(gardening) Roses in the Garden and Landscape - Diseases and.pdf - Ogrodnictwo - ang - bibiariel

R OSES IN THE G ARDEN AND L ANDSCAPE :

D ISEASES AND A BIOTIC D ISORDERS

Integrated Pest Management for Home Gardeners and Landscape Professionals

A variety of plant pathogens may attack

roses from time to time. By far the most

common problem in California is pow-

dery mildew, but a number of other

diseases including rust, black spot,

botrytis, downy mildew, and anthrac-

nose may cause problems where moist

conditions prevail. To limit problems

with pathogens, choose varieties and

irrigation practices carefully, promote

air circulation through bushes with

careful pruning and placement of

plants, and remove severely infested

material promptly. Although some rose

enthusiasts consider regular application

of fungicides a necessary component of

rose culture, many others are able to

produce high quality blooms with little

to no use of synthetic fungicides, espe-

cially in California’s dry interior valleys.

during midday may limit the disease by

disrupting the daily spore-release cycle,

yet allows time for foliage

to dry. The pathogen

requires living

tissue in order to

survive, so prun-

ing, collecting, and

disposing of leaves

during the dor-

mant season can

limit infestations,

but may not entirely

eradicate them; airborne spores from

other locations can provide fresh inocu-

lation. Rose varieties vary greatly in

resistance; landscape (shrub) rose vari-

eties are among the most resistant.

Glossy-foliaged varieties of hybrid teas

and grandifloras often have good resis-

tance to powdery mildew as well.

Plants grown in sunny locations with

good air circulation are less likely to

have serious problems. Fungicides such

as triforine (Funginex) are available but

generally must be applied to prevent

rather than eradicate infections, so tim-

ing is critical and repeat applications

may be necessary. In addition to syn-

thetic fungicides, sodium bicarbonate

(baking soda) in combination with hor-

ticultural oils has been shown to control

powdery mildew of roses when used in

a solution of about 4 teaspoons of bak-

ing soda per gallon of water with a 1%

solution (or about 1 oz) of narrow range

oil. The best time to apply this solution

to avoid problems with phytotoxicity is

during cool weather. Sodium bicarbon-

ate is deleterious to maintenance of soil

pH and soil structure and may leave

white foliar deposits, so numerous ap-

plications with resulting runoff should

be avoided. Commercial fungicides

containing potassium bicarbonate

(Kaligreen, Remedy) are also available.

Commercial formulations of neem oil

will also control powdery mildew.

Downy mildew, caused by the fungus

Peronospora sparsa, requires moist, hu-

mid conditions. Interveinal, angular

purple, red, or brown spots appear on

leaves, followed by leaf yellowing and

abscission. Fruiting bodies of the fun-

gus occasionally may be

observed on the under-

sides of leaves.

Downy mildew can

be reduced by in-

creasing air circula-

tion through

pruning and avoid-

ing frequent over-

head irrigation.

Control with fungi-

cides is very diffi-

cult; environmental management is

much more likely to be effective.

Downy mildew is most likely to cause

problems in coastal areas of California.

white areas:

powdery mildew

dark areas:

downy mildew

In addition to diseases caused by bacte-

rial, fungal, and viral pathogens, roses

may display symptoms similar to those

that are the result of chemical toxicities,

mineral deficiencies, or environmental

problems. Such problems are termed

abiotic disorders and can often be cor-

rected by changing environmental con-

ditions.

Rust, caused by the fungus Phragmi-

dium disciflorum, is favored by cool,

moist weather such as that found in

coastal areas of California and may also

be a problem inland

during wet years. In-

fected plants have

small orange pus-

tules on leaf under-

sides; upper sides of

leaves may discolor

and leaves may

drop. Avoid over-

head watering and prune back severely

affected canes. During the winter collect

and dispose of leaves remaining on the

LEAF AND SHOOT DISEASES

AND DISORDERS

Powdery mildew, caused by the fungus

Sphaerotheca pannosa var. rosae, is recog-

nized by its white to gray powdery

growth on leaves, shoots, sepals, buds,

and occasionally on petals. Leaves may

distort and drop. Powdery mildew does

not require free water on the plant sur-

faces to develop and is active during

California’s warm, dry summers. Over-

head sprinkling (irrigation or washing)

P EST N OTES

Publication 7463

University of California

Agriculture and Natural Resources

Revised October 2003

October 2003

Roses: Diseases and Abiotic Disorders

plants as well as those that have fallen

off. Low levels of damage can be toler-

ated without significant losses. Preven-

tive applications of fungicides can be

used, but frequent applications may be

needed and may not be justified in gar-

den or landscape situations.

available. Hybrid teas and old-fash-

ioned climbing and rambler roses are

most often affected.

