Forest Pests: Insects, Diseases & Other Damage Agents

Applying Forest Health to Management Plans Forest Health Guide for Georgia Foresters Written by Terry Price, Georgia Forestry Commission Adapted for the web by the Bugwood Network

Improving Forest Stewardship and Management Plans by Incorporating Forest Health Recommendations

Foresters sometime fail to consider forest health recommendations in their management plans. Forest health prescriptions can be involved and require a working knowledge of forest entomology and pathology. Hopefully this handbook will enable foresters to refer more often to forest pests in the plans they prepare for landowners.

Most of the insects and diseases encountered by foresters are insignificant to forest health and do not deserve scrutiny in a forest plan. However, some are capable of becoming pests due to unfavorable conditions such as droughts and floods and because of the cultural practices we impose upon them.

The following exercise of questions and information has been inserted to challenge the forester to make associations between their management or stewardship plans and potential pest problems. Some of the information is a repeat and can be found in the previous sections of this handbook. Hopefully this section will serve as a beginning point for foresters and other land managers to better inform the private landowner about issues that affect forest health.

Geography, Geology, and Soils

• Have I classified the soils on this tract?
• Should I consider slope, aspect and physiographic region?
• Have I considered past land uses?
• Is this tract prone to flooding?

Foresters have spent many years focusing on above ground attributes such as basal area, diameter and height. It’s time we use our knowledge of soils and topography when assessing a particular tract of land.

Soil types, slope, aspect and physiographic region can be used to rate the relative risk of stands to many pests including damage from ice and wind.

Knowledge about past land uses can provide invaluable insight into potential pest problems. The white-fringed beetle grub is a common pest on pine in agricultural fields that once grew peanuts and soybeans. Recently the false chinch bug has become a problem on containerized and bareroot longleaf seedlings following herbicide applications.

Pasturelands converted to pine may present problems with white grubs. Scrub oak ridges provide food for adult white grub beetles and fields adjacent to these areas once converted to pine can sustain heavy root feeding from white grubs.

Fields that were used as dumping grounds for animal manure can cause serious yellowing in pine reproduction when the tree roots begin absorbing the high levels of nitrogen that have accumulated on top of the plow hard pan.

Land subject to flooding should be noted and dealt with accordingly.

Nantucket Pine Tip Moth

• Does the landowner know that loblolly pine is most susceptible to pine tip moths?
• Pine tip moths appear to increase in response to herbicide releases.
• Pine tip moths are more severe when loblolly pine is planted off-site.
• Has the landowner been informed on how to monitor pine tip moths with pheromone traps and when to apply the pesticide?

The Nantucket pine tip moth prefers loblolly pine to slash and longleaf. These moths appear to do more damage in the Coastal Plain and Lower Piedmont when loblolly pine is planted on deep sands and scrub oak ridges.

Also, there is speculation that when herbicides are used to control weeds and woody brush, the newly planted pine trees are more accessible to tip moth attacks.

If the landowner is regenerating a dry/sandy site, longleaf should be considered over loblolly pine.

Research indicates the potential for increased tip moth activity on seedlings with bent taproots. Stress the importance of planting the seedlings properly to minimize J and L rooting and the value of subsoiling in reducing the potential for root bending.

Applying insecticides can effectively control pine tip moths but each stand has to be monitored for moth emergence and the spray has to coincide with larval migration. Effectiveness of chemical control depends on many factors and at best is a gamble for most private landowners to undertake without the expert advice of an entomologist. In most cases tip moth damage can be reduced or eliminated by planting the least susceptible tree species.

Pine Reproduction Weevils

• When was the site harvested?
• When will the site be regenerated?
• How would I rate the quality of the harvesting operation?
• Have I examined natural pine reproduction on an adjacent site for weevil feeding?
• Have I determined whether any cutting will occur in nearby pine stands (within ½ mile) during the first year of the newly planted site?
• Does the landowner know the GFC upon request, at the time seedlings are ordered will spray his seedlings to protect them from weevils?

Pine reproduction weevils can do serious damage to young seedlings (1-2 years old) planted on recent cutover areas. Sites harvested before June can be planted the upcoming planting season without high risk to weevils.

Unwise logging can add to a potential weevil problem by providing breeding sites in partially buried, larger diameter tops and limbs. Sites with a minimum of pine logging debris will generally have less weevil damage.

Weevils feed on natural reproduction as well as planted seedlings. Examining nearby, natural pine reproduction for incidence of weevil feeding can aid in predicting how bad weevils could be on the proposed regenerated site. If the area to be regenerated is not a cutover site, it could still be infested with weevils from any logging activity nearby.

Larger diameter seedlings can withstand heavier weevil feeding than smaller ones. Be sure to advise the landowner to cull the smaller diameter seedlings. The GFC provides landowners with insecticide treated seedlings upon request for protection against weevils.

