1220 N Street, Room A-357

Sacramento, CA 95814

Telephone: (916) 654-0768

Facsimile: (916) 653-2403

July 15, 2003

Public Information and Records Integrity Branch (PIRIB)

Office of Pesticide Programs (OPP)

Environmental Protection Agency (7502C)

1200 Pennsylvania Avenue, N.W.

Washington, DC 20460-0001

Attention: Docket ID Number OPP-2003-0204

The United States Environmental Protection Agency (USEPA) issued a
Federal Register Notice announcing the availability and opportunity for
public comment on the notice "Zinc Phosphide: Notice of Filing a
Pesticide Petition to Establish a Tolerance." The notice was issued on
July 9, 2003, with a 30-day public comment period ending August 8, 2003.

Thank you for the opportunity to respond to the USEPA's notice entitled
"Zinc Phosphide: Notice of Filing a Pesticide Petition to Establish a
Tolerance." The California Department of Food and Agriculture would like
to enter the following comments entitled "Comments of the California
Department of Food and Agriculture on the USEPA's Zinc Phosphide: Notice
of Filing a Pesticide Petition to Establish a Tolerance", into the
public record.

If you have any questions please contact me at (916) 654-0768 or by
e-mail at <dschnabel@cdfa.ca.gov>.

Sincerely,

Duane L. Schnabel, Senior Agricultural Biologist

Integrated Pest Control Branch

Plant Health and Pest Prevention Services

Enclosure

DS:cj

cc: E. Silberhorn

M. Meyers

N. Dechoretz

L. Bezark

**[Comments of the California Department of Food and Agriculture on the
USEPA's Zinc Phosphide: Notice of Filing a Pesticide Petition to
Establish a Tolerance]{.underline}**

The California Department of Food and Agriculture (CDFA) would like to
comment on an important issue facing the alfalfa hay growing industry in
California. Yield loss and price variability caused by vertebrate pest
infestations in alfalfa specifically from meadow voles (*Microtus sp*.)
is a major economic concern to California alfalfa growers. Alfalfa is a
major feed crop for the dairy and beef cattle, as well as other
livestock industries in California. Alfalfa hay production in California
(all counties) for 2002 is estimated at 7.3 million tons grown on 1
million acres with a value of 873 million dollars to California alfalfa
growers. Even a 5% reduction in either yield or price has a detrimental
impact on not only alfalfa growers, but also the California dairy and
livestock industries. In 1998 the fiscal impacts of a severe vole
infestation combined for a yield and price reduction of 16% in
California alfalfa (all counties), resulting in a 134 million dollar
revenue decline for alfalfa growers and sharp rise in price and imports
to California for the dairy and livestock industries.

A survey of several University of California Cooperative Extension Farm
Advisors was conducted after the CDFA was contacted by California
Agricultural Commissioners who indicated that many of the growers in
their counties were again experiencing vole damage in alfalfa during
(2001/2002). Populations were estimated to range from 300 to 1,500 voles
per acre, with yield reductions to individual fields ranging from 10% to
40% and hay quality reduced by 10%. Additionally, producers of other
crops are experiencing damage due to immigration from meadow vole
infested alfalfa fields.

The CDFA has invested considerable resources to find a solution to the
problem. The CDFA has conducted food safety studies, efficacy studies
and wildlife safety studies to document the safe and effective use of
zinc phosphide to control meadow voles in alfalfa.

In 1998 and again in 2002 the CDFA requested and obtained a Section 18
Emergency Exemption for the use of zinc phosphide on alfalfa to control
meadow voles. Currently a FIFRA Section 24(c) Special Local Need
Registration with all appropriate documentation and data requirements
has been submitted to The California Department of Pesticide Regulation.
The 24(c) Special Local Need Registration submission in California is
pending the establishment of a federal food tolerance. Unless a federal
food tolerance is established for the use of zinc phosphide on alfalfa,
a FIFRA registration will not be issued. Alfalfa growers in California
will not have a viable means to control this economically devastating
pest.

Therefore the CDFA supports the establishment of a federal food
tolerance for the use of zinc phosphide on alfalfa.

