EB 1323E

Field Guide to

SweetCherryDiseasesin Washington

By Kenneth C. Eastwell, Gary A. Grove, Dennis A.Johnson, Gaylord I. Mink, Ralph S. Byther, Ronald P.Covey, Jr., and Robert Parker

Field Guide toSweet Cherry Diseases

in Washington

ContentsPage

BACTERIAL DISEASESBacterial Canker ....................................................2Crown Gall ...........................................................3

MYCOPLASMA DISEASEX-Disease ..............................................................4

FUNGAL DISEASESBrown Rot .............................................................5Cherry Leaf Curl ...................................................6Cherry Leaf Spot ...................................................7Coryneum Blight (Shot Hole)...............................7Phytophthora Crown and Root Rot .....................8Leucostoma Canker ..............................................9Powdery Mildew .................................................10Silver Leaf ............................................................11Verticillium Wilt .................................................12

VIRUS DISEASESCherry Decline (Cherry Leaf Roll Virus) ............13Cherry Mottle Leaf .............................................14Cherry Rasp Leaf .................................................15Cherry Twisted Leaf ............................................16Little Cherry .......................................................17Necrotic Rusty Mottle .........................................18Rugose Mosaic ....................................................19Rusty Mottle .......................................................20Sour Cherry Yellows............................................21

NONPARASITIC DISEASESDeep Suture ........................................................22Sweet Cherry Crinkle Leaf ..................................23Herbicide Disorders ............................................24Fasciation ............................................................25Fruit Doubling ....................................................25Gummosis ...........................................................26Shot Hole ............................................................26

By Kenneth C. Eastwell, Plant Pathologist,Gary G. Grove, Extension Plant Pathologist,Dennis A. Johnson, Extension PlantPathologist, and Gaylord I. Mink, PlantPathologist, WSU Irrigated AgricultureResearch and Extension Center, Prosser;Ralph S. Byther, Extension Plant Pathologist,WSU Western Washington Research andExtension Center, Puyallup; Ronald P. Covey,Jr., Plant Pathologist, WSU Tree FruitResearch Center, Wenatchee; and RobertParker, Extension Weed Scientist, WSUIrrigated Agriculture Research and ExtensionCenter, Prosser.

BACTERIAL CANKER

SymptomsThe classic symptom of this disease consists ofelongated cankers on trunk or scaffold limbs—most conspicuous during late winter or earlyspring. Canker surface sunken, dark purple in color(Fig. 1). Inner tissue of canker is orange to brown;narrow, brown streaks extend into healthy tissueabove and below canker. Gum is usually producedat canker margin (Fig. 2). Leaves droop, turn lightgreen to yellow in color and may die during hotweather. Cankers may eventually girdle limbs ortrunks. Limbs or entire tree may die. Dormant andsemi-dormant buds may blast, or wither, causinginfected trees to have a light bloom. Sometimesblossoms will wither suddenly, turn dark brown,and hang on the twig.

CauseRain or water splash, and pruning tools spread thebacterium, Pseudomonas syringae, which causes thedisease. Bacteria over-winter in active cankers, ininfected buds, and on the surface of infected andhealthy trees and weeds.

ControlPrune off cankered limbs well below visible canker.Avoid pruning in early spring and fall when bacte-ria are most active. Sterilize pruning tools beforepruning healthy trees.

Fig. 1. Surface ofbacterial cankerappears darkpurple.

Fig. 2. Gumexudes fromcanker margins.

2

CROWN GALL

SymptomsAn abnormal vegetative growth, or gall, appears onthe roots or trunk of the tree, generally below thesoil surface (Fig. 3). Round galls vary in size from1/4 inch to more than a foot in diameter. Largerrounded galls are somewhat irregular in shape.Young galls are soft and light tan, but becomehard, woody, and almost black with age. Thesurface of old galls may appear cracked or coveredwith small valleys. Galls are commonly found onlateral roots where they do little damage. Galls onthe below-ground portion of the trunk may causestunting and general tree decline.

