The Bugwood Network

Forest Pest Control

Douce, G.K., Moorhead, D.J., and Bargeron, C.T., Forest Pest Control, The University of Georgia, College of Agricultural and Environmental Sciences, Special Bulletin 16, Revised January 2002.

Diseases

Root/Butt Diseases

Pathogens that attack root systems may affect small feeder roots as with Littleleaf disease, or a pathogen like Annosum root disease can attack larger roots causing decay extending into the butt of the tree where lateral roots attach to the trunk. In general, root diseases are more prevalent on sites which have been altered by erosion, compaction, imperfect drainage, or other disturbances. Along with site factors, environmental stress, host characteristics, and interactions with other microorganisms lead to root disease complexes which may become prevalent in plantations.

Littleleaf Disease
Littleleaf is the most serious disease of shortleaf pine in the South (Figures 42-43). However, in localized areas, loblolly pine can also be severely affected. Other pine species are much less susceptible to littleleaf disease. As the name implies, littleleaf disease results in shortened, stunted yellow needles. Early symptoms are difficult to distinguish from nutrient and water deficiencies. As the disease progresses, the foliage is thinned; tufts of needles only remain on branch terminals; and twigs and branches die throughout the crown. Normal needle length of 3-5 inches is reduced to about 2 inch. Although cones may be abundantly produced, they will be very small and contain only a few viable seeds. Littleleaf disease is caused by a combination of poor soil-water drainage and subsequent attack of the feeder roots of pine by the fungus Phytophthora cinnamomi. The P. cinnamomi fungus is found throughout the growing range of shortleaf pines. The fungus requires free moisture to survive and reproduce. As new root-tips and very young feeder-roots are attacked and killed by the fungus, nitrogen uptake is reduced, resulting in slowed growth and yellowing of the foliage. Relationships between poor soil drainage and root infection confine the disease to heavier, fine-textured soils.

Figure 42. Littleleaf disease on pine,
USDA Forest Service Archives.
Figure 43. Littleleaf disease typical soil profile of susceptible site, USDA Forest Service Archives.

Stands are seldom affected prior to 20 years of age. The manifestation of the disease is most intense in stands more than 40 years old. Infected trees may survive for up to six years after first visible symptoms appear, although a few may die the first year. Infected trees rarely recover from the effects of the disease unless they can be fertilized, which is generally only practical in an urban situation.

Do not plant shortleaf pines on soils with poor internal drainage. The lack of oxygen in these soils prohibits regeneration of roots and restricts root development into the soil. When the available nitrogen is depleted in P. cinnamomi infested soil, littleleaf disease develops. Favor more resistant loblolly, slash and longleaf pine over shortleaf pine in areas susceptible to littleleaf disease.

Annosum Root Disease
Caused by the fungus Heterobasidion annosum, annosum root disease can infect all pine species in the South (Figures 44-45). Fungus fruiting structures (conks) may appear on the bark surface at the root collar area of the tree or stump. Spores liberated from these conks can cause local and long-distance spread of the fungus. Spores, which are air-blown to the surface of freshly cut stumps, germinate rapidly and infect the stump. Mycelium of the fungus grows into the stump root system and is transmitted through root contacts or root grafts to roots of healthy trees. Spores of the fungus have the ability to infect directly and are more prominent on stump roots than on roots of healthy trees. Roots damaged and exposed when plowing fire breaks or during road construction are susceptible to becoming infected as well.

Suspect annosum root disease if tree mortality begins the second or third year following thinning and continues for several years. Infected trees show a general lack of vigor, shortened needles and internodes, chlorosis and heavy cone production. However, infected trees frequently do not show the symptoms and may fall over before any injury is noticed. Decline can be rapid or may take several years. Examine lateral roots for pitch-soaking and white, stringy decay of terminal considered a high-hazard site for annosum. Obtain soil survey maps to study soil for characteristics of texture and drainage. Interpret these results as indications of a low- or high-hazard site. When soil maps are not available, roadside cuts offer clues

Figure 44. Annosum root disease pitch-soaked wood and sand, Robert L. Anderson, USDA
Forest Service.

Figure 45. Annosum root disease;
windthrown diseased trees, Robert
L. Anderson, USDA Forest Service.
about the soil profile. When 50 percent or more of the land area is determined to be high-hazard, the entire stand should be managed as a high-hazard site.

