Don’t take the chance that the soil is not infected. What if you had no signs of disease this year? Some gardeners found their plants untouched while their neighbors impatiens crashed. Soil from containers where impatiens grew must also be disposed of properly and the container thoroughly cleaned before storing for the winter. The soil and mulch, as well as the plants, need to be bagged and disposed of where they will be burned or buried in a landfill. The fungal spores of IDM will be present and tests have shown those spores will easily survive our winters. Remove not just the plant but the soil and mulch in the area where it was growing. So what do you do if you were growing impatiens, one of the most popular annuals, in your garden or containers this year? First start with a thorough clean-up. In 2011 it returned, apparently having developed a resistance to available fungicides. Greenhouses treated it with fungicides and it seemed to be under control. Remove non-saleable plants from the greenhouse at the earliest opportunity.The disease is called Impatiens Downey Mildew (IDM) and it showed up first in Europe nearly ten years ago.Keep plants well fertilized but not excessively succulent.Protect plants with fungicides containing active ingredients such as boscalid plus pyraclostrobin, chlorothalonil, copper, cyprodinil plus fludioxonil, fenhexamid, fludioxonil and iprodione used in rotation, according to labels.Remove spotted leaves before they develop sporulation.Keep greenhouse humidity low (wire mesh) benching so that air can move up between plants. Space plants well, so that air can move between plants and so that lower foliage is exposed to light.Know which plant species are especially prone to Botrytis leaf spots.Margery is a plant pathologist specializing in ornamentals at Cornell University’s Long Island Horticultural Research & Extension Center. Petals falling onto geranium leaves can give Botrytis leaf spots their start. Management is centered around manipulation of the environment to reduce relative humidity and minimize the length of time that leaf surfaces are wet. Botrytis leaf spots are easily recognized by the grayish brown sporulation that covers the surface of leaf lesions when humidity is high. Wounds made during cutting transit are a common site of entry. The fungus will attack shaded lower leaves, but may also colonize leaves killed by other causes because it can grow on dead plant tissue. Low light will favor Botrytis, so it is often seen in the greenhouse during winter. If the environment is favorable to disease development, the spots may progress down the petiole or via a cutting wound into the stem. The galloping leaf spots continue to enlarge at every opportunity, sometimes showing several zones that indicate a series of humid periods. Spots may be round or oval if they begin in the middle of the leaf blade, or form wedges if they develop at the leaf edge. Plants that are especially prone to Botrytis attack include begonia, geranium, vinca, snapdragon, lisianthus, osteospermum, poinsettia, New Guinea impatiens, exacum and zinnia. The ubiquitous fungus Botrytis cinerea is most famous for what it can do to flowers, but on some species, under favorable environmental conditions, it can cause spotting on leaves as well. Botrytis leaf spot is one of the aspects of a wide-ranging disease often called Botrytis blight.
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