WSP04263

• File Number: 8507
• Description: Rio Grande Project
• State: CO
• Basin: Rio Grande
• Date: 1/1/1957
• Title: Symposium on Problems of the Upper Rio Grande
• Water Supply Pro - Doc Type: Report/Study

maintenance pfOblem of contwlling the regwwth of
vegetation in the cleared floodway and along the
main conveyance channel. The answer to the re-
gwwth pwblem was to develop a program of control
of regwwth fwm those phreatophytes previously
cleared and new reseeding gfOwth which could be
normally expected. This program was set up around
the use of chemicals I using both airplane and ground
application methods.
Aedal spraying of floodways and other salt cedar
control areas was accomplished by contract with
Western Flying Service of Clovis, New Mexico.
Specifications called for the use of formulas con-
taining 2,4-D amine, and low volatile esters of
2,4-0 and 2,4,S-T, diesel oil, emulsifier and water.
Not less than 5 gallons of specified mixtures were
applied to each acre. Treatments were given July
1953, September 1953 and July 1954, allowing a
minimum of 42 days regrowth between applications.
Spmying operations pwvided for applications of
chemicals to four units of matured phreatophyte
growth located in certain bosque areas between
Bemardo and Nogal Canyon and appwximately 5,000
acres of cleared floadway in the San Marcial area.
During the three periods for spray applications a
total of appwximately 25,000 acres were treated
under the Bureau contract for aerial spraying.
During this same period, July 1953, the Bureau of
Reclamation cooperated with the State of New Mexico
in establishing a program of phreatophyte control
in other areas along the Rio Grande. Similar spec~
ifications were prepared and the same contractor
handled the aerial spraying work under the State
conhact. A total of 4,500 acres were treated three
times.
To check on the effectiveness of spraydistdbution
over the treated areas and to analyze the results of
the work, three steps were taken. First, in order to
determine scope of coverage, each area was inspect~
ed within 30 days after applications were made. The
vegetation which had received adequate amounts of
chemical was identified by the appearance of ep-
inasty, generally occurring at the tips of the gmwth.
The second step consisted of collection of root
samples from the various areas for laboratory tests
for carbohydrate food reserve analysis. Samples; of
course, were taken from both treated and untreated
areas for comparison. The last and possibly most
conclusive check was a field inspection of spray
areas to determine the degree of top kill and basal
regrowth generally occurring within 60 days of treat-
ment.
We are fortunate in having weed control special~
ists from the Agricultural Research Service, U. S.
Dept. of Agriculture, in addition to those from the
Bureau, Regional and Washington Offices, to help
us evaluate the results of the weed control program
thus far., The results from all airplane-sprayed
tracts of matured phreatophytes were found to be

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quite similar. Two or more repeated spray treat-
ments gave a high percentage top kill and genemlly
not much more than 50% plant kill and as Soon as
treatment was discontinued the phreatophyte gmwth
recovered to original density within 1 or 2 years
particularly in those areas where river over~flow
provided an annual irrigation.

It now appears that best results of aefial treatment
of matured phreatophytes cannot be accomplished
without removal of the dead canopy, which will fa-
cilitate the applications of chemicals to basal re.
growth. Our experience thus far indicates little was
gained by the use of 2,4-D and mixtures of esters of
D and T on the treatment of mature salt cedar. It
would appear, however, that the iso-octyl esters
(brushkiller) gave us a better top kill on willows.
A treatment of 725 acres of mixed phreatophyte
growth sprayed under the State Engineer's contract,
using 5 gallons to the acre containing 2 pounds of
amine, 1 gallon of nontoxic oil, as a substitute for
diesel oil, and the balance of water give the best over~
all kill accomplished so far. In this area the bac-
chafis had expefienced a 100% kill and willow and
cottonwood 80% and the salt cedar about 80% top kill
and 50% plant kill on matured plants.

Contwl of phreatophyte regmwth and seedlings
within the mechanically cleared floodway areas was
more effective than in the mature phreatophyte areas.
Plant kill has been considered very good, ranging
from poor in some few areas to excellent in other
areas. The pom kills appeared to be correlated with
heavy rain showers, which occurred immediately
following spray operations. ,We have also observed
that better plant kill is accomplished after regrowth
has obtained a height of about 18 inches.
We are in process of modifying the program of
phreatophyte contwl to include a plan pfOviding for
alternate mechanical clearing, using heavy gang disk
plows and ground application of chemicals, principally
2,4-D amine. This change of procedure is being
done in hopes of gaining time on ultimate complete
control of floadway regrowth with its reduction of
water use. Application of the chemicals will be
accomplished by the use of a heavy duty large vol~
ume gwund spray dg pulled by a tfactOf. It is plan-
ned also to initiate a re..seeding program through
which we may be able to establish various types
of grasses throughout the control areas. Control
in the mature salt cedar areas would be accomplished
by somewhat similar methods.
In addition to the use of presently available herbi-
cidal hormones for phreatophyte control, we are also
working in cooperation with various chemical com~
panies on experimental control of salt cedar in test
plots with the use of new Urea Herbicides.
From the amount of salt cedar, etc., that exists on
the Rio Grande and its tributaries, we can expect
the pfOblem of phreatophyte contwl to be with us Cm
a long time to come. Of course, we are always hope-

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