New Forests (2006) 31:253–271 DOI 10.1007/s11056-005-6571-0
Ó Springer 2006
Integrated pest management practices in southern pine nurseries DAVID B. SOUTH* and SCOTT A. ENEBAK School of Forestry and Wildlife Sciences, Auburn University, AL 36949-5418, USA; *Author for correspondence (e-mail:
[email protected]) Received 16 April 2004; accepted in revised form 19 April 2005
Key words: Insects, Loblolly pine, Longleaf pine, Nematodes, Pathogens, Slash pine, Weed control Abstract. Integrated Pest Management is a system that combines cultural, biological and chemical technologies to reduce insect, fungal and weed populations to levels below those that result in economic damage. Nursery managers in the southern United States currently use many practices to control pests of southern pine seedlings. Over the last three decades, improvements in chemical, cultural, and biological pest control practices have increased seed efficiency (defined as the number of plantable seedlings produced divided by the number of pure live seed sown) and reduced the percentage of production costs associated with pest control. As crop values increase, the economic thresholds for applying control measures decrease. However, since the statistical power of most trials in bareroot nurseries is low, the likelihood of experiments that detect ‘‘real’’ treatment difference (e.g. those that consistently increase seed efficiency to the point where economic returns are affected) will be low. This paper describes some current practices in southern pine nurseries and provides some economic injury levels for various pest control treatments.
Introduction In 2002, nurseries in the southern United States produced over 1.2 billion southern pine seedlings (McNabb and VanderSchaaf 2003). This total included over 955 million loblolly pine (Pinus taeda L.), 167 million slash pine (Pinus elliottii Englem. var. elliottii) and 67 million longleaf pine (Pinus palustris Mill.) seedlings. Most of the loblolly pine and slash pine were produced in bareroot nurseries while 48 million longleaf pine were produced in container nurseries. Although integrated pest management (IPM) is used in both container and bareroot nurseries, we focus our discussion on the production of bareroot seedlings. Managers use efficient management practices to keep production costs low. Retail prices range from less than 4 cents per seedling for bareroot loblolly pine and slash pine to 16 cents for container-grown longleaf pine to 38 cents for stock produced using somatic embryogenesis. One reason production costs for bareroot stock are low is because pest-related losses are kept to a minimum. Effective pest control practices not only increase seed efficiency (South 1987b), but they also help maintain a nursery’s reputation for producing pest free seedlings. This paper describes current pest management practices in southern pine nurseries. Documenting these practices will provide a baseline for comparison with future improvements in nursery management practices.
254 Historical damage from nursery pests In the first half of the 20th century options for pest management were limited and many seedlings died due to pest injury. For example, 25–40% of the seedlings were killed by white grubs (Phyllophaga spp.) at nurseries in Florida and the Carolinas (Wakeley 1954). Many seedlings died due to damping-off and many seeds were eaten by birds. Without the use of herbicides, seedbeds have required up to 10,000 h of handweeding per hectare (Cossitt et al. 1949) with many seedlings destroyed during the weeding process. In Alabama and Mississippi, 15–30% of slash pine seedlings in some nurseries were infected with fusiform rust (Cronartium quercuum f. sp. fusiforme) (Lamb and Sleeth 1940). In one case, nursery production ceased due to injuries from nematodes and fungi (Maki and Henry 1951). Today, we have many IPM options and the decision to apply a treatment is often based on economics.
Economic injury level and economic threshold The economic injury level for an IPM treatment is equivalent to the ‘‘breakeven point’’ at which the treatment cost equals the reduction in crop value due to pest injury. When the cost of an IPM treatment is known, the economic injury level can be easily expressed in terms of numbers of seedlings lost per ha. Examples of economic injury levels are presented in Table 1. Table 1. Economic injury level and economic threshold level for various IPM treatments in southern pine nurseries (assuming a value of 5 cents per seedling). Treatment
Prophylactic Methyl bromide/ chloropicrin Triadimefon Thiram Oxyfluorfen Triadimefon Oxyfluorfen Reactive Handweeding sethoxydim glyphosate
Application
Cost per ha Economic injury Economic level # seedlings threshold level (% crop loss)
Soil fumigation
$3700
74,000 (5.5)
Zero
Seed treatment Seed treatment Preemergence Foliar spray After crop emergence
$5 $10 $90 $55 $27
100 (0.0075) 200 (0.015) 1800 (0.135) 1100 (0.0825) 540 (0.0405)
Zero Zero Zero Zero Zero
2000 (0.15) 540 (0.0405) 800 (0.03)
After weed emergence $100 After grass emergence $27 After nutsedge emergence $40
Bacillus thuringiensi After emergence of sawflies fenoxycarb After emergence of mounds esfenvalerate After Lygus emergence
$40
800 (0.03)
$40
800 (0.03)
3 h of weeds/ha 1 h of weeds/ha 20 nutsedge plants per ha 600 defoliated seedlings per ha 1 mound
$22
440 (0.033)
1 insect
255 The ‘‘economic threshold’’ level is the point where the IPM treatment is applied before the economic injury level is reached (Tainter and Baker 1996). This is sometimes referred to as the ‘‘action threshold’’ and can be expressed either in terms of the pest population level or as a percentage of the crop value. Although the economic injury level (for a treatment that costs $100/ha) is a relatively precise value (in terms of crop loss), the economic threshold value is a subjective value that depends upon the viewpoint of the individual. For example, if we asked 10 experts for the economic threshold level for tarnished plant bugs [Lygus lineolaris (Palisot de Beauvois)] in loblolly pine nurseries, we might expect 10 different answers (most would be below the economic injury level). Therefore, the economic thresholds listed in Table 1 were derived with the experience of the authors and would vary from others who might have different views on the economics of pest management. In reality, economic threshold levels in southern pine nurseries are low because the economic injury level is low for many treatments (Table 1). This makes the determination of a precise action level more of an academic exercise than a practical one (Stejskal 2003). In addition, nursery researchers usually do not know how to accurately predict the population level of a pest 1 or 2 days into the future. In southern pine nurseries, some economic threshold levels are set at zero; that is before any crop injury is observed (Figure 1). IPM treatments with a zero threshold level are termed ‘‘prophylactic’’ treatments which may include oxyfluorfen (applied at time of sowing), thiram seed treatment, and triadimefon (applied before and after crop emergence). Treatments with economic
Seedling loss (%) 30 10 3 1 0.3 0.1
Economic injury level Action threshold
1981 1983 1985 1987 1990 1982 1984 1986 1988 1991 Figure 1. Seedling loss in control plots due to infection from fusiform rust (adapted from Carey and Kelley 1993). The economic injury level is 0.08% for a foliar application of triadimefon and the associated action threshold is 0% seedling loss.
