abstract on Rose diseases

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Disease Control

Multi-Purpose Fungicide Daconil 2787® Plant Disease Control

This product is widely used for broad spectrum disease control on lawns,

ornamentals and listed

fruits and vegetables. Controls many foliar diseases such as: rust, black spot, leaf

spot, blights,

anthracnose and powdery mildew as listed on the label. Also controls conifer

diseases and lawn

diseases such as brown patch, red thread, rust and dollar spot. Can be mixed with

insecticides as

specified on the label to make a multi-purpose spray.

WHAT IS POWDERY MILDEW?

Powdery Mildew looks like white fuzzy powder that accumulates on leaves and stems

predominantly in spring, and again to a lesser degree in fall. It is actually a fungus that

is spread by

millions of microscopic spores. It imbeds itself into tender new growth and feeds on

the sap of the

plant. By the time the naked eye can see the white ‘powder,’ it has already invaded

the plant tissue

and is feeding and reproducing at a rapid pace. As it spreads itself on the surface, it

eventually kills

the cells of the plant leaf, leaving the leaf rippled and curled.

Mildew spores are everywhere in the garden – in the air, the soil, on debris and on

plant surfaces –

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ready to sprout when the environment is just right. Warm days (50?-80?F) and cool

nights with

elevated humidity and resultant dew provide ideal conditions. Though humidity

promotes fungal

growth, it grows on DRY plant surfaces, unlike blackspot which requires immersion in

water for

about seven hours in order for infection to take place.

Tender new growth needs a chance to ‘harden’ and develop its waxy coating that

provides somewhat

of a barrier to fungal growth. Therefore, the rosarian must provide protection for new

spring growth

on a weekly basis.

CONTROLLING POWDERY MILDEW

Controlling mildew doesn’t have to mean spraying the planet into oblivion. It includes

plant genetics,

cultural practices and something as simple as WATER.

GENETICS: While rose hybridizers are chastised for breeding OUT fragrance, what

they are trying

to accomplish is breeding IN disease resistance. For scientific reasons beyond

explanation here, rose

genes don’t contain both features – it’s one or the other. Hence, you can expect either

fragrant roses

with little disease resistance, or clean plants with little fragrance. Plants with glossy or

waxy leaves

are less susceptible to mildew, as the leaf surface is harder for spores to penetrate.

Rugosas naturally

possess a high degree of disease and pest resistance. Where mildew is a constant

problem, the choice

in plantings can help prevent the need for extensive maintenance.

CULTURAL PRACTICE: Planting bushes with sufficient space between them and

away from walls

and fences will provide good air circulation which reduces the chances for mildew.

The annual pruning event plays a major role in disease prevention. Stripping leaves

from the bush at

pruning time, and cleaning up debris in the garden contribute to a cleaner

environment. Dormant

spraying will at least wipe out last year’s spores, leaving only this year’s to contend

with. Keeping the

centers of the bush open during the growing season will aid air circulation.

Avoid the use of other plant materials with high mildew susceptibility, such as

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euonymus and

tuberous begonias. Apply a thick layer of mulch in early spring to cover spores in the

soil that may

have wintered over. WATER is perhaps the most misconceived element surrounding

powdery

mildew. Many gardeners still subscribe to the belief that you should NEVER get rose

foliage wet.

On the contrary, a high-pressure spray of water will remove mildew spores that

haven’t imbedded

themselves yet, and prevent them from germinating. Higher incidence of mildew

during periods of

rain is caused by the moisture in the air and soil – increasing the humidity that

promotes mildew –

not by water on the leaves. Similarly, watering early in the day will allow the soil

surface to dry out

a bit before the cool night temperatures arrive, reducing humidity from moist soil.

PREVENTION IS THE ONLY CURE

Once powdery mildew is apparent to the eye, it can’t be eradicated. It simply must be

prevented.

Prevention is achieved by coating the plant tissue with something that provides a

barrier to prevent

fungus from gaining a foothold and invading the plant tissue. Growth is so rapid in

spring that the

leaves unfolding THIS week won’t be protected by what you sprayed LAST week.

This is the reason

you find application schedules of every 7-10 days on most fungicides, and the reason

you must

follow that schedule.