Pine Bark Beetles

• Have I considered stand age, basal area, tree species and site index?
• Have I looked for lightning strikes, logging damage, active spots?
• What is the stand’s accessibility to logging/salvage?
• Have I evaluated the stand for vigor i.e. (radial growth in last five years, live crown ratios)?
• Have I identified side slopes, dry ridges or flood plains?
• Have I thought about the landscape ecology of the tract?
• Have I discussed the effects of drought on bark beetle activity?
• Have I discussed the pros and cons of harvesting or thinning pine stands in different seasons?
• Have I discussed the role of prescribed fire in relation to bark beetles?
• Have I discussed the role of root diseases in relation to pine bark beetles?

Pine bark beetles prefer varied habitats and conditions depending on species. All five species are highly attracted to lightning struck pines.

The large six-spined Ips thrives during droughts and temperatures above 90 degrees F. This species will attack young pine reproduction up to mature-sized trees and recently decked logs. Most infestations are limited to 2 acres or less and generally decline after October and may not reappear the following season.

The small four-spined Ips thrives during droughts and prefers the tops and limbs of standing mature trees and logging slash and the boles of sapling-sized trees.

The southern pine beetle will attack any-sized pine during its characteristic outbreaks that occur every 6-12 years. Stands with basal areas above 120-sq. ft. per acre are most susceptible. Loblolly, shortleaf, Virginia and sand pines are preferred to slash and longleaf. Over-mature slash and longleaf are attacked but usually when associated with loblolly pine. Trees growing on dry sites and those adjacent to lightning struck trees are more likely to be attacked than trees on good sites not impacted by lightning.

The black turpentine beetle prefers trees damaged around log loading decks and along logging roads and skid trails. Trees struck by lightning are highly favored by the black turpentine beetle.

All of the pine bark beetles orient their movements to forests containing pine. The distribution of trees (pine and hardwood), fields and open areas can greatly affect the pattern of bark beetle activity on any given tract of land. Tracts broken up by fields, fire lanes, roads and non-susceptible species are less likely to suffer severe damage from pine bark beetles.

When talking to landowners about pine bark beetles distinguish between risk and hazard. Risk refers to population levels and hazard to conditions favorable for beetles (high basal areas, old age, root disease, loblolly/shortleaf vs slash or longleaf). During bark beetle outbreaks, beetles are maximizing their distribution throughout the landscape of the pine forests.

When high levels of any species of beetle are present, the risk of damage is high, even in well-managed stands. Contrarily, during low population years lightning struck trees, which are highly susceptible, may not be attacked. The risk of lightning striking in any given stand of trees is hard to predict. However, stands with high pine basal areas present a greater hazard and ideal conditions for pine beetle development. Stands should not be thinned when bark beetle populations are high. Improperly timed thinnings can create severe beetle problems. Prescribed fire can reduce the hazard of a severe beetle infestation but does not reduce the risk.

Southern pine beetle and Ips infestations are often associated with pines infected with Heterobasidion annosum and Leptographium spp. Heterobasidion annosum causes a root and butt rot and can be prevented or minimized by treating freshly cut pine stumps with the borate compound, Sporax® during the first thinning. The stumps must be treated within a 12-hour period following cutting. Leptographium species have been associated with loblolly pine decline (LPD) and southern pine beetle attack. Slope and aspect can be used to hazard rate stands for LPD and southern pine beetle attack.

White Pine Weevil

• Consider a mixture of white pine and hardwood?
• Evaluate for shallow hardpan?

The white pine weevil can cause considerable damage to white pine reproduction. Damage appears to be reduced when a mixture of pine and hardwood is managed. A shallow hardpan favors white pine weevil.

White-fringed Beetles, White Grubs and False Chinch Bugs

• Is the landowner regenerating an old-field site that was previously occupied by soybeans, peanuts or cotton?
• Will herbicides be used to prepare the site?
• Have you considered tree spacing?
• Physiographic Region?

White-fringed beetle larvae can be very detrimental to recently planted pine seedlings. There are about seven distinct races of this beetle but a positive identification is not necessary since the damage they do is identical. The adult white-fringed beetle feeds on the foliage of over 500 different plant species. Abandoned soybean and peanut fields tend to harbor this insect. When pines are established on such sites the larvae will readily attack and feed on pine roots. The use of herbicides reduces native vegetation and therefore forces the larvae to feed on pine roots.

Another example of an agricultural pest becoming a forest pest is the false chinch bug. These insects are very common in and around cotton fields. When these sites are converted to containerized longleaf heavy damage can occur on the pine needles. The use of herbicides, particularly the broadcast method appears to accentuate the damage from this bug.

Gypsy Moth

• Consider the potential long-term risk of gypsy moth establishment in the area?
• Identify the most susceptible tree species to defoliation?