CauseAgrobacterium tumefaciens, a bacterial agent, causescrown gall. The disease is spreadby nursery stock and cultivator tools.The bacterium is common and persistsin most agricultural soils.

ControlUse clean rootstocks. Avoid wounding the treetrunk or major roots at or below the soil surface.

Fig. 3. Stripped of soil, tree roots showrounded galls. L. W. Moore photo.

3

X-DISEASE

SymptomsLight pink and dark red fruit can occur on thesame spurs (Fig 4). Pink fruit tend to be small.Initially only a few spurs on one branch are af-fected. The infection eventually spreads through-out the tree. Terminals are slightly rosetted. Leavesof terminal may be slightly undersized and bronzeor rusty green in color. Stipules may be enlarged(Fig. 5). Trees on Mahaleb rootstock may collapseand die within one or two seasons.

CauseX-disease phytoplasma causes this disease, which isspread by leafhoppers, budding; and grafting. X-disease attacks peach, nectarine, sweet and sourcherries, and chokecherry. Symptomless hosts areflowering cherry and plum.

ControlUse disease-free rootstock and scion wood. Removediseased trees. Destroy chokecherry stands nearcommercial orchards.

4

Fig. 4. Pink, small fruitdevelop on same spur asdark red fruit inX-disease.

Fig. 5. Leaf stipules maybe enlarged.

BROWN ROT

SymptomsBlossom blight: Blossoms suddenly witherand turn brown (Fig. 6). During moist weather,masses of buff-colored spores cover surface ofdead blossoms (Fig. 7).

Fruit: Dark spots expand rapidly into a relativelyfirm rot of entire fruit. Tufts of gray to buff-coloredspores may cover surface of collapsed fruit. Fruitsmummify and may remain on tree.

Twigs: Fungus spreads from blighted blossomsand fruit to cause twig dieback and sunken browncankers on small branches. May produce gum(Fig. .6).

CauseOne of the most common disease problems oncherries in western Washington, brown rot iscaused by fungi Monilinia laxa and Moniliniafructicola. Wind and water splash spread thisdisease.

ControlWhen feasible, remove and destroy mummifiedfruit in tree and on ground. Prune out infectedtwigs in early summer. Prune tree to improve aircirculation. Avoid wounding fruit during harvest.Keep fruit cool.

5

Fig. 6. Brownrot blossomswither sud-denly; someproduce gum.

Fig. 7. Sporescover deadblossomsurface.

CHERRY LEAF CURL(witches'-broom)

SymptomsTufts of nonfruit-bearing branches develop, knownas witches'-broom (Fig. 8). During blossom, theseare leafy and lack blossoms. Leaves on affectedbranches are thickened, puckered, distorted, andwill appear off-color. A white fungal growth ap-pears on under-surfaces (Fig. 9). Diseased leavesmay also occur on normal, nonbroomed branches.

CauseTaphrina cerasi, a fungus, causes this disease, whichis spread by wind or water splash. Once infected, abranch will produce infected leaves each year.

ControlPrune out witches'-broom 12 inches below the lastvisible symptom.

6

Fig. 8. Witches'-broom branchesbear puckered,distorted leaves.

Fig. 9. Whitefungal growthappears onunderside of leaf.

CHERRY LEAF SPOT

SymptomsThis disease is very rare in eastern Washington. Numer-ous small purple spots develop on upper leaf surface(Fig. 10). Tissue in the center of the spot dies andsometimes falls out, leaving a shothole appearance. Inmoist weather, on leaf under-surface, a small mass ofcream-colored spores develop on these spots. Leavesturn prematurely yellow in the fall.

CauseCoccomyces hiemalis, a fungus, causes this disease.Spores are spread by wind or water splash. This diseasehas not occurred in eastern Washington. Shotholesymptoms resulting from this disease are uncommonin western Washington.

ControlWhere feasible, rake up and destroy fallen leaves. Sprayfungicide to protect new foliage at petal fall, shuck,and two weeks after shuck in wet areas. Because ofcontinuing tree growth, nursery stock may needadditional sprays.

