Researching Maintenance

Choosing a plant supplier How do you choose a reputable nursery? And how does a contractor decide between using a nursery vs. a wholesaler?--New Jersey

Developing a relationship with a good supplier is not difficult, but there is no objective methodology to it. The supplier you use should be the one that best fills your needs--it just depends on what you're looking for and what's available in your location.

Obviously, good-quality plant material is important, and you shouldn't deal with suppliers of poor stock. Pricing also is important, but sometimes too important. Warren Quinn, director of operations and landscape services for the American Nursery & Landscape Association (ANLA), warns against using the bidding process as a method of selecting a supplier. The bidding process does not help you locate quality or service--only low price.

The key, according to Quinn, is building personal relationships with suppliers, which has many advantages (including intangible ones, such as trust). Quinn notes that design-build operations especially benefit from such relationships. Knowing what's available allows you to create designs with assurance that the installation can proceed without requiring substitutions.

It's difficult to generalize about choosing a supplier because markets vary by region. For example, contractors in rural areas often form purchasing cooperatives to help increase availability and reduce price for material shipped to their remote markets.

Larger markets support a greater variety of suppliers, including garden centers that discount to contractors, grower-wholesalers that deal directly with contractors and what the ANLA terms horticulture distribution centers (HDCs), which essentially are "re-wholesalers" that sell exclusively to contractors. HDCs can be a great way to "fill in the blanks" even if you obtain the bulk of your material wholesale. Like other suppliers, some HDCs deliver to the work site and some do not. The importance you place on this relative to other factors depends on your particular needs.

HDCs and grower-wholesalers are active in state and local associations and trade shows. That's why Quinn advises becoming involved with industry shows and organizations--such gatherings are great places to get to know suppliers. When you find one you like and know you can trust, stick with them. Loyalty often is rewarded with service that goes "the extra mile."

Soft spot for animals How do you control ground squirrels and burrowing owls without hurting or killing them?--California

You have four basic options for controlling ground squirrels (not to be confused with tree squirrels, which, instead of burrowing, often infest houses): shooting, poisoning, fumigating and trapping. Each has its advantages, but for larger populations, poison baits usually are the only practical option.

It is fairly simple to catch and remove the stress of trapping and transporting squirrels, in addition to releasing them into an area where they are unfamiliar with food and water sources, inflicts a high mortality rate (defeating the purpose of using traps).

Exclusionary tactics--fences or other barriers, or wire mesh laid over ground where the squirrels dig--can work for small areas. However, squirrels are extremely persistent, so this tactic often fails and, due to the great effort it requires, it isn't really practical for most situations.

For practical purposes, it's far more efficient to use poison baits. Most baits use strychnine, chlorophacinone, diphacinone or zinc phosphide as the active ingredient. As I mentioned above, shooting and fumigation are also options but are inefficient for larger numbers of squirrels. If philosophical or other reasons preclude using any of these tactics, you're limited to what could be a futile trapping effort.

Burrowing owls are a different matter. Like all predatory birds, they are legally protected and you must not harm them. Regardless, why would you want to? They consume large numbers of rodents. On balance, they're worth keeping around.

Controlling nutsedge Are there any pre-emergence products for nutsedge control in cool-season turf?--Ohio

No, at least not for controlling seedlings. However, pre-emergence control of nutsedge is not a viable control option in mowed turf because the nutsedge plants usually never have a chance to produce seedheads. Therefore, post-emergence products are the primary chemical tool for controlling nutsedge, which propagates by underground nutlets and rhizomes (as distinct from annual sedges, which reproduce by seed).

Several products provide selective post-emergence control of nutsedge in cool-season turf. Halosulfuron (Monsanto's Manage) and bentazon (BASF's Basagran T/O and LESCO's Lescogran) are two of the most effective products. Halosulfuron is a systemic chemical that controls both yellow and purple nutsedge (the two major weedy species) and also exhibits a limited degree of soil-residual activity (but this is not its primary mode of action). Bentazon primarily works as a contact and does not control purple nutsedge but is highly effective against yellow nutsedge.

