Researching Maintenance

The wrong kind of trunk paint I care for a 25-year-old tree that was recently vandalized with red paint or stain (I'm not sure which). Do you know of any safe methods for removing paint from trees?-via the internet

Keep in mind that bark will wear and weather as trees age. Therefore, the graffiti eventually will disappear on its own. However, if you need to be more proactive, you have at least a couple of options.

You could try mechanical removal, such as with wire brushes or power washing. This might be a good strategy if the tree has thick bark that could stand to have a layer or two removed without reaching living tissue. However, some trees do not develop the type of bark that would allow this, so it depends on the species.

If mechanical removal isn't possible, you could paint over the graffiti with trunk paint. This is not exactly a subtle way to deal with the problem, and certainly not the solution you're looking for if you want to return the tree to a natural-looking state. However, it is one possibility.

You should avoid chemical removers in this instance. The suppliers with whom I checked all expressed concern that their products-even so-called "non-toxic" graffiti removers-could harm trees.

Isolating resistance How can I definitively determine if I have a DMI-resistant strain of dollar spot on bentgrass fairways?-Illinois

So many variables exist that you cannot automatically blame fungicide application failures on resistance. A laboratory assay is necessary to provide the needed controls for environmental and application variables.

I asked two turf pathologists about this-Dr. Peter Dernoeden at the University of Maryland and Dr. Jon Powell at the University of Minnesota. Their answers suggest that, while laboratory techniques for analyzing suspected resistant pathogens may vary, certain basic elements are standard.

Labs will always culture the fungal samples, or isolates, in the presence of some level of the fungicide to which resistance is suspected. Culturing a known susceptible (non-resistant) isolate for comparison is standard as well, and some labs will also use a third isolate that is known to be resistant.

Some labs will use several rates of the fungicide in the cultures to see how the pathogens respond to various levels of the material, while others will test with just one or two rates. In most cases, either method should reveal whether resistance is present.

Dernoeden noted that an additional step, though not necessarily standard, would be to spray plants in a greenhouse and "challenge" with three isolates: known-resistant, known-susceptible and suspected-resistant. This step would provide confirmation of the lab results.

As this shows, determining resistance is not simple. There's no quick and easy field method for doing so. You must use a plant-pathology laboratory, which will instruct you on how to submit samples.

Turf and pH What are the preferred pH levels of the various turfgrasses?-Via the internet

Most turfgrasses are similar to the majority of plants in their pH preference. That is, they succeed best in soils that are slightly acidic. The following table was supplied by Dr. Peter Landschoot of the Pennsylvania State University (University Park, Pa.).

Tall tails I have a bad problem with horsetail in a public planting that I maintain. It consists of raised beds with ornamental trees and shrubs and pine-bark mulch. What are my best options for control?-via the internet

Several chemical products are labeled for control of horsetail: glufosinate-ammonium (AgrEvo's Finale), several selective broadleaf products and halosulfuron (Monsanto's Manage, which lists horsetail on supplemental labeling).

None of these products are labeled for over-the-top spraying in ornamentals, so directed sprays are your only option. If the horsetail is intermingled closely with the desirable plants, even this is not safe.

A Monsanto representative informed me that halosulfuron actually is reasonably harmless to many ornamentals, so this product may give you a somewhat wider margin of safety than other products mentioned above, which definitely will harm ornamentals. Nevertheless, you should not take chances-direct your sprays carefully to avoid contact with desirable ornamentals.

Also be aware that none of these products provides complete control of horsetail: you can expect some regrowth. As with many weeds, the status of the horsetail at the time of application seems to affect herbicide performance, so apply when it is small and, if possible, when stress is minimal. For example, halosulfuron can provide up to a year's worth of control if applied to small, actively growing plants. Conversely, you might see significant regrowth if the chemical did not translocate well.

Plastic sheeting over the soil surface is an option, though it's not likely that this could completely stop a weed as tenacious as horsetail. Over the long run, physical control (digging), though labor intensive, might yield results as good as other methods.

High-pressure injection (HPI) is gaining popularity as a means of applying pesticides and other products to turf. HPI units place material directly into the soil beneath the turfgrass canopy by using pulsed liquid jets propelled with pressure as high as 5,000 psi.

This technique offers great advantages. For example, HPI simultaneously increases insecticidal effectiveness by placing products closer to soil-inhabiting pests while reducing surface residues that could contact nontarget organisms or people. HPI accomplishes this with minimal surface disruption.

Another possible use of HPI is emerging. Dr. Milt Engelke of Texas A&M University (College Station, Texas) has been studying HPI as a method of sowing bentgrass seed into existing turf stands. A non-surface-disruptive method of converting existing stands to new varieties is not currently available, so this would be a significant development, especially for courses that want to convert older greens to newer varieties.

HPI seeding must meet several conditions to be a viable method of sowing. First, the seed must be small enough to pass through the HPI unit. Second, the seed must be able to survive and remain viable. Finally, after being injected through the turfgrass canopy and into the underlying soil, the seed must be able to germinate and establish within the existing stand.

Bentgrass seed, at 6 to 10 million seeds per pound, is small enough to pass through an HPI unit (Engelke used a Cushman Envirojet unit with the filter screen removed). By intercepting seeds ejected from the HPI nozzles and then germinating them, Engelke found that more than 70 percent were undamaged and viable. This is an acceptable level; 1 to 2 pounds of seed per 1,000 square feet equals several million seeds even with a 30-percent loss.

Ultimately, what counts is whether the seed becomes established successfully. Depth of placement is a critical factor. Excavations by Engelke showed that, while HPI was capable of injecting seeds to a variety of depths, most seeds that germinated were at 1/8 inch or less. Additional observations by Engelke indicate that the bentgrass does establish successfully after sowing with HPI, but more observations are needed to determine long-term success.

The greatest potential for HPI sowing seems to be for seeding bentgrass into existing stands. Experiments with new stand establishment (that is, with bare ground) show HPI to be too surface-disruptive. Plus, the seeds of most other turfgrass species are probably too large to pass through HPI units. Nevertheless, this research shows that superintendents may have a new tool for seeding their bentgrass greens and other areas without interrupting play.

All-America Selections (AAS, Downers Grove, Ill.) is a non-profit organization dedicated to evaluating new plant varieties. Each year, AAS selects winning cultivars that excel in attractiveness and reliability in landscape situations. AAS recently released its latest list of winners-New Varieties for the New Millennium-and it includes several exceptional bedding plants that should be available in 2000. Among them:

* 'Fiesta Del Sol', the first commercially available dwarf Tithonia (Mexican sunflower). It attains a mature height of 2 to 3 feet-not exactly petite, but much smaller than a typical Tithonia. This variety is essentially pest-free and reportedly unappealing to deer. 'Fiesta Del Sol' prefers full sun and produces abundant, 2- to 3-inch, orange blossoms.

* 'Cosmic Orange', an improved Cosmos sulphureus that grows to about 12 inches. 'Cosmic Orange' is a "no fuss" variety that is essentially pest- and disease-free and prefers full sun. It blooms all summer, producing abundant, 2-inch flowers.

* 'Stardust Orchid' vinca (Catharanthus roseus), the first vinca with orchid and white blooms. This variety is relatively pest free and tolerates drought and heat. It will reach up to 16 inches tall and wide. Most notably, 'Stardust Orchid' blooms freely in a variety of weather conditions.

The nearly 200 AAS display gardens around the nation are open to the public. You can find locations listed on the organization's website, At these gardens, you can view firsthand the performance of these and other new varieties in a landscape setting. This gives you an unbiased resource to help you choose new material for bedding displays.

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