Rose Black Spot
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Rose Black Spot  Rose black Spot is caused by a fungus, Diplocarpon rosae and is spread by rain splash, on hands, and on tools. Attacks are worst in warm moist conditions.. It overwinters on stems, fallen leaves, and soil.Susceptible Plants- Rose Symptoms-Small, round spots, ranging in size from 1/16" to 1/2" in diameter, appear on the upper sides of leaves. Leaf tissue adjacent to the spot turns yellow. Whole leaves eventually turn yellow and fall prematurely. Black spot can be distinguished from other leaf spot diseases of rose by the generally fringed margins and the darker and consistently black color of the leaf spots. Similar spots may appear on petioles and fruit. Raised, reddish-purple spots may also appear on canes. If black spot is left uncontrolled and early defoliation occurs, bushes are weakened and cane dieback the following spring may be severe. Weakened plants may continue to die even after the plants leaf out.
Life Cycle--During dormancy the fungus survives in infected canes and fallen leaves. Spores are spread to the highly susceptible, young, unfolding leaves in spring by splashing water. Infection takes place only when water remains on the leaves for seven or more hours.
Therefore, the disease is most serious in regions of high rainfall and high humidity. Because the fungus tolerates a wide range of temperatures, symptoms can continue to develop all season long if moisture is adequate. Prevention and Control- A preventative program for rose black spot should begin in the fall with a thorough sanitation program. Diseased leaves on the ground should be raked and burned or removed. All diseased canes should be pruned back to healthy wood. These practices will reduce the amount of overwintering fungus. During the growing season, overhead irrigation, which prolongs leaf wetness, should be avoided. If plants are overhead irrigated, watering should be done in the morning rather than the afternoon so that leaves dry quickly. Grow resistant cultivars such as ‘Veilchenblau’. ‘New Dawn’, and ‘Knock Out’. Mulch with compost or leaf mold before buds burst in spring to reduce risk of overwintering spores splashing up from the ground. Fungicide Control- Bonide Rose Rx 3 in 1
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