SHOT HOLE (CORYNEUM BLIGHT)

SymptomsSmall areas of damage (lesions) on leaves are round oroval, and tan to purple in color(Fig. 11). These spotsoften fall from the leaf, leaving a shothole appearance.Some infected leaves yellow and drop from the tree.Sunken, dark brown to black areas develop on youngfruit. Damage may vary from small spots to half ormore of the fruit surface area (Fig. 11).

CauseA fungus, Wilsonomyces carpophilus, spreads by wind,rain, and water from sprinklers to cause this disease.

ControlPrune and destroy dead buds and cankered twigs ifpresent. 7

Fig. 10. Smallpurple spots coverupper leaf surface.

Fig. 11. Spotsappear on leavesand fruit. Sunkenareas may coverlarge portion offruit.

PHYTOPHTHORA CROWN ANDROOT ROT

SymptomsInitial symptoms of crown rot resemble those ofmechanical girdling (also rodent damage, winterinjury). Infected trees exhibit no terminal growth;leaves may be small and yellowed. These treesfrequently blossom profusely. Death may occurduring the year of initial infection or several yearslater. Smaller trees die more quickly. Usually con-fined to the rootstock, infected tissue also may befound on the main trunk. Production of a gummysubstance often is associated with the disease whenit appears on the trunk, making it difficult todistinguish the disease from bacterial canker. If theouter bark is removed, damaged areas marked withtan to black zones or bands may be seen (Fig. 12).These areas often expand vertically faster thanlaterally.

CauseSeveral Phytophthora species cause this disease oncherries. The fungi are spread by irrigation water,on implements, and on nursery stock.

ControlAll common rootstocks are susceptible to crownrot. Mahaleb is highly susceptible, and should beavoided in locations where the diseaseis present. Be sure to plant disease-free material.

8

Fig. 12. With bark removed, crown rot bands appear ontrunk. S. Mircetich photo.

LEUCOSTOMA (CYTOSPORA)CANKER

SymptomsDepressed areas on the bark of main leaders andbranches indicate Cytospora canker (Fig. 13).Canker margins on bark and discolored wood aresharp and distinct. Cankers often are perennial;young cankers usually produce gum at the margin.The black, pimplelike fruiting structures found inCytospora cankers of other crops seldom appear oncherry cankers.

CauseWind and rain spread the fungus Leucostomacinctum, which causes this disease.

ControlNo chemical control is available. Keep trees ingood vigor. Avoid slow-healing wounds. Cut outcankered wood well below visibly discolored areasof bark. Avoid directing irrigation sprinklers towardcankers.

9

Fig. 13. Depressed areas occur on branches or leaders. A. W.Helton photo.

POWDERY MILDEW

SymptomsGrayish white, powdery spots develop on theundersurface of leaves (Fig. 14). When infection issevere, leaves yellow and become distorted (Fig.15). Symptoms first develop on leaves of youngshoots where air circulation is poor. Powdery spotson fruit may become severe prior to any obviousleaf infections.

CauseWindblown spores of the fungus Podosphaeraclandestina cause this disease. Fruit symptomsfrequently are brought on by rains just beforeharvest.

ControlAvoid high rates of nitrogen fertilizers.

10

Fig 14. Powdery mildew spots appear on underside of leaf.

Fig. 15. Severely affected leaves become distorted.

SILVER LEAF

SymptomsUpper leaf surface appears silver in color. (Seeinfected leaves of apricot, left, and healthy leaves,right, in Fig. 16.) Affected leaves first appear onone or two small branches, then spread tobranches and limbs throughout the tree. Affectedleaves curl slightly at the margins, and turn ashenin color, sometimes with a tinge of green. Brancheslose vigor and eventually die. Thin, leathery fruit-ing bodies occur on dead branches and trunks,either flat against the host surface, or forming asmall extended shelf. The upper portion of thefruiting body is brown to purple, and hairy; theunder surface is purple to lilac and smooth intexture.

CauseWind and splashing water spread the disease-causing fungus Stereum purpureum. This fungusgrows saprophytically in dead trees, prunings,stumps, and posts. It enters living tree tissuesthrough surface wounds, such at those caused bypruning. Infected trees have recovered in areaswith warm summer temperatures.

