- , A reprint from WILDLIFE AND REFORESTATION IN THE PACIFIC NORTHWEST , T Hugh C. Black hI'S f ile W Ab ' as c out T iV1iss reat hi.s F cans ed b ile· I·de y sca , h o ntI·.(:· nn " We. v lle. d ing t - er, S bY th he P Otne e so rint tnls ftw a ed P take re h Ublic s tna ave atio y rern be en n \ ain. Cor recte d, : I 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 Pacific 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 concentrations of the formulation does not impair the effectiveness of the bait (W. E. Dodge, personal Regeneration of conifers from seed is often delayed or communication). More infonnation is needed to accurately entirely prevented by various biota that destroy the determine levels of rodent populations that require baiting before the seeding of conifers and whether baiting is really disseminated seed before germination. The destructive agents · include seed-cating rodents, birds, insects and other necessary when seeds are treated with endrin . invertebrates, and fungi (2, 6, 14, 17). Although the \ Today, control of rodents is possible only for short periods depredation by these agents varies by area, seed species, and of time with poison baits, because elimination of the initial year, seed-eating rodents, especially deer mice (PeromysclIs sp.), rodent populations is incomplete and reinfestation from shrews (Sorex sp.), ground squirrels (Citelllls sp.), and untreated areas is often rapid. Control may sometimes be chipmunks (ElIlumias sp.) are generally recognized to cause the effective if buffer strips are included in the baiting operation greatest losses of seed in the Pacific Northwest. Although we (8)-or by rebaiting (24). Also, poisons today are hazardous to have measures to protect seed primarily from rodents, valuable nontarget species, antidotes are ineffective against primary and seed is still lost to them and to other destructive agents. If, secondary poisoning of nontarget species, and warning however, the actual causes of the loss of seed and effective symptoms are absent after ingestion. The University of chemicals to protect seed from each of these agents can be more California at Davis is now experimenting with Diphacin accurately determined, surely a mixture of chemicals can be (Diphacinone) at concentrations of from 0.005 to 0.05 percent formulated to protect seed from all the destructive agents. Until in oats. This chemical is a slow-acting anticoagulant and its then, a thorough knowledge of available methods of protection antidote is vitamin K-I. It is considered much safer than the will help to guide our present and future efforts. acute poisons, and preliminary experiments in California show it as effective as 1080. DISCUSSION Compound 1080, directly applied at low concentrations to coniferous seed, has successfully protected untreated seeds Mechanical Methods because, after a sublethal dose of the bait, the rodents Seed in seed spots has been protected, with variable subsequently avoid the seed (25). Similar experiments with success, by many mechanical devices. These include mulches 1080 (15) and tetramine (3) failed, however. Consequently, the (26), paper pieces (7), and beer cans· (I I ). hypothesis of aversion to protect direct seeding or natural Wire screens, made of hardware cloth, or window screens seedfall appears unpromising today. provide the most practical protection, mechanically (12, 16 ). Addition of chemosterilants to poison baits to inhibit the Some screens are partially closed at the top and do not require reproductive ability of rodents that survive the toxicant has not removal after the seed germinates (21). Screens, securely been tried. This approach might be possible, if suitable anchored with stakes, can withstand some trampling and frost chemosterilants were available. heaving. Although they offer positive protection from rodents and birds, screens do not protect the seed from insects or fungi. Direct Application of Toxicants and Repellents to the Seed For many years, chemicals have been applied directly to Poison Baits seed to protect it from rodents. Compounds tested in early A formulation of oats or wheat, with thallous sulfate or trials included borax, carbolic acid, iodoform. naphthalene, sodium fluoroacetate (1080) and a coloring material, has been quinine, tannic acid, zinc chloride,. zinc phosphide, and 1080 devised to control seed-eating rodents (8. 