**[DISCUSSION OF ECONOMIC LOSS\*]{.underline}**

**California Alfalfa Hay Production for Selected Counties\*\***

+-----------+-----------+-----------+-----------+-----------+-----------+
| **Year**  | **Acres** | **Yie     | **Pro     | **Pr      | **Value** |
|           |           | ld/Acre** | duction** | ice/Ton** |           |
|           | **Ha      |           |           |           | **\$      |
|           | rvested** | **Tons**  | **1,000   | **\$**    | 1,000**   |
|           |           |           | Tons**    |           |           |
|           | **1,000** |           |           |           |           |
+===========+===========+===========+===========+===========+===========+
| 1992      | 713       | 6.7       | 4777      | 80        | 382160    |
+-----------+-----------+-----------+-----------+-----------+-----------+
| 1993      | 682       | 6.6       | 4501      | 96        | 432096    |
+-----------+-----------+-----------+-----------+-----------+-----------+
| 1994      | 706       | 6.9       | 4871      | 103       | 501713    |
+-----------+-----------+-----------+-----------+-----------+-----------+
| 1995      | 691       | 6.3       | 4353      | 106       | 461418    |
+-----------+-----------+-----------+-----------+-----------+-----------+
| 1996      | 686       | 6.6       | 4528      | 107       | 484496    |
+-----------+-----------+-----------+-----------+-----------+-----------+
| 1997      | 698       | 6.8       | 4746      | 121       | 574266    |
+-----------+-----------+-----------+-----------+-----------+-----------+
| 1998      | 787       | 5.9       | 4643      | 103       | 478229    |
+-----------+-----------+-----------+-----------+-----------+-----------+
| 1999      | 799       | 6.4       | 5113      | 92        | 470396    |
+-----------+-----------+-----------+-----------+-----------+-----------+
| 2000      | 764       | 6.3       | 4813      | 94        | 452422    |
+-----------+-----------+-----------+-----------+-----------+-----------+
| 2001      | 727       | 6.3       | 4580      | 115       | 526700    |
+-----------+-----------+-----------+-----------+-----------+-----------+

\* Data compiled by the California Agricultural Statistics Service.

\*\* California counties where significant meadow vole populations are
present: Alameda, Butte, Colusa, Contra Costa, Fresno, Glenn, Kern,
Kings, Lassen, Madera, Merced, Modoc, Sacramento, San Joaquin, Shasta,
Siskiyou, Solano, Stanislaus, Sutter, Tulare, Yolo, Yuba

**Estimated 2002 Revenues for Alfalfa Hay Production**

With & Without the Use of Zinc Phosphide for Selected Counties\*\*

+-----------+-----------+-----------+-----------+-----------+-----------+
|           | **Acres   | **Yie     | **Pro     | **Pr      | **Value** |
|           | Ha        | ld/Acre** | duction** | ice/Ton** |           |
|           | rvested** |           |           |           | **        |
|           |           | **Tons**  | **Tons**  | **\$**    | \$1,000** |
+===========+===========+===========+===========+===========+===========+
| With Zinc | 725,000   | 6.5       | 4,713,000 | 102       | 480,726   |
| Phosphide |           |           |           |           |           |
+-----------+-----------+-----------+-----------+-----------+-----------+
| W/Out     | 725,000   | 5.9       | 4,276,000 | 92        | 393,392   |
| Zinc      |           |           |           |           |           |
| Phosphide |           |           |           |           |           |
| \*\*\*    |           |           |           |           |           |
+-----------+-----------+-----------+-----------+-----------+-----------+

\*\* California counties where significant meadow vole populations are
present: Alameda, Butte, Colusa, Contra Costa, Fresno, Glenn, Kern,
Kings, Lassen, Madera, Merced, Modoc, Sacramento, San Joaquin, Shasta,
Siskiyou, Solano, Stanislaus, Sutter, Tulare, Yolo, Yuba \*\*\*Estimated
losses based on a 10% decline in alfalfa yield/acre and 10% price
decline from reduced quality of alfalfa stand. The U.C. Cooperative
Extension estimates individual alfalfa field losses from vole damage at
10% to 40%.

The data supports the argument that meadow vole damage to alfalfa in
California is substantial. 1997 and 1998 were years in which the State
of California experienced an increase in meadow vole populations. A
comparison of 1997 to 1998 data indicate a general decline in yields per
acre as well as a decline in price per ton. Yield and price declines can
be attributed to many variables, including a decline in yields and
quality from weather related crop performance, reductions in yield and
quality from newly established alfalfa stands, decline in price from
market saturation (previous years production and imports), and a yield
and price decline attributed to meadow vole damage to alfalfa fields.
For the selected counties identified for inclusion under this economic
model, an overall economic loss (yield and price) for the 1997/1998,
growing season is placed at \$96 million. This amount includes a net
increase in farmed alfalfa acreage of 89,000 between 1997 and 1998. The
\$96 million loss in 1998 represents a 17% loss based on 1997 revenues
of \$574.3 million. Estimating what percentage of the economic loss that
can be attributed to each variable is difficult. As previously stated an
individual alfalfa field can sustain yield losses ranging from 10% to
40% and hay quality price reductions of 10%. Using this model, economic
losses in 1998, sustained from meadow vole damage can be estimated at
between \$19 million and \$48 million.

Employing the same economic model used above, an economic loss from vole
damage in 2002/2003 can be estimated at between \$18 and \$45 million on
an overall economic loss from all causes of \$89.5 million (17%) on 2001
revenues of \$526.7 million.