ControlTake care not to injure trees unnecessarily. Destroyall prunings. Where disease is present, prune outaffected tree parts, and treat wounds and cutsurfaces.

11

Fig. 16. Silvery colored affected leaves contrast with healthy greenfoliage.

VERTICILLIUM WILT

SymptomsLeaves at the bottom of current season growth turnchrome yellow or reddish orange in mid-June tomid-July (Fig. 17). Leaf discoloration progresses upthe shoot during midsummer. Leaf drop follows(Fig. 18). By fall, only upper leaves remain. Diseasemay affect only a branch or one side of a tree (Figs.17, 18). Young trees usually are more severelyaffected. A brownish red discoloration occurs inwoody vascular tissue of some affected branches.

CauseThe disease is caused by the fungus Verticilliumdahliae, and spread through soil, surface andground water, nursery stock, and infested potatofeed lot manure. The fungus survives in the soil formany years, and may increase in soils infested withcertain weed species.

ControlAvoid planting in soil where susceptible crops(potato, tomato, pepper, raspberry, strawberry,peach, apricot) have been grown. Control weedsin orchards (e.g., phlox, geranium, shepherdspurse, lambs quarters, nightshade). Avoid excessiveirrigation, high nitrogen fertilization, severepruning, or other practices that promote succulentgrowth. Prune out dead branches; plant onlyhealthy trees.

12

Fig. 17. Lowerleaves of newgrowth turn colorwith Verticilliumwilt.

Fig. 18. Leaf dropfollows. Only partof a tree may beaffected.

CHERRY DECLINE(CHERRY LEAF ROLL VIRUS)

SymptomsCherry leafroll virus (CLRV) alone causes delayedbloom and excessive leaf senescence 2 to 3 weekspre-harvest. In the early stages, infected trees setabundant fruit but it is small and ripens late (3 to14 day delay in years with cool springs) relative touninfected trees. Over several seasons, fruit produc-tion declines dramatically and the canopy becomesopen and sparse. When CLRV occurs in combina-tion with either Prunus necrotic ringspot virus(PNRSV) or Prune dwarf virus (PDV), trees declinerapidly. Initially, only one or two scaffold limbsmay show symptoms (Fig. 19), but the symptomswill spread to the remainder of the tree.

CauseThis form of cherry tree decline is caused by CLRV,alone or in combination with PNRSV or PDV. Theseviruses are spread by use of infected budwood, andthrough root grafting in the orchard. These virusesare also pollen-borne and may be transmitted bypollen.

ControlRemove affected trees. Herbicide treatment offreshly cut stump of symptomatic trees may helpidentify root-grafted neighboring trees. Test treesfor virus before propagation.

Fig. 19. Die-back of fruit bearing shoots to the scaffold isevident in trees infected with CLRV. The rate of decline isaccelerated if the tree is also infected with PNRSV or PDV.Symptoms may only appear in one limb initially.

Fig. 20. Abundant leaf dropbefore harvest and small,late-ripening fruit areindications that CLRV maybe present.

Fig. 21. Whitish veins with darkgreen areas along the midrib on thelower surface and enlarged, yellow-green veins on the upper surface areevident on some leaves that emergedearly in the season.

13

CHERRY MOTTLE LEAF

SymptomsIrregular light green to yellow mottling appears onexpanded leaves (Fig. 22), which become distortedand puckered (Fig. 23). Fruit set is reduced; fruitmay be small, ripen late, and lack flavor. Lack ofterminal growth and shortening of space betweenleaf nodes makes infected trees appear rosetted.

CauseCherry mottle leaf virus causes this disease, whichis spread by budding or grafting, and by the micro-scopic scale mite, Eriophyes inaequalis. Trees on theorchard's edge usually are infected first. CultivarsBing and Napoleon (Royal Ann) are severely af-fected. Black Tartarian, Van, Chinook, Lambert,Rainier, and Sam are symptomless carriers.

ControlRemove infected trees to prevent new infections.Destroy stands of wild cherry near commercialorchards. Use virus free nursery stock and scionwood.

