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WILDLIFE AND REFORESTATION
IN THE PACIFIC NORTHWEST
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SYMPOSIUM PROCEEDINGS
1969
COPIES OF THESE PROCEEDINGS are available for
$3.00
each from School of Forestry Oregon State University Corvallis,
Oregon
97331 SCHOOL OF FORESTRY
OREGON ST ATE UNIVERSITY
PROTECTION OF CONIFEROUS SEEDS FROM RODENTS
M. A. Radwan Pacifi c Northwest Forest and Range Expt. Sta. Olympia, Washington ABSTRACT
Methods for protecting coniferous seed from rodents are reviewed. These include mechanical devices, poison baits, toxicants and
repellents, and biological control. The review suggests the need for strengthening research on the protection of seeds, because today,
available methods for the control of rodents arc inadequate.
INTRODUCTION
Regeneration of conifers from seed is often delayed or
entirely prevented by various biota that destroy the
disseminated seed before germination. The destructive agents
include seed-cating rodents, birds, insects and other
invertebrates, and fungi (2, 6, 14, 17). Although the
depredation by these agents varies by area, seed species, and
year, seed-eating rodents, especially deer mice (PeromysclIs sp.),
shrews (Sorex sp.), ground squirrels (Citelllls sp.), and
chipmunks (ElIlumias sp.) are generally recognized to cause the
greatest losses of seed in the Pacific Northwest. Although we
have measures to protect seed primarily from rodents,valuable
seed is still lost to them and to other destructive agents. If,
however, the actual causes of the loss of seed and effective
chemicals to protect seed from each of these agents can be more
accurately determined, surely a mixture of chemicals can be
formulated to protect seed from all the destructive agents. Until
then, a thorough knowledge of available methods of protection
will help to guide our present and future efforts.
DISCUSSION
Mechanical Methods
Seed in seed spots has been protected, with variable
success, by many mechanical devices. These include mulches
(26), paper pieces (7), and beer cans· (I I ).
Wire screens, made of hardware cloth, or window screens
provide the most practical protection, mechanically (12, 16).
Some screens are partially closed at the top and do not require
removal after the seed germinates (21). Screens, securely
anchored with stakes, can withstand some trampling and frost
heaving. Although they offer positive protection from rodents
and birds, screens do not protect the seed from insects or fungi.
Poison Baits
A formulation of oats or wheat, with thallous sulfate or
sodium fluoroacetate (1080) and a coloring material, has been
devised to control seed-eating rodents (8. 18).
Now, most poison baits for rodents on forestlands in the
Pacific Northwest contain Compound 1080. It is applied to
grain (usually soft. white wheat) at 2 ounces for each 100
pounds for hand distribution of from 2 to 4 pounds of grain for
each acre, and at 10 ounces for each 100 pounds for aerial
application of Y2 pound for each acre. The basis for these
formulations and rates of application is not clear, although the
original basis for th concentration of the formulation centered
on the development of a bait that contained enough poison on
one grain to kill a mouse. Recent tleld trials by the U. S. Bureau
of Sport Fisheries and Wildlife have shown that reduction in the
52
concentrations of the formulation does not impair the
e ffectiveness
of the
bait
(W.
E.
Dodge,
personal
communication). More infonnation is needed to accurately
determine levels of rodent populations that require baiting
before the seeding of conifers and whether baiting is really
·
necessary when seeds are treated with endrin .
\
Today, control of rodents is possible only for short periods
of time with poison baits, because elimination of the initial
rodent populations is incomplete and reinfestation from
untreated areas is often rapid. Control may sometimes be
effective if buffer strips are included in the baiting operation
(8)-or by rebaiting (24). Also, poisons today are hazardous to
nontarget species, antidotes are ineffective against primary and
secondary poisoning of nontarget species, and warning
symptoms are absent after ingestion. The University of
California at Davis is now experimenting with Diphacin
(Diphacinone) at concentrations of from 0.005 to 0.05 percent
in oats. This chemical is a slow-acting anticoagulant and its
antidote is vitamin K-I. It is considered much safer than the
acute poisons, and preliminary experiments in California show
it as effective as 1080.