In high-hazard areas, thin the stand only in the summer as high summer temperatures limit spread and viability of the spores. Stumps may also be treated with borax immediately following harvest. If mortality continues for five years after the first thinning, clearcut the stand and regenerate.

Stem Decays/Cankers

Gall and canker forming pathogens pose serious problems in forest management through tree loss and stem quality degrade. The most serious problems occur in southern pines, although canker diseases of hardwoods cause significant losses as well. Chestnut blight, caused by Cryphonectria (Endothia) parasitica, eliminated American chestnut in North America in less than 50 years after it was introduced from the Orient in 1900. Other frequently observed hardwood canker diseases include, most hypoxylon dieback (H. atropuntatum), nectria canker (N. galligena), strumella canker (Urnula craterium), and fusarium canker (Fusarium spp.). These hardwood cankers seldom result in direct mortality but cause substantial stem quality degrade and increase stem breakage. Most hardwood canker diseases occur when individual tree vigor declines following environmental stress and/or mechanical damage, such as fire, wind damage, or logging damage.

Fusiform Rust
Fusiform rust of slash and loblolly pine causes extensive economic loss annually in pine stands (Figures 46-48). These losses are compounded by the impact fusiform rust has in nurseries and young plantations.

Figure 46. Fusiform rust gall, Robert
L. Anderson, USDA Forest Service.
Figure 47. Fusiform rust infected seedlings,
Robert L. Anderson, USDA Forest Service.

The most easily recognized symptom is the spindle shaped canker on pine branches or main stems. In early spring these swellings appear yellow to orange as the fungus produces powdery spores. Older stem cankers may become flat or sunken as host tissue is killed. Cankers often girdle trees; wind breakage at the canker is common. Spores of the fungus Cronartium quercum f. sp. fusiforme produced on pine infect oak leaves. Brown, hairlike structures are produced on the underside of the oak leaves in late spring. Spores are produced, which in turn reinfect pine trees, completing a typical rust cycle.

Disease control in pine stands is primarily achieved by removing infected trees during thinnings and using genetically superior seedlings. On high-hazard sites, plant resistant species using locally or regionally improved selections. Plant pines within their natural range,

Figure 48. Fusiform rust pycnia,
Robert L. Anderson, USDA
Forest Service.
especially slash pine. Plant only disease-free nursery stock.

On bare, high-hazard sites, use a minimal level of site preparation to give satisfactory plant survival and growth. Destroy present host oak populations by burning, herbicide treatment or girding large residual oaks. Prevent resprouting of oaks. Limit the size of planting blocks to increase variation in age classes and plant material. Planting density can be adjusted to compensate for random rust infection and mortality but only to the extent that growth and yield are not affected before scheduled thinning.

Delay fertilization of slash and loblolly until the 10th year in regions of moderate or high-hazard. In low-hazard, flat-wood sites, growth response of slash pine to fertilizer will offset the rust impact.

When the stand is 3-5 years old, estimate rust incidence to determine future management policy. If disease incidence is high, consider sacrificing the stand early to replant with resistant plant material. Burning will help keep intruding oak hosts under control. Potential losses in older, heavily infected stands can be reduced by presalvage harvesting of rust infected trees. Burn after harvesting.

Nurseries should be located in low-hazard areas. Host oaks and infected pines should be eradicated from the area before establishing a nursery. Apply protective fungicides according to the label. Since warm, moist conditions are required for fungus infection, irrigate only during the middle of the day during the rust season. This allows the foliage to dry, rather than remain wet overnight.

Pitch canker
The pitch canker fungus, Fusarium subglutinans (Wollenweb. & Reinking), causes growth loss and mortality to many pine species including Virginia, slash, loblolly, shortleaf and longleaf (Figures 49-50). Pitch canker is characterized by copious pitch flow and pitch-soaked wood. Shoot cankers result in dieback, characterized by wilting and killing of the crown. Needles on infected shoots turn yellow to reddish-brown, later turning greenish-brown to dark gray.

Figure 49. Pitch canker: stem canker,
Robert L. Anderson, USDA Forest Service.
Figure 50. Pitch canker fungus growing from
seed, Robert L. Anderson, USDA Forest Service.