256 thresholds greater than zero include pydrin (applied after observing tarnished plant bugs), sethoxydim (applied after observing emerged grasses) and handweeding after emergence of herbicide resistant weeds. A list of prophylactic and reactive treatments is presented in Table 1.
Economics vs. statistics There are hundreds of chemical and biological products in the marketplace. Deciding which ones to use in an IPM program is difficult since most advertisements claim the product will effectively reduce pest injury. If an advertised treatment costs $1000/ha, then increasing the production of loblolly pine seedlings by 1.5% might pay for the investment (assuming seedlings sell for 5 cents each). This economic injury level is so low that most research trials will not detect this level of seedling increase as statistically significant. Many research trials in bareroot loblolly pine nurseries have low statistical power (VanderSchaaf et al. 2003) and therefore some are unable to declare a 9% increase in stand value as statistically significant (Barnard et al. 1997; Carey 2000). Interpreting the results from such trials might result in an incorrect conclusion that an effective treatment had no ‘‘real’’ effect on seedling production (Steel and Torrie 1980; Murphy and Myers 2004). This mistake would be very important for a nursery that produces 30 million seedlings a year. For example, assume that five researchers each conduct separate trials at different nurseries to determine if a treatment increases seedling production. After analyzing their data, none of the researchers reported a significant treatment effect (Table 2). In fact, the probability of a greater F-value was not less than 0.25 in any study. Since a numerical increase in crop value occurred in each trial, should the nursery manager apply the treatment? Some might advise against using the treatment since all five research papers indicate there was no significant treatment effect. Although few managers would use an IPM treatment with benefit/cost ratios ranging from 10 to +1.2, most would likely use a treatment with ratios ranging from 14 to 68, even if the power of the statistical design was so low that significant F-values were not detected (a belief held by 18 out of 18 nursery managers surveyed in 2004). For most nursery managers, economic significance is more influential than statistical non-significance.
Economic profits While some nursery managers base pest management decisions on securing economic profits and on maintaining good reputations, others are told by their supervisors to reduce pest control costs. For example, to comply with the Forest Stewardship Council criteria number 10.7, a supervisor might reduce the nursery’s pesticide budget (Forest Stewardship Council 2002). As a result,
Number of plantable seedlings/m2 without treatment
212 232 192 199 307
Study
1 2 3 4 5
8.6 4.3 20.5 12.9 10.8
(4.0%) (1.8%) (10.6%) (6.5%) (3.5%)
Observed increase in plantable seedlings/m2 due to IPM treatment 30.1 23.7 38.7 26.9 22.6
Least Significant Difference (a = 0.05)
14.2% 10.2% 20.1% 13.5% 7.4%
Percentage increase required to be statistically significant 0.3042 0.3788 0.6512 0.2550 0.4332
Treatment p-value
0.000 0.132 0.000 0.227 0.102
Post priori power of test
$2870 $1435 $6817 $4305 $3588
Increase in crop value due to IPM treatment $/ha
Table 2. Results from 5 nursery studies where the IPM treatment did not result in a significant (a = 0.05) increase in the production of plantable loblolly pine seedlings. The cost of the IPM treatment was $100/ha and the benefit/cost ratio of the treatment ranged from 14 to 68.
257
258 the economic profits from a nursery can vary depending upon the objectives of management. Differences in management philosophy are illustrated by five hypothetical nurseries in Table 3. At Nursery A, reputation and profits are not a concern of the nursery supervisor. As a result, the supervisor tells the nursery manager to not spend $100/ha on an IPM treatment. At this nursery all seedlings are sold for 4 cents, regardless of seedling grade or presence of disease. On paper, an increase in diseased seedlings does not affect crop value (i.e. there is no culling of diseased seedlings or small, Grade 3 seedlings). However, the reputation of the nursery is affected since some customers will decide to buy seedlings from other nurseries (e.g. Nurseries B and C). The supervisor of Nursery A is rewarded for reducing production costs but the demand for Nursery A seedlings declines over time. Eventually, the nursery closes due to loss of market share to Nurseries B and C. The manager at Nursery B spends $100/ha on the IPM treatment and this eliminates diseased seedlings. At this nursery, diseased seedlings are culled prior to packing, but small, Grade 3 seedlings [Root Collar Diameter (RCD) 4.7 mm). A bag containing 1,000 seedlings sells for $40 and the benefit cost ratio for the IPM treatment is about 25. The management plan of Nursery C is to attract customers away from both Nursery A and Nursery B. Therefore, the policy at this nursery is to not charge customers for the small, Grade 3 seedlings. Based on sampling data, the nursery includes an extra 53 seedlings in each bag. Under this pricing system, the benefit/cost ratio of the IPM treatment increases to 80. Even though the economic injury level is the same at both nurseries, the economic Table 3. The effect of crop value and an IPM treatment on the profit and economic injury level at five hypothetical loblolly pine nurseries. The treatment costs $100/ha and reduces the amount of diseased and cull (i.e. Grade 3) stock but has no effect on total production (each nursery produces 200 plants/m2). Seedling classification
Cull-diseased Cull-grade 3 Grade 2 Grade 1
Production without treatment
Production with treatment
Nursery A
No./m2
No./m2
Value per plant ($)
10 30 100 60
0 10 120 70
0.04 0.04 0.04 0.04 low N/A
Incentive to reduce losses due to disease Economic injury level (# plants/ha) Profit due to treatment ($/ha)
$100
Nursery B
Nursery C
Nursery D
Nursery E
0 0.04 0.04 0.04
0 0 0.04 0.04
0 0 0.04 0.05
0 0 0.38 0.38
moderate 2500
high 2500
high 2244
very high 263
$2566
$8000
$8666
$75,900
259 incentive to use the IPM treatment is three times higher at Nursery C than at Nursery B. Some nurseries grade hardwood seedlings and sell the larger seedlings at a higher price than the small seedlings. At Nursery D, seedling price is a function of seedling grade and Grade 1 seedlings are sold for 1 cent more than Grade 2 seedlings. Therefore, a bag of 1000 Grade 1 seedlings at this hypothetical nursery is $50. Since the seedlings have a higher value, the economic injury level for the IPM treatment is lower than at Nursery C. Nursery E is operated by a forest industry nursery that does not sell seedlings on the open market. This company invests in a tree improvement program and produces clonal stock using somatic embryogenesis that cost 38 cents each. Since the crop value is highest at this nursery, the economic injury level is the lowest of any of the hypothetical nurseries. The economic incentive to use the IPM treatment is greatest at Nursery E since the benefit cost ratio is approximately 759. In the past when fumigation and pesticides were not available, pest control costs often exceeded 25% of all production costs. With the use of effective IPM treatments, less than 7% of today’s production costs are due to pest control. Currently, fumigation with methyl bromide/chloropicrin mixtures accounts for a large portion of these costs (Table 4). Although these fumigants are effective against nematodes, fungi, nutsedge and soil borne insects, for simplicity, we allocate the cost to the control of nematodes (Table 4). In other cases, the cost of fumigation could be distributed over two or more pest groups.