**[Other comments:]{.underline}**

Large population fluctuations are characteristic of meadow voles.
According to literature, a meadow vole is capable of conceiving 17
litters per year under laboratory conditions. Under field conditions,
four (4) to six (6) litters are common. Reproduction may occur
throughout spring and fall. Slight decreases in mortality and increases
in litter size and number of litters can trigger population irruptions.

Each litter averages three (3) to six (6) offspring. A female is capable
of producing offspring in 35 days. The gestation period is 21 days.
Consequently, a breeding pair during a four (4) month period - assuming
a 30 day gestation period and six (6) offspring per litter with an equal
gender mix - will procreate 258 individuals. Even with a 90 percent
mortality rate, 100 meadow voles are capable of producing 2,580
individuals in four (4) months.

An adult meadow vole weighs approximately 3.0 to 4.5 ounces. To sustain
its metabolic requirements, a meadow vole must consume daily at least 51
percent if its body weight. Accordingly, a single meadow vole, assuming
a body weight of 3.5 ounces, will consume 41 pounds of plant material a
year. While seemingly insignificant in and of itself, the quantity
foraged by even a moderate infestation (500 meadow voles per acre) is
staggering - 20,360 pounds of plant biomass annually.

Meadow Voles feed both on the root system and the above ground portion
of plants. During winter, feeding on root crowns can severely deplete a
perennial alfalfa stand. Without the use of zinc phosphide, meadow voles
will reduce the quality and quantity of alfalfa hay. Meadow voles reduce
forage biomass, encourage weed invasion, reduce stand longevity, degrade
hay quality, and reduce the price received.

Meadow voles can quickly devitalize a stand predisposing it to the
invasion and establishment of weedy species. Some weeds, such as hare
barley (foxtail), downy brome (cheatgrass), ripgut brome, and green
foxtail (bristlegrass), can injure the mouths of livestock, rendering
the forage less palatable. Others, such as fiddleneck and the widespread
yellow starthistle, are poisonous. If present in sufficient quantities,
the forage is unsuitable for livestock consumption. The problematic
*Poa* complex includes both annual and perennial species. Its robust,
competitive nature displaces seedling alfalfa. Some weeds are subject to
quarantine restrictions, resulting in hay that may not be transported or
sold. Scotch thistle and a number of the knapweed species are A-rated
(subject to eradication or holding actions) and occur in alfalfa hay
growing regions of California. Quackgrass (*Agropyron repens*) is
particularly troublesome and is not tolerated in hay exported to Japan.
At the very least, the intrusion of weeds will necessitate supplementary
applications of herbicides. In general, hay containing objectionable
plants can incur a \$10 to \$50 per ton discount.

A high meadow vole population can reduce stand longevity by weakening
the stand and allowing weed establishment in open areas. With
establishment cost of \$534 per acre (based on a 1994 Washington State
University Cooperative Extension enterprise budget), it is highly
advantageous for a producer to perpetuate a stand. With annual
production costs (including a prorated stand establishment charge)
exceeding \$892 per acre (based on a U.C. Cooperative Extension
enterprise budget), the financial integrity of farm operations can be
readily compromised if the time frame in recapturing establishment costs
is significantly condensed. A reduction in stand longevity intensifies
soil erosion. Open ground (eg. devoid of vegetative cover) is exposed
for longer periods to the erosive forces of wind and water.

A large-scale meadow vole population irruption occurred in 1957- 1958.
Irrigated valleys in eastern Oregon, Idaho, northeastern California,
Nevada and Washington were impacted. Over one million pounds of poison
bait were sold (Beck, 1959). Severe impacts have been historically
observed in alfalfa hay production in Nevada, which has growing
conditions similar to those in northeastern California. In 1907-1908 the
first recorded meadow vole outbreak in the United States occurred in
Nevada. Approximately 15,000 acres of alfalfa were completely destroyed
by meadow vole populations, which in some areas, reached thousands per
acre (Piper, 1909). Jameson (1958) estimated that 100 meadow voles per
acre would consume 1,000 pounds per acre of alfalfa in a seven-month
growing season. Considering the history of meadow vole populations in
California and historical impacts, a 40% reduction in alfalfa production
is easily possible without control methods.

**[LITERATURE CITED]{.underline}**

Beck, J. R. ed. 1959. The Oregon Meadow Mouse Irruption of 1957-1958.
Coop. Ext. Serv. Oregon State College . Corvallis, Oregon. 88pages.

Jameson, W.L. 1958. Consumption of Alfalfa and Wild Oats by *Microtus
californicus.* J. Wildlife Management, 22:433-435.

Piper, S.E. 1909. The Nevada Mouse Plague of 1907-1908. U.S.D.A. Farmers
Bulletin No. 352.