Compound 1080, directly applied at low concentrations to
coniferous seed, has successfully protected untreated seeds
because, after a sublethal dose of the bait, the rodents
subsequently avoid the seed (25). Similar experiments with
1080 (15) and tetramine (3) failed, however. Consequently, the
hypothesis of aversion to protect direct seeding or natural
seedfall appears unpromising today.
Addition of chemosterilants to poison baits to inhibit the
reproductive ability of rodents that survive the toxicant has not
been tried. This approach might be possible, if suitable
chemosterilants were available.
Direct Application of Toxicants and Repellents to the Seed
For many years, chemicals have been applied directly to
seed to protect it from rodents. Compounds tested in early
trials included borax, carbolic acid, iodoform. naphthalene,
quinine, tannic acid, zinc chloride,. zinc phosphide, and 1080
(22, 26). Recently, the U. S. Bureau of Sport Fisheries and
Wildlife tried tetramine and endrin.
Tetramine was obtained by the Bureau's Denver Wildlife
Laboratory from the Bayer Company in Germany in the early
1950's. At first, the chemical was applied by soaking seed in an
acetone solution for I hour. Later the treatment was changed to
coating the seed with the chemical. The number of seedlings
produced from treated seed shows that both treatments
protected the seed somewhat (4, 9). The treatments, however,
sometimes inhibited seed germination (5, 19) and did not
protect seedlings, unaffected at germination, from rodents as
originally claimed (19). Also, the Bayer Company discontinued
,
manufacture of the chemical, mainly because of its extreme
toxicity. Tetramine, therefore, became unavailable for further
seed treatment.
Endrin to protect coniferous seed has been recommended
by the U. S. Bureau of Sport Fisheries and Wildlife since 1956.
A coating at 0.5 percent concentration (active ingredient from
50 percent wettable endrin powder), with an adhesive (Dow
latex 512 R or Rhoplex AC 33) to hold the ingredient to the
seedcoat and a coloring material (aluminum flake or monastral
green pigment) is recommended. The treated seed is
identifiable, and feeding by some birds may be discouraged with
this treatment. Sometimes, 2 percent Arasan has been added to
the formulation to protect the seed from disease, to repel birds,
and to increase effectiveness of the treatment against rodents.
Essentially, seed is treated by either of two ways. A mixture of
the endrin (or endrin and Arasan) with the adhesive is applied
to the seed. Or the seed is moistened with the adhesive and the
active ingredient is applied. The seeds are then coated with
aluminum flake or coloring pigment. Then, they may be
returned to containers or left to dry overnight.
The treatment with endrin protected the seed adequately
from rodents and produced satisfactory regeneration of
Douglas-fir in several field trials (I, 4, 13, 20). The treatment,
however, especially when Arasan was added, sometimes
inhibited germination (23). Also, it protected ponderosa pine
seeds inadequately from chipmunks and ground squirrels. Some
forest managers have recently indicated dissatisfaction with the
recommended treatment of 0.5 percent on Douglas-fir seeds and
have frequently increased t.l1e concentrations of endrin.
For more than a decade, the endrin treatment of
Douglas-fir seed has remained unchanged, except for the
elimination of Arasan. This fungicide apparently failed to
increase the effectiveness of the treatment as originally claimed
(1). Improvement of the treatment can be done by carcful
evaluation, both in cages and in the Held, to determine: (I) the
best method for treatment of seed, (2) the minimum amount of
endrin required for effective protection of seed, (3) the need for
prebaiting when seed is treated with endrin, (4) the hazards to
nontarget species, and (5) the possible benefits- of adding more
effective bird repellent to the treatment.
