1. Was blackspot a problem last year in your garden? 
2. What are some general treatments for blackspot?
3. Other notes on blackspot, including a list of disease resistant roses for Maryland
4. What is mildew, and how do I treat it?
5. Does the blackspot treatment Rosa Flora work?

1. Rake up all of the fallen leaves which will harbor the blackspot fungus. Otherwise, it will over-winter in your rose garden and be ready to attack your plants in the spring when conditions are right. Heavily infected foliage still clinging to the plant should be removed too. Don’t put this waste on your mulch pile; discard it as garbage. The time to do this is a continuous process, with a final clean up in late fall or early winter.
2. Use Ortho Dormant Disease Control Lime-Sulfur Spray--in accordance with the label directions-- when the plants are dormant. This will normally occur, in this area, in January and February. Spray the foliage, canes, and soil around the rose plants. Do not use this product at full recommended strength (10Tbs [5fl oz] per gal of water) if there is doubt of dormancy or if there is evidence of new foliage, as foliar damage may result. If you will recall, January and February, 2000 temperatures were not severe, and as a consequence, your Editor used 5 tablespoons to a gallon of water in a pump sprayer.
3. Start your regular seasonal spray program as soon as new foliage is evident. Decide to spray regularly every week, 10 days, or in accordance with the directions for the fungicide you decide to use. Also, use the precautions as prescribed by the manufacturer. This past year, I used Banner Maxx as my principal spray. Although it is expensive, it is a very effective product. As with any fungicide, it is a good idea to switch off periodically to a different product. It is believed that blackspot is a fungus that can accommodate to a specific fungicide.

The two principle tasks in the above are: good garden hygiene (clean up) and a regular spray program.?

     A number of rose growers have expressed the opinion that the prevalence of blackspot in their gardens during the past year was greater than they had experienced in some years and wondered what the reason might be. There are probably a multiplicity of reasons depending on the specific garden, and I thought it might be of value to readers of this newsletter to comment on the practices which might be helpful in the coming year to control this omnipresent rose disease.
      In my experience, other than the Rugosas, R. rugosa and hybrids of that class of roses, there are few roses which can be termed completely resistant. Among the hybrid teas, floribunda and miniatures, the most prevalent classes of roses in our gardens today, there are not any varieties, in my judgment, that are completely blackspot resistant. They are all vulnerable, some more so than others. I used to tout Sun Flare, for example, as a blackspot resistant floribunda; however, it too is susceptible at times. The best we can hope for is to keep blackspot under control and, therefore, at an acceptable level in our gardens.
      There are a number of things we can do to minimize the amount of blackspot present. Cleanliness is certainly important. When we recall that the spores that cause blackspot, in most instances, get on rose leaves from splashing water from the soil surface, it suggests that we keep the soil surface clean of diseased leaves that have fallen from the bush. This should be done regularly. Care should be exercised also in watering to minimize splashing of water on lower leaves. This splashing explains why blackspot normally begins on lower leaves and also why climbers seem to be less susceptible than bush roses. This concept gives meaning, too, to spraying after rain has occurred.
      Maintaining good air flow around your roses is also important. To accomplish this, refrain from planting roses too close together and remove twiggy growth and foliage near the crown. This foliage is the first to be affected by spores from the ground, particularly if it remains damp. Blackspot spores germinate on new or old leaves in 9 to 18 hours on moist leaves when the temperature is in the 70 to 80 degree range. Normally, leaves must be wet for at least 7 hours for germination of spores to occur; this is the rationale behind watering in the early part of the day, if overhead watering is practiced, thus allowing time for the foliage to dry. Evening watering by methods which wet the foliage should be avoided. An additional point to keep in mind also is that good drainage facilitates the leaf-drying process.
      Fall pruning in this area is generally recommended for hybrid teas and some floribundas. It should occur normally after Thanksgiving and should consist of removing top growth to about three to four feet from the crown, to prevent the rose canes from whipping around in the wind and loosening the soil around the crown exposing it to the cold winter winds and temperatures. At the same time, remove all diseased foliage from the plant and soil. This waste should be disposed of and not placed on your compost pile. If blackspot was a particular problem for you during the year, you might consider the lime-sulfur treatment of your plants during their period of dormancy. You will find the product at garden centers and it should be applied in accordance with the directions on the container.
      Although the suggestions given above will help you get a more firm handle on the blackspot problem, the most important thing you can do next year is to adopt a regular preventative spraying program. There are many fungicides which can be used. The following are some of those recommended by Howard Walters, The Rambling Rosarian:

     Spraying is recommended in calm air flow and in the cool of the morning or evening to prevent leaf-burn. Apply spray on the upper and lower (undersides) of leaf surfaces. Your spray program should begin in early spring, when foliage first appears, and should continue throughout the year until frost appears.
      Most consulting rosarians also recommend that the kind of spray used be varied periodically on the theory that blackspot spores can accommodate to a given product. I am not aware of experimental evidence on this point, but tend to believe it to be true. If the product you have been using somehow seems less effective than it was in the past, change to another product or alternate with a second product part of the time, say every second or third spraying. -Editor

      * The fungal disease’s common name is properly spelled as two words; however, spelling it as one word has become more popular in the literature.

