IL 59 June 1996 Strategies for Reducing Deer Damage to Soybeans
Strategies For Reducing Deer Damage To Soybeans S.U. Wallace and J.H. Palmer Department of Agronomy Clemson University J.M. Barnes Clemson University Cooperative Extension Service, Walterboro, SC and L.C. Francoeur and G.K. Yarrow Department of Aquaculture, Fisheries, and Wildlife Clemson University Introduction The white-tailed deer population has increased rapidly in many parts of the Southeast in recent years. Deer numbers in South Carolina have been estimated to be in the range of 750,000 to one million animals. The increase in deer population has been accompanied by a decrease in crop acreage. There has been severe deer pressure on soybeans in some parts of the state because soybeans are a preferred food by deer. Some South Carolina producers have given up on growing soybeans in potentially productive fields because of the deer problem. In a statewide survey conducted by Clemson University, crop producers reported that 70% of their 1991 soybean acreage was damaged to some extent by deer. Based on the reported acreage and degree of damage, it was estimated that deer damage cost soybean producers in South Carolina more than $7.8 million in 1991 (Smathers et al., 1994). Soybean Plant Damage from Deer Browsing Until recently, most reports indicated that damage from deer occurred from occasional browsing around the edges of fields, primarily in the early stages of crop development. The available information also indicated that only a small percentage of plants in a field would likely be damaged by deer, so that crop losses would be small (Garrison and Lewis, 1987; 2
DeCalesta and Schwendeman, 1978). However, because deer populations have continued to increase, many southern producers now report that deer are feeding in their fields throughout the growing season and that deer are much more likely to damage entire fields or significant portions of fields. Crop damage at all soybean growth periods from seedling emergence through vegetative and Figure 1. Soybean seedlings that have been browsed by deer. Some stand loss has probably occurred, but the plants that remain have the potential to recover if browsing is not repeated. reproductive growth has been reported in South Carolina (Wallace, 1995). Total crop loss with no harvestable yield has become a common producer complaint in some areas. Deer damage to soybean seedlings (Figure 1) sometimes kills the plant, but in other situations the deer-damaged seedling has a reasonable chance for recovery. The difference in these two scenarios depends on how much of the plant shoot is removed. If the entire shoot is removed below the cotyle- Cotyledons Figure 2. A soybean seedling in early development. The seedling will die if the plant shoot is removed below the cotyledons. If the cotyledons or upper leaves are not removed, the plant may be able to recover. 3 Figure 3. Deer browsing during early plant development often results in Y-shaped plants.
Figure 4. This plant was repeatedly damaged by deer. The Y shape resulted from damage early in the season. Note the small pod near the clippers; this tiny plant is in the pod-fill stage of growth. 4 dons (Figure 2), then the plant will die because there are no stem buds remaining to produce new shoot growth. However, if the deer bite occurs above the cotyledons, then buds on the remaining stem can produce new growth. Deer damage in the seedling stage often results in Yshaped plants (Figure 3). The two stems are really branches that developed from lower stem buds. (Cultivation can throw soil up on the base of a Yshaped plant, hiding the evidence of early, non-repeated deer damage.) The Y-shaped plants that result from early deer damage can recover and produce reasonable yields if deer damage is not repeated. Unfortunately, deer often do revisit a feeding site and can inflict repeated damage from which a plant cannot recover. The little plant in Figure 4 was damaged at least four times by repeated deer browsing. Notice the small pod near the clippers; this plant is in the period of pod-fill and obviously cannot recover to produce a harvestable yield. We have seen fields in South Carolina which were destroyed by deer, replanted, destroyed again, and later abandoned. This cost the producers the expense of preparing and planting the field as well as the loss of the crop. As previously stated, deer damage Figure 5. Deer browsing has removed upper leaves from this plant, which is at the flowering stage. can occur at any stage of soybean development, including flowering (Figure 5). Damage that removes the
plants tops at these stages can make a field appear to have been mowed. Damage during late vegetative and reproductive growth can have serious consequences. The top of the plant in Figure 6 was eaten by deer during reproductive growth. Some pods remain on the upper stem, but many of them are dying because there are no leaves to support their growth. This plant does not have time to recover, and it will only produce a fraction of the yield that it could have achieved without deer damage. Stripping of mature pods at harvest time can also seriously reduce yield. Clipping Study to Simulate Browsing Damage In order to assess the potential of a soybean crop to recover from moderate to severe deer damage, a clipping study was conducted by Clemson University to simulate deer browsing. The study was conducted at the Simpson Experiment Station near Pendleton, SC, during 1993 and 1994. Hagood soybeans were planted in May of each year; fertilization followed soil test recommendations. Plots were four rows; each row was 38 inches wide and 30 feet long. Plots were irrigated three times in 1993. No irrigation was applied in 1994. Weeds were controlled with herbicides and handweeding. Clipping treatments to simulate deer damage consisted of removal of the upper one-quarter to one-third of each plant in a plot. Clipping was done at three vegetative growth stages (V4, V6, V10; see Table 1 for growth stage descriptions) and at the full-pod stage (R4; Fehr and Caviness, 1977). There were 16 clipping treatments which included all combinations of clipping/no clipping at each date. Table 1 gives 2-year average plot yields for the study. Yields ranged from over 41 to less than 17 bu/ac. Yields were severely reduced by clipping during reproductive growth (the R4 growth stage). The lowest yields were for treatments that were clipped several times during vegetative growth and also at the R4 stage. These plants were unable to recover from 5 Figure 6. Deer damage during reproductive growth removed the upper leaves and stems of this plant, thus removing the source of photosynthesis for growth of upper pods. Several of the pods that remain on the upper portion of this plant are shriveled and will not produce seeds.