14

Fig. 22. Irregularmottling onleaves.

Fig. 23. Cherrymottle leaf alsocauses distortionand puckering.

CHERRY RASP LEAF

SymptomsProminent lumps or outgrowths form on theunderside of leaves between lateral veins and alongthe midrib (Fig. 24). Leaf narrowing, folding anddistortion may occur; the upper leaf surface turnsrough and pebbly in texture. Symptoms firstappear on lower leaves in newly infected trees.Trees develop an open, bare appearance (Fig. 25) asspurs and lower branches die.

CauseThe dagger nematode, Xiphenema americanum, andgrafting spread cherry rasp leaf virus, which causesthis disease. Spread within a tree or orchard isusually slow. The virus does not affect pears, butcauses flat apple on apple trees.

ControlRemove infected trees and other trees close by.Fumigate soil with a nematicide before plantingcherry or apple trees. Use virus free nursery stockand scion wood.

15

Fig. 24. Out-growths form onunderside of leaf,between veins.

Fig. 25. As spursand lowerbranches die,trees appearopen and bare.

CHERRY TWISTED LEAF

SymptomsAbrupt kink appears in leaf midrib or petiole(Fig. 26). Leaves twist, curling down and to theside; leaves remain small, or developasymmetrically. Sections of tissue die on theunderside of the midrib and lateral veins.Shortened areas between spur joints cause spursto bunch together.

CauseCherry twisted leaf virus causes this disease, whichis spread through budding and grafting in or-chards. How disease spreads in fields is unknown.The cultivar, Bing, is the most severely affected.Napoleon, Rainier, and Van may also show symp-toms, which can be severe. Most other cultivars donot show symptoms when infected.

ControlTo prevent spread, remove infected trees as soon assymptoms appear. Destroy choke-cherry standsnear commercial orchards.

16

Fig. 26. Affected by a kink in petiole or leafmidrib, leaves curl down and to one side.

LITTLE CHERRY

SymptomsDelayed fruit ripening. Fruit on the same branchvary widely in maturity. At harvest, fruit are some-what pointed or angular, small and medium red topinkish red, and bitter in taste. Compare infectedfruit, left, with healthy fruit, right, in Fig. 27. Somevarieties develop reddish purple leaves in early fall(Fig. 28).

CauseThis disease is caused by either of two Little Cherryviruses. One of them can be transmitted by applemealybug. Both are spread by budding and graft-ing. Several small fruited pollinating varieties, sourcherry, and ornamental flowering cherries can besymptomless carriers of the virus. Sweet cherry,sour cherry, and ornamental flowering cherries arehosts of the virus.

ControlUse virus free planting stock. Destroy infected treesand remove suckers from nearby ornamentalflowering cherry trees.

17

Fig. 27. Affectedfruit, at left,ripens slowlyand is bitter tothe taste.

Fig. 28. Leaveson some affectedvarieties turn red-purple in fall.

NECROTIC RUSTY MOTTLE

SymptomsAngular spots or large areas of dead tissue appearon leaves 3 to 6 weeks after bloom (Fig. 29). Spot-ted leaves develop shotholes. Severely decayedleaves drop. Before harvest, remaining leaves turnmottled yellow, with green bands or islands. Budson terminal shoots fail to open or swell; eventuallythey die. Leaves are earlier than normal. Barksymptoms consist of shallow areas of decay withgum blisters or deep gum pockets.

CauseNecrotic rusty mottle virus causes this disease,which spreads through infected bud-wood. How itspreads in the orchard is unknown. Cool, latesprings promote earlier and more severe symp-toms. Leaf symptoms usually are not noticeableduring summer and fall where temperatures re-main high.

ControlRemove affected trees. Use virus free nursery stockand scion wood. Several pollinating cultivars aresymptomless hosts. Test for virus before takingbudwood for propagation.

18

Fig. 29. Spots on large areas of leaf tissue die about a monthafter bloom. H.R. Cameron photo.