Cankers on trunks and large limbs are perennial, while cankers on shoots are usually annual. Infected pole-size trees usually have annual shoot cankers and may die from extensive infections. Less affected and younger trees may not be killed but may suffer reduced growth and loss form. Infected seedlings exhibit yellow-green to reddish-brown needles and wilting foliage. Pitch-soaked lesions occur at and just above the soil line. Infected seedlings will inoculate healthy stock when inter-mixed during handling and transit. Take care to cull out pitch canker infected stock during transplanting. Infected seedlings are usually killed by the disease. Systematic removal of infected trees reduces inoculum sources and fire hazard, as well as providing growth space for other trees.

Foliage Diseases

Maintaining optimum leaf area is critical to tree health, growth and yield. Premature shedding of infected foliage is a defense mechanism which isolates and removes the attacking pathogen. However, repeated loss of effective photosynthetic leaf area from foliage diseases reduces growth and yield, predisposing trees to damage by secondary agents such as insects and environmental stress.

Hardwood Anthracnose
Numerous hardwoods are susceptible to anthracnose (Apiognomonia spp.) which may only cause lesions on foliage or may invade and kill leaves, twigs, and branches. Anthracnose is common throughout the South and is most prevalent on sycamore and oak (Figures 51-52). Initial infection occurs in the spring during cool wet periods following leaf emergence, most commonly from mycelium that over-wintered in previously infected twigs on the host tree. Severe infections occur when temperatures are below 50o F for two weeks following leaf emergence. The infection enters the leaf and may grow into the leaf petiole and twig; and as twigs are girdled, dieback occurs. A canker may form which will girdle twigs in the following years. Necrotic areas develop along the veins and midrib of the leaves. Deformed blighted leaves may remain on the tree, but generally they are shed as the infection spreads over the leaf. As leaves, twigs and shoots die, complete crown defoliation can occur in the spring, but this is generally followed by a second leaf flush. Secondary infections can occur throughout the growing season when moisture is present. In intensively managed sycamore plantations, use wide spacing to increase airflow between trees to aid in drying to reduce secondary disease cycles. Fungicide sprays may be applied at bud break and during early leaf development to provide protection for trees in plantations and ornamental settings.

Figure 51. Oak anthracnose leaf symptoms,
Robert L. Anderson, USDA Forest Service.
Figure 52. Sycamore anthracnose leaf blight,
Robert L. Anderson, USDA Forest Service.

Needlecast
Needlecast (Lophodermella spp.) is a very common disease of conifers throughout the southern United States. The disease rarely causes significant economic impact on forest trees although there is undoubtedly some reduction in growth associated with premature loss (cast) of foliage (Figure 53). Severe needlecast, in combination with other stresses, may contribute to vulnerability of trees to bark beetle attack.

Infected needles develop chlorotic spots beginning in

Figure 53. Needlecast close-up of fruiting
bodies, USDA Forest Service Archives.
winter or early spring that rapidly turn tan to reddish-brown from their tips. Characteristic black, raised football-shaped fruiting structures form on the infected needles. Thinning of the crown may result from needle drop of infected needles, leaving tufts of green uninfected needles at the branch tips. Needle cast symptoms rarely affect the entire needle. At maturity, these fruiting structures discharge spores that can infect healthy foliage.

Control is seldom feasible under forest conditions. In nurseries, shade trees and Christmas tree plantings, recommended fungicide applications may be economical.

Brown Spot
The most serious needle disease of longleaf pine is caused by the brown spot needle fungus, Mycosphaerella dearnessii (Scirrhia acicola). Infected needles in the early stages are irregularly yellow to brown spotted, with green tissue in between the spots. Needles are eventually killed by the girdling action of the fungus. Longleaf pine seedlings can be seriously damaged. Severe needle blight on young seedlings can increase the length of time it takes longleaf pine to grow out of the grass stage. The disease affects both planted and natural seedlings in the field. Brown spot

Figure 54. Brown spot: prescribed burn for control, USDA Forest Service Archives.
can be controlled in nurseries by spraying with an approved fungicide. Prescribed burning can control the disease in longleaf pine seedling stands (Figure 54).

Fungicides

Disease control measures and fungicide applications in most forest situations are not usually cost effective. Fungicides are recommended in nursery production to protect these high volume seedlings from infections. Seeds are generally treated with fungicides prior to planting to inhibit fusiform rust and soil-borne damping-off fungi.

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