RESEARCHING MAINTENANCE

No herbicide is that selective

Are you aware of any post-emergence herbicide selective for broadleaf weeds in wintercreeper (Euonymus f. coloratus)? — Via the Internet

I know of none. Most broadleaf herbicides are pretty effective against nearly all broadleaf plants. The trouble is, that includes ornamentals, too.

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If your problem is with annual broadleaf weeds, then a pre-emergent will be your best bet. I can't recommend a particular chemical, because you don't specify which particular weeds are infesting your plantings. But several effective products are available. Established perennial weeds will need to come out the old-fashioned way — hand-pulling.

Poa in zoysia

Are you aware of a post-emergent herbicide selective for Poa annua that could be used on Zoysiagrass, either dormant or while actively growing? — via the Internet

Perhaps the easiest way to achieve post-emergence control would be to spray a non-selective herbicide while the zoysiagrass is dormant (make sure it's completely dormant). This, in effect, creates selective control.

One product with such labeling is Syngenta's Reward (diquat). Interestingly, Monsanto's Roundup Pro and Chipco's Finale both list dormant bermudagrass for exactly this type of use, but not zoysiagrass. A representative of Chipco Professional Products explained that this is merely because this use has not been tested by the company, not because they know of any problem that would arise.

However, Roundup and Finale both list spot-spraying on their labels and, although it may be somewhat open to interpretation, such a use on dormant zoysiagrass seems to be permissible according to the label language. One caveat, however: Anytime you use a product in a way that is not explicitly labeled, you should try it out in a small area, just in case some unexpected damage occurs.

An alternative is the use of pre-emergents, of which there are several labeled for use against Poa annua in turf. Late summer applications should prevent most of the fall germination flush of Poa annua. Clemson University's Dr. L.B. McCarty stated in a January 1999 Grounds Maintenance article on Poa annua that a fall application may not be enough to prevent the continuing germination that often occurs through winter and, to a limited extent, even into spring. Therefore, a repeat application may be called for, depending on the product and environmental factors.

Worrisome worms

I noticed green worms in some topsoil I had delivered. They look like earthworms but I've never heard of them being green. Is this some kind of pest I should be worried about? — via the Internet

Green earthworms do exist. Though most people equate earthworms with the common night crawler, which is colored brown or reddish brown, numerous other species of earthworm inhabit soils in the United States. A few of them are greenish in color, but otherwise look essentially like other earthworms. It wouldn't seem that you have anything to worry about.

Aluminum confusion

I've seen aluminum sulfate labels that give directions for using it to lower soil pH. But I also have heard that you should not use aluminum sulfate for soil acidification because it could harm plants. What does this do to hydrangeas when people use it to turn the blooms' color? Why the contradictory information? — via the Internet

Aluminum sulfate is an effective material for lowering soil pH, but the aluminum may be toxic to some plants. Though plants vary in their sensitivity to aluminum, some are quite susceptible. Thus, many experts feel it's better to recommend generally against its use. Hydrangeas appear to handle aluminum sulfate just fine as long as the application rate is not too high, as evidenced by the generations-old practice of turning their flowers color with this product.

It's the aluminum that turns hydrangea blossoms color, not acidic soils, per se. However, some people find that simply acidifying the soil is enough to cause hydrangea blossoms to color up. The acidity allows roots to more easily take up aluminum that already is present in the soil. Aluminum sulfate acidifies soil and provides aluminum, making it very effective for this specific purpose.

If you just need a material to acidify your soil, consider elemental (powdered) sulfur or iron sulfate. Both effectively lower pH and are inexpensive and easy to apply.

Acidifying fertilizers such as urea and ammonium sulfate have a more gradual effect on pH, but will definitely lower it if used consistently.

Eric Liskey has a bachelor's degree in ornamental horticulture and a master's degree in botany. He has been licensed for pesticide advising and applications in California and Missouri, and has more than 10 years combined professional experience in landscape installation and maintenance, nursery retailing, pest management and botany.

If you have a question about landscape or turf management, write to “Researching Maintenance,” Grounds Maintenance, P.O. Box 12901, Overland Park, KS 66282-2901, or send you question by e-mail to eliskey@primediabusiness.com.

Questions are selected on the basis of current general interest. Unfortunately, we are unable to guarantee a response to individual letters.

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