Cultural IPM practices Several cultural practices affect seedling development, production and health. These factors include sandy soils, good seed, adequate fertilization, growing seedlings at low seedbed densities and sanitation.
Table 4. Some approximate costs of pest management in loblolly pine and slash pine nurseries. Pest group
$ Per thousand seedlings
$ Per ha
Percentage of total production costs
Abiotic Fungi Birds and mice Annual weeds Insects Nematodes Total
0.38 0.13 0.15 0.14 0.19 1.39* 2.38
500 175 200 190 250 3700 5015
1.0% 0.4% 0.4% 0.4% 0.5% 4.0% 6.7%
*Assumes two seedling crops per fumigation with methyl bromide/chloropicrin.
260 Soil texture Root decay fungi can proliferate when soils remain anaerobic due to low soil water infiltration rates and excessive soil moisture (e.g. above field capacity) plays an important role in several disease cycles. Therefore it is important to avoid soils that have low infiltration rates. Even on sandy soils, subsoil conditions can reduce infiltration rates. Seedlings grown in wet areas are often smaller than seedlings in adjacent, dryer soil (Retzlaff and South 1985). For this reason, nursery managers prefer to manage sandy soils (>75% sand) and when infiltration rates are low, they apply IPM strategies to improve infiltration rates. For example, some managers install tile drainage to remove excess moisture and they subsoil the ground between crops to break-up plowpans. Managers often avoid sowing fields that have low infiltration rates or high clay content. The importance of soil texture is reflected by the fact that over the past two decades several nurseries located on soils with less than 75% sand have closed.
Good seed Using seed with a high germination percentage is a key factor in a successful IPM program. Time and money invested in soil preparation are wasted if the seed does not germinate or dies after germination. In some cases, seedling production can be doubled when good seedlots are used. Seedlots contaminated with the pitch canker fungus (Fusarium circinatum) are likely to increase both damping off (Dwinell and Fraedrich 1999) and late season mortality (Carey and Kelley 1994). In addition, seed with a high germination potential is important when sowing with vacuum sowers (either in container nurseries or bareroot nurseries). When sowing cover-crops, certified seed is less likely to be a source of noxious weeds than non-certified seed (South 1984).
Rapid emergence of seed Nursery managers routinely stratify pine seed to promote rapid germination after sowing. Reducing the time between germination and the formation of cuticles on needles reduces the susceptibility to preemergence and postemergence damping-off. Seedlings that do not emerge for 4 weeks after sowing are more likely to die than seedlings that emerge 2 weeks after sowing (Boyer et al. 1987). In addition, germinants that emerge quickly are more likely to develop into large seedlings (Boyer et al. 1985; Mexal and Fisher 1987). Although there are exceptions, larger seedlings are more resistant to infection by fungi than younger seedlings (Tesche 1969; Bergdahl and French 1976; Rowan 1978).
261 Low seedbed density Seedlings grown at high seedbed densities are more susceptible to disease than seedlings grown at low seedbed densities (Gibson 1956). Since 1930, nursery managers have gradually lowered their target seedbed density. Wakeley (1935) recommended loblolly pine be grown at seedbed densities of 430–540 per square meter. However, these densities produced small seedlings, many with primary needles and non-lignified stems. By 1980, the target sowing density ranged from 260 to 320 per square meter (Boyer and South 1984) and a decade later the average density was 260 per square meter (South and Zwolinski 1996). Today, several nursery managers grow morphologically improved slash pine and loblolly pine at densities less than 215 per square meter (South 2000) and longleaf pine is grown at densities of 50–90 per square meter (South 1993).
Fertilization Improper fertilization can affect seedling physiology and the susceptibility of seedlings to damping-off fungi. As a result, most IPM programs avoid applying large amounts of nitrogen fertilizers prior to sowing. Once seedlings have emerged and cotyledons have developed some epicuticular wax, then nitrogen is applied around the first or second week of June. Although fertilization with nitrogen may increase the susceptibility of seedling to fusiform rust (Rowan 1978), the use of triadimefon reduces this concern. When certain fungi are not controlled by fumigation, nitrogen fertilization can increase the incidence of black-root rot (Rowan 1971). However, when nematodes are not abundant, fertilization with more than 150 kg/h of nitrogen increased the number of short-roots and the number of mycorrhizal roots (Marx 1990). Due to promising results from fall fertilization trials (Irwin et al. 1998; South and Donald 2002) some nursery managers fertilize so at the time of lifting, loblolly pine seedlings will have 2% nitrogen in the needles. These ‘‘nutrient loaded’’ seedlings are able to use internal sources of nitrogen for photosynthesis as opposed to relying on soil uptake to restore foliar nitrogen to normal levels.
