WSP05273

• File Number: 8210.470
• Description: Pacific Southwest Interagency Committee
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 8/30/1966
• Author: Unknown
• Title: Phreatophyte Symposium 66-3 Meeting - August 30 1966
• Water Supply Pro - Doc Type: Report/Study

removal but is ineffective as a control on small plants because of
the tendency of the small plants to bend over rather than break off
or pull up.

To obtain the maximum control when removing tamarisk, it is necessary
to remove the crown of the plant without burying any stems. One of
the most effective machines for removing the crowns of large adult
plants is the rock rake (photograph 6).

When conditions permit, ground spray equipment is used extensively
for application of herbicides. From field applications which have
been made, it appears that approximately 3 pounds of silvex per acre
will result in reasonably good control of tamarisk. Two pounds of
2,4-D amine salt have been effective on willows. Herbicides are most
effective when applied to plants that are young, tender, and full of
vigor. During 1965, 1,900 acres of phreatophytes in New Mexico and
160 acres in Nevada were sprayed with various formulations of herbi-
cides using ground spray equipment (photograph 7); and about 1,500
acres in New Mexico were sprayed in 1966.

The cost for operating ground spray rigs has averaged from $6 to $9
per acre depending on the rate of chemical application and the type
of material used.

Aerial application (photograph 8) of herbicides can be an effective
procedure for phreatophyte contro~ particularly where the plants are
small and growing rapidly. Most of this work has been accomplished
on the Middle Rio Grande floodway near Albuquerque and in areas where
annual reinfestation is common. The helicopter has been used exten-
sively for application. From field tests, the best results have been
obtained when spraying 3 pounds of silvex per acre. The cost of this
work has varied from $8 to $13 per acre when accomplished by contract.
During 1965, approximately 2,300 acres of phreatophyte-infested areas
were sprayed by helicopter on the Rio Grande and 410 acres were sprayed
in Nevada. The cost of application in Nevada was $11.47 per acre. In
1966, the floodway above and below Albuquerque was sprayed with an
invert formulation of 2,4-D amine at a cost of $8.50, and an additional
area near Bernardo was sprayed with (2) 2,4,5-TP (silvex) at a cost of
$13 per acre. An invert formulation of herbicide is used to reduce
spray drift.

The Bureau continues to collect data to support benefits that will be
realized for establishment and maintenance of phreatophyte control
projects. Other projects of this nature are now being considered.
There is still much to be learned, but at least the first steps have
been taken toward making water available for beneficial use.

30