RUGOSE MOSAIC

SymptomsAcute infection: Brown dead tissue spots developsuddenly on leaves of one limb or one side of the treein late April to mid-May. Dead tissues drop out, givingleaves a tattered or lacelike appearance (Fig. 30).Sometimes fruit symptoms do not appear the first year.Fruit may ripen unevenly.

Chronic infection: Leaves appear with twisted tips.Small outgrowths of dark green tissue may developalong the midrib on lower leaf surface (Fig. 31). Termi-nal growth and elongation between nodes or joints isoften reduced. Severe strains cause uneven maturationof fruit (Fig. 32). Green fruit may be cylindrical.

CauseGrafting, seed, or pollen from diseased trees spread strainsof Prunus necrotic ringspot virus, which causes thisdisease. Mild forms show leaf symptoms, with little or noeffect on fruit. Fruit ripening may be delayed 7 to 10 dayswith no leaf symptoms present. Severe forms exhibitblossom blast or withering, severe leaf deformity, pro-nounced leaf curl, reduced shoot growth, fruit ripeningdelayed 10 or more days, and reduced tree vigor (Fig. 33).

ControlRemove infected trees before bloom. Use virus freeplanting stock and scion wood. Use the serologicaltest, ELISA, to detect symptomless, infected trees.

19

Fig. 30. Leavesappear lacelikeor tattered inMay.

Fig. 31.Outgrowths oftissue growalong midrib.

Fig. 32. Fruitmatures unevenly.

Fig. 33. Tree at left of photo shows reduced vigor.

RUSTY MOTTLE

SymptomsOlder leaves turn a mottled yellow midway be-tween blossom and harvest (Fig. 34). Leaves showvariable yellow rings and patterns (Fig. 35). Af-fected leaves turn abruptly to yellow and red fallcoloration (Fig. 35). Symptoms appear first andmost intensely on leaves in the lower center of thetree. Two to three weeks before harvest, rusty-yellow colored leaves drop, taking 30 to 70 percentof a tree's leaves. Infected trees decline in vigor;main limbs die back. Fruit ripening may be delayedon severely affected trees.

CauseRusty mottle virus causes this disease, which isspread by infected budwood.

ControlRemove diseased orchard trees when they are firstdiscovered. Plant virus free nursery trees.

20

Fig. 34. Olderleaves turn amottled yellow.

Fig. 35. Yellowrings and patternsare distinctive. Fallcoloring appearsearly and abruptly.

PRUNE DWARF VIRUS

SymptomsSour cherry: The disease caused by Prune DwarfVirus is called Sour Cherry Yellows. Leaves developstriking pale green to yellow areas 3 to 4 weeksafter petal fall. Later, entire leaf turns yellow exceptfor green along larger veins (Fig. 36). Leaves soondrop. Growth is willowy, and the number of fruit isreduced.

Sweet cherry: May show yellow rings, mottling orshotholes on leaves, or may show no symptoms atall. Many strains cause no acute effects, whileothers induce the formation of blindwood.

Symptom development requires warm days andcool nights. Infected trees may not show symp-toms some years. Trees grown in warm climatesmay never show symptoms.

CausePrune dwarf virus is spread by budding, grafting,seeds, and pollen.

ControlEstablish sour cherry orchards with virus free treesisolated from older orchards. Rogue out and re-plant sour cherry trees in orchards 1 to 5 years old.Rogue out and do not replant trees in orchards 6 to10 years old. Older orchards do not benefit fromrouging out trees.

21

Fig. 36. Pale green areas appear a few weeksafter petal fall on sour cherries.

DEEP SUTURE

SymptomsPronounced depressions along fruit suture. Fruitapex is usually rounded. Leaves are often narrow,longer than normal, and appear pebbly on uppersurface. Contrast affected fruit and leaf, left, withhealthy specimens, right, in Fig. 37. Leaf marginshave few or no serrations. A slight yellowing mayoccur between veins in late spring. Severity ofsymptoms may vary from year to year.

CauseThis disease is caused by a genetic abnormality.Affected limbs often develop on healthy trees.Trees propagated from trees with deep suture willbe affected.

ControlUse budwood from healthy trees. Remove affectedyoung trees or graft them over with healthy scions.Remove affected branches in older trees.

