Oleoresin Capsicum Has Potential as a Rodent Repellent in Direct Seeding

Direct seeding of southern pines has been a versatile and inexpensive alternative to planting on many reforestation sites across the South. Successful direct seeding has required that seeds be coated with thiram to repel birds, and with endrin to repel rodents. Endrin, which is extremely toxic, is no longer produced in the United States. Therefore, a substitute is needed. Oleoresin capsicum, a natural substance derived from pepper plants, has potential as a repellent. It occurs in an extremely concentrated form, and its repellency is caused by the heat of the capsicum. Preliminary tests have shown that at low rates oleoresin capsicum had little effect on the germination of longleaf pine (Pinus palusfris Mill.) seeds, and significantly reduced losses from predation. INTRODUCTION Direct seeding is an affordable alternative to planting on many sites needing reforestation of the southern pines. It is a lso an appropr ia te supp lement to natura l regenerat ion where seedfall is inadequate. Techniques were thoroughly researched during the 1950’s and 1960’s by Derr and Mann (1971) and the 1970’s by Campbell (1981a, 1981b). Studies show that success depends on protection of seeds from birds and rodents (Derr and Mann 1971; Campbell 1981a, 1981 b). The recommended formulation of thiram and endrin protects against all important species of seedeating birds, and deters small mammals common to most southern pine sites. Many field studies, tests with caged an imals , and opera t iona l seed ings have conf i rmed the repe l len t p roper t ies o f these chemica ls (Campbe l l 1981c). Thiram, a fungicide currently marketed as Gustafson 42-S??, is safe, effective, and easy to use. Anthraquinone is almost as effective, but is more difficult to apply because it is a powder. It is, however, a good alternative as a bird repellent. Endrin, an insecticide, is very toxic. Although still registered as a rodent repellent in forestry due to the small quantities used (Barnett and others 1980), endrin is no longer manufactured in the United States because of the lack of demand. Thus, the continued use of direct seeding in southern forestry may depend on finding,a satisfactory substitute. In a series of tests evaluating potential repellents, Barnett (1995) and Campbell (1981c) could not find an effective replacement. Recently, the substance oleoresin capsicum (OC) has shown promise. For example, it is added to the paint used for hulls of ships to deter barnacles. Oleoresin capsicum, a rustto red-colored liquid obtained from dried cayenne peppers (Capsicum frutescens L.), is standardized with olive oil. The chemical in capsicums that can produce a burning sensation in the mouth is capsaicin. Its strength is measured in parts per million (ppm). These ppm are converted into Scoville Units (SV), the industry standard for measuring the heat of peppers (American Spice Trade Association 1960, Hoffman and Lego 1983). One ppm is equivalent to 15 SV. The material used in this study has an SV of 500,000. Although oleoresin capsicum is a natural and nontoxic chemical derived from pepper plants and is used in many foodstuffs to increase their pungency, it is an irritant to the skin or eyes. Protective gloves and eyewear are recommended when hand l ing th is p roduc t . The repellancy of capsicum is attributed to its heat. This paper describes initial evaluations of oleoresin capsicum as a rodent repellent for direct seeding. METHODS Candidate chemicals for direct seeding must meet these criteria: (1) they must be relatively benign to the seeds, and (2) they must repel the target animals. The first tests described, therefore, measure effects of various formulations of capsicum on germination of longleaf pine (Pinus pa/us&is Mill.) seeds. Lab Tests for Germination Longleaf pine seeds were chosen for the evaluations because they are the most sensitive of the southern pines to such treatments. Germination was tested under standard laboratory conditions for 28 days (Association of Official Seed Analysts 1980). Results were recorded three times weekly during the periods of peak germination. Three replications of loo-seed samples from each treatment replication were tested. The seed treatments used were: an untreated control: thiramand clay-slurry treatments with and without latex; and 1 x, 2x, 4x, 8x, and 16x dilutions with capsicum and with thiramor clay-latex slurry. The 1 x capsicum treatment (500,000 SV, American Mercantile, PO. Box 