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Research Update: High-tech soil analysis

Horsetail control How do you get rid of horsetail?--New York

Horsetails can be tenacious weeds (several species can be troublesome). Due to their perennial habit and extensive underground rhizomes, control may be difficult. Although certain species grow in relatively dry conditions, horsetails are most troublesome in wet sites, where they may run rampant with vegetative spread.

Several herbicides are registered to control horsetail, including some of the phenoxy broadleaf herbicides (which is interesting considering that horsetails are not dicots). In most turfgrass situations, these products would be your best chemical option. In open areas or locations where spot spraying is possible, non-selective products also are options.

The following broadleaf herbicides have registration for horsetail: Chlorsulfuron (LESCO's TFC), 2,4-D (Riverdale's Solution) and 2,4-D + MCPP + dichlorprop (Riverdale's Dissolve, Triamine and Tri-ester products, Scotts' Jet-Spray 3-Way and LESCO's 3-Way Ester).

AgrEvo's Finale (glufosinate) and Zeneca's Reward (diquat), non-selective products, and Uniroyal's Casoron (dichlobenil, a soil-active herbicide), also have registration for use against horsetail. Regardless of the chemical you use, some regrowth is likely to occur due to the perennial structures of horsetail, so retreatment may be necessary.

Another tactic to consider is, if practical, improving drainage in horsetail-infested areas. Drier soil could discourage the horsetail from spreading.

Choosing a plant supplier What do you look for when choosing 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. No inherent advantage exists to dealing with a wholesaler vs. a nursery vs. some other supplier--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-quality material. Pricing also is important--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 and service--only low price.

The key, according to Quinn, is building personal relationships with suppliers. Being personally familiar with your suppliers (and vice versa) has many advantages, not the least of which are the intangibles ones, such as greater trust. Quinn notes that design-build operations especially benefit from close ties with a supplier. Knowing what's available allows you to create designs with assurance that the installation can proceed as planned. Working from someone else's plans may send you scrambling to find material that isn't readily available or negotiating to make changes to the plant material.

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 services 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."

Rolled vs. slabbed sod What is the difference between sod that is rolled up vs. flat when it's delivered?--Virginia

No agronomic or practical advantage exists to harvest sod one way or the other. Even sod-harvesting machinery, in many cases, can switch from stacks to rolls, or vice versa, with minimal modification.

Douglas Fender, executive director of Turfgrass Producers International, explains that the method that predominates in a region is a product of local user preference. Specifically, contractors use about 80 percent of all sod. So, if the contractors in an area prefer rolls, that's the form that sod producers will supply.

In general, you see warm-season turf "slabbed" or folded, and cool-season turf rolled. But this mainly is a matter of tradition: sod harvesters can roll warm-season turf, or slab cool-season turf, with no apparent problems. If, for some reason, you have a preference, ask your sod supplier to deliver the sod in the form you prefer. Many will accommodate such requests.

When light strikes an object, the object absorbs some colors (wavelengths) and reflects others. The apparent color of the object is the color of the light that is reflected, not that which is absorbed. Exactly which wavelengths an object will absorb depends on what it's composed of--different substances absorb different wavelengths.

Using the same principle, a team of researchers (consisting of faculty from the University of Guam and the Pennsylvania State University) has found that emitting infrared radiation at soil samples and then measuring the reflection can reveal important information about the soil sample. This is known as near infrared reflectance spectroscopy (NIRS) and scientists have used it for decades to study all kinds of things (including soil). Knowing that substances absorb some wavelengths and reflect others in unique patterns, an analysis of the reflectance of a substance can tell you what it is.

Until now, though, no one had ever used NIRS on intact soil samples; typical preparations consisted of drying and grinding samples to produce a homogeneous sample. The value of analyzing intact samples is considerable, however. This allows you to characterize each layer of soil--important information from an agronomic perspective and not something that ordinary soil analysis permits. Also significant is the reduced time and effort required for NIRS compared to other soil-analysis techniques. With properly calibrated equipment, a scan takes just seconds. And the soil sample does not need to be dried, ground or sifted.

The researchers used NIRS to analyze soil samples with known characteristics and compared the results to other soil-analysis techniques. They obtained a high degree of accuracy using NIRS, even exceeding the accuracy of other analysis techniques in most cases. Plus, NIRS was able to accurately measure moisture content, organic matter, density, texture, pH and potassium--a wide range of characteristics in one scan.

This research illuminated the primary hurdle for NIRS, as well as its promise. The reflected radiation, by itself, provides little information. However, if you have analyzed other samples and recorded their reflectance characteristics, you have a basis for comparison, which allows you to make predictions about subsequent samples. Thus, a database with reflectance properties of soils with known qualities is the key to interpreting NIRS information. Development of such a database must occur before NIRS can be used as a management tool. However, it has the potential to be a quick, accurate and relatively inexpensive way of defining a variety of soil characteristics.

As it becomes more difficult to dispose of grass clippings due to landfill restrictions, other means of dealing with clippings are receiving attention. One method--the preferred strategy, when it's practical--is simply to return clippings to the turf. In spite of the advantages this provides, many people still prefer to remove clippings. Further, during the spring growth push, it may be difficult or impossible to mow often enough to avoid excessive clippings that require removal. Thus, a need still exists for clipping-disposal options.

A practice gaining in popularity, especially with homeowners, is the use of grass clippings as mulch around bedding and vegetable plants. This conserves moisture, moderates temperature swings and reduces weed growth. However, the presence of pesticide residue, especially herbicides, in grass clippings poses a potential hazard of which some people may not even be aware. To better define the possible dangers of mulching with pesticide-treated clippings, Michigan State University researchers performed a study using tomatoes, impatiens, bush beans and petunias.

The researchers applied post-emergence herbicides (triclopyr, 2,4-D, and clopyralid + triclopyr), a pre-emergent (isoxaben), an insecticide (chlor-pyrifos) and a PGR (flurprimidol) to plots of fine fescue, perennial ryegrass and Kentucky bluegrass. They then mowed 2, 7, 14 and 28 days after the applications, each time removing the clippings for use as mulch around the test plants. The clippings were applied to a depth of about 4 inches and outward about 6 inches from the stems. Irrigation was applied within 24 hours.

Sensitivity to the chemicals varied among species and, for unclear reasons, from year to year (illustrating the notorious unpredictability of phytotoxic injury). As expected of an insecticide, the chlorpyrifos caused no visible phytotoxicity. However, the remaining chemicals were injurious to varying degrees, depending on elapsed time and the number of mowings after application. Obviously, as more time passed after the application and as more mowings had taken place, chemical residues and the resulting damage decreased.

Based on the results of this study, the researchers recommend waiting at least 2 weeks or 3 mowings after applying herbicides or PGRs before using clippings as mulch. Lawn-care applicators could avoid potential trouble by informing their customers of this precaution.

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