I have noticed lately that since I started misting my outdoor trees 3-6
times a day, some things are happening to some of the trees. Two dwarf
Myrtle have caught mildew fungus pretty badly, a flowering quince has
developed yelow and deformed leaves, a barberry has had it's blossoms
stop developing. There is an overall funk over a some of the plants.
Though, it has not affected the junipers. I live in zone 12 in the
desert, Tucson, humidity has been low, 15-25%. The dew point has been
24-30. Is there a point where there is too much water on the leaves and
top soil, or is it just learning which species like it and which species
do not? Brian

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I have noticed lately that since I started misting my outdoor
trees 3-6
times a day, some things are happening to some of the trees.
Two dwarf
Myrtle have caught mildew fungus pretty badly, a flowering
quince has
developed yelow and deformed leaves, a barberry has had it's
blossoms
stop developing. There is an overall funk over a some of the
plants.
Though, it has not affected the junipers. I live in zone 12 in
the
desert, Tucson, humidity has been low, 15-25%. The dew point
has been
24-30. Is there a point where there is too much water on the
leaves and
top soil, or is it just learning which species like it and
which species
do not? Brian

Fine dropletlets of water are one of the major means of spreading
funguses, so a little misting can go a long way . . . the WRONG
way.

In the dry Arizona air, you will do much better to water your
trees morning and late afternoon, rather than spraying the leaves
with a fine spray of water. Keep your trees under shade cloth
and out of direct drying winds (but still keep sufficient
distance between trees to assure air movement) and you won't have
to mist as often. Once in the a.m. and once in the p.m. (during
daylight) is probably MORE than enough. Let them be exposed to
only morning sun. Shade from anything after noon will let them
grow healthily.

When temps climb in late summer, you COULD water 3 times a day,
BUT your trees probably pretty much shut down (a second dormancy)
at that time of year, so most of them may need less water,
anyway -- natives excepted, of course -- maybe.

Jim Lewis - - Tallahassee, FL - A "native"
of Nogales and Tempe, with stints in Prescott in between, and
many long climbs in the Grand Canyon

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I have noticed lately that since I started misting my outdoor trees 3-6
times a day, some things are happening to some of the trees. Two dwarf
Myrtle have caught mildew fungus pretty badly, a flowering quince has
developed yelow and deformed leaves, a barberry has had it's blossoms
stop developing. There is an overall funk over a some of the plants.
Though, it has not affected the junipers. I live in zone 12 in the
desert, Tucson, humidity has been low, 15-25%. The dew point has been
24-30. Is there a point where there is too much water on the leaves and
top soil, or is it just learning which species like it and which species
do not? Brian

It's not clear to me why you're misting the trees. I mean, yeah,
you're in Arizona, but misting isn't helping to raise the relative
humidity to any significant degree, and *is* benefitting foliar
pathogens, so why do it? To increase humidity, put plants in an
environment that will encourage humidity without encouraging leaf
wetness. Erect a lathe roof to create partial shade. Screen plants
from drying winds.

The best thing to do about the powdery mildew (besides using a
fungicide) would be to increase air circulation. That will change
the microclimate of the leaves, making sure that microdroplets of
water evaporate as quickly as possible.

I don't know what's wrong with the quince: check for thrips, which
cause the symptoms you describe. Your quince is always going to have
problems; in hot climates, quince typically put out a burst of
flowers and leaves in the spring, then get blasted by the summer heat
and drop their leaves. They then reflower and re-leaf in the fall.
If you shade them during the summer, they should retain their leaves.
--
Nina Shishkoff

Frederick, MD

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At 06:28 PM 4/10/03 -0700, Brian Berggoetz wrote:
I have noticed lately that since I started misting my outdoor trees 3-6
times a day, some things are happening to some of the trees. Two dwarf
Myrtle have caught mildew fungus pretty badly, a flowering quince has
developed yelow and deformed leaves, a barberry has had it's blossoms
stop developing. There is an overall funk over a some of the plants.
Though, it has not affected the junipers. I live in zone 12 in the
desert, Tucson, humidity has been low, 15-25%. The dew point has been
24-30. Is there a point where there is too much water on the leaves and
top soil, or is it just learning which species like it and which species
do not?

Brian

You have already been given a lots of good advice, and I will will
hopefully give you a little more. I also live in a very hot dry climate,
although not quite as bad as Tucson. I have overcome this in the nursery by
the use of shadecloth and appropriate watering. A shadecloth or lath house
is your best bet. Nearly all plants will grow just as good under 40-50%
shadecloth (all day sun) as they would under full sun in a milder climate.
The shadecloth slows the air flow and helps keep up the humidity if you
water properly.

Your humidity undoubtedly goes up at night and drops in the morning as the
sun heats up the air. Therefore, it is best to water just before the heat
of the day. Here, I find that 11am is just about ideal. That may mean a
timer and automatic watering system. Such a system also has the added
benefit that it can water slowly and thoroughly over a long period of time.
For me this is typically 45 minutes to an hour. This give you wet foliage
for up to an hour (to 12pm), high residual humidity for perhaps another
hour (1pm), then gradually falling humidity the rest of the day. Those last
four hours of heat can be the killer. As long as the temperature is under
100F here, I don't have a problem. I just allow the shadehouse to dry out
naturally.

Over 100F may require additional measures. Misting is not the answer,
because, as Nina said, it will cause more problems than it solves. You are
currently finding that out. In addition to increased disease problems, it
leaves mineral salts on the leaves which can actually increase the chance
of attracting mites. I would check those plants with "powdery mildew" on
the undersides for mites instead. (see
http://www.evergreengardenworks.com/mites.htm ) . A single additional, but
shorter watering on very hot days in the middle of the afternoon period
(around 2pm) can give you enough protection for the rest of the
day. Alternatively, you can use a dual water system if your plants are off
the ground and on benches. Your secondary system should mist or water the
ground only, not the plants. This will give you a cooling and humidifying
effect without wetting the plants. This involves a complete addtional water
system, so you should consider the cost and complexity.

When you do water your plants, it is best to water thoroughly and for a
long period of time. Watering very slowly or misting often allows the water
to continually evaporate from the leaf surface, leaving mineral deposits
behind. Adequate rate continual watering will keep the leaf surfaces wet
during the watering cycle and flush off deposits and dust rather than
contribute to the problem. Additionally, making sure that the soil is
really saturated and relaxed (expanded), such as from a long one hour
watering, insures that the plant will get all the water it can possibly get
and have its maximum retained reservoir level just before it needs it at
the beginning of the dry heat of the day.


Brent in Northern California
Evergreen Gardenworks USDA Zone 8 Sunset Zone 14

http://www.EvergreenGardenworks.com

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G'day all...

Brent, Nina...and others who have responded to this thread...

I suspect that Brian may be trying to cultivate moss...we do have some sucess
(not me, even though retired, I don't have the time for the misting) with moss
here in Southern Arizona.

If "moss" is the goal...

Brian... you may need to mist 3 or 4 time a day...but, be sure to mist the moss
directly. Avoid leaves, needles, branches, etc.

Hope this helps.

Have a good day...

Pat

Dez of the Arizona High Dezert, at 4550', Oracle, AZ,
2000' above Tucson Sunset Zone 10 USDA Zone 8
aka: Pat Patterson 'riding off in all directions'