Powdery mildew on blooming phlox proves tough problem to fix

A Presque Isle gardener has been trying for years to grow phlox, but every year the plants are covered with unsightly powdery mildew before the first blossoms appear. She wonders whether soil quality could contribute to the problem.

Hardly anyone can grow summer blooming phlox (formerly called Phlox paniculata, now renamed P. decussata) without encountering powdery mildew. The disease gets started in early summer and grows steadily worse, often defoliating the plant from the base upwards and always covering leaves with a thick layer of white powdery fungus. Soil quality may contribute to the problem only in the sense that overly rich soil leads to lush, soft foliage which is generally more apt to succumb to any disease.

Fungicides are more or less effective against this pest, but I am not legally entitled to make recommendations in this area. I suggest anyone with an interest in knowing which fungicide to use as well as when and how to apply it should contact his or her county extension office or the University of Maine’s Pest Management Office located on College Avenue in Orono (581-3880).

If spraying is not a viable option, there are other things one can do. First, relocate the phlox to the sunniest, breeziest and least humid spot on the property. Unlike most fungus diseases, powdery mildew requires only high humidity, not wet foliage to infect and spread rapidly. Second, try new varieties as some are a good deal less susceptible to mildew than others. Dark-leaved varieties seem to be generally healthier.

There are two closely related species of phlox that are nearly immune to powdery mildew. P. carolina (varieties: Miss Lingard and Rosalind) and P. maculata (varieties: Alpha and Omega) are commonly available and well worth growing. Neither is quite as luxuriant and heavy blooming as some named varieties of P. decussata, but given a few years to fill in, both make very showy garden plants.

An East Holden gardener encountered a common problem with his recently planted raspberry canes last summer. An insect girdled the new canes about halfway up from the ground and in a few days the top of the cane broke off. He tried spraying to no avail.

Cane borer is about as hard to escape in raspberries as powdery mildew is in phlox. The good news is that it usually is not as damaging. Most growers just put up with the natural pruning job done by these insects because the bugs don’t tend to hit every stem, and since raspberries produce far too many canes per foot of row, one can usually just eliminate damaged canes at thinning time.

Again, I do not make recommendations for spray materials, but the same sources given above may be able to help. I have the impression that this is not an easy insect to control with chemicals.

A Lincolnville reader wants to know how I managed to locate Burpee Seeds’ famous Fordhook Farm in Lancaster County, Pa., land of the Amish, when Bucks County has always been home to the Burpee spread.

The answer is that those two counties are both so incredibly pastoral and beautiful that they run together in the atlas of my mind. Thanks for the correction.

Finally, a reminder that this weekend is the third annual Bangor Garden Show at the Bangor Auditorium and Civic Center. After a winter like this one, you owe it to yourself to brave the crowds and pay a visit.

Even more finally, the Penobscot County Soil and Water Conservation District will hold its annual tree and shrub sale on May 4 (May 5 if the preceding day is too rainy) at 970 Illinois Ave., Bangor. Orders are no longer taken in advance and all plants are sold on a first-come, first-served basis. For a list of plants offered, contact them by mail at the above address or by phone at 941-8973.

Michael Zuck of Bangor is a horticulturist and the NEWS garden columnist. Send inquiries to him at 2106 Essex St., Bangor, Maine 04401.