Integrated Pest Management in Southern Pine Forests

R.C. Thatcher - Program Manager, Integrated Pest Management RD&A Program for Bark Beetles of Southern Pines, Pineville, LA.,
G.N. Mason - Project Leader, Silvicultural Options for Gypsy Moth, Northeastern Forest Experiment Station, Morgantown, WV, and
G.D. Hertel - Program Manager for Gypsy Moth Research, Northeastern Forest Experiment Station, Broomall, PA.
Mason and Hertel were Research Coordinator and Applications Coordinator for the IPM Program when this work was conducted.

Integrated Pest Management Handbook, USDA, Forest Service, Agriculture Handbook 650, April 1986.

In 1980, the Forest Service and the Cooperative State Research Service of the U.S. Department of Agriculture initiated the Integrated Pest Management Research, Development, and Applications Program for Bark Beetles of Southern Pines. This research/applications effort concentrates on pine bark beetles and associated tree diseases in the South. This is one in a series of Integrated Pest Management handbooks.

Relationship of Stand Growth and Development to Management Practices

The planning and execution of pest management programs are closely correlated with changes in tree size and stand structure and the influence of these factors on tree susceptibility to pest attack and possible preventive strategies. The growth and development of a forest can be described in terms of a sequence of six distinct developmental stages (Harms 1983): (1) Regeneration, (2) establishment, (3) precompetition, (4) competition/premortality, (5) competition/self-thinning, and (6) post competition. The forest should be monitored through each of these stages to determine changes in pest population and forest conditions. Findings can serve as input for predictive and simulation models to project trends in pest populations and/or forest conditions and evaluate the effects of treatments on forest stands or pest outbreaks as they occur. The use of these models can also provide meaningful information for evaluating outcomes of alternative treatment strategies and making better and more timely decisions regarding possible intervention through cultural treatments.

Regeneration: Stage 1
Stands are regenerated either naturally through seeding or by planting. This stage is critical since provision must be made for adequate and proper distribution of seeds or seedlings and for seedling survival and initial stand establishment. Silvicultural treatments during this stage include evaluation of the potential seed crop; pre- and post-harvest site preparation as required; seed tree removal, or the planting of seedlings; weed control treatment schedules as needed; and evaluation of and prompt response to the occurrence of insect and disease pests. The major pests of direct concern to most foresters during the regeneration stage are reproduction weevils, Texas leaf-cutting ants, pine tip moths, and fusiform rust (Hertel and others 1984). Table 1 lists the management considerations for each of the major pests of concern during the regeneration stage.

Table 1 – Management considerations during the regeneration stage

Important pests		Management considerations
Reproduction weevils (Hylobius pales (Herbst.); Pachylobius picivorus (Germ.))		Identify high-hazard sites Delay planting for one year Treat seedlings – root dip                           top dip                           in-field spray
Pine tip moths (Rhyacionia frustrana (Comst.))		Do not treat stands managed for pulpwood rotations
Texas leaf-cutting ants (Atta texana (Buckley))		Do not plant near active colonies Treat colonies prior to planting
Southern pine beetle (Dendroctonus frontalis (Zimm.))		Favor mixed pine/hardwood stands Improve damage Consider use of resistant tree species
Annosus root rot (Heterobasidion annosum (Fr.) (Bref.)		Increase initial spacing of seedlings Consider use of resistant tree species
Fusiform rust (Cronartium quercuum (Berk.) Miyabe ex Shirai f. sp. fusiforme)		Avoid rust-infected planting stock Use resistant seeds or seedlings in high-hazard areas Delay fertilization until age 8-10 (if planned) Reduce oak population Increase planting density to offset future losses Minimize site preparation Delay prescribed burning until age 8 or later Consider use of resistant tree species
Littleleaf disease (Phytophthora cinnamomi Rands)		Hazard rate sites Regenerate high-hazard sites with resistant species

Fusiform rust – The regeneration period is an especially important time to consider opportunities for reducing losses to fusiform rust. In all planting situations, care should be taken to avoid using planting stock from rust-infected nurseries and to cull infected seedlings during the planting operations where possible. Sites that are particularly rust-prone or have a history of high rust infection levels should be planted with rust-resistant seedlings or from resistant geographic seed sources. Cultural practices that encourage branching, rapid growth, or otherwise result in an abundance of succulent young tissue should be discouraged in areas rated high hazard for rust. Site preparation should be minimized, fertilization delayed until age 8-10, and prescribed burning delayed until age 8 or later. Inoculum levels can be reduced by removing oak (the alternate host) in or adjacent to the regeneration area. In areas where projected future losses are high, such losses can be offset by increasing planting densities to allow for early mortality, while retaining a fully stocked stand. At the same time, the landowner or forester should be aware of the possible conflict between this tactic and recommendation for reducing stocking density to lessen future susceptibility to both annosus root rot and southern pine beetle (SPB) attack. Such conflicts should be weighed on the basis of management objectives, rotation length, and geographic area or site hazard.

