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Trial Applications of Low-Impact Herbicides
1
for Pifton-Juniper Control in the Southwest
Douglas Parker2 , Max Williamson 3 , Richard Edwards4 , and Russell WardS
Abstract.-A significant need exists to develop effective, efficient, safe, and
environmentally sound approaches to control pinon-juniper trees, especially
for small trees, those less than 6 feet in height. To meet this need, a new
approach using a low-volume application of the herbicides Tordon 22K
(picloram) and Spike 80W (tebuthiuron) in water was evaluated. Herbicides
mixtures were applied to the base of selected trees just above the ground
using a backpack sprayer. Tordon 22K was tested at 10, 20, 40, and 80
percent concentrations in water and Spike 80W was tested at 0.5 and 1.0
pounds of product in one gallon of water. This low-volume approach was
selected to allow applicators to carry sufficient product and carrier into
rough and remote areas. The goal was to only treat selected trees and
avoid adversely affecting grasses and other nearby plants. The results of
trial application done on the Gila and Lincoln National Forests show that
satisfactory control of small trees can be achieved. The approach also may
be useful for control of larger trees under selected circumstances.
INTRODUCTION
key will be to have effective, safe, economical,
environmentally sound, and socially acceptable
methods that can be used by those responsible for
managing affected lands.
An excellent overview of the various management options and related recommendations is included in the publication entitled "Watershed
Management Practices for Pmon-Juniper Ecosystems" (USDA Forest Service, 1993). Acceptable
methods are available to some extent to treat larger
trees, those above 6 feet in height, such as through
fuelwood harvests. The control of small trees and
sprouts, however, has proven to be a much more
difficult problem. Hand methods (cutting, chopping, and grubbing) have and are being used,
although the effectiveness, cost, and safety of these
Pinon-juniper (P-J) woodlands occupy a vast
acreage in the Southwest. Over the past 100 years,
tree densities have increased many fold and trees
have spread into adjacent ecosystems. This situation has and will continue to cause numerous adverse environmental and social effects. Although
considerable controversy exists over the causes of
the problem and past control measures, it appears
there is general agreement that on-the-ground
management actions are needed to restore deteriorating ecosystems and enhance protection of areas
that will be in an unsatisfactory condition in the
near future. An enormous opportunity exists to
create and maintain healthy p-J ecosystems. The
1A/1 pesticides must be registered by appropriate State and/or Federal agencies before they can be used. Pesticides can be injurious to
humans, domestic animals, desirable plants and other wildlife - if they
are not handled properly. Use all pesticides selectively and carefully.
Follow recommended practices for the disposal of surplus pesticides
and pesticide containers.
2Entomologist, USDA Forest Service, Southwestern Region, A/buquerqpe, NM.
Private consultant on vegetation management, Marietta, GA.
4Forester, USDA Forest Service, Lincoln National Forest, Smokey
Bear Ranger District, Ruidoso, NM.
5Range/Wildlife/Watershed Staff Officer, USDA Forest Service, Gila
National Forest, Mimbres Ranger District, Mimbres, NM.
209
techniques cause concern. Herbicides have been
shown to be the most efficient, effective, and safe
approach to control small trees, but they have not
been widely used in recent years. A lawsuit in the
9th Circuit Court of Appeals and a subsequent
temporary suspension of the use of herbicides on
National Forest Systems lands in 1984 all but ended
herbicide use on National Forests and other Federal
lands in Arizona and New Mexico. This legal barrier no longer exists. In addition, certain herbicide
formulations and application methods developed
and used in the 1970's and 80's do not meet the
needs of current resource managers. The high cost
of compliance with the National Environmental
Policy Act (NEPA) and the public controversy over
the use of herbicides also contributed to the lack of
herbicide use.
In 1993, we decided to take another look at the
herbicide option for control of unwanted trees. A
review of herbicide performance showed that
picloram and tebuthiuron were the most promising
products, since they were broadleaf and brush
products, registered for range and pasture uses
Gohnsen 1987; McDaniel and White-Trifaro 1987).
A positive aspect for both of these herbicides is that
they will have minimal effects on established
grasses at application rates specified on their respective labels. It should be noted that both of
these herbicides are considered "soil active" materials; however, we decided to test a new application
approach of applying the herbicide directly to the
base of target trees. A major objective of the herbicide evaluation was to attempt to develop a
low-volume, selective application technique that
could be effectively used to treat small trees, especially in rough and remote terrain, where other
alternatives would not be appropriate. Broadcast
applications and directed foliar sprays were excluded because of environmental concerns and operational constraints, especially the need for a large
volume of water.
APPLICATION APPROACH
Low-volume, basal applications of Tordon 22K
(picloram) and Spike 80W (tebuthiuron) mixed
with water were evaluated. Tordon 22K is a liquid
formulation and Spike 80W is a wettable powder.
The herbicide mixtures were applied to the base of
selected trees at. ground level using a backpack
sprayer with a diaphragm pump (fig. 1). A model
30 gunjet with a 0002 or DE-2 spray tip was used.
