF, AP, SP, BS, NS, WS

Rate: 1- 4 qt/acre (1- 4 lb ai/acre)

When: Apply after transplanting; for established trees, apply in fall or early spring; for quackgrass control, apply after quackgrass begins growth in the spring.

Weeds Controlled: Many annual broadleaves and grasses.

Limitations: Apply to transplants at least 2 years old. Several broadleaves, including Powell amaranth, redroot pigweed, common lambsquarters, common ragweed, common groundsel, are resistant to PSII inhibitors. Simazine has 6-8 weeks residual life.

Mode of Action: PSII inhibitor. Do not exceed 4 lb ai/acre of atrazine plus simazine in one year.

Goal 2EC and Goal Tender 4SC (oxyfluorfen)

Species: DF, FF, GF, NF, AP, SP, WP, BS, NS

Rate: 2-4 qt of EC, or 1-2 qt of SC (1-2 lb ai/acre) preemergence

When: Seedbeds: preemergence or 5 weeks after emergence;

New transplants: after transplanting;

Established trees: in spring before bud break; may be used on conifers in containers

Weeds Controlled: Most annual broadleaves and grasses preemergence; most broadleaves postemergence; weak on mustards, smartweeds, and all perennials.

Limitations: Goal has both preemergence and postemergence activity; it is weak on grasses.

Mode of Action: PPO inhibitor

Gallery 75 DF (isoxaben)

Species: BF, WF, WP, SP, BS, WS

Rate: 0.66 -1.33 lb/acre (0.5-1 lb ai/acre)

When: Established plantings, fall or early spring

Weeds Controlled: Most annual broadleaves

Limitations: No grass or perennial weed control; 6-8 weeks residual life

Mode of Action: Cellulose synthesis inhibitor

Kerb 50 WP (pronamide)

Species: All fir, pine and, spruce.

Rate: 2-4 lb/acre (1-2 lb ai/acre)

When: Mid-late fall

Weeds Controlled: Winter annual broadleaves; annual and perennial grasses, including quackgrass.

Limitations: 4-6 weeks residual life if applied in spring; fall application should last 6-8 weeks; cover crops may be sensitive to Kerb; poor weed control in soils with more than 4% organic matter. .

Mode of Action: Mitosis inhibitor; unrelated chemically to other Christmas tree herbicides.

Pendulum 3.3 EC or Pendulum Aquacap 3.8 CS (pendimethalin): (Prowl in food crops)

Species: DF, BF, FF, WF, AP, SP, WP, BS, NS, WS

Rate: (2.4-4.8 qt of EC or 2.1-4.2 qt of CS (2-4 lb ai/acre)

When: Apply after transplanting or to established trees.

Weeds Controlled: Most annual grasses, many annual broadleaves

Limitations: No perennial weed control; short to moderate (4-8 week) residual activity. Most effective when used in combination with another herbicide, eg. a PSII inhibitor.

Mode of Action: Mitosis inhibitor, similar chemically to Surflan.

Surflan 4 AS (oryzalin)

Species: All true fir; all pine; all spruce; do not use on DF.

Rate: 2-4 qt/acre; 2-4 lb ai/acre

When: Early spring; apply only on established plantings

Weeds Controlled: Germinating annual grasses

Limitations: Short (4-6 weeks) residual life; do not use on Douglas fir.

Mode of Action: Mitosis inhibitor; similar to pendimethalin.

Sureguard (flumioxazin) 51 WDG: (Valor or Chateau in food crops)

Species: DF, FF, GF, NF, WF, AP, SP, WP, BS, NS

Rate: 8-12 dry oz/acre (0.25-0.38 lb ai/acre)

When: Apply to established trees at least 3 years old in the spring before budbreak or after trees have hardened in the fall. Do not apply when foliage is wet.

Weeds Controlled: Preemergence and postemergence activity on most annual broadleaves and grasses.

Limitations: Young trees may be sensitive; application to wet foliage can injure trees. Trees normally grow out of injury. Poor horseweed (marestail) control with spring application.

Mode of Action: PPO inhibitor

Velpar (hexazinone) 2L or 75 DF

Species: FF, GF, NF

Rate: 1-2 qt of 2L or 0.67-1.33 lb of DF; (0.5-1.0 lb ai/acre) 1 application per year

When: Apply after transplanting (plants at least 2 years old) after soil has settled around roots. On established transplants, apply preemergence before budbreak.

Weeds Controlled: Most annual and perennial broadleaves and grasses; woody perennials and vines. Velpar will not control well established woody plants.

Limitations: Do not use on soil with less than 1% organic matter, or soils with greater than 85% sand; use low rate on sandy loams with less than 2% organic matter; Velpar is very soluble and may leach into root zone and cause tree injury. To avoid problems, use only once in 2 years.

Mode of Action: PSII inhibitor

Westar (hexazinone 68.6% + sulfometuron methyl 6.5%) 75% DG:

Species: DF, FF, GF, NF

Rate: 6-8 oz/acre; (0.28-0.357 lb ai/acre)

When: On new transplants, apply after rain has settled soil around tree roots; on established plantings, apply before budbreak in the spring.

Weeds Controlled: Many annual and perennial broadleaves and grasses.

Limitations: Westar may stunt or injure young trees; use the lowest rate (6 oz/acre) on most soils.

Mode of Action: Hexazinone: PSII inhibitor; sulfometuron methyl: ALS inhibitor.

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