TREE & SHRUB DISEASES OF

TEXAS

Compiled by: THOMAS Isakeit, Ext. Plant Pathologist

Modified for use in Fort Bend by: Vince Mannino, CED-FBC

FUNGAL DISEASES

AFFECT A WIDE HOST RANGE AND CAUSE

DEATH

WOOD DECAY FUNGIMature trees affectedGradual decline over several yearsWounds and environmental stress

(e.g. drought) are pre-disposition factors

Diagnosis: presence of fruiting bodies (conks)

WOOD DECAY FUNGI

WOOD DECAY FUNGI

LIVE OAK IN A NATIVE STAND

AVOCADO IN AN ESTABLISHED ORCHARD

DIAGNOSIS OF GANODERMATHE PRESENCE OF FRUITING BODIES (CONKS) OF GANODERMA LUCIDUM ON TREES THAT ARE STILL ALIVE IS DIAGNOSTIC FOR THIS SPECIES OF WOOD DECAY FUNGUS. IT CAN ALSO OCCUR

ON DEAD TREES AS A SAPROPHYTE.

OTHER WOOD ROT FUNGI

A CONK ON A LIVING TREE IS EVIDENCE OF INFECTION !

GANODERMA LUCIDUM seems to be the most prevalent species in

south and central texas, but other species of wood decay fungi have been identified (INONOTUS RICKII

shown here).

WOOD ROT FUNGUS - DIAGNOSIS

sometimes conks may not be produced on infected trees

until they are dead. the presence of rhizomorphs (white or brown fungus

strands on the root surface) on a tree that is gradually

dying may support a tentative diagnosis of fungal infection

WOOD DECAY FUNGI There is no treatment once trees are infected. Prevention: keep trees watered, try to

minimize other stress. Prevention: proper pruning technique to

promote rapid wound healing. there is no benefit to pruning paint.

Wood decay fungi may be transmitted by wood-boring beetles

A living, infected tree may be in danger of falling!

COTTON ROOT ROT Rapid death (weeks or within season) of

trees and shrubs of any age Symptom onset during summer months Diagnosis: microscopic examination of

fungal strands on roots, presence of spore mats on soil surface (not always produced)

If cotton can grow in the vicinity, then so can cotton root rot!

COTTON ROOT ROT

COTTON ROOT ROTASH TREE & CAPE HONEYSUCKLE

COTTON ROOT ROT

Progression of cotton root rot on Pittosporum

COTTON ROOT ROT

Spore mats of the fungus are

sometimes produced on

the soil surface near

the dying plant, in moist, shaded areas

COTTON ROOT ROT No treatment for infected plants Fungus survives indefinitely in soil &

doesn’t move; infection occurs when plant roots grow to it

Monocot plants (e.g. agave, banana, palms) are immune

Dicot plants vary in resistance: see tx plant diseases handbook (b-1140) or tx ag. expt. station bulletin 527

DISEASES CAUSED BY FUNGI AND OTHER ORGANISMS THAT

CAUSE DEATH AND HAVE A MORE LIMITED HOST RANGE IN TEXAS

FUNGAL CANKER AND DIEBACKCaused by several species of fungi,

with some host specificityFungi are “weak” pathogensHost predisposed by injury and/or

environmental stressDiagnosed by the presence of the

fungus to differentiate from insectsTreatment: corrective pruning

FUNGAL CANKER AND DIEBACK

Canker on Oleander stem, caused by Botryospaeria obtusa spores are

produced in black, pimple-like structures in the bark.

OAK WILT Caused by a fungus Affects: live oak, shumard oak,

spanish oak, and blackjack oak Spread by sap-feeding beetles, root

grafts Prevention: prune during periods of

low insect activity, removal of infected trees and soil trenching to prevent root grafts

OAK WILT

Some trees

will not die, but

are stunted forever.

OAK WILTCHARACTERISTIC LEAF SYMPTOM ON LIVE OAK

OAK WILTInjectors thatsupply fungicides will do little, but cost a lot.

NOTE: This tree’s infection was caused by stress from too much soil added…Where are the root flares?

SLIME FLUX (WETWOOD)

This is a water soaking of heartwood affecting many tree species & is associated with various bacterial species. Liquid will drain from openings of trunks, often staining the outside. it is associated with branch dieback, but its role in tree mortality is not certain. there is no treatment or prevention for this condition.