Sanitation Sanitation is a key factor in reducing weed and disease problems in IPM programs (Hansen et al. 1979; Wichman 1982; South 1984; Dumroese et al. 1990). Sanitation practices include using pest-free mulches, using weed-free seed, filtering irrigation water, use of well-water instead of pondwater (Shokes and McCarter 1979), use of windbreaks, cleaning borrowed machinery, controlling weeds in non-cropland and minimizing the movement of diseased transplant stock. Culled seedlings with root disease are not recycled as organic amendments and ‘‘strip’’ fumigation is no longer used since fumigated strips
262 can be contaminated with soil from non-fumigated strips. However, fences to keep deer and other animals out of seedbed are not used.
Biologicals There are a number of biological products on the market and several have been tested in southern pine nurseries (Vonderwell and Enebak 2000) but only a few have been used operationally. Mycorrhizal spores have been added to container media (Marx et al. 1989) and to a few bareroot seedbeds (Marx et al. 1979). While Bacillus thuringiensis has been used to protect seedlings from certain insects, the use of biologicals have not caught on yet in nurseries because many of the agents have a short shelf-life, have a short field persistence and have a narrow spectrum of activity (U.S. Congress 1995). In addition, some strains may work well in one nursery in one year but not in another year or nursery.
Current practices for controlling fungi Fungicides In the past, it was recommended that oaks surrounding the nursery be removed to reduce the incidence of fusiform rust (Lamb and Sleeth 1940; Sleeth 1943). Today, instead of clearcutting surrounding hardwood stands, seed and seedlings of loblolly pine and slash pine are treated with triadimefon (Carey and Kelley 1993). Seed treatment with this fungicide costs about $0.004 per thousand seedlings and foliar sprays cost about $0.04 per thousand seedlings (South 1994). Without treating seedlings with effective fungicides, a nursery might lose 1–30% of the crop due to infection from fusiform rust (Figure 1). Typically, this fungicide is not used on species like longleaf pine that have resistance to fusiform rust. Other fungicides commonly used in nurseries include captan, chlorothalonil, metalaxyl, and thiram (South and Zwolinski 1996).
Fumigation The soil at most pine nurseries is fumigated once every 4 years (two crops of pines followed by two cover-crops) but hardwood seedbeds are more likely to be fumigated prior to each seedling crop. The increase in seedling production associated with fumigation varies with nursery but at some nurseries, crop value increases by 6–40% (Carey 2000). Many nursery managers believe that soil fumigation with methyl bromide is more effective in reducing damping-off than applying fungicides after sowing (Smith and Bega 1966). When nurseries do not have a history of
263 disease problems, nursery managers typically use methyl bromide with 2% chloropicrin. For example, in 1978, 10 out of 11 nurseries that used methyl bromide used a formulation that contained 1.6–2% chloropicrin (Marx et al. 1984). At these 10 nurseries, spring fumigation reduced pythiaceous fungi from 1000 to 45,000 propagules per liter of soil to between zero and 6000 propagules per liter of soil. Chloropicrin is a more effective fungicide than methyl bromide and should be favored where fungal diseases have been damaging (Enebak et al. 1989; South et al. 1997). For example, a mixture containing 33% chloropicrin was recommended at a nursery with a history of disease associated with Macrophomina phaseolina (Seymour and Cordell 1979). Fumigation with methyl bromide and chloropicrin often results in an increase in beneficial species such as Trichoderma (South et al. 1997). The increase in Trichoderma combined with a reduction in Pythium propagules might result in an increase in seed efficiency due, in part, to more rapid emergence (Huang and Kuhlman 1991).
Sowing date Sowing date affects damping-off, seedling development (Huberman 1940; Boyer and South 1988) and mycorrhizal development (Rowan and Marx 1976). For these reasons, most managers sow loblolly pine and slash pine seed in April and avoid sowing in May or June (when damping-off rates increase). Early sowing produces larger seedlings that can tolerate weeds, fungi and insects better than small seedlings. In general, longleaf pine is more sensitive to late sowing than slash pine (Huberman 1940) and at one nursery, fall sowing of longleaf pine reduced the incidence of root rot when compared with spring sowing. For this reason, some say ‘‘Where longleaf is fall-sown, no further precaution against root rot is deemed necessary’’ (Maki and Henry 1951).
Soil acidity The level of soil acidity can affect disease incidence in seedbeds. At one nursery, liming soil before sowing reduced crop value of longleaf pine seedlings by 37% (Maki and Henry 1951). In general, loblolly pine grows better in acid soils than in neutral soils. One study found the dry weight of loblolly pine seedlings was reduced by 24% if soil acidity was maintained at pH 6.8 instead of pH 4.8 (Marx 1990). Today, many managers attempt to keep acidity below pH 5.8 to reduce the probability of chlorosis and disease (Roth and Riker 1943; Pawuk 1981). Applying sulfur to increase soil acidity is a routine IPM practice.
264 Current practices for controlling insects For most insects, nursery managers do not apply insecticides until an infestation has been observed. For example, baits for mole crickets (Scapteriscus spp.) are not applied until tunnels have been detected in seedbeds. Exceptions to this approach include the tarnished plant bug and Tayloirlygus palidulus (Blanchard). For these plant bugs, insecticide applications begin as soon as the adults have been detected on weeds (Bryan 1989; South 1991; South et al. 1993). Nantucket pine tip moths (Rhyacionia frustrana [Comstock]) can occasionally be found in nurseries in mid-summer to early fall (Mortimer 1941). If seedlings are tall enough, top-clipping the terminal reduces the presence of dead tissue and improves the appearance of the seedlings (Bacon and South 1989). However, insecticides for tip-moth may need to be applied for species like longleaf pine (Doggett et al. 1994). Damage by other insects also occurs on an infrequent basis (Dixon et al. 1991). For example, at one nursery over a million pine seedlings were destroyed by cutworms (Family Noctuidae) in 2003 (USDA Forest Service 2004). White grubs have caused some nurseries to be abandoned (St. George 1935). However, routine fumigation has helped keep grub populations low and outbreaks can now be treated with spot applications of insecticides (Bacon and South 1989).