The choice of what the SOMEthing is that you choose to spray is widening.

Fungicides are the most

widely used because they are chemically formulated to specifically combat fungus

diseases. Recent

reports of non- toxic, environmentally-friendly products such as baking soda and

anti-transpirants

are proving very encouraging also.

FUNGICIDES are any of a number of chemicals labeled to combat powdery mildew,

and do so by

interfering with its metabolic life process, rendering it unable to grow and spread.

Although they

must be in place on the plant before the spores arrive, they do have systemic action –

meaning they

move into the plant tissue – providing a residual effect for a short period.

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Water is essential to plants in many ways. It first provides the major substance for living, to keep cells from shriveling up and dying. The second major function is to keep the plants rigidity. As plant cells become turgid, full of water, the cells expand, filling the extent of their cell walls, which are kept taught with turgor pressure. If the cells lose water, two problems occur. First, the ...

Fungicides are available in many forms – liquids (mix readily with water), emulsifiable

concentrates

(a thicker, usually milky substance), wettable powders (require thorough mixing prior

to

application).

Each has its own properties, all are effective. Most, however, have a

medium-to-high

degree of toxicity to humans. Extreme caution should be used to cover eyes, skin and

hair, and use a

painter’s mask or respirator during application. They are mixed at various rates,

usually 1

tablespoon per gallon of water, and require application every 7-10 days.

BAKING SODA: “New research shows that simple baking soda is a powerful weapon

against

fungus-caused rose diseases”, wrote Kristi Clark in her September 1992 American

Rose Magazine

article.

In a world that is becoming increasingly aware of environmental concerns, more

attention is being

paid to finding alternative measures to widespread chemical use. Sodium

bicarbonate

(grocery-variety baking soda) was tested originally to determine its effectiveness in

preventing

blackspot. During the experiments, it was noticed that no powdery mildew was found

on any of the

test roses.

Controlled experiments were conducted for some three years, using sodium

bicarbonate or

potassium bicarbonate in various combinations with insecticidal soap, Sunspray®

ultra-fine spray

oil, or only water. The result: both diseases were subdued by a weekly spraying of

either sodium or

potassium bicarbonate at 3 teaspoons per gallon of water, combined with Sunspray at

2 tablespoons

per gallon of water. The bicarbonates eliminated the fungi, but addition of the

Sunspray provided a

spreader-sticker action that increased its performance.

Sunspray is available commercially as Safer® Sunspray. As Clark cautioned, do not

attempt higher

concentrations of the solutions, as leaf burn may result. Rain or overhead watering

may wash the

solution off, reducing its effect.

ANTI-TRANSPIRANTS are another group of substances that hold promise as a

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non-toxic method

of controlling powdery mildew (as well as pests).

Anti-transpirants are emulsions and

acrylic

polymers that were developed to form an impermeable film on plant surfaces to

substantially reduce

moisture loss. Several brands are available; look for a white liquid, about the

consistancy of milk.

They are widely used on cut Christmas trees to retard drying and needle drop, and on

plants to

provide protection from drought, heat, wind and transplant shock. Since the thin film

prevents

transpiration of moisture – both in and out of the leaf – it makes sense that it would also

prevent

fungus spores from permeating the leaf surface.

Some rosarians have used antitranspirants in combination with fungicides, and feel

the combination

works better than fungicide alone. Others have used it entirely alone, and find that it

works very well

all by itself. Packaging directs us to water plants well and allow them time to take up

the water

before spraying. Since anti-transpirants are NOT yet labeled for disease protection,

there is no

accepted formula for application. They come in various concentrations that would

require more or

less dilution – anywhere from 1 tablespoon to 1/2 cup per gallon of water. Again,

frequency is not

addressed … once a week … once a month? At this stage it’s sort of experimental. If a

residue is left

on the foliage (objectionable to you as an exhibitor) then reduce the ratio.

Whether we choose the fungicide method or the non-toxic approach to controlling

powdery mildew

probably depends upon the degree of severity we encounter on a regular basis.

Regardless of the

product selected, it must be used on a regular basis in the proper dilution to prevent

fungal growth

without damaging plant tissue.

What is Blackspot?

