![]() ![]() Pat Munts is co-author, with Susan Mulvihill, of the “Northwest Gardener’s Handbook.” Munts can be reached at. Simply wind a soaker hose amongst the plants and set it on a timer for three to four hours every two weeks. You need to water the plants deeply and periodically during the dry weather in August and September. The best way to do this is to install a simple watering system for your plants separate from the lawn sprinklers. The plants will probably recover but it is going to take a couple of years and a little extra watering. As a result, the plant can’t support its full canopy of leaves and is now beginning to retire the excess. Two years of drought probably damaged roots, reducing the plant’s ability to properly take up water and fertilizer, especially during the hot weather we had in August. This doesn’t match any other disease profile and is likely caused by cultural problems around watering, fertilizing and drought stress. The leaf veins are still green but the leaf is a pale yellow-green with a few brown patches. Instead, the leaves appear to be chlorotic. However, what the Master Gardeners have been seeing in the clinic doesn’t quite match the description of lilac bacterial blight. Lastly, if you have had the disease in the past, the plants can be sprayed in the early spring with a copper sulfate solution to reduce the potential of the disease. Clean up old leaves in the fall to remove disease reservoirs hiding out in the leaves. Provide regular water in the driest months to reduce drought stress. Too much fertilizer or fertilizer put on too late in the year can over-stimulate the plants. Fertilize the plants lightly in the spring. Improve air circulation around plants by pruning out dense growth. Maintaining healthy plants is the best defense against the disease. The common lilac (Syringa vulgaris) and its cultivars that we all have in our gardens can be quite susceptible to it under the right conditions. Carol Savonen is a naturalist and writer. To see photos of this disease, visit OSU Extension’s PNW Plant Disease Management Handbook. We have had a few minor occurrences of it in the Inland Northwest. How to prevent lilac bacterial blight in future seasons. However, it can also appear when the plants become drought-stressed like they have been for the past two years. Normally this disease pops up in the spring when it’s wet and cool. The most common issue we see here is lilac bacterial blight that results in leaves and shoot tips turning black. In fact, they are so resilient that they still mark the sites of old homesteads all over the region decades after the farmhouses have fallen down. They are drought tolerant (to a point) and need little fertilizer and little pruning beyond removing old flower heads right after they bloom. In our climate, lilacs are one of the tougher shrubs in the garden. Several people have contacted the WSU Master Gardener Plant Clinic over the last couple of weeks with questions about pale leaves and tip dieback. You know we have had some rough weather over the past few years when the nearly indestructible lilac starts having some issues.
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