22

Fig. 37. Fruit indentation and distorted leafof deep suture appear at left.

SWEET CHERRY CRINKLE LEAF

SymptomsDistorted leaves have indented and abnormallyserrated margins. Some leaf tips and bases accentu-ated. Light green to greenish-yellow mottling ondark green leaves (Fig. 38). Blossoms frequentlydefective and smaller than normal. Fruit is small,pointed, and may have raised suture (Fig. 39). Abranch, a few branches, or the whole tree mayshow symptoms. Severity of symptoms varies fromyear to year.

CauseHealthy trees often develop affected limbs fromthis genetic abnormality. It is not spread by anyagent. Trees propagated from affected limbs willdevelop the disorder.

ControlUse budwood from healthy trees. Remove affectedyoung trees or graft them over with healthy scions.Remove affected branches in older trees.

23

Fig. 38. Leaves abnormally serrated, with some mottling.

Fig. 39. Fruit is small and pointed, often with raised sutures.

SIMAZINE (Princep) INJURY

SymptomsYellowing of the leaf tissue between the veins ischaracteristic of simazine injury. In a severe injury,leaf dies from the tip and margins inward. Thesesymptoms are typical of damage from other herbi-cides in the triazine family (Fig. 40).

CauseHerbicide damage.

DICHLOBENIL(Casoron) INJURY

SymptomsYellowing of the leaf margin creates a characteristichalo effect. Yellowing develops between the veinsas symptoms progress. Leaves die and tree is defoli-ated in severe cases (Fig. 41, symptoms on plum).

CauseHerbicide damage.

24

Fig. 40.Characteristictissue yellowingfollowssimazineinjury.

Fig. 41. Haloeffect yellowingproduced bydichlobenilinjury.

FASCIATION

SymptomsStem tissue joins side by side to form a flattenedlayer rather than a normal stem. The stem layer(Fig. 42) may curl and branch to form curiousshapes. Normal growth may occur the followingyear, or fasciation may continue.

CauseNo cause is known for fasciation, which appears tobe a noncontagious growth irregularity. Sub-lethalexposure to some herbicides and some bacteria areassociated with this disorder.

ControlPrune out affected stems.

FRUIT DOUBLING (TWINNING)

SymptomsDouble pistils form in the flower, resulting in twoattached fruits (Fig. 43), or an attached fruit andsmaller spur.

CauseHigh summer temperatures during flower buddifferentiation cause this physiological abnormal-ity the following year.

ControlCultivars differ in their susceptibility to fruitdoubling. Bing, Royal Ann, Early Burlat, and Vanall have a high doubling potential. Select cultivarsthat do not have a high fruit doubling potential forwarm locations.

Fig. 42. Stemtissue joinsabnormally, curlsto odd shapes.

Fig. 43. Hightemperatures asbud tissuesdevelop will causefruit doubling thefollowing season.P.R. Fridlundphoto.

25

GUMMOSIS

SymptomsClear-to-amber gum exudes from bark (Fig. 44)during the dormant season-November to March.Heavy flow may drip onto the ground. The cleargum is seldom associated with a disease problem.Bacterial canker is an exception. Crotch gummosisand other nondisease gum formations are oftenmisdiagnosed as bacterial canker. When a disease isresponsible for gum formation, dead tissue (sunkencanker, brown cambium, dead twigs, etc.) is usuallypresent.

CauseNarrow-angle crotches or wounds from pruning,disease or insects cause formation of gum.

ControlNone necessary unless disease is present. Seebacterial canker, brown rot, Coryneum blight andnecrotic rusty mottle.

SHOT HOLE

SymptomsSpots and blotches of varying sizes, shapes, andcolors develop on leaves. Affected tissues turnbrown, die, and fall out, leaving holes in the leaves(Fig. 45). Rely on other symptoms to diagnosedisease or injury.

CauseA number of viral diseases, fungus leaf spot, nutri-ent imbalance, chemical toxicity, and unknownphysiological stresses can cause a shot hole appear-ance.

ControlSee viral diseases and fungal leaf spot for recom-mendations. Try to determine exact cause beforeworking on problem.

