Connie writes~
This spring my husband and I made a Zen garden. I began to plant several ground covers and perennial herbs in the soil sections of the Zen garden. Everything has flourished! So much so that it is hard to believe that this is the garden's first year. Suddenly, our sage (Labiatae) has started to droop, turn brown, and die. I see no aphids or other insect damage. It is planted in a sunny well-drained location. Nothing else in the garden appears unhealthy or unhappy. Do you have any comments or suggestions about growing conditions, likes and dislikes, and pests or organisms that attack this particular plant?

A. When an apparently healthy bush dies suddenly, with the withered and dried leaves remaining attached to the bushes, the most usual cause of death is primary root disease, a common occurrence. A bush may also be killed completely also by a secondary root disease. Primary root disease is one in which the fungus attack is the direct cause of death of the bush. Even the most vigorous and healthy bushes may be attacked and killed. The common symptom of primary root diseases are wilting and dying of foliage, but the withered leaves remain attached to the branches for sometime before dropping off. Sometimes a root disease may be recognized by the presence of a dead branch or branches on the side adjoining the center stem. Fungi may kill by invading the roots already weakened by other factors and perhaps accentuate the death of the infected plant. Mulch and other organic materials should be removed around the plant. Soil should be drenched with Dithane M 45/Capton - 50 g per 10 liters water or dilute according to package directions. Soil rehabilitation should be avoided. Before taking up this fumigation, all dead and dying branches must be cleared in addition to any dead and dying bushes. The soil patch to be treated is leveled and loosened with a digging fork and then application is made.

Article Source - Article Monster.com