QUESTION: “I just planted some salvia in my garden and noticed some
white spots on the leaves. Any suggestions?” – Mazzocco
ANSWER: The white spots could be from mineral deposits from watering,
fertilizer residue or a fungus known as powdery mildew.
You will need to determine what is causing them before you can take
any action. Fortunately, the first two wouldn’t require any action,
but if they are caused by a fungus, you might want to apply a
Powdery mildew is one of the most common landscape fungus problems.
The first sign is often curled and twisted leaves before the white or
grey powder is apparent. When the mildew appears, you might see the
grey patches gradually enlarge and spread until they cover large areas
on one or both sides of the leaf. If you are seeing that, then you
have powdery mildew.
Severe infection can result in yellow or dry brown leaves and
disfigured shoots. Although powdery mildew is not usually fatal, it
can bring on early defoliation and unsightly plants.
Powdery mildew fungi are most likely to produce airborne spores and
infect plants when temperatures are moderate and will not be present
during hot summer days. When plants are overcrowded and shaded,
creating a cool, humid environment, they are at greatest risk for
powdery mildew infection.
Pick up any fallen infected leaves and pick off any severely damaged
or dead leaves and destroy them, preferably by burning. If it’s any
consolation, powdery mildew generally won’t adversely affect a plant’s
overall health, so if it appears to be quite mild, or if you can live
with unsightly plants, you could probably ignore it, other than
destroying the infected leaves.
However, you can use a fungicide to treat the problem. For best
results, begin to spray the plants as soon as the mildew is detected.
Repeat the spraying as needed, which is usually during the cooler
weather seasons. Not all fungicides are suitable for all plants, so
be sure to check on the recommended usage before you spray. Read the
Here are two very useful sites with photos to help you identify
powdery mildew and helpful instructions on how to treat the problem
and create an environment that will discourage the fungus from
returning. One article is posted by Cornell University’s Plant Disease
Diagnostic Clinic and the other is from Ohio State University’s
<a href="http://plantclinic.cornell.edu/FactSheets/powdery /
<a href="http://ohioline.osu.edu/hyg-fact/3000/3047.html ">http://
You can click on direct links to those sites when you find this column
at my Web site, <a href="http://
QUESTION: “I have a very steep slope in my back yard leading from a
patio down to our lake front. There is a retaining wall at the top
and a retaining wall at the bottom. I would guess that the incline is
about 45 degrees in some areas. There are trees on one side leaving
part of the slope in deep shade, part is dappled shade and a few areas
good bit of sun, but the bulk of the area is pretty shady.
“Since it is so steep, we have concerns about erosion control. It's
steep enough to be difficult to get out there and weed or do any other
normal garden "tending", so it has to be very self sufficient. Can
you give any advice on types of plants to use?” – Margaret Wilson
ANSWER: Anything you try to plant will most likely take several years
to fill in at best. Vinca, pachysandra, purple wintercreeper and
liriope will grow well on sloped shaded areas. Ivy might grow well,
too, but may be a bit too invasive for your landscape.
If there is a problem with erosion now, I would recommend putting down
erosion netting first and then planting. You can plant right through
the netting, just cut an X out where you want to insert each plant.
Erosion netting decomposes over 5 or so years allowing the ground
cover time to take hold and spread. In the meantime, it does a good
job at keeping weeds at bay. I hope this gives you some ideas to
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