This equipment is relatively inexpensive; the total
cost being about $125. The major advantage of the
210
Figure 1.-Backpack sprayer used to apply herbicides to the base
of trees.
backpack sprayer is that the pump is sealed at the
factory and tested to 70 psi to prevent leaks. The
herbicide mixtures were not applied to the soil;
rather, they were applied to the base of trees and
sprouts just above the ground. Tordon 22K was
tested at 10,20,40, and 80 percent concentration in
water and Spike 80W was tested at 0.5 and 1.0
pounds of product in one gallon of water. These
different concentrations were tried to determine
the lower limit of the product that might yield satisfactory control. Larger trees were also treated to
determine if treatment success could be achieved.
A band from 2-4 inches was sprayed on these trees.
The widest band of herbicide mixture was applied
to the largest trees and the band was reduced progressively as the diameter of the trunk decreased.
Initially, the spray mixture was herbicide and
water; however, a silicone wetting agent was
added to the mixture beginning in March 1994 to
increase the movement of the herbicide down the
stem. The goal of the basal application technique
was to only treat selected trees and not affect desirable trees and shrubs within two to three feet. The
low-volume approach was selected to allow applicators to carry sufficient product and carrier into
remote areas to optimize a pplica tion efficiency.
40, and 80 percent concentrations (Table 1). A 10
percent mixture of Tordon, which was applied six
months previously, controlled about 70 percent of
alligator juniper sprouts and seedlings. Since the
levels of tree brown-out on the Lincoln National
Forest are similar to that observed on the Gila
National Forest, a separate table was not included.
The mortality of pmon exceeded that of junipers on
both treatment sites. On the Lincoln National
Forest, exceedingly high treatment effects were
observed on larger trees.
For trees less than 6 feet in height, the 20
percent Tordon mixtures produced control results
as good as the 40 and 80 percent concentrations.
More time is needed for to evaluate the 10 percent
mixture, but it appears the lower limit that will
yield satisfactory results could be below the 20
percent concentration level. Thus, the current cost
for the herbicide will be somewhere in the range of
$8-16 per acre. Also, the silicone wetting agent
appeared to improve the movement of the spray
mixture down the stem, which could be a critical
factor when lower concentrations of herbicide
might be used.
Although the Spike 80W treatments have not
produced tree brown-out as high as that observed
with Tordon 22K, the overall treatment success may
be similar in a few more months. As shown in Table
I, the half pound per gallon of water mixture of
Spike 80W yielded better initial foliage brown-out
than the pound per gallon mixture. This was
probably due to the higher volume of the spray
mixture applied to each tree. The results on the
Lincoln National Forest are similar, except no
sprouting stumps were treated.
It will take more time before the final
conclusions can be made. about the effects of the
various treatments, especially for the larger
junipers.
The tests were done on the Gila National Forest, North Star Mesa, and the Lincoln National
Forest, Carrizo Demonstration Project site. Pmon
pines (pinus edulis) were treated at both sites;
however, the juniper species were different. Alligator juniper, Juniperus deppeana, a sprouting species,
was the target on the Gila National Forest, and
one-seed juniper, J. monosperma, was the primary
species treated on the Lincoln National Forest.
Permanent rectangular-shaped plots were established and marked with stakes and flags to enable
evaluation of treatment effects in the future. The
applications were done by walking through each
plot spraying selected trees. Treatments were applied in August and November, 1993, and March,
1994. Evaluations of effectiveness were made in
November, 1993; March, 1994; and June, 1994.
Additional evaluations are planned over the next
six to nine months.
TREATMENT RESULTS
The results of the trial applications for both
herbicides are very promising.
After only three
months, significant browning of foliage was
observed in over half of the treated alligator
juniper sprouts, seedlings and saplings of both
juniper species, and pinon saplings. Larger trees
showed some effects, although to an extent less
than the smaller trees. Treatment effects were more
apparent with the picloram mixtures, but
tebuthiuron is a slower acting herbicide and the
results are expected to. improve over time.
Treatment success continued to increase after six
months, but few effects were observed on nearby
untreated trees and shrubs. By nine months,
foliage brown-out of trees on the Gila National
Forest site exceeded 90 percent for the Tordon 20,
Table 1.-Piflon-juniper herbicide trail results, Gila National Forest, North Star Mesa, Evaluated on June 1. 1994.
Foliage Brown-out (percent)
Plot No.
Date Treated
Herbicide
Sprouts
Seedllngs/Sapllngs
Larger Trees
1
8/23/93
2
8/23/93
Tordon 22K 40%
3
8/23/93
Tordon 22K 80%
4
8/23/93
Spike 80W (1/2Ib./gal.)
5
8/23/93
6
7
Tordon 22K 200"{'
90+
90+
20
90+
90+
20
90+
90+
30
60
60
10
Spike 80W (1 Ib./gal.)
40
40
5
11/15/93
Tordon 22K 10%
70
70
10
11/15/93
TORDON 22K 20%
80
80
10
8
3/7/94
Tordon 22K 200;{'
80
80
10
9
3/7/94
Spike 80W 1/2 Ib./gal.)