     Also on the subject of blackspot, there appeared an article in the 1998 American Rose Annual, which gives additional information and describes a system for evaluating the degree of impairment of a variety by the fungus. The system seems complicated and cumbersome; however, the same article describes a nontoxic spray for black spot which is worth trying. It was developed at Texas A & M University at College Station, Texas. Rose Flora™ is the product name and it consists of nontoxic, organic soil-based bacteria, which is reported to be safe environmentally for humans and pets. It is supplemented by a natural pine oil emulsion, Wilt-Pruf®, which is a polyterpene polymer and has been on the gardening market for a long time. The two products are mixed together and, according to the article, provide good control of blackspot and powdery mildew.
      On December 4, 1998, your Editor ordered both Rose Flora™ and Wilt-Pruf® from the source recommended in the 1998 American Rose Annual article for a conscientious trial during the 1999 growing season.  Like so many rosarians, I have been looking for a nontoxic solution to the blackspot problem. I firmly believe that the growing of roses is dependent upon finding a reasonable solution, and maybe this is it. We were very disappointed in the results of two prior trials conducted by members of the Maryland Rose Society. As you may remember, with both a garlic based product and a neem based product, our results were unsatisfactory.
      It should be noted that the recommended formula may result in an augmented rose leaf surface, which may be construed as a “foreign substance” by Rose Show Judges. It may be that suspending the use of the Wilt-Pruf addition, when a show is coming up, will overcome that potential problem.

BLACKSPOT RESISTANT ROSE VARIETIES FOR THE MARYLAND AREA

    As some of our members are aware, the Maryland Rose Society has an effort underway to identify varieties of roses which are disease resistant for our area. This seems to be a noble pursuit in view of several concerns:

1. The public seems to shy away from planting roses because, in its judgment, they are too difficult to care for. They mention concepts like, “All that spraying with chemicals,” and “Roses are disease prone.”
2. There are repeated requests from gardeners and Garden Clubs for recommendations of roses that are “easy to grow.”
3. The almost universal desire to dispense with the spraying of toxic chemicals.
4. The repeated admonition of writers on the subject to purchase roses that are known to be disease resistant. Recall Malcolm Manners; “One of the best ways to avoid black spot is to choose and plant highly resistant varieties.”

     The next consideration in the preparation of a list of disease resistant varieties was to come to grips with what a “disease resistant” rose really is. Let’s face it, what variety of rose is completely free of the two prevalent--and most exasperating--rose diseases in this area, blackspot and powdery mildew? At one point, I would have said, the Rugosas and their hybrids, but the American Rosa Annual article shows them to be less than perfect, 99% resistant, but not 100%.
      For practical purposes, I believe any list should contain those varieties which may be affected by blackspot, but to a tolerable degree, without spraying. in a Maryland garden. Take Sun Flare, for example. In my garden, I almost never see blackspot on it. That is not to say it is completely immune, because I have seen blackspot on Sun Flare. The degree of infection, however, is minor and would not prevent my recommending it as a “Highly Disease Resistant” variety for this area.
       With the above as a background, the first listing of Highly Resistant Rose Varieties for the Baltimore, Maryland area appears on Page 9 of this Newsletter. The list is tentative, and will be expanded upon and amended depending on reports from members of the Maryland Rose Society. If you have not made your opinions known to the Editor, I wish you would do so.

HIGHLY DISEASE RESISTANT ROSE VARIETIES RECOMMENDED FOR THE BALTIMORE, MARYLAND AREA
(Initial Release: December 15, 1998)

      The varieties listed here were selected on the basis of little or no blackspot present upon them while using a weekly or every ten-day preventative spray program or none to tolerable levels of blackspot without a preventative spray program. Sources for these roses might be found by searching the EveryRose Rose Reference Database, Google, HelpMeFind Roses, and other internet search tool and online catalogs.
 

     Members of the MRS and others familiar with rose growing in the Baltimore, MD area may suggest amendments and/or additions to this list by contacting Al Ford (fordrose@comcast.net), MRS Newsletter.