Annosus root rot and southern pine beetle – Although the southern pine beetle and annosus root rot are of little concern in the early life of a stand, measures can be taken to reduce the likelihood of damage in later years. Future SPB risk can be reduced through improved drainage of low-lying sites in the Coastal Plain or protection of sensitive sites during site preparation in the erosion-prone Piedmont. Where management objectives permit, mixed pine or pine-hardwood stands should be favored, since they are less susceptible to beetle infestation. Future annosus root rot damage can be reduced by identifying high-hazard sites (Anderson and Mistretta 1982) and increasing initial spacing of seedlings so as to delay the need for future thinning or reduce root contacts on such sites. Where practical, more resistant pine species (such as longleaf) or hardwoods may be considered where site hazard and the likelihood of infection are very high.

Other pests – Tip moth larvae kill buds and twigs of young loblolly and shortleaf pines throughout the South. Heavy attacks by multiple generations each year can stunt trees for up to 5 to 6 years. Severe, recurring infestations can cause volume losses. However, studies have shown that only those pines growing on the poorest sites suffer serious growth loss from tip moths over a rotation.

Adult reproduction weevils are attracted to fresh pine stumps where they feed on young seedlings and lay their eggs in the large roots of the stumps. Emerging weevils feed on the bark of young seedlings. These insects can kill up to 20 to 30 percent of all pine seedlings planted in cutover, storm-damaged, burned, or otherwise disturbed areas. Mortality may range as high as 60 percent in localized areas. All pine species are susceptible to damage. Damage is most severe during February through June and less so in late summer and early fall. Consideration should be given to delaying planting after cutting or treating seedlings (before or after planting).

Texas leaf-cutting ants are important pests of pines in many parts of east Texas and western Louisiana. Ant colonies (or towns) most frequently occur in more open areas of deep, sandy soil. Damage results from the cutting and removal of needles from natural reproduction and planted seedlings. Most severe losses occur during the winter when there is little or no other green vegetation for the ants to forage. In areas where ant populations are high, it may be impossible to establish pine seedlings by planting or to naturally regenerate cleared areas until the ants have been controlled.

Littleleaf disease rarely affects trees younger than 20 years of age and becomes increasingly severe in older shortleaf pine stands in the Piedmont region of the southeastern United States. Future risk of infection can be determined by evaluating the site or soil characteristics of areas to be regenerated. Seed or seedlings from loblolly pine seed orchards should be used or the area planted with such nonhost species as longleaf pine or hardwoods.

Establishment: Stage 2
During the stand establishment stage (approximately age 3-5 years), seedlings in planted stands and in properly stocked, naturally seeded areas become well rooted and grow at a rapid rate without competition from surrounding seedlings. They are generally vigorous and suffer few pest problems; in fact, because of high vigor, rapid growth, and better establishment of root systems, susceptibility to insects and diseases decreases with age through this stage. Possible exceptions include fusiform rust infections on new growth, particularly in high-hazard areas and during periods when environmental conditions favor the development and spread of the disease. Some seedling mortality may result from fusiform rust developing from earlier field infections or nursery-infected stock. The abundance of existing stem infections should be determined and future losses projected so that alternative management actions can be taken, if warrented.

Pine tip moth creates an alarming tree appearance in heavily infested stands (foliage may be quite red), but experience has shown that growth, permanent deformation, or mortality losses are relatively small over time. There are, of course, exceptions in high-value stands, high-hazard areas, or certain pine species.

Table 2 shows the management considerations for each pest of concern during the establishment stage.

Table 2 – Management considerations during the establishment stage

Important pests	Management considerations
Fusiform rust	Delay fertilizatrion until age 8-10 (if planned) Reduce oak populations Delay prescribed burning until age 8 or later
Pine tip moths	Take no control action

Precompetition: Stage 3
The precompetition stage of stand development is a period of unrestricted tree growth. Height and diameter of individual trees increase at a rapid rate, vigor is high, and susceptibility to insect and disease attack is low. During this stage, there is little need for silvicultural treatment. The availability of essential nutrients may be the only major factor limiting tree growth. Fertilization and woody vegetation control with herbicides may be needed to maintain maximum growth. Recognizable differences in size among individual trees begin to show up as a result of genetic variation, microsite differences, or variation in germination time or seedling size at planting time.

The period of time that a stand remains in the precompetitive stage will vary with site quality and initial stocking density. In other words, the initial spacing of seedlings and rate at which they grow will determine when the site is fully occupied; competition for available space, moisture, and nutrients occurs; and initial pest problems begin to be of some concern.