30
.30
5
211
DISCUSSION
inaccessible areas would be most suited for this
approach.
It appears that the spray mixtures flow down
the stem following root profiles and the herbicide
is absorbed by root hairs around the base of treated
trees. Susceptible trees and shrubs within two to
three feet of treated trees have shown little signs of
herbicidal activity. Besides being selective, a major
benefit of the basal application approach is that the
herbicides are not applied to the soil.
The next step will be to focus attention on how
to utilize this low-volume, selective application
approach to achieve desired future conditions. A
few possible circumstances where this new technique maybe useful follow:
Creation of Snags. Snags are important habitat
for several birds and other wildlife. Creation of
snags may be one of the few economical uses of
herbicides to treat large trees. Areas that are inaccessible would be best suited because snags
are usually harvested by the public in accessible
areas.
Protection of Archaeological and Historic
Sites. In some cases, these sites can be Adversely affected by erosion and arroyo cutting
and may need to be protected through watershed improvement efforts. Since mechanical
treatments can damage these fragile resources,
management options are often limited. Herbicides may offer an attractive option to restore
p-J woodlands to a healthy condition to provide
prolonged protection of these sites.
Create or Maintain Existing Openings. Treatment of undesirable or excess seedlings and
saplings to create or maintain existing openings
in p-J stands would be one of the most economical uses of this new application technique.
It probably would cost less than mechanical
grubbing, and a major advantage would be to
avoid ground disturbing activities within protected areas.
CONCLUSIONS
Ecosystem management is a concept that will
guide vegetation management on public lands in
the future. Ecosystem management involves using
an ecological approach to achieve multiple-use objectives by blending the needs of people, environmental values, and scientifically based techniques.
It must be realized that p-J ecosystems, which are
threatened or are being damaged by an "over
abundance of trees", c~n only be restored to a
healthier state through the removal of trees. All
available methods-fuelwood harvest, mechanical
methods, prescribed fire and cultural practices, like
limiting livestock grazing-will need to be used.
Herbicides will be one of these tools to achieve
management objectives, used individually or in
combination with other methods, as part of an integrated vegetation management approach.
There has been a wealth of information to show
that herbicide formulations used in modern resource management are "safe" when used properly. Herbicides are among the most rigorously
tested consumer products on the market today.
Before they are registered for use, herbicides must
meet strict standards of human health protection
and environmental safety. In addition, a major
benefit of the herbicides evaluated in this study is
that they provide selectively through both directed
application and the inherent selective nature of the
products. It will be particularly important to have
Fuelwood Harvest Areas. Treatment of alligator
juniper sprouts and excess seedlings and saplings would be another economical use following fuelwood harvest. This approach would be
particularly desirable in areas where prescribed
fire might not be an option.
Thinning. Thinning in P-J woodlands has been
done to promote growth of remaining trees,
release understory ground vegetation, and
most recently, to create fuels to enable the use
of prescribed fire. The low-volume, selective
herbicide technique would be appropriate
where trees are too small to be of commercial
value or in rough and remote terrain. Removal
of small trees that occur under larger trees
would help to prevent fire from moving into
the crown of the larger trees that are considered to be desirable.
Wildlife Openings. Large expanses of dense
canopied p-J woodlands are common in the
Southwest and offer little in terms of plant and
animal diversity. A directed basal herbicide
treatment could be used to create openings in
selected areas across the landscape. to increase
diversity, release native plants, and reduce
sheet erosion. Dense stands of smaller trees in
212
and social problems that are occurring in p-J ecosystems in the Southwest.
thorough environmental analyses for projects on
Federal lands, which incorporate available risk
assessments, to respond to possible challenges to
proposed herbicide projects. It is important to note
that risk assessments developed in recent years,
such as the Risk Assessment For Herbicide Use in
the Forest Service Regions 1,2,3,4, and 10 and on
Bonneville Power Administration Sites, which
includes the Southwest, have withstood legal
challenges.
As always, well trained applicators and specialists will be needed to ensure program success.
Significantly, the public will demand that resource
managers and applicators be knowledgeable about
the methods and herbicides that are proposed for
use. Comprehensive training and certification
programs will need to be developed and implemented before this new herbicide approach can be
used to help solve the enormous environmental
LITERATURE CITED
Johnson, 'T.N. Jr. 1986. Using herbicides for pinyon-juniper control in the Southwest. P.330-334. In:
Everett, R.L." compiler. Proc. Pinon-Juniper Conference. January 13-16, 1986, Reno, NV. GTR INT-215.
Ogden, UT:USDAForest Service. Intermountain Research Station.
McDaniel, K.C. and L. White-Trifaro. 1986. Selective
control of pinyon-juniper with herbicides. p. 448-455.
In: Everett, R.L., compiler. Proc. Pinon-Juniper Conference. January 13-16, 1986, Reno, NY. GTR INT-215.
Ogden, UT: USDA Forest Service. Intermountain Research Station.
USDA Forest Service. 1993. Watershed management
Practices for Pinon-Juniper Ecosystems. Southwestern Region, Albuquerque, NM.
213