Current practices for controlling nematodes Soil fumigation is an integral part of a nematode control program at almost all bareroot nurseries in the South. Prior to the use of methyl bromide and chloropicrin, nematodes were common in southern pine nurseries (Hansbrough and Hollis 1957; South et al. 1997). For example, during the 1950s black rootrot (typically associated with nematodes) occurred in 30% of southern pine nurseries (Hodges 1962). Pre-fumigation levels of nematodes might range up to 1690 per liter of soil while effective fumigation can reduce the level to zero (Marx et al. 1984). Even with soil fumigation, some nematodes are difficult to eradicate (Fraedrich and Cram 2002; USDA Forest Service 2004). Many nursery managers do not use soybeans (Glycine max L.) as a cover-crop, in part because soybeans are a host for root-knot nematodes. Nematicides are typically not applied in pine nurseries after seedlings have emerged.
Current practices for controlling weeds Effective weed control is essential to successful nursery management. Prior to 1947, seedbeds were weeded almost entirely by hand or in combination with
265 mechanical cultivation. A hectare of seedbeds often required from 500 to 10,000 h of weeding (McKellar 1936; Umland 1946). Today, nursery managers rely on herbicides, fumigants, sanitation and cultural practices to keep handweeding times low, sometimes less than 25 h ha 1 (South 1995).
No weedy composts In the past, composts were used to increase soil fertility but they were a source of weed seed. Using leaves from lawns or municipal sludge can introduce weeds. Therefore, composts often increased weed control costs. For example, at one nursery the use of compost increased the amount of handweeding by 1588 h per ha (Muntz 1944). Although sawdust and pine bark are used as amendments, the presence of weed seed is one reason why weedy composts are not used in IPM programs in southern pine nurseries.
Weed free mulches Weed seed can also be found in mulches such as pinestraw, wheat straw and, in some situations, sawdust. During the 1950’s, pine straw was the favored mulch at many southern pine nurseries but it often introduced a significant amount of weed seed (South 1976). Purple nutsedge (Cyperus rotundus L.) and yellow nutsedge (Cyperus esculentus L.) tubers can be introduced in pinestraw mulch. Due to increasing costs for pinestraw and to reduce the introduction of weeds, only 28% of the southern pine nurseries were still using pinestraw in 1986 (Vanderveer 1986). Today, many managers do not use straw mulches but instead use weed-free polyethylene soil stabilizers (Carlson et al. 1987).
Weed free cover-crop seed Several nursery managers use certified seed when growing cover-crops to reduce the introduction of noxious weeds. Regulations require certified seed to be free of primary noxious weed seed and only a small amount of common weed seed is allowed. Saving a few dollars by using less expensive, uncertified seed is false economy since the presence of herbicide resistant weeds can be greatly increased. For example, at one nursery, the use of uncertified seed increased the weed population (South 1984).
Dense cover-crops Several managers use herbicides to suppress weeds in cover-crops. In addition, some sow crops at densities to keep soil shaded to suppress weed growth. In
266 particular, nutsedge does not compete well when shaded by certain covercrops.
Screened irrigation water Irrigation water can be a major source of weed seeds, especially when pumping from a lake, pond, or river (Wilson 1980). For this reason, several nurseries use in-line screens to filter weed seed. Some of the newer filter systems are selfcleaning.
Cleaned equipment Weed seed, rhizomes, and tubers are easily introduced to a nursery when farm equipment is either rented or borrowed from adjacent landowners. For this reason, some managers thoroughly clean rented combines before harvesting cover-crops. Some managers avoid this potential weed source by not harvesting corn (Zea maize L.) crops. One tuber of purple nutsedge can produce 1300 tubers after only 20 weeks (Hauser 1962). For this reason, special efforts are made to avoid spreading tubers to nutsedge-free fields. Infested areas can be mapped during the summer to help identify the sequence of cultivation during the winter. Nutsedge-free areas are cultivated first to avoid the spread of tubers on cultivators and equipment is cleaned prior to use in another area of the nursery.
No mechanical cultivation Prior to 1954, millions of southern pine seedlings were mechanically cultivated with more or less satisfactory results (South 1987a). At one nursery, mechanical cultivation reduced handweeding requirements from 4120 to 2448 h per million seedlings (Umland 1946). However, because of narrow drill spacing, seedlings can be destroyed by cultivation and incidence of injury and disease is increased (South 1988). Therefore, as part of an effective IPM program, mechanical cultivation is no longer practiced in southern pine seedbeds.
Herbicides The most extensively used herbicides in southern pine seedbeds include oxyfluorfen, lactofen, sethoxydim and fomesafen (South and Zwolinski 1996). Typically, oxyfluorfen is applied just after sowing. As part of an IPM program, postemergence applications of oxyfluorfen are made at low rates (e.g. 1/4th the labeled rate) at more frequent intervals (Blake and South 1987). This approach
267 provides more efficient use of the herbicide since 3-day-old weeds are easier to kill than 3-week-old weeds. Many nursery managers now apply a tank-mix of fertilizer and herbicides which reduces both labor and wear on tractors. Spot applications of glyphosate are made in seedbeds to suppress the development of nutsedge tubers. Broadcast applications of glyphosate are used on fallow fields to reduce nutsedge populations.
Handweeding Even with herbicides, handweeding is used to keep herbicide resistant weeds from producing seed. Weeding frequency is important since handweeding once every 6- to 8-weeks can increase total workload by 30–100% or more because it takes less time to weed small weeds on a 3- to 6-week interval (Aldhous 1972). It is also important to remove resistant weeds before they can produce seed. For this reason, the practice of allowing weeds to develop in seedbeds before herbicide treatment (Meyer et al. 1993) has not been adopted in southern forest nurseries.