Management considerations for the one pest of concern during the precompetition stage are shown in table 3.

Table 3 – Management consideration during precomposition stage

Important pests	Management considerations
Fusiform rust	Take no action

Competition and Premortality: Stage 4
During this stage, root systems extend to (and presumably, fully occupy) the available growing space. Competition for space, moisture, and nutrients begins to reduce growth rate of individual trees, competition increases, and competition-induced mortality begins. Individual tree crowns continue to enlarge and differentiate into crown classes. Silviculture practices during this stage are designed to reduce competition--by precommercial thinning if the stand is young or by commerical cutting if the stand is old enough and the trees large enough to support the cut.

Management considerations for each major pest of concern during the competition and premortality stage are shown in table 4.

Table 4 – Management considerations during the competition and premortality stage

Important pests	Management considerations
Southern pine beetle	Perform frequent surveillance in high-hazard areas Avoid excessive damage to site and/or residual trees Consider thinning or salvage cutting Remove high-risk trees Manage species composition Use uneven-age management
Annosus root rot	Treat stumps--use borax if annosus is already present; Phlebia, if not Consider prescribed burning before and after thinning Thin stands during summer to reduce infection level
Fusiform rust	Reduce oak population Remove severely infected trees to prevent inoculum dispersal to oaks in adjacent stands and to recover loss through salvage
Littleleaf disease	Remove severely damaged trees
Ips engraver beetles (Ips avulsus (Eichh.), I. grandicollis (Eichh.), I. calligraphus (Germ.))	Prevent logging damage Remove high-risk trees Remove or distribute logging residue; avoid piling residue around base of trees.
Black turpentine beetle (Dendroctonus terebrans (Oliv.))	Spray heavily damaged or individual trees infested with BTB

Silviculture techniques to reduce pest problems – This is also the growth stage in which potential pest problems become quite evident. Competition, increased trees stress, and uniform stocking, age, and species composition provide a setting for pest establishment and outbreak development. Stand and site conditions should be evaluated to determine potential risk for infestation by the southern pine beetle, fusiform rust, littleleaf disease, or annosus root rot. In the case of the SPB, frequent surveillance should be preformed to monitor high-hazard stands (usually dense, older, slower growing stands on poorly drained sites or those growing on severely eroded sites of poor quality), particularly during periods of increased beetle activity in such areas. Along with other silvicultural considerations, thinning should be undertaken to maintain vigorous growth and to harvest high-risk trees that may be severely rust-infected or those that may be affected by littleleaf disease or damage by other causes such as recent logging operations, lightning, or wind (Belanger and others 1985; Belanger and Malac 1980). During these treatments, care should be taken to avoid excessive damage to the site or residual trees. If heavy logging damage should occur, Ips engraver beetles or black turpentine beetle (BTB) might invade injured trees. These pests are capable of killing individual trees or small groups of trees on their own, or they may serve as a precursor to attack by the potentially more destructive SPB. The type of logging system, logging equipment employed, and quantity and distribution of logging residue will do much to determine the damage potential from Ips and BTB.

On high-hazard annosus sites (deep sandy soils with good internal drainage), it may be advisable to treat stumps with borax if there is no evidence of the disease in the stand (Redmond 1985). Where annosus is known to be present, Phlebia gigantea² should be applied to fresh stumps. Prescribed burning prior to thinning or thinning during the warmer, drier summer months has also been shown to reduce annosus infection and tree mortality.

²A competing fungus that can be applied as a liquid suspension with a plastic squeeze bottle or garden sprayer. Contact pest management specialists in State forestry organizations for advice on commercial availability.

For mixed pine/hardwood stands growing under natural conditions, consideration should be given to fusiform rust occurrence. On these sites, there may be need for reducing the oak population and removing severely infected pines to reduce the potential for infection of younger trees in the same or adjacent stands (Anderson and Mistretta 1982). Stands that have high rust levels should be evaluated to determine whether immediate action is justified. Individual tree-rating systems are available to project the likelihood of tree mortality. Salvage cutting guidelines provide recommendations for removal of high-risk trees prior to harvest if infection levels and management goals warrant.

On high-hazard littleleaf sites (those that have low soil fertility, poor international drainage, plant-parasitic nematodes, and the fungi Phytophthora cinnamoni Rands and Pythium spp.), it may be necessary to selectively remove obviously diseased trees (where fewer than 25 percent of the stems are infected and/or the residual stand will be inadequately stocked). Sites that are at high hazard for littleleaf disease (or that have a previous history of it) should be regenerated with seed or seedlings from a superior seed source of shortleaf pine, a loblolly pine seed orchard, or with nonhost species such as longleaf pine or hardwoods.

