CONTROL OF ROSE LEAF DISEASES IN

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1 400 the slow growth characteristics of this species. The undipped zoysiagrass was no taller at the termination of this experiment than that clipped two inches. Neither nitrogen levels or height of cut pro duced any effects on the root growth of zoysia grass. This can possibly be explained again by the slow growth habit of this grass and the fact that the roots did not grow sufficiently during this experiment to reflect treatment effects. Even with St. Augustine and bermudagrasses in creasing nitrogen above N2 did not increase root growth, thus adding the higher nitrogen treatment only increased growth of above ground portions of the plants. This situation might not have occurred in the field where root systems would be less restricted than in the containers used in this experiment. The dif ference in photosynthetic area between grasses cut at the and 1 inch heights was apparently insufficient to affect root development. At the higher cut and undipped treatments there was enough additional photosynthates to increase root development as compared with the lower cuts. Data from this experiment indicate that the medium rate of nitrogen was adequate for zoysia and St. Augustine grasses, but the highest nitrogen level was best for bermudagrass. Summary A 3 x 3 x 4 factorial experiment was initiated to test effects of three nitrogen levels and four heights of cut on bermuda, zoysia and St. Augus tine grasses. Data included average and total dry weights of clippings, terminal top weight and total root weight. Increasing nitrogen in the substrate increased clipping weights of all grasses. There was an interaction between nitrogen treatments and height of cut on clipping weight. Interactions between the variables on term inal top weights and root development are given. LITERATURE CITED 1. Nutter, G. C Variability in rate of growth and fertilizer response among selections of bermudagrass. Turf Mgn.t. Proc. 3: Roberts, E. C The grass plant-feeding and cutting. Golf Course Reporter 26(3): Roberts, E. C. and E. J. Bredakis What, why and how of turfgrass development. Golf Course Reporter 28(8): 'White, R. W. Jr The effect of rate of frequency of fertilization on the year around performance of 'Bayshore and 'Everglades 1' befrmudagrass greens. Masters Degree Thetis, University of Florida. CONTROL OF ROSE LEAF DISEASES IN FLORIDA H. N. Miller University of Florida Gainesville Foliage diseases of roses are limiting factors in the growing of roses in Florida. While the diseases encountered by a Florida rose grower may, for the most part, be the same as those found elsewhere, certain ones may be more per sistent over a longer period during the year and more difficult to control here than in other parts of the country. For this reason, and because of a difference in climatic factors which may influence a plant disease and its control, recommendations for control made elsewhere may not be the best for the Florida grower. The most important leaf disease of roses in Florida is black spot caused by the fungus Diplocarpon rosae Wolf (Fig. 1A). Black spot is particularly prevalent and severe, occurring at Florida Agricultural Experiment Stations Journal Series, No all seasons of the year. If black spot is not controlled, repeated defoliation of the plants occur, leading to their early decline and death. Powdery mildew (Sphaerotheca pannosa var. rosae Wor.) (Fig. 1C) occurs on roses in Florida during the spring and fall. It is not generally present during the mid-summer months when black spot is the most severe. The disease is inhibited by high temperatures and frequent rains. Mildew appears to be increasing in preva lence and severity in Florida, frequently requir ing additional emphasis on control. A third leaf disease of roses in Florida is Cercospora leaf spot caused by the fungus Cercospora rosicola Pass. (Fig. IB). This disease is not to be confused with black spot. Character istically, Cercospora leaf spots have distinct gray centers with purplish or reddish-brown borders. In contrast, black spot lesions have irregular serrated margins and are uniformly black throughout. Cercospora leaf spot is usually of minor importance if good cultural practices are

