Answer: It could be herbicide damage or Botrytis cinerea fungal blight, says Jim Childs, horticulturist at Heard Gardens, growers of more than 70 varieties of lilacs in Johnston, Iowa. Lilacs have shallow root systems, so herbicides commonly used on lawns, such as 2,4-D, when spread close to lilac bushes can cause curling and dying of the new growth, says Childs. If the leaves curl and seem thicker than normal and you've been applying herbicides on your lawn in the area of the lilacs, then this may be your problem. If you must use herbicides on your lawn, apply them at least several feet beyond the drip line of the lilacs. A less likely possibility is Botrytis blight. We see this problem on the new growth of lilacs that have poor fertility and inadequate air circulation combined with warm (70 F) and humid spring weather, says Childs. The flowers will be deformed and the new growth will have brown spots, which eventually kill the new leaves. Old growth usually isn't affected. According to Childs, the best solution to Botrytis blight is to thin out several main branches after flowering to promote air circulation and then apply a complete fertilizer, such as 10-10-10, to rejuvenate the plant.
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