Diseases of... Conifer Root

SAND PINE ROOT DISEASE

Choctawhatchee Sand Pine
Pinus clausa var. immuginata
Ocala Sand Pine Pinus clausa var. clausa

TABLE VII- FUNGI ASSOCIATEDWITH SAND PINE ROOT DISEASE IN FLORIDA

Sand pine root disease is the most serious disease affecting sand pine in Florida. It is a disease complex in that two or more pathogens are usually involved, apparently acting in sequence or combination. In certain cases, however, only one pathogen is involved. A 1979 estimated place timber losses to this disease in Florida at between $1.5 and $2.5 million annually.

Sand pine is vulnerable to root disease in virtually all environments, but the disease is far worse where water tables or impermeable soil layers are shallow or soils poorly drained. Surveys have shown a significantly greater level of root disease in Ocala variety sand pine as in compared to the Choctawhatchee variety. As a rule, damage caused by sand pine root disease increases with tree or stand age. Root disease typically results in eventual death of infected sand pines. Death of infected trees may occur rapidly (within 1 to several years) or many years following infection depending on the fungus or fungi involved, local site conditions, age of affected trees, weather conditions, and other related factors.

Infected trees exhibit varying degrees of crown or foliage thinning and/or discoloration (yellowing, reddening, etc.) and frequently lean to one side due to the failure of structural root support. Mortality is common, and infected trees often exhibit some degree of resinosis (exudation of resin) at or near the ground line. Internally, diseased woody roots are discolored and usually saturated with resin. In some cases, infected woody roots are watersoaked.

In the advanced stages of root disease some roots exhibit decay patterns typical of specific fungus pathogens (white pocket rot, brown cubicle rot, etc.). Depending upon the particular fungus or fungi involved and the stage of disease development, diseased woody roots frequently exhibit characteristic patterns of decay. Infected feeder roots are simply necrotic (dead). Sloughing of the root cortex (external tissues) on infected feeder roots is common. This symptom can often be detected by pinching and sliding suspect feeder roots between the thumb and forefinger.

The accumulation of clumps or cakes of soil around diseased roots of all sizes is common as a result of the bleeding or exudation of resin by diseased roots. Fungal conks or sporophores at or near the bases of trees are often a useful indicator of root disease, depending of course on the identity of the particular fungus.

Many of the fungi which cause root disease on sand pine are disseminated by airborne spores (basidiospores) produced at various times of the year in above?ground fruiting bodies (sporophores). Other root disease fungi are soil-borne and do not produce aerially disseminated spores.

In the first group, infections are likely to occur when basidiospores are deposited on wounds at the bases of trees, adjacent stumps of cut trees, or on the surface of injured or intact roots. Spores are presumably washed downward into the soil by rainwater. In the latter group, infections result as the growing roots of susceptible pines come into contact with either a resting stage (various types of spores) or the actively growing, vegetative stage of a soil-borne fungus in infested soil. Conceivably, both groups of fungi are capable of infecting root wounds created perhaps by various small animals or insects. Local spread of root disease is effected by root-to-root growth of the various pathogens directly through the soil or through root grafts or root contacts.

Old dead stumps and roots may harbor one or more root disease fungi from previous infections and serve as potentially dangerous sources of inoculum, resulting in associated pockets of diseased trees . Infections and disease development are largely enhanced by adverse soil conditions, including poor drainage and shallow water tables or impervious soil layers.

No effective control measures are known for sand pine root disease in field situations once the disease has become established. Soil fumigation with methyl bromide in forest tree nurseries provides effective control of seedling root diseases. Methyl bromide or steam sterilization of potting soils, together with appropriate cultural practices (clean pots, tools, etc.) are recommended for ornamental nurseries.

Excessive watering of seedlings should be avoided. Certain types of soil fungicides may prove helpful in some nursery situations. Losses to sand pine root disease in commercial forest stands can be minimized by applying the following guidelines. Be sure planting sites are good sand pine sites; a deep, well?drained sand. Consider alternative species (for example, Longleaf pine) on marginal or questionable sites. Avoid planting nursery stock infested with Phytophthora spp. or Macrophomina phaseolina.

Do not replant sand pine on sites with a previous history of severe sand pine root disease problems, especially if Phytophthora cinnamomi was involved. Avoiding sites where P. cinnamomi is known to be present or has previously been a problem on other crops is also advisable. Avoid, as practicable, the movement of site preparation and planting equipment, etc., from sites where Phytophthora cinnamomi is known (little leaf disease sites, etc.) to sand pine sites. Such equipment could be contaminated with Phytophthora cinnamomi-infested soil and result in the unwanted introduction of the pathogen into sand pine stands. Harvest stands on an early rotation schedule because older and over-mature stands tend to sustain increased losses to root disease fungi, especially Inonontus circinatus and Phaeolus schweinitzii. The use of clean planting stock, good site selection, and minimum irrigation is recommended for sand pines in urban or ornamental situations. Also, avoid injuries to roots and bases of ornamental pines.

Basal resinosis indicating root disease infection in sand pine..