Symptoms

Blackspot is a plant disease caused by a fungus (Diplocarpon rosae) that is generally

damaging and

usually a source of major problems. Blackspot looks like circular black spots with

irregular edges

on the top side of the leaves. The tissue around the spots or the entire leaf may turn

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yellow and the

infected leaf may drop off. Plants with a severe case may lose all of their leaves if not

treated. Flower

production is often at a minimum and the quality of bloom suffers badly.

Biology

High humidity is one factor that helps the spores to germinate. The spores germinate

in 9-18 days on

a moist leaf at 70-80°F temperatures. The spores can be spread by splashing water

and by the

Rosarians themselves. The spores are wind-borne only in water drops. The spores

can be spread on

clothing, tools or even your hands, but the way it is spread most often is by infected

leaves that have

wintered over in the rose bed.

Control

Blackspot can be satisfactorily controlled by spraying with a good fungicide every

seven to ten days

(read the label and follow the directions).

There are also a number of measures that

should be taken

to keep from getting and/or controlling the disease. Avoid watering in a way that

splashes water up

on the leaves and avoid watering late in the evening with a hose or sprayer. Make

sure to clean up

the beds completely of all leaves or stems to help keep the disease from wintering

over. Always have

good ventilation through the plant and good soil drainage. Apply fungicides after a

rain to keep

down spores. Put the plants on a spray schedule and spray with a fungicide that gives

good control,

such as, Manzate®, Maneb®, Daconil® and Lime-Sulfur compounds.

There are also organic methods of controlling Blackspot. Baking soda has been tried

as a cure and

as a preventative measure. It was found that using baking soda and spray oil mixed

with water as a

spray can damage roses if it is not mixed in the proper proportions. It was also found

that baking

soda gave only moderate control of Blackspot, but appeared to be effective as a

preventative. There

is a new product coming on the market that has been used by our local Rose Society

that does show

promise. This product is derived from the Neem tree. It is called “Rose Defense” by

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The Green Light

Co.

One other way to prevent Blackspot is to plant roses that are disease resistant. There

are some roses

that have some resistance built into their genes. But remember, they are Resistant not

Immune. They

still need to be sprayed on a regular schedule.

Roses should be kept on a regular spray schedule regardless of which method is

used. Remember,

prevention is the key to controlling Blackspot.

Since RM is not fatal to the plant and often has no obvious detrimental effect on a

rose, nurserymen

and rosarians tend to be unconcerned about the problem. When leaf symptoms

appear on a plant, the

affected branch is pruned off, temporarily ridding the plant of its symptoms. If (as many

growers

believe) the only effect of RM were an occasional chlorotic or disfigured leaf, there

would be little

cause for concern about the disease. However, RM has been shown to cause flower

distortion

2,3,4,8, reduced flower production 3,4,6,8,9, reduced flower size 8,9, reduced stem

caliper at the

graft union 8,9, reduced vigor 2,3,7,8,9, early autumn leaf drop 8, lower bush survival

rates 6,

increased susceptibility to cold injury 6, and more difficult establishment after

transplanting 8. The

symptoms are highly variable among rose cultivars and are strongly influenced by

weather and

growing conditions. Infected plants may appear to be quite healthy for much of the

year, and any

symptoms which do appear may be attributed to other causes, such as spray burn,

nutrient

deficiencies, high temperature, or poor horticultural practices. It has been suggested

that the

“deterioration” which often occurs in rose cultivars several years after their

introduction may be a

result of virus infection 1.

Etiology

Rose mosaic is a complex of several viruses which cause similar symptoms in rose

plants. The most

important of these in the United States is prunus necrotic ringspot virus, a common

disease of stone

fruit trees 5. Of lesser importance in the USA are apple mosaic virus and arabis

mosaic virus. There

may be additional viruses involved in the RM complex 6. Several other virus diseases

of rose are

quite distinct from RM and will not be considered in this paper. These include rose

wilt, rose leaf

curl, rose streak, rose rosette, and rose spring dwarf.

Means of Transmission

RM is believed to be non-contagious in the field, except possibly through rare natural

root grafts.