In the Animal Damage Project of the Pacific Northwest
Station, we have attempted to iIT,lpregnate Douglas-fir seed with
endrin. Our laboratory experiments showed that impregnation
is possible, without impairment to the viability of seed,
immediately following impregnation or after 4 months of
storage. Our feeding tests with caged Peromyscus showed that
impregnated seed was as effective as a coating treatment of I
percent and significantly better than the recommended
treatment of 0.5 percent. Impregnated seed had endrin in and
on the seedcoat and in the edible portion of the seed. The total
endrin present, however, was less than that possible with the
treatment of 0.5 percent. Also, seedlings produced from
impregnated seed were normal in appearance and growth. This
method of treating seed appears promising. Because the edible
portion of the seed is impregnated with the chemical, the
chemical is protected from weathering and seeding equipment.
Therefore, impregnated seeds may be effective against rodents
for a longer time and. possibly. more effective against
chipm unks and ground squirrels than coated seeds. But
impregnated seeds may be more hazardous to some seed-eating
birds and other nontarget species.
Another approach to the protection of seed with chemicals
has been tried. Laboratory studies at the University of
California showed that deer mice detect seeds by sense of smell
(10). Possibly, then, the odor of the seed could be masked with
a chemical to make the seed undetectable by rodents.
As our knowledge of factors that affect preferences of
rodents and birds for seed increases, the application of naturally
occurring compounds as repellents may be possible. Such
compounds, I believe, will be safer and more effective than the
chemicals now available.
Biological Control
Introduction of predators or disease to reduce rodent
populations and thus protect seeds is among the possibilities for
biological control. Today, however, such methods may lack
sufficient promise for serious consideration.
CONCLUSIONS AND RESEARCH NEEDS
Methods now available for protection of coniferous seed
from rodents are: (1) screens, (2) poison baits, and (3) endrin.
Each method has limitations that can be eliminated only
through research. Research is needed to: (I) reduce the cost of
screens; (2) determine the minimum concentration of 1080
required for effective control of rodents, examine the value of
prebaiting, and introduce safer rodenticides with attractants and
chemosterilartts; (3) devise a more effective bird repellent for
addition to the recommended endrin treatment; and (4) test, in
the field, seed impregnated with endrin. Also, chemicals and
other factors that affect detection of and preference for seed by
animals should be investigated. Such investigations may lead to
nonchemical methods of protection or, to chemicals that are
safer and more effective than endrin.
LITERATURE CITED
I. DICK, JAMES, J. M. FINNIS, LEE O. HUNT, and NELSON
B. KVERNO. "Treatment of Douglas-Fir Seed to Reduce Loss
to Rodents." 1. Forest. 56:660-661. 1958.
2. DICK, JAMES, and NORMAN E. JOHNSON. "Carabid
Beetles Damage Douglas-Fir Seed." J. Econ. Entomol.
51:542-544. 1958.
3. DICK, JAMES, and W. H. LAWRENCE. Protective Seeding
with Tetramine-Coated Douglas-Fir Seed. Weyerhaeuser Timber
Co. Forest. Res. Notes, 10 pp. 1957.
4. DIMOCK, EDWARD J. II. A Comparison of Two Rodent
Repellents in Broadcast Seeding Douglas-Fir. U. S. D. A. Forest
Servo Pacific Northwest Forest & Range Exp. Sta. Res. Pap. 20,
17 pp. 1957.
5. FINNIS, J. M. The Use of Tetramine in the Direct Seeding of
Douglas-Fir in Coastal British Columbia. Brit. Columbia Forest
Servo Res. Notes 31, 22 pp. 1955.
6. GASHWILER, JAY S. "Conifer Seed Survival in a Western
Oregon Clearcut." Ecology 48:431-438. 1967.
7. HATTERSLEY, JOSEPH G. "A Method of Direct Seeding in
S3
I
Rodent Infested Areas of Summer Drought. " J. Forest. 51:579.
1953.
8. HOOVEN, EDWARD F. Some Experiments in Baiting Forest
Lands for the Control of Small Seed Eating Mammals. Oreg.