26

Fig. 44. Withoutother symptomspresent, dormantseason gum flowdoes not indicatedisease.

Fig. 45. A shot holeappearance occurswhen dead tissuefalls from leaves.

NORFLURAZON (Solicam)INJURY

SymptomsA whitish-yellow discoloration along the veins witha faint pink to purple cast around the edge is char-acteristic. Bark on new growth may split and appearbleached (Fig. 46). Leaves die in severe cases.

CauseHerbicide damage.

27

Fig. 46. Bark splits, appears bleached on new growth.

2,4-D (Various Trade Names)INJURY

SymptomsLeaves deformed, may be cupped. New leaves maydevelop parallel veins. Symptoms appear first onleaves that were expanding at time of exposure to2,4-D. See example of symptoms on apricot, Fig. 47.

CauseHerbicide damage.

GLYPHOSATE(Roundup, Touchdown, Rascal)INJURY

SymptomsNew leaves do not expand and may appear tightlyrolled (commonly referred to as needle leaf). Seesymptoms on apple (Fig. 48). Proliferation of budsand stunted shoots, producing a witches'-broomeffect (Fig. 49, symptoms on apple). Internodesmay be shortened on new growth.

CauseHerbicide damage. Exposure to glyphosate sprayedthe previous season, or very early before newgrowth starts for current season.

28

Fig. 47. Leaves expanding when 2,4-D was applied cup orappear deformed.

Fig. 48. New leaves roll tightly, fail to expand.

Fig. 49. Buds and stunted shoots produce broom on apple.

PARAQUAT (Gramoxone Max,Cyclone) INJURY

SymptomsYellow spots appear where spray droplets touchedleaves, sometimes within hours of direct contactwith herbicide. Yellowed tissue dies and may fallfrom leaf (Fig. 50).

CauseHerbicide damage. Spray droplets contacting greentissue.

29

Fig. 50. Yellow spots appear on leaves within hours of directcontact with herbicide.

Some of the diseases in this bulletin haveregistered chemical controls. For home-owner chemical control recommendationsplease consult the Hortsense Website at:http://pep.wsu.edu/hortsense/. For com-mercial chemical control recommenda-tions please consult the most recent CropProtection Guide for Tree Fruits in Wash-ington (EB0419). Hard copies can beobtained from your local county exten-sion office, or through the WSU Bulletinsoffice (phone 1-800-723-1763 or emailbulletin@wsu.edu). Electronic copy isavailable at: http://cru84.cahe.wsu.edu/cgi-bin/pubs/EB0419.html.

Use pesticides with care. Apply them onlyto plants, animals or sites listed on thelabel. When mixing and applying pesti-cides, follow all label precautions toprotect yourself and others around you. Itis a violation of the law to disregard labeldirections. If pesticides are spilled on skinor clothing, remove clothing and washskin thoroughly. Store pesticides in theiroriginal containers and keep them out ofthe reach of children, pets, and livestock.

College of Agricultural, Human, and NaturalResource Sciences

Copyright 2005 Washington State University

WSU Extension bulletins contain materialwritten and produced for public distribution.You may reprint written material, provided youdo not use it to endorse a commercial product.Alternate formats of our educational materialsare available upon request for persons withdisabilities. Please contact the InformationDepartment, College of Agricultural, Human,and Natural Resource Sciences, WashingtonState University for more information.

You may order copies of this and otherpublications from the WSU Bulletin office,1-800-723-1763, or online http://pubs.wsu.edu

Issued by Washington State University Extensionand the U.S. Department of Agriculture infurtherance of the Acts of May 8 and June 30,1914. Extension programs and policies areconsistent with federal and state laws andregulations on nondiscrimination regardingrace, sex, religion, age, color, creed, nationalor ethnic origin; physical, mental or sensorydisability; marital status, sexual orientation,and status as a Vietnam-era or disabled veteran.Evidence of noncompliance may be reportedthrough your local Extension office. Tradenames have been used to simplify information;no endorsement is intended. Published Novem-ber 2005. Subject code 238. EB1323E.