FIRE BLIGHT Caused by a bacterium Affects plants in the rose family: in

Texas, particularly apple, pear & photinia

Bacterium can be spread by pollinating insects at bloom time

Confirm diagnosis since may mimic herbicide damage

Prune affected branches at least 8” below symptoms

FIREBLIGHT• left: branch

dieback

• right: quick death of leaves, often associated with flowers (source of infection)

FOOT ROT OF CITRUSCaused by a fungus, Phytophthora

(several species) Infection through wounds of trunk,

leading to defoliation and fruit dropSoilborne, other plants susceptible,

depending upon the fungus species involved

Treated with fungicides

FOOT ROT OF CITRUS

FOOT ROT OF CITRUS

DETAIL OF SYMPTOMS ON LOWER TRUNK

PHYTOPHTHORA ROOT ROT AND LEAF BLIGHT OF HIBISCUS

Too much soil

moisture and/or poor

drainage

PHYTOPHTHORA ROOT ROT AND LEAF BLIGHT OF HIBISCUS

PYTHIUM ROOT ROT OF HIBISCUS

EXTENSIVE ROOT ROT LEADS TO WILTING AND DEATH. CONTROL WITH SANITATION,

GOOD DRAINAGE AND FUNGICIDES.

OLEANDER LEAF SCORCH Caused by a bacterium, Xylella fastidiosa: a

pathovar (strain) specific to oleander Started showing up in late 1990’s Bacterium can be spread by some

leafhoppers & sharpshooters Confirm diagnosis at p.d. clinic No treatment, but some cultivars may have

resistance

OLEANDER LEAF SCORCH

Landscapers’ nightmare!

OLEANDER LEAF SCORCH

PHOENIX LETHAL DECLINE Cause: a phytoplasma (ultra-small, wall-less

type of bacterium) Some strains spread by leafhoppers &

planthoppers Confirm diagnosis at p.d. clinic Phoenix spp. susceptible, Sabal and

Washingtonia palms resistant recent outbreak (2001) in Corpus Christi

PHOENIX LETHAL DECLINE

PHOENIX LETHAL DECLINE

RACHIS BLIGHT OF PALMS

NON-INFECTIOUS (NON-LIVING) CAUSES OF TREE

AND SHRUB DEATH

FREEZE DAMAGE

LIGHTNING DAMAGE• If lightening

makes a spiral the trees is DEAD.

• If the strike is mostly straight up and down, then there is a chance

DROUGHT & SALT STRESS

Right: typical symptoms.

Left: salt residue on soil surface

SOIL-APPLIED HERBICIDE

Herbicide (Krovar) was applied to citrus orchard soil. Live oak roots grew into

orchard soil and picked up the herbicide.

SOIL-APPLIED HERBICIDE

variations in foliar damage from krovar

SOIL STERILANT

INFECTIOUS DISEASES (FUNGI AND OTHER ORGANISMS) THAT

DISFIGURE OR BLEMISH SHOOTS AND LEAVES,

BUT DO NO CAUSE DIEBACK

CROWN GALL Cause: bacterium wide host range spread by pruning

tools and splashing water

galls formed at base of shoot

OLEANDER OLIVE KNOT

Caused by a bacterium with a narrow host range.

GALL RUST FUNGI

Gall Rust on Acacia

GALL RUST FUNGI

GYMNOSPORANGIUM SPECIES - infect members of the cypress and rose families.

infection of both types of plants are required to complete the life cycle of the fungus and

different spores infect each type.

FUNGI INFECTING FOLIAGE

TOP LEFT: Entomosporium on photinia.

TOP RIGHT: Rust on live oak

BOTTOM LEFT: Lembosina quercina on live oak

CERCOSPORA LEAF BLIGHT OF PITTOSPORUM

ANTHRACNOSE FUNGI

Shows up mostly in summer. Treat at

budbreak.

DOWNY MILDEW OF ROSE

Cool weather fungus

POWDERY MILDEW FUNGI

TOP: on wild olive

RIGHT: on live oak

VIRUS DISEASES

Ring Spot Virus on rose.

NON-INFECTIOUS (NON-LIVING) CAUSES OF TREE

AND SHRUB DISFIGUREMENT OR

BLEMISHES, BUT NOT DEATH

HERBICIDE DRIFT

HERBICIDES (E.G. 2,4-D) -can drift onto foliage,

causing growth deformations

NUTRIENT DEFICIENCIES

IRON DEFICIENCY IN TEXAS IS USUALLY

RELATED TO HIGH PH SOILS

NUTRIENT DEFICIENCIES

Zinc Deficiency – less pronounced than iron def.

INSECTS AND PLANTS THAT DISFIGURE OR

BLEMISH SHOOTS AND LEAVES, BUT DO NO

CAUSE DIEBACK

INSECT GALLS

GALL MITE on live oak leaf. INSECT GALL on bark of

Texas ebony.

INSECT DAMAGE (FOLIAGE)

TRUE MISTLETOEParasite –

popular during Christmas, better than

Love Potion #9.

DODDER

Parasite like mistletoe.

OTHER, LIVING CAUSES OF TREE AND SHRUB DISFIGUREMENT OR

BLEMISHES, BUT NOT DEATH

FOLIAR DAMAGE

LEAF SPOT ON MAGNOLIA caused by algae.

SOOTY MOLD FUNGUS ON LIVE OAK. The fungus is usually

associated with insect honeydew.

LICHENS

BALL MOSS

FASCIATION

ON HIBISCUS ON MOUNTAIN LAURELFASCIATION is a flattening of the

stem, caused by a mutation in the plant