Herbicide damage may be manifest in a

variety of symptoms, which include

cupped, curled, or yellowed leaves,

small leaves, or death of the entire

plant. The herbicide class and the dos-

age to the plant determine which symp-

toms appear and their severity. Injury

from glyphosate (e.g., Roundup) is

relatively common. Damage symptoms

caused by this herbicide may not ap-

pear during the season of application,

especially if application is made in au-

tumn, but may appear the following

spring as a proliferation of small shoots

and leaves from buds. The plant will

outgrow the injury if the dosage was

not too high.

Viruses, including rose mosaic virus

and others, may infect rose plants al-

though damage may be mostly cos-

metic with little reduction in plant

vigor. Mosaic viruses can cause a vari-

ety of yellow zig-zagging patterns,

splotching, or vein clearing. Symptoms

are most pronounced in spring but may

disappear almost completely during

summer. Rose leaf curl virus causes

leaves to curl downward and die, often

with some overall yellowing. There is

no known treatment for viruses. Toler-

ate or destroy infected plants and ob-

tain virus-free stock for future

plantings. Because mosaic viruses are

not vectored by insects but rather are

spread through propagation of plant

parts, obtaining clean planting stock is

the primary management strategy.

Black spot, caused by the fungus

Diplocarpon rosae, produces black spots

with feathery or fibrous

margins on the upper

surfaces of leaves and

stems. Small black

fruiting bodies are

often present in spots on

the upper sides of leaves.

There is no fungal growth on

the undersides of leaves.

SYMPTOMS ON FLOWER

PETALS AND BUDS

The fungus requires free water to repro-

duce and grow, so leaves should not be

allowed to remain wet for more than 7

hours. (When hosing off aphids, do it in

the morning so leaves have a chance to

dry by midday.) Provide good air circu-

lation around bushes. Remove fallen

leaves and other infested material and

prune out infected stems during the

dormant season. Black spot is usually

not a problem in most of California.

Miniature roses are more susceptible

than other types, although a few variet-

ies are reliably resistant to all strains of

black spot. If required, fungicides (such

as chlorothalonil or triforine) can be

applied preventively. A combination of

sodium bicarbonate or potassium bicar-

bonate plus horticultural oil (as dis-

cussed above under “Powdery

mildew”) or neem oil has also been

shown to be effective in reducing black

spot.

Botrytis blight, caused by the fungus

Botrytis cinerea, is favored by high

humidity. Affected plants

have spotted flower petals

and buds that fail to open,

often with woolly gray

fungal spores on decaying

tissue. Twigs die back and

large, diffuse, targetlike

splotches form on canes. Reduce

humidity around plants by modi-

fying irrigation, pruning, and

reducing ground cover. Remove and

dispose of fallen leaves and petals.

Prune out infested canes, buds, and

flowers. Botrytis blight is usually a

problem only during spring and fall in

most of California and during summer

along coastal areas when the climate is

cool and foggy.

Nutrient deficiencies cause specific

symptoms. Nitrogen deficiency causes

leaves to yellow and older leaves to

drop. Because many California soils

have low percentages of organic matter,

the nitrogen reserve is typically low

and this nutrient should be added as

inorganic fertilizer or from organic

sources. Micronutrient deficiencies,

especially iron and zinc, appear as

interveinal chlorosis of new leaves.

These elements may be deficient be-

cause soils are too wet or too alkaline,

or because the soil type, such as sandy

loam, is low in micronutrient content.

Because inorganic forms of iron and

zinc form insoluble precipitates in alka-

line soils, iron and zinc may be applied

directly to foliage. Iron and zinc in a

chelated form may be applied to either

soil or foliage.

CANKERS OR GROWTHS

ON CANES

Anthracnose, caused by the fungus

Sphaceloma rosarum, results in leaf spots.

When first formed, spots are red or

sometimes brown to purple. Later the

centers turn gray or

white and have a dark

red margin. Fruiting

bodies may appear in

the middle of the spot

and the lesion may

fall out creating a shot

hole symptom. No infor-

mation on management is

Botrytis blight (see above).

Nutrient excesses may limit rose

growth if the total salt level becomes

too high. The results are a lack of vigor

and short shoots, although no definitive

leaf symptoms may occur. A few nutri-

ents cause specific toxicities. Boron may

be found in excess in some California

soils and will cause stunting of plants,

chlorosis, and marginal necrosis of the

newest leaves.

Stem cankers and diebac k can be

caused by a number of different fungi.

Cankers are brown, often with gray

centers or small, black, spore-producing

structures on dead tissue. Provide

proper care to keep plants vigorous.

Prune out diseased or dead tissue, mak-

ing cuts at an angle in healthy tissue

just above a node. Avoid wounding

canes. Cankers often develop after cold

2 ◆

◆

October 2003

Roses: Diseases and Abiotic Disorders

temperature injury, so early spring

pruning may not effectively eliminate

them if late frosts occur, and additional

late spring pruning may be necessary.

woody plants including fruit trees, or-

namentals, and roses as well as some

herbaceous plants including chrysan-

themums and daisies. Crown gall bacte-

ria invade tissue after

wounding. Galls, in the

form of large, distorted

tissue growth, form at

the base of the cane or

sometimes on roots or

farther up on stems.

