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Abstract On Rose Diseases

abstract on Rose diseases title = abstract on Rose diseases 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 – ready to sprout when the environment is just right. Warm days (50-80F) and cool nights with elevated humidity and resultant dew provide ideal conditions.

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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 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. 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 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 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 70-80F 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 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. Rose Mosaic Virus Disease by Malcolm M. Manners, Lakeland, FL Many of you know that the primary reason we grow roses at Florida Southern College is our involvement in indexing and heat-treating roses for rose mosaic disease. While we have had articles about the subject in numerous other publications, over the past decade, I’ve not mentioned the subject in The Cherokee Rose, nor has there been any extensive discussion of the subject at any of our meetings. Yet it is a subject I believe to be quite important, particularly in that a grower, through ignorance of the problem, could introduce a viral infection to an antique rose which may have survived hundreds of years without the disease.

A few simple precautions could have prevented the infection. Also, some old rose nurseries are notorious for shipping virus-infected plants, while others have made a great effort to provide virus-free bushes. I certainly commend (and recommend) the latter group. The following is an updated version of a paper I presented to the Florida State Horticultural Society, in 1985: The Citrus Institute of Florida Southern College initiated a program to rid infected rose plants of rose mosaic (RM) disease in 1984. This paper will describe the disease, its effects on rose plants and their culture, and the heat therapy program at Florida Southern College.

Rose mosaic is a disease caused by a virus complex infecting cultivated roses (Rosa spp. and hybrids). Cochran 3 reported that …


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