18). (22, 26). Recently, the U. S. Bureau of Sport Fisheries and Now, most poison baits for rodents on forestlands in the Wildlife tried tetramine and endrin. Pacific Northwest con tain Compound 1080. It is applied to Tetramine was obtained by the Bureau's Denver Wildlife grain (usually soft. white wheat) at 2 ounces for each 100 Laboratory from the Bayer Company in Germany in the early pounds for hand distribution of from 2 to 4 pounds of grain for 1950's. At first, the chemical was applied by soaking seed in an each acre, and at 10 ounces for each 100 pounds for aerial acetone solution for I hour. Later the treatment was changed to application of Y2 pound for each acre. The basis for these coating the seed with the chemical. The number of seedlings formulations and rates of application is not clear, although the produced from treated seed shows that both treatments original basis for th concentration of the formulation centered protected the seed somewhat (4, 9). The treatments, however, on the development of a bait that contained enough poison on sometimes inhibited seed germination (5, 19) and did not one grain to kill a mouse. Recent tleld trials by the U. S. Bureau protect seedlings, unaffected at germination, from rodents as of Sport Fisheries and Wildlife have shown that reduction in the originally claimed (19). Also, the Bayer Company discontinued 52 , manufacture of the chemical, mainly because of its extreme Another approach to the protection of seed with chemicals toxicity. Tetramine, therefore, became unavailable for further has been tried. Laboratory studies at the University of seed treatment. California showed that deer mice detect seeds by sense of smell Endrin to protect coniferous seed has been recommended (10). Possibly, then, the odor of the seed could be masked with by the U. S. Bureau of Sport Fisheries and Wildlife since 1956. a chemical to make the seed undetectable by rodents. A coating at 0.5 percent concentration (active ingredient from As our knowledge of factors that affect preferences of 50 percent wettable endrin powder), with an adhesive (Dow rodents and birds for seed increases, the application of naturally latex 512 R or Rhoplex AC33) to hold the ingredient to the occurring compounds as repellents may be possible. Such seedcoat and a coloring material (aluminum flake or monastral compounds, I believe, will be safer and more effective than the green pigment) is recommended. The treated seed is chemicals now available. identifiable, and feeding by some birds may be discouraged with this treatment. Sometimes, 2 percent Arasan has been added to Biological Control the formulation to protect the seed from disease, to repel birds, Introduction of predators or disease to reduce rodent and to increase effectiveness of the treatment against rodents. populations and thus protect seeds is among the possibilities for Essentially, seed is treated by either of two ways. A mixture of biological control. Today, however, such methods may lack the endrin (or endrin and Arasan) with the adhesive is applied sufficient promise for serious consideration. to the seed. Or the seed is moistened with the adhesive and the active ingredient is applied. The seeds are then coated with CONCLUSIONS AND RESEARCH NEEDS aluminum flake or coloring pigment. Then, they may be returned to containers or left to dry overnight. Methods now available for protection of coniferous seed The treatment with endrin protected the seed adequately from rodents are: (1) screens, (2) poison baits, and (3) endrin. from rodents and produced satisfactory regeneration of Each method has limitations that can be eliminated only Douglas-fir in several field trials (I, 4, 13, 20). The treatment, through research. Research is needed to: (I) reduce the cost of however, especially when Arasan was added, sometimes screens; (2) determine the minimum concentration of 1080 inhibited germination (23). Also, it protected ponderosa pine required for effective control of rodents, examine the value of seeds inadequately from chipmunks and ground squirrels. Some prebaiting, and introduce safer rodenticides with attractants and forest managers have recently indicated dissatisfaction with the chemosterilartts; (3) devise a more effective bird repellent for recommended treatment of 0.5 percent on Douglas-fir seeds and addition to the recommended endrin treatment; and (4) test, in have frequently increased t.l1e concentrations of endrin. the field, seed impregnated with endrin. Also, chemicals and For more than a decade, the endrin treatment of other factors that affect detection of and preference for seed by Douglas-fir seed has remained unchanged, except for the animals should be investigated. Such investigations may lead to elimination of Arasan. This fungicide apparently failed to nonchemical methods of protection or, to chemicals that are increase the effectiveness of the treatment as originally claimed safer and more effective than endrin. (1). Improvement of the treatment can be done by carcful evaluation, both in cages and in the Held, to determine: (I) the LITERATURE CITED best method for treatment of seed, (2) the minimum amount of endrin required for effective protection of seed, (3) the need for I.