Q: Enclosed are two pictures&emdash;one of my seemingly healthy primrose, the second one taken a few weeks later&emdash;not so healthy. Could you please diagnose this problem and suggest a cure or possible preventive treatment for later use? I enjoy your column very much. Thank you for helping. – Pat Ritter, Bloomfield, Ind.
A: This is a direct result of our extremely wet weather this year. Oenothera species have many different names, including Ozark Sundrop or Evening Primrose. They all prefer well-drained soils to moist ones and will die quickly in wet environments. Plant them where they are allowed to dry out between waterings and plant them so the crowns are slightly raised, especially in soils with a lot of organic matter. The brown margins on the leaves are symptomatic of edema (or excessive water). This year’s wet weather and cloudy skies can cause plants to suddenly exhibit the scab-like spots and burned edges shown in your photographs. In drier weather, the plant may recover if the roots have not rotted.
Q: We have a five-year-old Japanese maple and the leaves have started to turn brown and shrivel. Any thoughts? – Lynn Hegewald, West Lafayette, Ind.
A: Cut a branch that has wilting leaves and look for a brown to black ring in the outer sapwood. If the ring exists, the tree is infected with Verticillium wilt. The fungus lives in the water-conducting tissues of the tree and spreads rapidly. Our wet weather seems to have caused plenty of cases of Verticillium wilt this year, especially on Japanese maples and redbuds. If you see the dreaded dark ring, remove all dead branches showing wilt at least a foot below the wilted portion. Pruning doesn’t eliminate the fungus but may help prevent further spread. During dry periods, water at two-week intervals with the equivalent of two inches of rainfall. Verticillium wilt can exist in the soil for many years so if you replant a tree in the same area, it must be resistant to the wilt. Avoid ash, maples, redbud and others in favor of beech, birch, conifers and crabapples. For a more complete list of plant susceptible and resistant to Verticillium wilt, contact your local extension office and ask for a copy of BP-6, “Verticillium Wilt of Shade Trees.” If the pruned branch doesn’t have a dark ring, a number of possibilities exist. These include leaf scorch and root rot. Japanese maples prefer a sheltered spot away from the wind and evenly moist soils.
Q: We live in a new subdivision and are trying to establish a foundation planting of yews, but they keep dying. First, they turn yellow, then brown. We water them regularly, so that’s not the problem. -Jean Dittmeyer, Marion, Ind.
A: Yews are intolerant of wet feet or poor drainage. Quite often, the rich topsoil is removed from a new development before the lots are sold to builders. The builders compact the remaining soil with their equipment and bring up subsoil when they excavate for the basement. This does not provide a happy home for a yew. The compacted soil doesn’t allow water to percolate through the soil; instead, it remains around the root zone of the yew. To correct the situation, water only when necessary and make sure all downspouts take water away from the planting bed. If you replace some of the yews, plant the replacements higher than normal so the top inch of the root ball is above soil level. Apply 3-4 inches of mulch. On the other hand, consider replacing the yews with another evergreen, such as arborvitae or juniper, that is not so finicky about drainage.