Diseases of... Conifer Root

Common Name:

OTHER ROOT ROTS OF PINES

Pathogens:

Various fungi

Common Hosts:

Pines Pinus spp.

Significance:

Numerous fungi are capable of causing root diseases on Florida's pines. With the exceptions of the root diseases already discussed (sand pine root disease and annosum root rot) however, root diseases of pines are usually of little consequence. Nonetheless, some fungi can be significant problems in nursery situations, for example, while others can cause substantial damage in certain field situations.

Recognition:

Pines with root disease problems appear generally unhealthy and exhibit varying degrees of foliage thinning and/or discoloration. Infected trees may die or become uprooted. Diseased roots typically exhibit varying degrees and types of resin exudation (resinosis), staining, and/or decay. Conks or sporophores of certain pathogenic fungi may appear at or near the bases of infected trees at various times of the year. Other pathogenic fungi sometimes produce characteristic spore forms or vegetative structures which can be detected in or on infected roots.

Infection Biology:

As with most root rot fungi, those affecting pines are apt to take advantage of root or basal injuries to gain entry into susceptible root systems. Many infections result from the deposition of airborne spores of the pathogens on wounded tissues or the intact surface of vulnerable roots. These spores germinate and the fungi grow into the roots causing disease and decay.

Other infections occur as a result of susceptible roots growing in close proximity to resting spores of certain pathogens in infested soil. Resting spores are of different types, but all function as an aid to the pathogens' survival in the soil in the absence of suitable hosts or growing conditions. Such spores are stimulated to germinate when suitable host root tissues grow nearby. Still other infections result from root contacts or grafts between healthy trees and adjacent infected trees or stumps.

Control:

Control methods for pine root diseases vary with the type of disease and the particular location of the problem. Soil sterilization using steam or an appropriate methyl bromide formulation is highly effective for controlling most nursery root rot problems. Certain fungicides may also be useful in nursery situations. Curing diseased trees in the field is a fallacy. The life of infected trees may be prolonged, especially in urban situations, by providing adequate water and fertilizer to debilitated root systems.

Prevention of root disease by avoiding root and basal injuries to tree is the best method of control in urban or shade tree settings. In commercial forest stands timber losses can be reduced in severely diseased stands by salvage cuttings. Be wary of planting pines near old dead pine stumps because such stumps often harbor root disease fungi which can pose a threat to newly planted trees.

Table VIII: Some Fungi Associated with Other Root Rots of Pine In Florida

Phaeolus schweinitzii (formerly, Polyporus schweinitzii): The cause of Brown Cubicle Root and Butt Rot.	Not a major problem on pines in Florida, but frequent on old or overmature trees. Sometimes causes distinct pockets or centers of root disease in younger, 10-20-year-old slash pine stands, frequently in association with residual, resin- impregnated (lightered) stumps from previous naval stores operations. See Table VII for other details.
Inonotus circinatus (formerly Polyporus tomentosus var. circinatus): The cause of Red Root and Butt Rot	. Not a major problem on most pines in Florida. Frequently occurs in association with basal fusiform rust cankers on slash pine, but not limited to this habit. See Table VII for other details.
Macrophomina phaseolina: The cause of Charcoal Root Rot.	Historically and potentially a major root disease problem on pines in commercial forest nurseries. Infects primarily small feeder roots and seedling tap roots. Sometimes involved in plantation failures as a result of planting infected planting stock. Swelling, cracking and blackening of infected tap roots are common in advanced infections. The occurrence of microsclerotia beneath the bark of infected roots is a key diagnostic feature. See Table VII for other details .
Armillariella tabescens (formerly, Clitocybe tabescens): The cause of Mushroom Root Rot.	Common on a variety of pines, but of no serious consequence, except perhaps on sand pine. See Table VII for details.
Fusarium spp.: Cause of Fusarium Root Rot (sometimes called Black Root Rot).	Infrequent, but occasionally causes root disease problems in nurseries and young plantations. Primarily affect feeder roots and seedling tap roots. Varying degrees of resin impregnation in infected tap roots sometimes present. No visible fruiting bodies or other fungal structures with the exception of sporodochia of the pitch canker fungus which are sometimes present on infected tap roots and lower stems.

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Bulletin No. 196-A | Printed October, 1983 | Contact the Forest Health Section

Florida Department of Agriculture and Consumer Services