Table 1. Influence of clipping at various growth stages on yield and height of Hagood soybeans, Pendleton, SC. Values are 2-year averages (1993 & 1994). Clipped (+) or Not Clipped (-) Yield Height V4* V6 V10 R4 (bu/ac) (in) - - - - 40.2 a 37.0 a + - - - 40.2 a 33.1 b - + - - 39.7 a 29.0 c - - + - 40.9 a 27.2 cd + + - - 41.8 a 26.5 cd + - + - 40.8 a 22.4 ef - + + - 36.0 a 20.7 fg + + + - 39.7 a 20.9 fg + - - + 26.7 b 24.4 de - - - + 24.0 bc 29.2 c - + - + 21.2 bc 22.5 ef - - + + 20.8 bc 22.1 ef + + - + 18.5 bc 17.9 gh + - + + 16.3 c 16.8 hi - + + + 16.5 c 15.5 hi + + + + 16.4 c 14.4 i * V4, V6, and V10 are vegetative growth stages with 4, 6, and 10 fully developed leaves above the cotyledons. R4 is the full pod stage (plant has a pod at least 3 /4 in. long at an upper node). Within a column, values followed by the same letter are not significantly different (P = 0.05; Tukey s mean separation). the repeated loss of vegetation and the loss of pods from the upper part of the plant canopy. Plants in treatments that were clipped only in early vegetative growth were able to recover, and their yields were similar to the unclipped control (Table 1). However, it should be noted that this study was conducted under very good crop growth conditions, including excellent weed control and supplemental irrigation. The final plant height data for this study (Table 1) show that heights were reduced by most of the clipping treatments, including those at early vegetative growth stages. Canopy closure of clipped plots also lagged behind canopy closure in the unclipped control treatment (Francoeur, 1995). These results suggest that under less-than-ideal conditions, a soybean field that was browsed by deer only during early vegetative growth could be expected to be less competitive with weeds and therefore might not recover its yield potential as well as the plots in this study. 6
Fencing, Repellents, and Scare Devices A number of methods to control deer damage in crops have been suggested. There are several designs of fencing that can keep deer out of an area, but effective fences are expensive to install and maintain and are generally not cost-effective for soybeans. Numerous repellents, including commercial products and home remedies, have been suggested. These may have some temporary effect in some situations, but generally the effectiveness of repellents and scare devices diminishes over time. Information about fencing designs, repellents, and scare devices is available in Clemson Extension brochure AWF 6, Reducing Deer Damage at Home and on the Farm (Cummings and Yarrow, 1996). Insect-Resistant Varieties and Drilling Other potential ways to reduce deer damage to soybeans include use of certain insect-resistant varieties and drilling, which may be beneficial in some situations. The results in Table 2 are from a study conducted in Colleton County, SC, in a field with a history of severe deer damage to crops. Two varieties, the insect-resistant Crockett and the insect-susceptible Perrin, were planted with a drill (7.5 inch rows) as well as in wide (36 inch) rows. Yields were low because of late planting (July) and drought and heat stress. However, yield determinations from an area of the field with heavy deer damage showed a definite advantage of Crockett over Perrin, whose yield was less than 4 bu/ac (Table 2). (Figure 7 shows a side-by-side view of the two varieties in mid-season.) In addition to the difference between varieties, yields were higher for drilled Crockett as compared with Crockett in wide rows. It is believed that Crockett and some other insect-resistant varieties are less palatable to deer. As for the possible reasons for the advantage of drilling over wide rows, it may be that deer prefer the open environment of the wide row planting. In drilled plantings with close rows, it is also probably easier for the crop to compensate for deer damage; lessdamaged plants can fill in for their damaged neighbors. Table 2. Influence of variety, row spacing, and deer pressure on soybean yield (bu/ac), Colleton Co., SC, 1993. Deer Crockett Perrin Pressure Drilled 36 rows Drilled 36 rows High 16.8 a 12.5 b 3.2 c 3.8 c Low 17.4 a 20.1 a 17.3 a 21.9 a Within a row, values followed by the same letter are not significantly different (P=0.05; protected LSD). 7
Figure 7. Soybean varieties Perrin (l) and Crockett (r) in a field in Colleton County, SC in 1993. Note the difference in deer browsing for these two varieties. This study was repeated in 1994 and 1995. In 1994, there was abundant rainfall which resulted in excellent crop growth, but there was negligible deer damage to the experimental field. In 1995, the study was planted in a small field with extremely high deer pressure, and deer damage started early and continued throughout the season. Figure 8 shows this field, with an exclosure used to protect a part of a plot from deer damage. Deer dam- Figure 8. A heavily browsed field in Colleton County, SC in 1995. The cage is an exclosure to allow observation of soybean growth without deer damage. Soybeans outside the exclosures were repeatedly browsed, and the yield potential of plants outside the exclosures was destroyed. There were no differences among treatments (varieties and row spacings) at this location. 8
