Whitish-Grayish Coating on Grass Leaves

Question:

I have several large areas in my back yard where a white/grayish fungus is on the grass blades. A couple of years ago a nursery suggested Daconil. When I used it the past two years, I don't think it spread very much but the Daconil, about the same color as the fungus itself, made that part of the lawn gray and did not clear up the problem. Recently I noticed the same spots re-occurring plus some other areas. This time the nursery recommends Sulfur Hydroxide. What is really best? Either of these, a combination of both, or something else? The grass is well established, probably about 35+ years old and is mainly a fescue. At least that is my estimation since the lawn was sowed by the previous owner as Albuquerque Mix.

- Larry L., Albuquerque

Answer:

I wonder if this is really a fungus. Powdery mildew makes a thin whitish coating on the leaves. Powdery mildew can be a significant problem, but can often be managed by reduced night humidity - irrigate early in the morning every third day or so. Some fungicides (labeled for treatment of powdery mildew) can also be used if irrigation scheduling changes can't eliminate the problem. Even so, irrigate in the morning and infrequently to keep the fungus from reappearing.

If it is a thicker grayish coating on leaves of grass over an area less than a foot in diameter, it may be slime mold which is not a real problem and can be washed off with a strong stream of water. Slime mold should not damage the grass (except to exclude light from the coated leaf blades).

The best way to know for sure is to take a sample of the affected grass to the County Extension office and have the agent determine what specific problem is present.

Ants on Willow Tree

Question:

I have three Weeping Willows in my yard that are about four years old. One of them has red & black ants on it. Are they a problem? Don M. via internet

Answer:

The ants are probably not a major problem, but an indication of other problems. While it is possible that the ants are carpenter ants which can mine dead wood in the tree, it is more likely that the ants are present because there are aphids in the tree. Aphids feed on the sap of the tree and can spread plant diseases. They are likely to be the real problem. Do you see a silvery sheen on some of the leaves? This is the honey dew excreted by the aphids. This is also the sugary substance which is attractive to the ants.

Aphids can often be washed from small trees and shrubs with a strong jet of water from the garden hose. Of course, they will climb back into the tree or shrub, but while climbing they will not be harming the tree. However, even while they are climbing into the tree after being washed out, they are prey for many types of predatory insects. You can use a pesticide, but this will harm the beneficial insects that prey on the aphids. This is a good time to avoid the chemicals if possible.

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Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

Links:

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook page.

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