I have a problem with my lilacs, as well as a few other plants(geraniums). The leaves get yellowish, but the veins are still green. Then the lilac leaves turn red & die. The geraniums turn black.
Lilacs probably are chlorotic...soil lacking in iron or magnesium.....alkaline soils tend to lock up these elements, preventing the tree to absorb what they need.....luckily, it is close to leaf fall (end of the season) and this will not affect the health of your lilac......The geraniums sound like they have botrytis fungus which will kill your plants if too many leaves are affected......fortunately this is a seasonal/weather related fungus and you may not get it on your geraniums next year......