Organic arsenicals--DSMA and MSMA (many brands are available)--also can control nutsedge, but Kentucky bluegrass is the only cool-season turfgrass for which they have registration. PBI/Gordon's Trimec Plus is a combination broadleaf herbicide that includes MSMA. If you're treating for broadleaf weeds, this product can control emerged nutsedge at the same time.

Regardless of the chemical, be aware that heavy nutsedge infestations often require multiple treatments due to underground parts that grow and emerge after the initial treatment. Also, check for (and eliminate, if possible) areas of poor drainage--nutsedge thrives in moist conditions.

Several years ago, the media reported that taxol, a chemical found in the bark of the Pacific yew tree (Taxus brevifolia), exhibited significant anti-cancer properties. This announcement put environmentalists in a peculiar position. The potential pharmaceutical value of chemicals found in plants often is cited as a reason to preserve habitat. And yet, when the Pacific yew was found to produce a valuable anti-cancer drug that could not be economically synthesized, preservationists worried that this would spell trouble for the tree. The low levels of the chemical in the plant meant that massive harvesting would be necessary to extract useful amounts of the drug.

Fortunately, as most horticulturists are aware, the genus Taxus includes many widely used ornamentals. Naturally, it didn't take long for researchers to look to the ornamental varieties as possible sources of taxanes (which include taxol and several related compounds). To this end, researchers at the National Center for the Development of Natural Products (at the University of Mississippi) tested commercial Taxus varieties to assess their potential as sources of taxanes.

An analysis of Taxus stems and leaves identified several varieties with taxane levels several times higher than those found in the Pacific yew. These include some well-known cultivars, such as 'Capitata', 'Densiformis' and 'Hicksii'. The researchers also note that selective breeding easily could produce Taxus varieties with even higher levels of taxanes.

Noting that nurseries generate large amounts of clippings from routine shaping of the more than 30 million yews in cultivation for landscape use, the researchers suggest that this is a possible source of large quantities of taxane-bearing plant material. Not only does this ease worries about the Pacific yew tree, it presents an unexpected--but important--new use for one of the most widely planted landscape ornamentals.

Some of the most-applauded successes in biological control have been those resulting from classical biological control--the release of natural enemies of a weed or insect pest introduced from other parts of the world. For example, Klamath weed, a serious imported weed of the Northwest, was brought under control by an introduced beetle. And ash whiteflies were devastating trees in the Western United States until an imported wasp practically eliminated the problem. But is there an unseen risk to these programs? An unsettling study at the University of Nebraska suggests there may be.

"Classical" biological-control programs, typically conducted by the U.S. Department of Agriculture, only release imported organisms with narrow host ranges to ensure their attacks are limited to the target pest. Considering how accidental introductions have devastated the American landscape (consider the gypsy moth and Dutch elm disease), this is no small matter.

However, University of Nebraska researchers apparently have found an example of biological control gone awry. The investigators have studied Nebraska rangelands for many years. In 1993, they discovered a weevil they had never seen before, and by 1996 it was clear that the weevil's numbers were increasing dramatically. They soon identified the weevil as a species that was introduced in Nebraska in the late 1960s and early 1970s to control musk thistle. However, musk thistle did not grow at the study sites--only native thistles were being attacked.

The researchers are still evaluating the direct effects of this unexpected assault (the weevil's larvae feed on the flowerheads and developing seeds of thistles), but they have found that seed production of the native thistles has declined dramatically, and they expect a corresponding drop in thistle populations. This is not good news for the Platte thistle, one of the native species the weevils are attacking. This plant has a limited range and could be vulnerable to population declines. Nor would it be good news for a similar, threatened species native to the Great Lakes region, should the weevil find its way there.

Indirect effects are also troubling. The weevil appears to be outcompeting a native insect that also feeds on the thistles. This insect has two generations per year, the second of which feeds on late-season thistles. If it declines, the researchers fear that certain thistles (late-season bloomers) could become new weed problems. Plus, birds and insects that rely on thistles for food may be harmed by the decline of this resource.

This is the first well-documented case of serious negative ecological impacts of introduced biological control organisms. It demonstrates the dangers of releasing imported organisms, even with good intentions and after careful study, and the difficulties of predicting their future ecological effects.

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