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.
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Effective weed control in the years after transplanting Christmas trees is essential to obtain a good stand of healthy trees and to achieve maximum growth. Poor weed control during 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.