Infected canes can be

stunted and discolored.

Do not plant susceptible

plants in infested soil or near infected

plants. Purchase and plant only high

quality planting stock.

A Nonpesticidal Method for Controlling

Diseases, Nematodes, and Weeds. Oak-

land: Univ. Calif. Agric. Nat. Res. Publ.

21377.

Winter injury from cold temperatures

results in dead or dying flowers, twigs,

and stems. Roses may be protected over

the winter in cold mountain areas with

a thick layer of leaf mulch. Winter in-

jury may be followed by stem canker

diseases caused by pathogens that

move into injured tissue.

Flint, M. L., and J. F. Karlik. Sept. 1999.

Pest Notes: Roses in the Garden and

Landscape—Insect and Mite Pests and

Beneficials. Oakland: Univ. Calif. Agric.

Nat. Res. Publ. 7466. Also available

online at www.ipm.ucdavis.edu.

Horst, R. K. 1983. Compendium of Rose

Diseases. St. Paul: APS Press.

Sunburn appears as blackened areas,

especially on the south and west sides

of canes. Sunburn is caused by exces-

sive temperatures on rose canes, usu-

ally as an indirect result of defoliation

caused by drought stress or spider mite

pressure. Reflected heat from masonry,

vinyl siding, or rock mulch may also

cause canes to sunburn.

Karlik, J. F. July 2003. Pest Notes: Roses

in the Garden and Landscape—Cultural

Practices and Weed Control. Oakland:

Univ. Calif. Div. Agric. Nat. Res.

Publ. 7465. Also available online at

www.ipm.ucdavis.edu.

REFERENCES

Dreistadt, S. H. 1994. Pests of Landscape

Trees and Shrubs. Oakland: Univ. Calif.

Agric. Nat. Res. Publ. 3359.

Crown gall, caused by the bacterium

Agrobacterium tumefaciens, affects many

Elmore, C. L., J. J. Stapleton, C. E. Bell,

and J. DeVay. 1997. Soil Solarization:

For more information contact the University

of California Cooperative Extension or agri-

cultural commissioner’s office in your coun-

ty. See your phone book for addresses and

phone numbers.

AUTHOR: J. F. Karlik

TECHNICAL EDITOR: M. L. Flint

DESIGN, COORDINATION, AND

PRODUCTION: M. Brush

ILLUSTRATIONS: Karen Ling.

Produced by IPM Education and Publica-

tions, UC Statewide IPM Program, Universi-

ty of California, Davis, CA 95616-8620

WARNING ON THE USE OF CHEMICALS

Pesticides are poisonous. Always read and carefully follow all precautions and safety recommendations

given on the container label. Store all chemicals in the original labeled containers in a locked cabinet or shed,

away from food or feeds, and out of the reach of children, unauthorized persons, pets, and livestock.

Confine chemicals to the property being treated. Avoid drift onto neighboring properties, especially

gardens containing fruits or vegetables ready to be picked.

Do not place containers containing pesticide in the trash nor pour pesticides down sink or toilet. Either

use the pesticide according to the label or take unwanted pesticides to a Household Hazardous Waste

Collection site. Contact your county agricultural commissioner for additional information on safe container

disposal and for the location of the Household Hazardous Waste Collection site nearest you. Dispose of

empty containers by following label directions. Never reuse or burn the containers or dispose of them in such

a manner that they may contaminate water supplies or natural waterways.

This Pest Note is available on the World

Wide Web (http://www.ipm.ucdavis.edu)

This publication has been anonymously peer re-

viewed for technical accuracy by University of Cal-

ifornia scientists and other qualified professionals.

This review process was managed by the ANR

Associate Editor for Pest Management.

To simplify information, trade names of products

have been used. No endorsement of named products

is intended, nor is criticism implied of similar products

that are not mentioned.

This material is partially based upon work

supported by the Extension Service, U.S. Department

of Agriculture, under special project Section 3(d),

Integrated Pest Management.

The University of California prohibits discrimination against or harassment of any person employed by or

seeking employment with the University on the basis of race, color, national origin, religion, sex, physical

or mental disability, medical condition (cancer-related or genetic characteristics), ancestry, marital status,

age, sexual orientation, citizenship, or status as a covered veteran (covered veterans are special disabled

veterans, recently separated veterans, Vietnam-era veterans, or any other veterans who served on active

duty during a war or in a campaign or expedition for which a campaign badge has been authorized).

University policy is intended to be consistent with the provisions of applicable State and Federal laws.

Inquiries regarding the University’s equal employment opportunity policies may be directed to the

Affirmative Action/Staff Personnel Services Director, University of California, Agriculture and Natural

Resources, 300 Lakeside Drive, 6 th Floor, Oakland, CA 94612-3550, (510) 987-0096.

3 ◆

◆

(gardening) Roses in the Garden and Landscape - Diseases and.pdf

Plik z chomika:

Inne pliki z tego folderu:

Inne foldery tego chomika: