White spots on leaves could be powdery mildew fungus

QUESTION: “I just planted some salvia in my garden and noticed some white spots on the leaves. Any suggestions?” – M.

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 fungicide.

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 package directions!

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 Extension Service.

http://vegetablemdonline.ppath.cornell.edu/factsheets/Cucurbits_PM.htm

http://ohioline.osu.edu/factsheet/HYG-3081


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 get a
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?” – W.

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 build on.

“Alien” slime mold invades mulch!

QUESTION: “A couple of mornings ago, I noticed a strange yellow clump of something had appeared, apparently overnight, in one of our flower beds. It was a bright, almost neon, yellow and very moist and slimy. It looked almost like some kind of alien being! “By the next day, it had formed a skin or crust on top and was turning brown. It now looked like a very large, stale egg foo yong! The following day, a second patch appeared, about six feet away in the same bed. Is this some kind of fungus? I am planning to remove the two clumps with a shovel and replace the mulch. But I'd also like to know if there's a way I can treat the soil to discourage it from happening again.” – Mike H

ANSWER: We’ve had these things show up too and they do look weird, don’t they? The good news is that they might be unsightly but they are not plant parasites.

Slime mold is indeed a type of fungus that produces large, single-celled bodies called plasmodia. Plasmodia are the feeding stages of the fungus and can be seen on mulch, lawns and dead wood, according to the folks at the Plant Disease Clinic at Cornell University. You can read their complete article at http://plantclinic.cornell.edu/factsheets/slimemolds.pdf.

Although slime mold is not a plant parasite, small or vulnerable plants can suffer if the mold covers or shades them. Slime molds will eventually disappear if left alone, but they are unsightly and you might want to remove them.

The folks at Cornell say that on mulch, they can be raked or turned under and on turf they can be mowed. In my case, I wait until the slime turns to a dry, flaky crust and remove it with a shovel. It will probably return when the conditions are right, but it’s good to know that slime mold isn’t really harmful to plants.

QUESTION: “Thank you so much for your helpful tips each week! I have a question about pruning in general. We have two azalea bushes and a very large bush (8-10 feet in diameter, 12 feet high) in our back yard (I'm afraid I don't know what kind it is, but its leaves turn bright red in the fall and it has small leaves about the size of a large thumb nail).

“We need to prune these back, as they are starting to creep into walkways and phone lines. What is the best time to prune? I don't want to kill the azaleas and the bush, but I want to keep them under control. The azaleas are currently blooming, and the bush has produced leaves. I appreciate any advice you may have.” – Sonja R.

ANSWER: From your description of the large bush, it sounds as if it is a non-blooming variety so you should be able to trim it now or most any time. As for the azaleas, the best time to trim these is after the blooms are spent or finished.

I received the following note from a reader in response to a question here about spiders:

“My brother has a good solution for spiders but it must be used with care.

”Old fashioned mothballs will kill spiders and insects. When my brother is going to be gone for a few days he throws a few under his trailer. He never has problems with the black widows, etc., that frequent his area. They die because the mothballs close off their lungs. (They will also damage human lungs if we are inhaling those fumes for any length of time.) Besides putting them under porches or other areas spiders love, you can sprinkle them around the outside of your arbor, house, etc. Note that they should not be allowed to vaporize close to food.

”I prefer to use more natural methods but this is a solution that works with some very unwelcome ‘critters’.”

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