2 maintained and a regular spray program is con ducted for the control of black spot and mildew. Rust, a serious leaf disease of roses in other areas, does not occur on cultivated roses in Florida. Experimental Procedures Spray trials have been conducted over the past three years for the control of black spot and powdery mildew of roses. Two separate tests were conducted each year, one in the spring and early summer and the other in late summer and fall. Plants were not sprayed in mid-summer to allow for uniform disease build up and to lessen the carry-over effect from previous treatments. Rose varieties used in the spray trials were selected for high susceptibility to black spot and mildew. These included Crimson Glory, Mc- MILLER: ROSE LEAF DISEASES 401 Greedy's Sunset, Eclipse, Peace, Pink Delight, K. A. Victoria and Summer Snow. Natural in fections occurred consistently, and uniformly for variety types on unsprayed plants, assuring adequate inoculum for disease. Usually moder ate to severe infection was allowed to develop before spraying was started. While this is not recommended for a control program, it did assure the evaluation of the fungicides under severe disease conditions. Except for blocks of roses planted in a plastic house and under saran shade for phytotoxicity studies, spray trials were conducted on open field grown roses. All roses were main tained according to recommended cultural prac tices. Irrigation was by overhead sprinklers. Plot outlines, varieties used, and the number of treatments were not consistent for all tests. Table 1. Summary of tests conducted over a 3 year period for the control of black spot and powdery mildew on field grown roses. Fungicide Rate of application Phaltan (75 WP) Dodine (65 WP) Haneb Captan (80 WP) (50 WP) Ferbam (75 WP) 1 IA lbs/100 gals. 3 A lbs/100 gals. 1 1/2 lbs/100 gals. 2 lbs/100 gals. *Percent disease control Black spot Mildc oo lbs/100 gals * Percent disease control calculated from disease index (0 = no infection, 10 = very severe infection) based on number of tests for each material Table 2. Summary of tests conducted for the control of powdery mildew on field grown roses. Fungicide Rate of application *Percent mildew control Acti-dione PM (.027%) Acti-dione PM (.027%) Phaltan (75 WP) Karathane (25 WP) 2 ppm 1 ppm 1 IA lbs/100 1/2 lb/100 i fungicides at weekly intervals. Percent i 10 = very severe infection) based each material

3 402!igure 1. leaf disease, of rose. A. Black spot. B. Cereosp.ra leaf spot. C. Powdery mildew. Figui

4 MILLER: ROSE LEAF DISEASES 403 However, certain general procedures were fol lowed. Three to five plants were used for each experimental unit. All treatments were ran domized in at least three replicates. Sprays were applied once a week for approximately three months in each test. The plants were sprayed until run-off with either a three gallon Hudson hand-pumped pressure sprayer or a 15 gallon Bean motor-driven sprayer. A screen was used between plots during spraying, when needed, to prevent spray drift. Various other fungicides, in addition to those reported here, were tested. They failed to give satisfactory control under the conditions of these tests and are not included in this discussion. Each fungicide listed was included in two or more separate tests and was used at different dosage levels. Dosage levels given are those found most satisfactory. Results Evaluation of fungicides. Disease control was determined for each experiment by rating each plant according to severity of infection, using the scale 0 = no infection and 10 = ap proximately 100 percent of leaves infected. The ratings were averaged for the total num ber of plants in each test and the number of tests performed for each fungicide. From these data, percentage disease control was calculated and is given in Table 1 and Table 2. These data summarize the results of different tests conducted over a three year period and under different disease conditions. No attempt, there fore, is made to give a statistical comparison of the fungicides. Discussion Data show dodine to be the most effective fungicide used in these tests for the control of black spot. It failed to control mildew, and was less effective in suppressing mildew than Phaltan or maneb. Dodine at } lb. per hundred gallons caused injury to rose foliage. This oc curred as small brown flecks on the leaves. Leaves became hard and leathery and the plants assumed a dull green appearance. No injury occurred until the latter part of June and was not serious until early July during higher temperatures and after 9 to 12 applica tions of the fungicide. There was no reduction in flower yield or plant growth. Dodine at lb. per hundred gave good control of black spot with no injury to rose foliage. All Phaltan sprays gave excellent control of black spot. While Phaltan did not eradicate mildew, it did give satisfactory control when used routinely for black spot and spraying was begun before heavy mildew infection developed. Severe phytotoxicity may occur under certain environmental conditions when Phaltan is used in combination with various spreader-stickers and emulsifiable insecticides on a weekly schedule. This injury is expressed as a burning of older leaves. Russetted or blackened irregular areas occur on the upper leaf surfaces. Subse quent yellowing of the leaves and defoliation may occur. Tests conducted on roses growing in the field, under saran shade, and in a plastic greenhouse indicated that this injury increases with increasing temperatures and repeated ap plications. Phaltan when used alone gave ex cellent control without injury. Maneb at 1 lbs. per 100 gallons gave good control of black spot, but did not give satis factory control of mildew. Slight injury to rose foliage may occur at this spray concentration under certain conditions. Lower rates of maneb failed to give satisfactory black spot control under severe disease conditions. Four applications of acti-dione PM at 2ppm at weekly intervals eradicated powdery mildew on roses. A slight amount of injury occurred on some varieties as a crinkling and yellowing of new leaves. The injury was not considered serious and the plants continued to grow normally. Acti-dione PM at 1 ppm was not as effective as the higher rate. Phaltan and Karathane gave fair control but did not eradicate mildew. Summary Phaltan (75 WP) at 1± lbs. per hundred (U tbs. per gallon), gave excellent control of black spot and satisfactory control of powdery mildew on field grown roses. Phaltan should be used without a spreader-sticker to lessen the chances of injury under conditions of high temperature and repeated applications. Phaltan sprays leave a noticeable deposit on rose foliage. Dodine (65 WP) at lb. per hundred (1} tsp. per gallon) gave superior control of black spot, but did not satisfactorily control mildew. Injury to rose foliage may result from repeated applications of dodine at the f lb. rate during high temperatures. If this occurs the spray strength should be reduced to lb. per hundred. Rates above f lb. should not be used under Florida conditions. Maneb (80 WP) at 1J. lbs. per hundred (1 tbs. per gallon) gave satisfactory control of

