June 30, 2006

Chemical control of eastern redcedar

Herbicides can be used to control eastern redcedar, however, they should be viewed as just another tool in the integrated management program. Depending on the application method and chemical type, the use of herbicides can be time consuming and expensive, especially when used on denser tree infestations or large tracts of land. Effectiveness also is variable depending on the tree size and label directions and/or restrictions. Always read and follow herbicide label directions. Herbicide information on control of troublesome plant species, including eastern redcedar, is updated annually in UNL Extension's Guide for Weed Management in Nebraska (EC-130). In general, herbicides for eastern redcedar control can be used for broadcast application or individual-tree spraying.

Table 1: Percent eastern redcedar control and grass injury levels at about 100 days after treatment as influenced by the tree height (feet) where herbicide treatments were broadcast applied. Dose Tree Height (ft) Grass injury Treatmentsa pt/acre 0 to 1 1 to 2 2 to 4 4 to 6 1. Surmount 4 84 70 52 12 35 2. Surmount 5 95 81 46 20 55 3. Grazon P & D 6 90 59 51 16 15 4. Grazon P & D 8 95 79 60 18 20 5. Tordon 22K 2 85 65 33 25 20 aTreatments 1, and 2, were mixtures of picloram + fluroxypyr each at 0.66 lbs ae/gal Treatments 3 and 4 were picloram at 0.54 lbs ae/gal + 2,4-D at 2.0 lbs ae/gal Treatment 5 was picloram at 2.0 lbs ae/gal.

Broadcast treatments

Broadcast application is the most common method of applying herbicides in agricultural settings. The key message for the efficacy of broadcast treatments in eastern redcedar control is: “the shorter the tree the better control.”

Since tree height was the most important factor influencing the level of chemical control (tree injury) with broadcast treatments, the herbicide efficacy data from a Nebraska study was categorized by tree height (Table 1). Recommended herbicides for trees that are up to two feet tall include: Surmount, Grazon P&D and Tordon (Table 1). However, the same herbicides will not provide satisfactory control of trees taller than two feet, indicating the importance of tree height. Surmount at a rate of 5 pts/ac can cause short-term grass injury in the form of leaf yellowing and top growth burning (Table 1). Cost of Grazon P+D and Tordon 22 K for broadcast applications can range from $21 to $26 per acre. Since Surmount is not a marketed product yet, its cost is unknown.

Individual-tree treatments

Individual-tree treatments can be applied directly to the tree foliage or to the soil around the tree base. Soil treatments can minimize the amount of herbicide used and the exposure to non-target species; however, soil treatments may not be effective unless applied before rainfall, preferably in spring or fall. Rain water is needed to move the herbicide into the root zone, allowing easier uptake by a tree. Recommended herbicides for soil application around a tree base include Tordon 22K at the rate of 1 cc (ml) per foot of tree height or Velpar-L at 4 (cc) ml and Spike 20P at 1cc (ml) for every inch of tree diameter. Cost of Tordon is about $85 per gallon, Velpar is about $65 per gallon and Spike 20P is about $9 per pound.

Individual-tree foliage also can be treated . Based on a study conducted in northeastern Nebraska, recommended herbicides for control of 2-10 feet tall trees include Surmount at 1.5 % volume per volume (v/v), Grazon P+D at 2.0% (v/v) and Tordon 22K at 1.0% v/v (Table 2).

Table 2: Percent of eastern redcedar and grass injury at 100 days after treatment to individual trees. Treatmenta Dose (v/v) (%)b Tree injury (%) Grass injury (%) Surmount 1.0 75 39 Surmount 1.5 89 48 Grazon P & D 2.0 90 50 Tordon 22 1.0 94 60 Roundup Ultra 1.0 5 55 Roundup Ultra 2.0 31 91 aTreatments 1 and 2 were mixtures of picloram + fluroxypyr, each at 0.66 lbs ae/gal Treatment 3 was picloram at 0.54 lbs ae/gal + 2,4-D at 2.0 lbs ae/gal Treatment 4 was picloram at 2.0 lbs ae/gal. Treatment 5 and 6 were glyphosate at 3.7 ae/gal bDose was a herbicide/water solution on a volume/volume basis

To help you determine volume per volume basis, for example, the 1% v/v equals 1 gallon of product per 100 gallons of water. For smaller backpack sprayers use an equivalent of 1.3 oz of product per every gallon of water. Apply about 1.5 oz of the herbicide spray solution for every foot of tree height. Walk around the tree and just spray enough solution to just get a glisten (shine) on the canopy surface. Solution dripping off the canopy indicates a rate that is too high, and a likely waste of time and money. As an example, it was calculated that 1 gallon of spray solution could cover 15 individual trees that are 6 feet tall at a pressure of 20 PSI and a single nozzle type XR8002.

Grass injury in the form of temporary yellowing and burning of top growth was evident among all treatments especially for Tordon 22K. Roundup is not recommended for use in pasture settings due to poor activity on cedar trees and high injury level to the grass (Table 2). Cost of Grazon P+D and Tordon 22 K can range from $11 to $16 per acre.

Practical hint for chemical control

Use of selective herbicide treatments should be based on tree height. Broadcast treatments are effective only on short trees (up to 2 feet tall), while medium height trees (2 to 10 feet) can be controlled with individual-tree treatments. For broadcast treatments use 6-8 pints of Grazon P&D or 4-5 pts of Surmount in 20 gallons of water per acre. To prepare 1 gallon of spray solution for individual-tree canopy treatments, use 1.3 ounces of Tordon, or 2.6 ounces of Grazon P&D, or 2 ounces of Surmount. For larger spray tanks adjust herbicide rates accordingly.

Take home message

Since there are many different scenarios under which eastern redcedar trees grow, they obviously can not be managed by a single control method; however, if the methods are implemented in a systematic manner, significant advances in eastern redcedar control can be achieved.

We recommend using the best combination of techniques discussed in Part 1 and Part 2 of this story, depending on your needs and your budget. There are many ways to start developing an integrated weed management program. The easiest way will be to try one or two techniques and then add more practices as you can or as field conditions change. Also consider the cost of control methods when selecting those that best fit into your overall operation.

Stevan Knezevic
Extension Integrated Weed Management Specialist
Haskell Ag Lab, NEREC
Stevan Knezevic
Extension Integrated Weed Management Speicalist
Haskell Ag Lab, NEREC

Copyright 2006 by the University of Nebraska Board of Regents. All rights reserved.

Published by University of Nebraska-Lincoln Extension in the Institute of Agriculture and Natural Resources Cooperating with the counties and the U.S. Department of Agriculture.

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