Cornell Cooperative Extension
of Westchester County

Q. Leaf Spot on Birch Trees
I have leaf spot fungus on my birch trees and powdery mildew on a dogwood planted two years ago. A well-meaning neighbor said that I
should have all of my trees sprayed, but it's costly. I've never had this happen before, just this season with all the rain. Must they be
treated or should I leave them alone? Quite a few of the leaves on the Birches have turned yellow, spotted and brown and are falling.

A. Given the wet conditions this season, we are seeing many more fungi on woody plants of all species. The general rule of thumb concerning fungi
that cause defoliation this late in the season or fungi that compromise the photosynthetic abilities of a leaf this late in the season is that, in most instances, treatment is not necessary. To paraphrase according to one well-known authority at Cornell, the tree has probably done everything it
needs to do for the season (regarding photosynthesis) by the middle of July and the rest, after this time, is pretty much "gravy". Only when the
fungus, bacterial infection or other pest repeatedly defoliates a tree or causes significant injury to the woody portions of a tree or shrub is treatment usually suggested. If you want to take things a bit further to reassure yourself that your woody plants are healthy, you might check to see how well next years buds are forming. Another way is to nick a twig of an infected branch and look for bright green tissue under the newly formed bark. Generally, however, powdery mildew found on dogwoods and other woody plant species in September is not unusual and of no general harm to plant health. In a similar sense, leaf loss on birches this late in the season due to leaf-infesting fungi is not usually a cause for concern. As a general practice, picking up and discarding any fallen or diseased leaves may reduce the incidence of certain diseases the following year.

Gerald G. Giordano
Senior Horticulture Consultant/
Extension Community Educator

Gardenia Question:
Q. Why does my gardenia fail to bloom even though it appears to be healthy?

A. Lack of bloom concerning gardenias can have a great deal to do with giving the plant proper night temperatures during the winter. Place your gardenia in a spot where it will receive ample bright light such as sunlight filtered through a sheer curtain or blind (an East window can also be suitable) but where night time temperatures fall to about 62 degrees. This night time temperature drop should assure flower bud formation. Always avoid placing the plant near radiators. When the weather warms in mid to late May, place your plant out of doors in partial shade. The sunlight that filters through a tree without dense foliage seems ideal. Bringing the plant back into the house in late summer before the heating system is turned on usually prevents a great amount of leaf loss from "relocation shock". Of course, cultural practices consistent with the healthy growth of gardenias still apply. Water the plant when the soil surface is just getting dry to the touch and remove any water that remains in the drainage saucer longer than 1/2 hour by using a turkey baster bought specifically for this purpose. Always remove the drainage saucer when the plant is summering out of doors. When transplanting, use a soil that is rich in organic matter, yet drains freely and does not become soggy. A standard flowering house plant fertilizer that is not too strong is best applied from spring to fall. If the plant shows signs of chlorosis, a house plant mix containing increased amounts of peat moss may be advisable the next time you transplant. Apply a standard acid-type fertilizer at the reduced house plant rate per label directions until the soil can be amended. A note about sunlight requirements: Despite many repeated and well intentioned attempts, the establishment of standardized yet understandable definitions of different light levels for house plants still seems elusive and sometimes both unintelligible and unattainable. Regarding gardenias, I have seen them grown successfully in a full sun, south facing bow window from late October to late February with no sign of foliage injury. Yet, many sources warn us to keep them (always) out of direct sunlight in winter often using the proverbial curtain or blind. Clearly, there are indoor "light microclimates" to match every window, window treatment and windowsill, so start by filtering bright light as best you can or by keeping the plant to the side of a sunny window in a bright room. If it's clear that your plant needs more light in winter, try slightly more exposure. Foliage injury from too much sunlight will occur fairly rapidly so be observant and adjust light levels accordingly. Remember also, that as spring approaches, the sun becomes increasingly more intense so be prepared to move your gardenia "back, aside or behind" until it's time for its summer vacation out-of doors.

Gerald G. Giordano
Senior Horticulture Consultant
Extension Community Educator
CCE Westchester Hort Team.

Trees:
Q. I have a question having to do with trees on my condominium's property. Our plums are losing their leaves. No sign of bugs. The trees are probably 15 to 20 years old. My tree company says they are probably dying of old age. Would that be your likely guess also? Are you aware of any other things that might be affecting them? Thanks. -----------------------, Irvington, NY

A. Although plum trees as well as most cherries are know to be relatively short lived insofar as trees are concerned...the term "dying of old age" would seem too simplistic when discussing tree health and longevity, for a variety of reasons. Barring other obvious symptoms in addition to the leaf loss, what could be more likely is that your plums may be suffering from Cherry leaf spot (Blumeriella jaapii, formerly coccomyces). This is a fungal disease that causes spotting and leaf loss on cherries, plums, almonds and other related plants. Mild, wet summer weather such as that experienced during the past two summers can promote this disease. Guidelines for control are available when warranted. As with other plant diseases, severity and the need for control can vary from year to year.

Thanks,
Gerald G. Giordano
Senior Horticuture Consultant
CCE Westchester Hort Team

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