Current practices for controlling birds and rodents Bird predation of seed was a problem in the first half of the 20th century. Southern meadowlarks (Sturnella magna argutula Bans), mourning doves (Zenaidura macroura carolinensis L.), bobwhite quails (Colinus virginianus L.), cowbirds (Molothrus ater Boddaert), red-winged blackbirds (Agelaius phoeniceus L.) and other blackbirds (Euphagus spp.) have a preference for longleaf pine seed (Burleigh 1938). As a result, several nurseries employed ‘‘bird patrols’’ that warned off birds with shotguns and firecrackers. In one year, 395 mourning doves were shot at one nursery in Louisiana (Kingsley 1958). At a Mississippi nursery, the cost for bird patrols (adjusted to 2004 dollars) was approximately $0.70 per thousand seedlings (King 1958). Seed predation decreased by treating seed with thiram (1 kg a.i./100 kg seed). This treatment costs approximately $0.15 per thousand loblolly pine seedlings and both eliminates the cost of bird patrols and reduces unnecessary killing of birds. Thiram also has some properties that repel mice (Nolte and Barnett 2000). Populations of rodents can be reduced with habitat management. Weeds provide cover from raptors in outplanting sites and mice can consume seed in relative safety (Stephenson et al. 1963; Boyer 1964). However, protective cover is rare in the nursery since managers keep riserlines and fencerows relatively free of weeds.
Conclusions Managers currently use a number of techniques for controlling pests in southern pine seedbeds. To some extent, the amount of money allocated to
268 IPM treatments will vary depending on the value of the crop. As the value of seedling crops increases, the economic threshold decreases. If the value of planting stock increases in the future, we predict an increase in investments in IPM treatments. No doubt, IPM treatment will evolve over time but investments in pest control will continue to keep seed efficiency high and production costs low. A problem that will continue to plague both managers and researchers is how to identify IPM treatments that increase crop value by 5% or less.
Acknowledgements The authors wish to acknowledge the many nursery managers who have shared their management practices with the authors. We also wish to thank Dr. William Carey for comments made on an earlier draft.
References Aldhous J.R. 1972. Nursery Practice. Her Majesty’s Stationary Office. Forestry Commission Bulletin 43, London, pp. 184 Bacon C.G. and South D.B. 1989. Chemicals for control of common insect and mite pests in southern pine nurseries. South. J. Appl. For. 13: 112–116. Barnard E.L., Kannwischer-Mitchell M.E., Mitchell D.J. and Fraedrich S.W. 1997. Development and field performance of slash and loblolly pine seedlings produced in fumigated nursery seedbeds and seedbeds amended with organic residues. In: Landis T.D. and South D.B. (eds), (Tech. Coordinators) National Proceedings: Forest and Conservation Nursery Associations. USDA Forest Service Gen. Tech. Rep. PNW-GTR-389, pp. 32–37. Bergdahl D.R. and French D.W. 1976. Relative susceptibility of five Pine species, 2 to 36 months of age, to infection by Cronartium comandrae. Can. J. For. Res. 6: 319–325. Blake J.I. and South D.B. 1987. Weekly herbicide applications prove beneficial in forest nurseries. Ala. Agr. Exp. Sta. Highlights of Agricultural Research 34(2): 12. Boyer W.D. 1964. Longleaf pine seed predators in southwest Alabama. J. Forestry 62: 481–484. Boyer J.N. and South D.B. 1984. Forest nursery practices in the South. South. J. Appl. For. 8: 67– 75. Boyer J.N., South D.B., Muller C., Vanderveer H., Chapman W. and Rayfield W. 1985. Speed of germination affects diameter at lifting of nursery-grown loblolly pine seedlings. South. J. Appl. For. 9: 243–247. Boyer J.N. and South D.B. 1988. Date of sowing and emergence timing affect growth and development of loblolly pine seedlings. New Forests 4: 231–246. Boyer J.N., Duba S.E. and South D.B. 1987. Emergence timing affects root-collar diameter and mortality in loblolly pine seedbeds. New Forests 1: 135–140. Bryan H. 1989. Control of the tarnished plant bug at the Carters Nursery. Tree Planters’ Notes 40(4): 30–33. Burleigh T.D. 1938. The relation of birds to the establishment of longleaf pine seedlings in southern Mississippi. USDA Forest Service. Occ. Pap. Sth. For. Exp. Sta. No. 75. pp. 5 Carey W.A. 2000. Fumigation with chloropicrin, metham sodium, and EPTC as replacements for methyl bromide in southern pine nurseries South. J. Appl. For. 24: 135–139. Carey W.A. and Kelley W.D. 1993. Seedling production trends and fusiform rust control practices at southern nurseries, 1981–1991. South. J. Appl. For. 17: 207–211.