The gypsy moth is moving further south each year. Three introductions have been eradicated in Georgia since the late 1980’s. The caterpillars prefer oak species and will avoid yellow poplar and most maples. The moths are spread to Georgia primarily by the movement of people and their infested items from the Northeast. The moth is more likely to establish north of Atlanta. Advise landowners/homeowners that stands can be managed for optimal resistance to gypsy moth if they are willing to favor certain tree species.

Annosum Root Rot

• Have I determined the soils for the tract?
• What is the depth of the sand?
• Is there any water mottling or clay within the top 12 inches of soil?
• Have I considered the age of the stand?
• Have I examined tree crowns for poor coloration and thinning?
• Have I considered prescribed fire?
• Have I determined when the stand was first and last thinned?

Annosum root rot is usually limited to well-drained sandy sites that are typical throughout the sandhill regions of the state. Root rot does not thrive in moist or wet soils. Water mottling and clay within 12 inches of the soil surface indicates a low hazard for root disease. The root rot organism is found on most forested sites throughout the state but the dry, sandy, sites are most susceptible.

Loblolly pine is slightly more susceptible than slash and longleaf but all three species can be severely damaged on high hazard sites. Root rot enters most stands following the first thinning. Disease spores land on fresh cut stump surfaces and spread to nearby healthy trees. Within 3-5 years following a thinning, affected trees will begin to turn a pale green and lose needles. Therefore, a landowner won’t know if the disease has invaded the stand until 3-5 years following a thinning. The hazard needs to be established before the first thinning.

Since thinnings promote the spread of root rot, recommendations that reduce the frequency of thinnings will also lessen the severity of the disease. Initial stocking levels should be lowered to around 545 trees per acre (8 x 10). This will postpone the first thinning and delay the spread of root rot.

Prescribed burning helps reduce the amount of organic litter that provides sustenance for the disease. Sites that are at risk for severe root rot should be regularly burned and monitored for bark beetle activity. If beetle activity becomes an annual event, the stand should be clearcut before annual mortality exceeds annual growth.

Pitch Canker

• Have I considered chicken houses?
• Have I considered tree species?
• Have I considered the use of fertilizer?
• Have I considered the weather?
• Have I considered cotton fields and the use of defoliants?

Wind and certain insects can spread the pitch canker-causing organism. Pine tip moths and weevils are likely candidates. The insects either act as wounding agents and/or vectors. Pitch canker appears to be cyclic with dry weather patterns. Pine plantations near chicken houses can become infected due to the presence of ammonia that is produced from the guano. Similarly, stands that have been fertilized or over sprayed with herbicides experience pitch canker flare-ups. Although the disease rarely kills trees, the terminal dieback that occurs can reduce product value and attract bark beetles. Advise landowners that damage may be incurred when pine stands are established near chicken houses and also following fertilization.

Hypoxylon Canker

• Determine site aspect and soil quality?
• Identify the oak species most susceptible?
• Did I notice signs of previous hypoxylon damage?

Drought, flooding, logging, sanitation and/or firewood cuttings, and lightning often trigger Hypoxylon canker exacerbations. Damage from hypoxylon can be devastating on dry sites. These would characteristically be the shallow, rocky side slopes and ridges in North Georgia and the sandy soils of the Coastal Plain. The oak species most susceptible to hypoxylon are: chestnut, water, blackjack, white and post. The more resistant species should be recommended as leave trees if possible. Stand disturbances should be minimized during logging.

Fusiform Rust

• Is the proposed planting site surrounded by an abundance of oak species?
• What physiographic region is in question?
• What type of weather is predicted for the planting season?

Fusiform rust is the most common disease affecting the southern pines. There are probably hundreds of strains of the disease. Rates of infection vary tremendously throughout the south. Even trees that have been bred for resistance are often heavily infected by the more virulent strains. Land managers often feel embarrassed when the so-called resistant trees they planted were hit hard by this fungus. The explanation is simple. Even the best of trees can succumb to fusiform rust under optimum conditions of host virulence and temperature and humidity. Fusiform rust sporulates in the early spring. If weather conditions are cool and wet during spore production then infection can be severe. On the other hand if the weather is hot and dry during sporulation the disease infection rate plummets. In general, genetically improved seedlings are more resistant to fusiform rust and should be used in areas where the disease has historically been a problem. Oak species serve as alternate hosts for fusiform rust and their abundance in an area may indicate a risk for pine infection.

Evaluating Planting Quality

• Did I inspect for bent taproots?
• Did I notice sinuous stems?
• Did I notice unusual levels of tip moth?

Stand quality can be evaluated now at the end of the third growing season by surveying for stem sinuosity. Pines that are J,L or bent root planted will develop sinuous stems therefore, indicating a poor planting job. If the sinuosity is severe enough, trees will generally be fit for pulp only. Landowners and tree planting vendors need to learn this new relationship between bent taproots and above ground deformity. Trees that are bent during planting will not straighten to become well-formed trees. Foresters and landowners need to insist on properly planted trees.

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