5 404 black spot, but not mildew. Maneb sprays should be started at the first sign of black spot and used routinely at weekly intervals. Maneb was only moderately effective as a clean up spray for heavy infection. Acti-dione PM at 2 ppm is recommended for powdery mildew control on roses if routine spraying for black spot fails to control mildew. It is especially effective as a mildew eradicant and can be used to clean up a heavy infetion. Four to six applications at weekly intervals is usually sufficient to eliminate mildew. Further applications are not recommended unless mildew again becomes a problem. For effective control of rose leaf diseases sprays should be applied routinely at weekly intervals. Thorough coverage of both top and bottom leaf surfaces is essential. Plants should dry rapidly following spray applications to lessen chances of injury. EXTENSION SERVICES CATER TO ORNAMENTAL HORTICULTURISTS L. J. DAIGLE Dade County Agricultural Service which speeded development of natural re sources, man found that he had more time each day to devote to the arts and sciences. Miami Two out of five people in the United States today, who are employed, are now engaged in some phase of agriculture, recent surveys tell us. Toward this end, the Dade County Agricul ture Agent must be at the service of farmers as well as home-owners, part-time agriculturists in assisting them with the many challenging and ever changing problems they confront daily. The Smith Lever Act of 1914, which estab lished the Co-Operative Extension Service, as sures this to the public as it provides that all citizens of the United States, regardless of whether they are engaged directly in agriculture or not should be provided information by the local Agriculture Departments." As the do-it-yourself fad became popular, espe cially in the gardening field, it became necessary to have an Ornamental Horticulture Specialist, which was done in November The culture of plants for the purposes of enhancing the beauty, comfort, and utility of dwellings can be found in the pages of early history. Because of man's constant struggle to provide for food and fiber, it was only in the courtyards of the wealthy that delicious fruits and beautiful flowering plants could be found. In many areas of the world today, thousands of people are not yet able to engage in this satisfying phase of agriculture. In the early years of this nation many hours each day of animal and man power was required to perform necessary chores. With the advent of machines Progress Is Made Only a few decades ago it was not uncommon to see, even in urban areas, a home-made in cinerator fashioned of woven wire, and a chicken coop in one corner of the yard. There was no well-maintained lawn in the front or the back of the property. Two or three plants along the front of the house and perhaps a shade tree constituted the entire planting. In the recent past, the attitude of the modern home-owner through education has changed so that today a new home is not considered livable until a basic planting is established. Many continue to de velop their properties until they have achieved a complete border enclosure, a foundation planting, a well maintained lawn and suitable trees for shade and enframement. The urbanization trend over the nation re sults from population increases and the migra tion of farm families to cities. This trend increases the number of requests for help with the agricultural problems of those living in urban areas. From the beginning of Extension work in Dade County, the agricultural agents have as sisted home-owners with their problems. But until recent years, only a few bulletins and very little other printed information for home gardeners was available. As a result of repeated requests by Florida Agents, working in metro politan areas, a number of excellent state bul letins covering the many phases of home garden ing have been published.