269 Carey W.A. and Kelley W.D. 1994. First report of Fusarium subglutinans as a cause of late season mortality in longleaf pine nurseries. Plant Disease 78: 754. Carlson W.C. and Anthony J.G. and. Plyler R.P. 1987. Polymeric nursery bed stabilization to reduce seed losses in forest nurseries. South. J. Appl. For. 11: 116–119. Cossitt F.M., Rindt C.A. and Gunning H.A. 1949. Production of Planting Stock in Trees The Yearbook of Agriculture. USDA Government Printing Office, Washington, DC pp.160–169 Dixon W.N., Barnard E.L., Fatzinger C.W and Miller T. 1991. Insect and disease management. In: Duryea M.L. and Dougherty P.M (eds), Forest Regeneration Manual. Kluwer Academic Publishers, Dordrecht, The Netherlands, pp. 359–390. Doggett C., Langston F.W. and Worley W.L. 1994. Nantucket pine tip moths infests longleaf pine seedlings in a North Carolina Nursery. Tree Planters Notes 45: 86–87. Dumroese R.K., Wenny D.L. and Quick K.E. 1990. Reducing pesticide use without reducing yield. Tree Planters’ Notes 41: 28–32. Dwinell L.D. and Fraedrich S.W. 1999. Contamination of pine seeds by the pitch canker fungus. In: Landis T.D. and Barnett J.P. (eds), (Tech Coordinators) National Proceedings: Forest and Conservation Nursery Associations. USDA Forest Service Gen. Tech. Rep. SRS-25, pp. 41–42. Enebak S.A., Palmer M.A. and Blanchette R.A. 1989. Influence of disease management strategies on the production of white spruce in a forest tree nursery. For. Sci. 35: 1006–1013. Forest Stewardship Council. 2002. Forest Certification Standard for the Southeastern United States. The Forest Management Trust, Gainesville, FL.http://www.fscus.org/images/documents/ standards/SE_final_v8.7.pdf. Fraedrich S.W. and Cram M.M. 2002. The association of a Longidorus species with stunting and root damage of loblolly pine (Pinus taeda L.) seedlings. Plant Disease 86: 803–807. Gibson I.A.S. 1956. Sowing density and damping-off in pine seedlings. East Africa Agric. J. 21: 183–188. Hansen E.M., Hamm P.B., Julis A.J. and Roth L.F. 1979. Isolation, incidence and management of Phytophthora in forest tree nurseries in the Pacific Northwest. Plant Disease Rep. 63: 607–611. Hansbrough T. and Hollis J.P. 1957. The effect of soil fumigation for the control of parasitic nematodes on the growth and yield of Loblolly Pine seedlings. Plant Dis. Reptr. 41: 1021–1025. Hauser E.W. 1962. Development of purple nutsedge under field conditions. Weeds 10: 315–321. Hodges C.S. 1962. Black root rot of pine seedlings. Phytopathology 52: 210–219. Huang J.W. and Kuhlman E.G. 1991. Mechanisms inhibiting damping-off pathogens of slash pine [Pinus elliottii] seedlings with a formulated soil amendment. Phytopathology 81: 171–177. Huberman M.A. 1940. Studies in raising southern pine nursery seedlings. J. Forestry 38: 341–345. Irwin K.M., Duryea M.L. and Stone E.L. 1998. Fall-applied nitrogen improves performance of 1–0 slash pine nursery seedlings after outplanting. South. J. Appl. For. 22: 111–116. King J. 1958. Repellent treatment of pine seed for bird protection. Tree Planters’ Notes 32: 11–12. Kingsley C.E. 1958. Use of bird repellents for nursery sowing. Tree Planters’ Notes 32: 9–10. Lamb H. and Sleeth B. 1940. Distribution and suggested control measures for the Southern Pine fusiform rust. USDA Forest Service. Occ. Pap. Sth. For. Exp. Sta. No. 91, pp.5 Maki T.E. and Henry B.W. 1951. Root-rot control and soil improvement at the Ashe Forest Nursery. USDA Forest Service. Occ. Pap. South. For. Exp. No. 119, pp.17 Marx D.H. 1990. Soil pH and nitrogen influence Pisolithus ectomycorrhizal development and growth of loblolly pine seedlings. For. Sci. 36: 224–245. Marx D.H., Mexal J.G. and Morris W.G. 1979. Inoculation of nursery seedbeds with Pisolithus tinctorius spores mixed with hydromulch increases ectomycorrhizae and growth of loblolly pines. South. J. Appl. For. 3: 175–178. Marx D.H., Cordell C.E., Kenney D.S., Mexal J.G., Artman J.D., Riffle J.W. and Molinia R.J. 1984. Commercial vegetative inoculum of Pisolithus tinctorius and inoculation techniques for development of ectomycorrhizae on bare-root tree seedlings. For. Sci. Monogr.25: 101. Marx D.H., Cordell C.E., Maul S.B. and Ruehle J.L. 1989. Ectomycorrhizal development on pine by Pisolithus tinctorius in bare-root and container seedling nurseries. II. Efficacy of various vegetative and spore inocula. New Forests 3: 57–66.
270 McKellar A.D. 1936. The weed problem at the Stuart Forest Nursery. USDA Forest Service, South. For. Exp. Sta. Occasional Paper 55, Pollock, LA pp. 20 McNabb K. and VanderSchaaf C.L. 2003. A survey of forest tree seedling production in the South for the 2002–2003 planting season. Auburn University Southern Forest Nursery Management Cooperative. Tech. Note 3–02, pp. 6 Mexal J.G. and Fisher J.T. 1987. Size hierarchy in conifer seedbeds. I. time of emergence. New Forests 1: 187–196. Meyer T.R., Irvine M., Harvey E.M and McDonough T. 1993. Integrated pest management in Canadian forest nurseries – current perspectives and future opportunities. In: Landis T.D. (ed.), (Tech Coordinator) Proc. Northeastern and Intermountain Forest and Conservation Nursery Associations. USDA Gen. Tech. Rep. RM- 243, pp. 69–78. Mortimer M.F. 1941. The life history and control of the Pine tip moth, Rhyacionia frustrana (Comstock) (family Tortricidae) at Nashville, Tennessee. J. Tenn. Acad. Sci. 16: 189–206. Muntz H.H. 1944. Effects of compost and stand density upon longleaf and slash pine nursery stock. J. Forestry 42: 114–118. Murphy K.R. and Myors B. 2004. Statistical Power Analysis: A Simple and General Model for Traditional and Modern Hypothesis Tests. 2nd ed. Lawrence Erlbaum, Mahwah NJ pp. 160 Nolte D.L. and Barnett J.P. 2000. A repellent to reduce mouse damage to longleaf pine seed. Int. Biodeter. Biodegr. 