WANTED FOR: DEFACING
TREASURED PLANTS, BRINGING DISEASE AND DEATH TO PLANTS
Podosphaera spp.; Erysiphe spp.; Sphaerotheca spp.
Victims: Fruit and ornamental trees, especially roses; garden
Hangout: Fruits and leaves in areas that are cool, shady
and humid but not wet
Physical Features: Fruits and leaves affected
by powdery mildew will look as though they've been sprinkled with baby
powder. If the infection is bad, the mildew may also be speckled with
small brownish-black dots. Eventually the threads may look yellowish green.
Only yellow spots, not white ones, will appear on some plants, such as
tomatoes, peppers, and eggplant. Rhododendrons can have yellow or purplish
Powdery mildew spores survive the winter by taking leaf buds hostage and
using them as a cozy home. In the spring, they assault tender new plant
parts by stabbing them with root-like organs. These organs suck out nutrients
from the plant. After stealing food, the rascals reproduce rapidly and
continue to raid healthy tissue.
DURING MILD WINTERS, POWDERY MILDEW SPORES CONTINUE TO BUILD UP THEIR
FORCES BY REPRODUCING ALL YEAR LONG.
Take the POW out of Powdery Mildew!
1. Patrol the area
- Stake out new growth in
the spring. Powdery mildew spreads rapidly on humid, but not rainy,
- Be more attentive to shaded
- Carefully search for white
powdery marks and curling leaves.
- Make a record of any encounters
with powdery mildew. Be sure to record who its victims were and the
extent of injuries.
2. Make a positive I.D.
- Powdery mildew is usually
whitish, but remember it can cause colored spots. Cooperative Extension
has Master Gardeners that will help you identify the suspect for free!
Just bring in a fresh sample.
3. Do a thorough background
- Powdery mildew is one of
the only fungal diseases that doesn't benefit from plants being wet.
These spores die in water, which also inhibits growth of the powdery
strands. Humidity helps powdery mildew, but liquid water is lethal.
4. Determine the danger
- Healthy plants can withstand
most damage from powdery mildew. However, it doesn't hurt to take some
precautions, like pruning.
- Seedlings and water- or
nutrient-stressed plants are not as able to defend themselves from this
5. Make a plan
- Do-Nothing Method
-Letting nature run its course without intervening can be a good strategy.
-The inevitable rain and cool weather of the Lake Whatcom area will
help plants fight off powdery mildew.
-Select resistant varieties. See Passive-Aggressive
Plants for rose and rhododendron recommendations.
- Manipulative Measures
-Get the S.W.A.T team to ward off powdery mildew! Hack off infected
parts. Prune out young diseased tips anytime, but older infected parts
should be removed only in the spring.
-Let air circulation keep humidity between plants down. Remember to
space plants with plenty of breathing room and, if possible, plant on
the windy side of your property.
-Hose down the intruder. Use a forceful spray of water to kill powdery
mildew. But beware-wet leaves can be a breeding ground for other fungal
-In garden beds, don't put plants from the same family in the same place
every year since diseases usually assault plants from the same family.
Rotate plants from different families.
- Secret Agents
-Many lady beetles help in the fight against other bugs, but there is
one kind of lady beetle, Psyllobora spp., that actually eats powdery
mildew. It's very common in the Lake Whatcom area. Look for small beetles
mottled with black and cream colors.
- Armed and Dangerous
-If you've got a powdery mildew invasion going on, use sulfur products
to keep it from expanding. Most home and garden stores sell sulfur products
to combat fungi.
-When using a chemical weapon, be sure to read and follow directions
for use, storage, and disposal.
6. Evaluate the results
- After documenting the types
of plants assaulted by powdery mildew, note if you took any steps to
retaliate or if you just let Mother Nature handle it.
- Recording the outcome of
the strategies you choose will help you get better each year at fighting
off powdery mildew using as few chemicals as possible.