State Board Forest. Res. Jull. 8, 70 pp. 1953.
9. HOOVEN, EDWARD F. Field Test of Tetramine Treated
Douglas-Fir Seed. Oreg. State Board Forest Res. Note 29, I I
pp. 1956.
10. HOWARD, WALTER E.,and RONALD E. COLE. Olfaction
in Seed Detection by Deer Mice. 1. Mammal. 48:147-150. 1967.
I I. JUHREN, GUSTAF. Protecting Direct Seedings
Rodent-Infested Areas. J. Forest. 48:443-444. 1950.
in
12. KEYES, JOSEPH, and CLARENCE F. SMITH. "Pine
Seed-Spot Protection with Screens in California." 1. Forest.
41:259-264. 1943.
13. KVERNO, NELSON B., and HARRY D. HARTWELL.
(Comp.) Pacific Northwest 1955-56 and 1956-57 Experimental
Seeding Studies. Progr. Rept.-November 1957. U. S. Fish &
Wildlife Servo Bur. Sport Fisheries & Wildlife, 50 pp. 1957.
14. LAWRENCE, WILLIAM H., and J. H. REDISKE. Fate of
Sown Douglas-Fir Seed. Forest Sci. 8:210-218. 1962.
IS. MCKEEVER, STURGIS. Compound 1080 and Forest
Regeneration. Characteristics of the Poison in Relation to Bait
Shyness, Poison
Shyness, Toxicity to Rodents, and
Phytotoxicity to Conifer Seed. Calif. Dep. Conserv. Div. Forest.
Resources Agency, 18 pp. (n. d.)
16. MILLER, CHARLES I. "An Economical Seed Spot
Protector." J. Forest. 38:733-734. 1940.
PURCHASED
54
BY
17. MOORE, A. W. Wild Animal Damage to Seed and Seedlings
on Douglas-Fir Lands of Oregon and Washington. U. S. Dep. of
Agr. Tech. Bull. 708,28 pp. 1940.
18. ORR-EWING, A. L. Rodent Control in Direct Seeding
Through Use of Poisons. Brit. Columbia Forest Servo Res. Note
17,8 pp. 1950.
19. ROY,D. F. Seed Spot Tests with Tetramine-Treated Seed in
Northem California. J. Forest. 55:442-445. 1957.
20. ROY, D. F. Seed Spotting with Endrin-Treated Douglas-Fir
Seed in Northwestem Califomia. U. S. D. A. Forest Servo Pacific
Southwest Forest & Range Exp. Sta. Tech. Pap. 61, 12 pp.
1961.
21. ROY, D. F., and G. H. SCHUBERT. K-S.creen Seed Spots.
U. S. D. A. Forest Servo Calif. Forest & Range Exp. Sta. Forest
Res. Note 88,2 pp. 1953.
22. SCHUBERT, G. H. A Trial of Three Chemicals as Rodent
Repellents in Direct Seeding. U. S. D. A. Forest Servo Calif.
Forest & Range Exp. Sta. Forest Res. Note 84, 2 pp. 1953.
23. SHEA, KEITH R. Field Survival of Thiram-Treated
Douglas-Fir Seed. Weyerhaeuser Co. Forest. Res. Note 38,8 pp.
1961.
24. STEIN, WILLIAM I. More Natural Regeneration by
Controlling Seed-Eating Rodents. U.S.D.A. Forest Servo Pacific
Northwest Forest & Range Exp. Sta. Res. Note PNW-12,10 pp.
1964.
25. TEVIS, LLOYD JR. Behavior of a Population of Forest
Mice When Subjected to Poison. J. Mammal. 37:358-370. 1956.
26. WILLIS, C. P. The Control of Rodents in Field Seeding.
Soc. Amer. Forest. Proc. 9:365-379. 1914.
THE FOREST SERVICE, U.S. DEPARTMENT OF AGRICULTURE, FOR OFFICIAL USE.