45: 169–174. Pawuk W.H. 1981. Potting media affect growth and disease development of container-grown southern pines. USDA Forest Service. Research Note SO-268, pp. 4 Retzlaff W.A. and South D.B. 1985. Variation in seedbed moisture correlated with growth of Pinus taeda seedlings. S. Afr. Forest. J. 133: 2–5. Roth L.F. and Riker A.J. 1943. Influence of temperature, moisture, and soil reaction on the damping-off of red pine seedlings by Pythium and Rhizoctonia. J. Agr. Res. 67: 273–293. Rowan S.J. 1971. Soil fertilization, fumigation, and temperature affect severity of black root rot of slash pine. Phytopathology 61: 184–187. Rowan S.J. 1978. Susceptibility to fusiform rust in slash pine seedlings depends upon fertilization and cumulative inoculum density in multiple inoculations. USDA Forest Service Research Note, Southeastern Forest Experiment Station. No. SE-254, pp. 5 Rowan S.J. and Marx D.H. 1976. Ectomycorrhizae and planting date affect rust incidence in forest tree nurseries. In: Lantz C.W. (ed.), Proc. Southeastern Area Nurserymen’s Conferences. USDA Forest Service Southeaster Area State and Private Forestry, Atlanta, GA, pp. 107–109. Seymour C.P. and Cordell C.E. 1979. Control of charcoal root rot with methyl bromide in forest nurseries. South. J. Appl. For. 3: 104–108. Shokes F.M. and McCarter S.M. 1979. Occurrence, dissemination, and survival of plant pathogens in surface irrigation ponds in southern Georgia. Phytopathology 69: 510–516. Sleeth B. 1943. Fusiform rust control in forest-tree nurseries. Phytopathology 33: 33–44. Smith R.S.Jr. and Begs R.V. 1966. Root disease control by fumigation in forest nurseries. Plant Dis. Reptr. 50: 245–248. South D.B. 1976. Pine straw mulch increases weeds in forest tree nurseries. Ala. Agr. Exp. Sta. Highlights of Agricultural Research 23(4): 15. South D.B. 1984. Integrated pest management in nurseries – vegetation. In: Proc. Integrated Forest Pest Management Symposium. University of Georgia, Athens, Georgia pp.247–265. South D.B. 1987a. A look back at mechanical weed control. In: Schroeder R.A. (comp.) (ed.), Proc Southern Forest Nursery Association. Florida Division of Forestry, Tallahassee, FL, pp. 97–106. South D.B. 1987b. Economic aspects of nursery seed efficiency. South. J. Appl. For. 11: 106–109. South D.B. 1988. Mechanical weed control for the forest nursery. Georgia Forestry Comm. Res. Report No. 1, pp. 10 South D.B. 1991. Lygus bugs: a worldwide problem in conifer nurseries. In: Proc. First meeting of IUFRO Working Party S2.07–09 (Diseases and Insects in Forest Nurseries). Information Report BC-X-331, pp. 222.
271 South D.B. 1993. Rationale for growing southern pine seedlings at low seedbed densities. New Forests 7: 63–92. South D.B. 1994. Managing pesticides and nitrogen in southern pine nurseries and some ways to reduce the potential for groundwater contamination. Ala. Agr. Exp. Sta. Forestry School Series No. 14, pp. 18 South D.B. 1995. Contrasting weed management systems in bare-root conifer nurseries. Forestry Chronicle 71: 331–342. South D.B. 2000. Tolerance of southern pine seedlings to clopyralid. South. J. Appl. For. 20: 51– 56. South D.B., Zwolinski J.B. and Bryan H.W. 1993. Taylorilygus pallidulus (Blanchard): a potential pest of pine seedlings. Tree Planters’ Notes 44(2): 63–67. South D.B. and Zwolinski J.B. 1996. Chemicals used in southern forest nurseries. South. J. Appl. For. 20: 127–135. South D.B., Carey W.A. and Enebak S.A. 1997. Chloropicrin as a soil fumigant in pine nurseries. The Forestry Chronicle 73: 489–494. South D.B. and Donald D.G.M. 2002. Effect of nursery conditioning treatments and fall fertilization on survival and early growth of Pinus taeda seedlings in Alabama, USA, Can. J. For. Res. 32: 1171–1179. St. George R.A. 1935. Forest nursery seedlings subject to arsenical injury in some soils. J. Forestry 35: 627–628. Steel R.G.D. and Torrie J.H. 1980. Principles and Procedures of Statistics: A Biometrical Approach. 2 ed. McGraw-Hill, New York, pp. 631 Stejskal V. 2003. ‘Economic Injury Level’ and preventive pest control. Anzeiger fur Schadlingskunde 76: 170–172. Stephenson G.K, Goodrum P.D. and Packard R.L. 1963. Small rodents as consumers of pine seed in east Texas uplands. J. Forestry 61: 523–526. Tainter F.H. and Baker F.A. 1996. Principles of Forest Pathology. John Wiley & Sons, New York. Tesche M. 1969. Influence of the age of Pinus sylvestris seedlings on their susceptibility to damping-off. Arch. Forstw. 18: 1049–1055. Umland C.B. 1946. Nursery weeding costs reduced by mechanical cultivation. J. Forestry 44: 379– 380. U.S. Congress. 1995. Biologically based technologies for pest control. Office of Technology Assessment. OTA-ENV-636. U.S., Washington, D.C. USDA Forest Service. 2004. Forest Insect and Disease Conditions in the United States, http:// www.fs.fed.us/foresthealth/publications/annual_i_d_conditions/ConditionsReport_03_final.pdf. VanderSchaaf C.L., South D.B. and Doruska P.F. 2003. The power of statistical tests of herbicide trials in forest nurseries. Proc. Southern Weed Sci. Society. 56: 202–211. Vanderveer H.L. 1986. Seedbed mulching–some alternatives. In: Schroeder R.A. (comp.) (eds), Proc Southern Forest Nursery Association. Florida Division of Forestry, Tallahassee, FL, pp. 44–53. Vonderwell J. and Enebak S.A. 2000. Differential effects of rhizobacteria strain and dose on the ectomycorrhizal colonization of loblolly pine seedlings. For. Sci. 46: 437–441. Wakeley P.C. 1935. Artificial reforestation in the southern pine region. Technical Bulletin 492. U.S. Department of Agriculture, Washington, DC, pp. 115 Wakeley P.C. 1954. Planting the southern pines. Agriculture Monograph 18. U.S. Department of Agriculture Forest Service, Washington, D.C, pp. 233 Wichman J.R. 1982. Weed sanitation program at the Vallonia nursery. Tree Planters’ Notes 33: 35–36. Wilson R.G. 1980. Dissemination of weed seeds by surface irrigation water in western Nebraska. Weed Sci. 1: 87–92.