age in this field was so heavy that, except for the exclosures, all the soybean plants were destroyed, regardless of variety or row spacing. Although the 1993 results showed that use of varieties like Crockett and drilled plantings may provide some reduction in deer damage with light-tomoderate deer pressure, the 1995 results indicated that they are not effective solutions if deer populations are extremely high. In addition, the choice of a variety for a particular situation should take into account other stresses like nematodes; Crockett has no nematode resistance, and therefore is a poor choice for many South Carolina fields, especially those infested with rootknot nematode. Previous work has also shown that some other insectresistant soybean varieties are more likely to be damaged by deer than is Crockett (Wallace et al.,1993, and unpublished data). Herd Management Shoot-to-kill or depredation permits are available to producers in some areas with severe crop damage. However, in the statewide survey of deer damage in 1991 (Smathers et al., 1994), only about 55% of South Carolina producers who had used depredation permits said they were effective. This may be due to the difficulty of adequately protecting a crop throughout the entire growing season. Deer hunting leases as well as crops provide income to many agricultural producers. A reduction in the deer population in an area can provide relief from crop damage, and it also may, over time, improve deer herd condition and increase the size of older trophy bucks. Crop producers who are experiencing deer damage and who also lease land to hunt clubs should insist that the hunters meet their antlerless deer (doe) quotas recommended by wildlife biologists. Because does can give birth to twins and triplets if food is plentiful, a sustained effort to reduce the number of antlerless deer over several years may be necessary in order to see an overall reduction in the deer population. Additionally, because the range of a deer population causing crop damage may be larger than a single producer s property, it would be desirable to involve neighboring landowners in the populationreduction effort if at all possible. Additional information about deer herd management in South Carolina can be found in the brochure Reducing Deer Damage at Home and on the Farm (Cummings and Yarrow, 1996). 9
References Cummings, C., and G.K. Yarrow. 1996. Reducing deer damage at home and on the farm. Brochure AFW 6. Cooperative Extension Service, Clemson University, Clemson, SC. DeCalesta, D.S., and D.B. Schwendeman. 1978. Characterization of deer damage to soybean plants. Wildlife. Society. Bull. 19: 46-52. Fehr, W.R., and C.E. Caviness. 1977. Stages of soybean development. Special. Report 80, Cooperative Extension Service, Iowa State University, Ames. Francoeur, L.C., 1995. Evaluating the effects of simulated deer damage on soybean growth and yield. M.S. Thesis, Clemson University, Clemson, SC. Garrison, R.L., and J.C. Lewis. 1987. Effects of browsing by white-tailed deer on yields of soybeans. Wildlife Society Bulletin 15:555-559. Smathers, W.M., Jr., G. R. Stratton, and D. Shipes. 1994. Crop damage associated with white-tailed deer in South Carolina. Report prepared for SC Wildlife and Marine Resources Department, available from Department of Agriculture and Applied Economics, Clemson University, Clemson, SC. Wallace, S.U. 1995. Managing difficult pests: Deer. pp. 37-41. In Proceedings of the 1995 Southern Soybean Conference, Memphis, TN, available from United Soybean Board through Trent-Jones, Inc., Princeton, NJ. Wallace, S.U., G.K. Yarrow, D. Shipes, E.J. Dunphy, and P.F. Reese, Jr. 1993. Assessing and reducing soybean crop losses from deer: An interdisciplinary, multi-agency effort. In Proc. Sixth Eastern Wildlife Damage Management Conference, Asheville, NC. Acknowledgments This publication was printed, and work on this subject was supported, by producer checkoff funds through a grant from the United Soybean Board. The outstanding technical assistance of Shelby A. Hull is also appreciated. Cover photo by Eric Darracq The Clemson University Cooperative Extension Service offers its programs to people of all ages, regardless of race, color, sex, religion, national origin, or disability and is an equal opportunity employer. Clemson University Cooperating with U.S. Department of Agriculture, South Carolina Counties. Issued in Furtherance of Cooperative Extension Work in Agriculture and Home Economics, Acts of May 8 and June 30, 1914 10