There is no evidence that it ever spreads naturally in the garden or nursery, or through

pollen, seed,

or seedlings 2. Extensive tests also have failed to transfer RM mechanically (e.g., on

pruning tools,

grafting knives, etc.) 3. The only known means for transmitting the disease is by

vegetative

propagation. Cuttings rooted from infected plants, or budded plants produced from

infected scions or

rootstocks, will be infected in virtually every case. The disease is systemic, so the

entire plant is

infected, whether or not all of the branches show symptoms. A plant which is infected

at the time of

propagation will remain infected throughout its life, and a healthy plant at the time of

propagation

should remain healthy for its entire life, unless an infected scion is budded or grafted

onto it.

It is probable that the disease was transferred to roses originally from one of the stone

fruits, by

graftage 4. It then spread from one rose cultivar to another through infected rootstocks.

Two nursery

practices contributed to the rapid spread of the disease in the United States:

1.Collecting scion wood for next year’s crop from this year’s budded plants in the

production field,

rather than from a separate, disease-free, scion-source garden 4. 2.Collecting

rootstock cuttings from

suckers on budded plants in the production field, rather than from a non-budded,

disease-free

rootstock planting. In Europe, where rootstock plants are usually produced from seed,

RM remains

quite rare 3.

Leaf Symptoms

Leaf symptoms of RM are highly variable, often making diagnosis difficult. Some rose

cultivars

show strong symptoms, while others may be nearly symptomless. Most cultivars will

be

symptomless for at least part of the year. The most severe symptoms usually are seen

during cool

weather, in the spring, and are much less severe during the summer months. Some

leaves may show

“vein-banding”, in which the veins are bright orange or yellow, on a green

background. Other leaves

may show a bright yellow or white “oak leaf” or “mosaic” pattern . A very faint

“watermark”

chlorosis is common on the leaves of some cultivars . These symptoms often fade as

the leaf ages

and may disappear completely. The chlorotic patterns associated with RM usually do

not closely

resemble any mineral nutrient deficiency or herbicide toxicity pattern and are

reasonably reliable for

diagnosing RM. The absence of any obvious symptoms is normal, and is no

guarantee of freedom

from RM; some infected cultivars seldom show symptoms, but their performance may

be impaired.

The Heat Therapy Program at Florida Southern College Florida Southern College’s

heat therapy

program was initiated with the following goals:

1.To produce rootstock plants adapted to rose culture in Florida that are known to be

free of RM,

particularly Fortuniana and Fun Jwan Lo . 2.To rid commonly grown scion cultivars

(including old

garden rose cultivars) of RM. 3.To provide propagating material of rootstock and scion

cultivars to

nurseries interested in cooperating with the program, thus enabling Florida residents

to purchase

disease-free plants on desirable rootstocks. 4.To maintain a RM-free garden for the

preservation of

healthy germplasm of the treated cultivars. The heat therapy procedures are similar to

those

employed by the programs at the Oregon State University and the University of

California at Davis.

Infected scionwood is budded or grafted to Fortuniana rootstock and grown to a

2-gallon size plant.

The potted plant is placed in a controlled-environment chamber, where the

temperature is held at a

constant 38° C (100° F) for 21-35 days. The heat treatment does not cure the plant,

but RM-free

material can be obtained as follows: Axillary buds from the treated plant are budded

onto RM-free

rootstocks. Most of the axillary buds on the heat-treated plant will be free of RM. Once

the new

budlings are growing, they must be tested to insure freedom from RM, a process

known as

“indexing.”

We use three indexing methods:

1.Mme. Butterfly — Buds from the plant to be tested are budded to established plants

of virus-free

Mme Butterfly an older Hybrid Tea which shows brilliant mosaic symptoms when first

infected.

This is usually done in the autumn. The plant is allowed to grow a new flush of Mme.

Butterfly

leaves during the spring, and those leaves are observed for symptoms. 2.Shirofugen

— Buds from the

plant to be tested are budded to branches of Shirofugen a Japanese flowering cherry

tree. Roses and

cherries are not graft-compatible, so the graft always dies. If the bud was not infected,

the cherry

branch heals over, cleanly. But if the rose bud contained mosaic virus, the virus will

be transferred

to the cherry branch, which will react by producing a sticky, gummy oozing sap, and

the area

around the graft union will die. Cherry trees don’t grow well in Central Florida, so we

contract with

the University of California to do this test for us. We ship them budwood to be tested,

in June.