A PRESCRIPTION FOR POWDERY MILDEW
By Albert Ford
(adapted from the November –December 1991 MRS Newsletter)

     Those who read regularly the literature on rose culture will have run across a treatment for mildew on roses consisting of spraying with bicarbonate of soda. There is a current report that Cornell University had performed some recent tests with positive results.
      The earliest reference I have found suggests the practice originated in Russia. Jesse A Currey, the originator of the International Rose Test Garden in Portland, Oregon, wrote in 1922 of a visit from Professor Arthur de Yacenski, a Russian plant pathologist, as follows:

"Professor Yaczenski told me that they had found the treatment for mildew to be a spray of bicarbonate of soda, dissolved in water in the proportion of one ounce of soda to one gallon (of water)...I have used a weak solution of this same baking soda for cleaning mildew from exhibition specimens on the advice of Dr. S.S.. Sullivan. I know that it removes the mildew, but have never experimented with it in the open." (American Rose Annual, 1922, p.76.)

     It is also of interest that at the time, (1922), the common treatment for mildew in this country was "..90 parts of sulphur and 10 parts arsenate of lead." (ARA, 1922, p.79.) -Editor.

SPRAY DAMAGE OR DOWNY MILDEW?
By Albert Ford
(adapted from the September – October 1991 MRS Newsletter)

     The rose gardener who confuses the affects of Downy Mildew and spray damage is not alone; there are many of us who make the same mistake.
      I recall a Colonial District meeting in Williamsburg, Virginia, to which a rosarian from this area brought several infected rose stems to find an answer to what was causing the discoloration and dark brown irregular spots and blotches on the stems.
      Those in attendance, who ventured an opinion, believed the problem to be spray damage or "pesticide toxicity," but a few people contended that the damage was the result of Downy Mildew. In my opinion, aided by some investigation on my return to Timonium, we were looking at the ravages of Downy Mildew. Even plant pathologists acknowledge it is easy to confuse the two.
      An excellent article appeared in the ARS, August, 1991 issue of The American Rose Magazine by John Mattia from Connecticut on Downy Mildew describing how he and other rosarians confused its devastation with that caused by "spray burn."
     His solution to the problem, once he convinced himself that the symptoms were caused by something other than his spray and feeding program, was to combine the use of a fungicide Subdue which had been developed to combat Downy Mildew on leafy vegetables. His normal spray program, it appears, already included Funginex which, in my opinion, is useful in controlling Pow dery Mildew but not Downy Mildew.
      If John's problem rings a bell, read his article and perhaps also Compendium of Rose Diseases on this subject. (p.13)

(The Compendium of Rose Diseases was published in 1983 by The American Phytopathological Society in cooperation with the Department of Plant Pathology, Cornell University.)

     In the past I wrote that I intended to use a new organic product as a safeguard against blackspot this year. I said at that time that I would report back to you on the results achieved in my garden. I was hopeful that the results would not be available until the fall of the trial year, however, I have decided to end my trial project early and return to the spray program used previously. My decision was based on the following.

1. Rosa Flora need be mixed 48 hours prior to its use and must be used before another 48 hours has expired. This limitation is at least bothersome. It is enough to spray in the first place and to plan the pleasure two days in advance is an annoying limitation. I would have been willing tolerate this inconvenience, however, had it not been for #2 below.
2. The product may be useful in curtailing blackspot to some degree, but the amount exceeds significantly at this point in the growing season than I have been accustomed to, and that in evidence in other gardens I have visited this year where more traditional products were used, i.e., Funginex and Immunox. There is a tolerance level for blackspot that varies from gardener to gardener, and mine has never been zero, but by using Rosa Flora™ since the first treatment in February, the level of blackspot in my garden, though not devastating, exceeds my threshold level. This is true even since brown sugar has been added to the formula to increase the population of bacteria.
3. I have noted a significant amount of leaf curling while using Rosa Flora™ which may be due to other causes, but, at least in my case, is consequent with its use.
4. In readying roses for exhibition, I detected a browning on the edges of petals of white and light yellow varieties which I have not experienced before. Here again, this malady, which obviates the use of the variety for rose shows, may be due to other causes, however, its appearance occurred during the time I was using Rosa Flora™ exclusively as a fungicide.
5. When Rosa Flora™ is mixed with Wilt-Pruf™, which is recommended a sheen is applied to the foliage that can be considered a foreign substance if a sprayed variety is exhibited in an Rose Show held under ARS guidelines. It is recommended that the Wilt-Pruf™ not be included in the formula before a show. This is just another annoyance to contend with.
6. The material is not inexpensive, but would be worth the price to some who are looking for an organic control of blackspot. Incidentally, Rosa Flora™ has not protected against powdery-mildew at all.

      Perfect after further experimentation with the product or a descendant of it, Rosa-Flora™ may be worth another try, however, for now, it is not the answer to my rose gardening problems.
     If you have had experience with its use, I would like to hear from you. –Editor