240654, Memphis, TN 38124) was applied at a rate of 1 tablespoon per 25 pounds of seed. The rates of application per pound (454 grams) of seed were: 76 mililiter of thiram, 3 mililiter of latex, 0.6 mililiter of capsium (lx), and 45 grams of kaolin clay in 100 mililiter of water. The latex was added to the mixture to improve binding of the materials to the seeds. The same proportion of materials was used for each treatment. The laboratory tests were conducted in the Alexandria Forestry Center Seed Testing Laboratory. Field Tests Longleaf pine seeds, selected from a single lot of Louisiana seed orchard origin, were selected for field evaluations. ’ Chief Silviculturist, USDA Forest Service, Southern Research Station, Pineville, LA 71360. 326 In: Haldrop, ThomasA.,edd.199& proceedings of the ninth biennial southern silvicultural research conference; 1997 February 2527; Clenson, SC. Gen. Tech. Rep. SRS-20. As&ville, NC: U.S. Lkpartment of Agriculture, Forest Service, Southern Research Station. p. 326-328. Empty seeds were removed from the lot by pentane flotation (Barnett 1971). Random samples were drawn for treatments. Repellent treatments were applied and the seeds were a i r -d r ied overn igh t . It is logical to evaluate candidate rodent repellents in caged animal trials before testing in the field. However, the Alexandria Forestry Center no longer has the facilities to conduct such tests. We, therefore, skipped the intermediate step and moved directly to field tests conducted on the Palustris Experimental Forest in central Louisiana. Five of the seed treatments were evaluated in the field: (1) an untreated control, (2) lx capsicum plus thiram (0.6 mililiter capsicum, 76 mililiter thiram, and 3 mililiter latex per pound of seed), (3) 2x capsicum plus thiram (1.2 mililiter capsicum, 76 mililiter thiram, and 3 mililiter latex), (4) lx capsicum plus kaolin clay (0.6 mililiter capsicum, 45 grams clay in 100 mililiter water, and 3 mililiter latex), and (5) 2x capsicum plus kaolin clay (1.2 mililiter capsicum, 45 grams clay in 100 mililiter water, and 3 mililiter latex). Treatment plots consisted of five IBinch circular spots arranged around a central stake. Each spot was sown with 100 seeds. Plots were randomly selected for a particular treatment and marked with a flagging pin. Twenty replications, separated by at least 50 feet, were established April 1, 1996, on a previously cleared site. Plots were randomly ar ranged. Seed losses were determined by counting seeds remaining on the spots at 2to 3-day intervals. Heavy rains washed the seeds from the spots 12 days after initiation of the test. Because the plots in this study were small and subject to overwhe lming p reda t ion , we eva lua ted them f requen t l y to determine predation patterns for each of the five t r ea tmen ts . RESULTS AND DISCUSSION The laboratory germination test results show that capsicum with thiram or clay reduced germination when applied at rates greater than 2x (table 1). However, the lx and 2x rates did not reduce laboratory germination more than the thiramor clay-latex controls. Thiram alone reduces germination in the laboratory (Campbell 1981c), but the reduction in these tests was more than expected. Previous studies have shown that thiram has less impact on germination in the field (Barnett and others 1980, Campbell 1981c). The key to success for a repellent is field performance, so field evaluations of capsicum were initiated. Results from the field evaluations indicate that the seeds were subjected to heavy predation. After 11 days, 78 percent of the seeds in the control treatment were lost due to predation (table 2). Because rapid losses were anticipated from the small seed spots, seed counts were started 4 days after sowing and continued at 2to 3-day intervals until heavy rains washed seeds from the spots. Though there were heavy losses in the control and in the clay-capsicum treatments, the thiram-capsicum treatments protected the seeds well through 11 days of the test, with average losses Table l-Effects of oleoresin capsicum with thiram or clay slurry on the germination of longleaf pine seeds Trea tment comb ina t ion Var iables None Th i ram Clay slurry ______ Percent-----Cont ro l 8 9 Without latex 45 85 With latex 4 6 6 9 l x caps i cum 4 1 7 6 2x caps i cum 4 7 6 8 4x caps i cum 3 5 5 9 8x caps i cum 3 4 4 6 16x caps i cum 2 3 3 7 Tab le 2-Percentages o f seeds removed or damaged on each plot 4, 7, 9, and 11 days after seeding on April 1, 1996, by treatment Seed losses at (days)