Minimizing pest losses through early detection and prompt control – If an SPB outbreak should occur, early detection of new infestations is the first step in minimizing losses. Stand stratification through hazard rating may be useful in reducing the total area requiring surveillance, particularly during periods of low beetle activity when the beetles tend to concentrate in high-hazard stands. During periods of high activity, the understanding of hazard levels may also provide additional insight into priority setting for control of individual spots. Periodic aerial surveys provide the fastest, most practical way of locating infestations; but under certain situations may be needed to detect single and small groups of infested trees before they are visible from the air (Billings and Doggett 1980; Billings and Pase 1979; Billings and Ward 1984). This approach may be particularly useful for small ownerships or in high-value areas during increased beetle activity periods, when the "acceptable loss" threshold is much lower.

Improved understanding of beetle behavior and beetle/host relationships has permitted us to rethink our control strategies and streamline activities to minimize both timber and economic losses. We now have much stronger biological basis for control guidelines. These guidelines recognize varied loss potentials under different stand and population conditions: that some spots require immediate treatment, that others can be monitored for a period of time, and that certain types of infestations require no treatment at all. Methods are available for setting control priorities based on field observations (Billings and Hynum 1980) or, if the situation warrants, spot growth, timber mortality, and economic losses can be projected for the next 30 to 90 days or longer by applying one of several stand growth and yield and SPB spot growth models (Billings 1985a, b; Coulson 1985). The latter requires that certain insect, site, tree, and stand information be collected. Rapidly expanding spots should be immediately controlled.

After control priorities have been established, prompt control action should be taken. Cut and remove involves the timely felling and salvage of actively infested trees and a buffer strip of uninfested green trees around the spreading edges of the spot. Cut and leave involves felling infested trees and a buffer zone of uninfested green trees toward the center of the spot and leaving them in the woods. The method is most effective in smaller spots (up to 50 trees) and is usually used during May to October. Pile and burn involves felling, piling, and completely burning infested trees during periods of low fire danger. Cut and spray involves felling, limbing, cutting into workable lengths, and throughly spraying the entire surface of infested trees using low-pressure sprayers and registered pesticides.

Cut and remove remains the most favored approach because of the partial financial return it provides. Cut and leave is practical, relatively inexpensive, and requires minimum labor and equipment but provides no direct financial return through salvage. Pile and burn is one of the oldest SPB control methods, and it is effective when properly applied, particularly in stands made up of smaller trees. Lindane and chlorpyrifos (Dursban^®) are most commonly used for chemical cut-and-spray treatments. Differences in the toxicity, persistence, and cost of these chemicals allow the tailoring of chemical use to specific management situations (Swain and Remion 1981).

SPB spots having fewer than 10 trees or those having no freshly attacked trees frequently become inactive. In situations where there are many widely dispersed small infestations, the best control strategy may be to monitor the area from the ground to air to determine whether these spots will become inactive or resume growth. Inactive spots require no control treatment and may provide natural, long-range benefits by offering habitat for survival or enhancement of such longer lived natural control organisms as predatory or competitive insects and birds. Also, if timber volume, access, and value warrant, inactive spots can be salvaged up to a year or longer after tree death (Levi 1981).

Competition and Self-Thinning: Stage 5
The competition/self-thinning stage begins when the stand completely occupies its growing space. Crown closure is complete, and branches at the base of the crowns die from lack of light. Competition for light, moisture, and nutrients is so severe that the smallest, weakest trees can no longer compete and begin to die or are killed off by insects or diseases. Larger, more vigorous trees continue to grow and occupy space provided by the dying trees; the process goes on until the site reaches its maximum carrying capacity. Simply states, for a given number of surveying trees, there is a maximum mean stand diameter that the site can support, and the maximum diameter can be changed only by reducing the number of stems occupying the site. Thinning a stand has the effect of reducing competition and maintaining vigorous growth. Stand development progresses from stage 4 to stage 5 (through tree growth). If the stand is thinned, the cycle reverts to stage 4, and the process repeats with additional growth and thinning. In unmanaged stands, reduced tree vigor resulting from competition sets the stage for insect and disease infestation.

When a stand has reached the competition and self-thinning stage, the threat of losses from such major pests as southern pine beetle, annosus root rot, and littleleaf disease is greatest. Trees are larger and more valuable at this stage, and losses resulting from pests can seriously erode the achievement of long-range management objectives and returns on investments. The approach for prevention or control of pests in older stands is the same as that described for stage 4 stands (competition and premortality stage). Preventive action, early detection, accurate forecasts of loss potential, selection of the most effective preventive or remedial treatments, and timely followup actions are key to optimizing growth and minimizing losses.

Pests and management considerations during the competition and self-thinning stage are the same as for the competition and premortality stage. Stand treatment serves to set the process back one stage and reduces potential pest damage.

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