3.ELISA — Enzyme-Linked Immunosorbent Assay is a laboratory method, using rabbit

antibodies.

It is a quick (less than one day) laboratory test, and not only tells whether any virus is

present, but

can often determine exactly which virus, and sometimes even which specific strain of

a virus, is

present. We contract with the Washington State University, to do this test, sending

them leaf samples

in cool weather.

The program at Florida Southern College is now nearly 10 years old. We have

heat-treated and/or

indexed hundreds of varieties, and now maintain more than 350 virus-free scion

varieties, including

around 200 old garden roses. We also have virus-free rootstocks, including

Fortuniana Fun Jwan Lo

and Dr. Huey. Mosaic-free plant material is available to commercial nurseries for

propagation, and

it is through our cooperating nurseries that mosaic-free plants are available to the

public.

Summary and Conclusions

Rose mosaic disease currently infects a large percentage of the roses grown in

Florida, and

throughout the United States. While hobbyist growers and most nurseries lack the

facilities to rid

plants of the disease, cultivars can be freed of RM by a simple heat treatment

program. Florida

Southern College is engaged in such a program, and offers virus-free material to

commercial

nurseries, to the extent that time and facilities will permit. Since RM is believed never

to spread by

natural means, there is no legitimate excuse for its continued existence in American

rose nurseries

and gardens. While RM is not deadly or otherwise devastating to a rose bush,

improved growth and

more flowers of higher quality may be expected from disease-free plants, so it is to a

grower’s

advantage to seek out plants known to be free of the disease.

1.You can’t cure it in your garden, but it is not going to spread from bush to bush. So

there is no

great need to dig up and destroy an infected bush. However, if you can find a

virus-free plant of the

same variety, you might want to consider replacing the bush, to gain more vigor and

greater flower

production. 2.If you do your own budding or grafting, remember that those procedures

spread the

disease, so try to use virus-free scion wood and virus-free rootstocks. If you root

cuttings of

Fortuniana that sprouted out from the base of a grafted bush, remember that those

cuttings will

contain the virus if the original bush was infected. Also, any scions collected from an

infected bush

will produce infected plants, when propagated. 3.Remember that a complete lack of

symptoms (i.e.,

a healthy looking bush) is the normal situation for an infected plant. Just because a

plant appears to

be healthy, even for several years, is no guarantee that it is indeed virus-free. Only

indexing can tell

you for sure. 4.One of the major reasons so many nurseries are “cleaning up” their

stock, in recent

years, is customer demand. Please support and commend nurseries that produce

clean plants.

Encourage nurseries who don’t, to begin growing virus-free roses. If they know it is

important to

you, the customer, they will likely respond favorably.

While I am not aware of any nursery which sells only virus-free plants, most of the

nursery-members

of the CFHRS do grow at least some clean varieties, and will gladly tell you, if you

ask, which of

their stock is clean. It will be quite a long time until all of the commercially propagated

heritage

roses can be cleaned up, but we’ve made a good start. Here’s a partial listing of older

roses available

from our program, through retail nurseries:

Insecticide chemicals have been linked to childhood immune disorders, nervous

system problems

and hyperactivity. Chemicals commonly found in insecticides-like PCB’s and DDT-

can cause

negative estrogen-like effects in some women, contributing to breast, ovary and

uterus cancer. Home

pesticide users may use an average of up to six times more pesticide per acre than

farmers.

Insecticide use has increased ten-fold since 1940, but insect induced crop losses

doubled to more

than 13 percent. 25-50 percent of air sprayed pesticide does not hit the field and drifts

into the

environment, contaminating soil, water, and air. Pesticide residues on fresh produce

can be reduced

by thorough washings with water, removing outer leaves, peeling and cooking.

However, not all

residues can be removed, especially residue from pesticides that enter fruits and

vegetables through

the soil. Pesticide chemicals remain in the environment long after they are no longer

used-DDT, chlordane and heptachlor can linger in the soil for more than 20 years.

Consuming

organically grown foods and using alternative pesticide control methods can

effectively decrease

chemical contamination of humans, animals and the environment.