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.tl Propagation—Pruning ............................................................................................................6.......664....... FOUR WAYS TO PRUNE Downy mildew differs from powdery mildew r in several ways. It is common in cool, moist conditions and spreads fastest on wet foliage. It can pop up almost anywhere in North America but becomes less serious where summers even- tually warm up. It is particularly troublesome in cool -summer areas such as the Northeast and Northwest but, in general, is less common than powdery mildew. Downy mildew also differs from powdery mildew in that the white fuzzy fungus appears on the undersides of the leaves. The leaves develop yellow spots on top, then often dry, become brittle, and drop. Clusters of grapes (a common host) may also be infected and fail to ripen properly. Besides grapes, downy mildew also infects many vegetables, Including peas and cucurbits, and flowers such as roses and pansies. vention through good cultural practices is the best method of control. Propagation In gardening usage, propagation refers to the many ways of starting new plants. These methods range from planting seeds to the more complicated arts of budding and grafting. With the exception of seed sowing, all meth- ods of starting new plants are known as vegeta- tive propagation: the new plants that result will be identical to the parent plant. Vegetative prop- agation therefore maintains uniformity—ensur- ing, for example, that each plant of the rose 'Queen Elizabeth' is like every other. Methods of propagating plants are described under their alphabetical listings: Budding (p. 548), Cuttings (p. 555), Dividing (p. 558), and Grafting (p. 565). Propagation by seed is described under Planting Techniques: Seeds (p. 584). Pruning Pruning is both a skill and an art. The skill is in making cuts that callus (form a thickened tissue that seals off wounds) properly and mini- mize the chance for decay. The art is In making cuts in the right places so that the plant takes on a handsome form and Is prolific if grown for flowers or fruit. No matter how much or how little pruning you do on an established plant, the objective is to modify the plant's growth. The modification can be done for any of the following reasons, singly or in combination: ■ To maintain plant health by removing dead, diseased, or Injured wood ■ To control or direct growth ■ To increase quality or yield of flowers or fruit ■ To train young plants to position their main branches or to ensure strong structure It shouldn't be necessary to cut back a plant continually to keep it in bounds. A plant that seems to require such treatment was the wrong choice for its garden location; the repeated cut- ting back only destroys the plant's natural beauty. Exceptions are pruning formal hedges, espalier- ing fruit trees, shaping topiary, and pollarding. A word of eaution. Pruning large trees over 10 to 15 feet high should be left to professional arborists or tree trimmers. They are properly trained and have the right equipment to do the job safely. To make sure you'll get the job done right, review pruning guidelines published by the International Society of Arb culture. Your pruner should have a copy. Pruning and growth. To understand how to approach the pruning of any plant, you need to know how growth occurs. Because all growth originates in buds, they are the first plant parts to consider. The terminal growth bud develops at the end of a stem or branch. This bud causes the stem to grow in length. Lateral buds grow along the sides of stems. These buds produce the sideways, or lateral, growth that makes a plant bushy. Some plants may have latent buds—buds that he dormant beneath the bark. Some of these buds may grow after pruning or injury removes the actively growing part of the stem. . Actively growing terminal buds produce hor- mones, called auxins, that stimulate their growth and, In many species, prevent lateral buds below them from growing during the current season. If the terminal bud is removed, either while the plant is growing or dormant, subsequent growth occurs from the uppermost lateral buds. These Controls. Several fungicides are effective at ;'. controlling powdery mildew. Triadimefon has been noted by rose growers as the most effective }: ? at both preventing and eradicating powdery ''! mildew, although it has a tendency to shorten growth and can be difficult to find. Other helpful chemicals are triforine and thiophanate-methyl. Some rose growers have had good luck control- f ling powdery mildew by spraying plants with antitranspirant products or the baking soda/oil spray described for Black Spot, under Leaf Spot (p. 575). Overhead watering can also reduce problems with powdery mildew. To control downy mildew, avoid overhead watering and irrigate early in the morning so �I foliage dries out quickly. Prune plants to keep them open for good air circulation. Clean up plant debris to prevent reinfection. Some plant `.i a species are available in varieties that resist -` downy mildew. Controlling downy mildew with fungicides is a "r difficult. Although several are labeled for con- ,,, . trol of downy mildew, not all are effective. Pre- vention through good cultural practices is the best method of control. Propagation In gardening usage, propagation refers to the many ways of starting new plants. These methods range from planting seeds to the more complicated arts of budding and grafting. With the exception of seed sowing, all meth- ods of starting new plants are known as vegeta- tive propagation: the new plants that result will be identical to the parent plant. Vegetative prop- agation therefore maintains uniformity—ensur- ing, for example, that each plant of the rose 'Queen Elizabeth' is like every other. Methods of propagating plants are described under their alphabetical listings: Budding (p. 548), Cuttings (p. 555), Dividing (p. 558), and Grafting (p. 565). Propagation by seed is described under Planting Techniques: Seeds (p. 584). Pruning Pruning is both a skill and an art. The skill is in making cuts that callus (form a thickened tissue that seals off wounds) properly and mini- mize the chance for decay. The art is In making cuts in the right places so that the plant takes on a handsome form and Is prolific if grown for flowers or fruit. No matter how much or how little pruning you do on an established plant, the objective is to modify the plant's growth. The modification can be done for any of the following reasons, singly or in combination: ■ To maintain plant health by removing dead, diseased, or Injured wood ■ To control or direct growth ■ To increase quality or yield of flowers or fruit ■ To train young plants to position their main branches or to ensure strong structure It shouldn't be necessary to cut back a plant continually to keep it in bounds. A plant that seems to require such treatment was the wrong choice for its garden location; the repeated cut- ting back only destroys the plant's natural beauty. Exceptions are pruning formal hedges, espalier- ing fruit trees, shaping topiary, and pollarding. A word of eaution. Pruning large trees over 10 to 15 feet high should be left to professional arborists or tree trimmers. They are properly trained and have the right equipment to do the job safely. To make sure you'll get the job done right, review pruning guidelines published by the International Society of Arb culture. Your pruner should have a copy. Pruning and growth. To understand how to approach the pruning of any plant, you need to know how growth occurs. Because all growth originates in buds, they are the first plant parts to consider. The terminal growth bud develops at the end of a stem or branch. This bud causes the stem to grow in length. Lateral buds grow along the sides of stems. These buds produce the sideways, or lateral, growth that makes a plant bushy. Some plants may have latent buds—buds that he dormant beneath the bark. Some of these buds may grow after pruning or injury removes the actively growing part of the stem. . Actively growing terminal buds produce hor- mones, called auxins, that stimulate their growth and, In many species, prevent lateral buds below them from growing during the current season. If the terminal bud is removed, either while the plant is growing or dormant, subsequent growth occurs from the uppermost lateral buds. These