Research Update

Bermudagrass invasion I maintain several zoysiagrass lawns that have bermudagrass growing in them. Is there any herbicide that I can use to eradicate or suppress the bermudagrass without harming the zoysiagrass?-Georgia

Two herbicides are registered for control of bermudagrass in zoysiagrass: AgrEvo's Acclaim Extra and Zeneca's Fusilade II. Acclaim Extra's label specifies common bermudagrass, while the Fusilade II label lists both common and hybrid bermudagrass.

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Ward Upham, of Kansas State University, has conducted some research on this topic. He found that both materials suppressed-but did not eradicate-bermudagrass growing in zoysiagrass. Therefore, these products may slow further encroachment but will not eliminate the bermudagrass.

According to Upham, both products can cause minor discoloration of zoysiagrass. If you spray an entire lawn, the discoloration probably will not be apparent. However, spot-treated areas are likely to be visible due to the contrasting color of the adjacent untreated turf. To alleviate this problem, Upham suggests using either a green spray colorant or adding an iron supplement to the spray mix.

To completely eliminate bermudagrass, you must use a non-selective systemic product to kill all vegetation in the infested area. Retreating several weeks after the first application helps ensure a complete kill. This is an important precaution, because it only takes one surviving sprig or stolon to re-establish the bermudagrass. (However, Upham found that some bermudagrass escaped even a second treatment, requiring spot treatments the following year.) Obviously, this method necessitates reseeding or sodding.

Unfortunately, no product exists that will totally eradicate bermudagrass while sparing the zoysiagrass.

Turf paint We have to paint boundary lines on our soccer fields weekly. Is there a longer-lasting paint or some other method that could reduce this frequency?-Tennessee

The growth rate of the turf primarily determines the length of time turf paint lasts, not the material you use. Faster turf growth means the paint will not last as long because the increased mowing removes more of the painted grass blades. Therefore, longer lasting paint usually provides no benefit because you've typically mowed it off before durability becomes a factor.

Trevor Vance, groundskeeper for the Kansas City Royals, states that he applies new stripes to the Royals' field every 3 days during the playing season. Weekly applications such as yours, therefore, are not overly frequent.

Given that so much depends on turf's growth rate, you can see that one way to reduce the frequency of painting is to slow the growth of the turf. According to Vance, some field managers do this by applying plant growth regulators (PGRs) to turf areas that undergo regular painting. This reduces the need for mowing and, as a result, the need to re-apply turf paint. Vance states that some managers even mix PGRs with field paint and apply them together as a mix. However, this is not a well-researched method, and I would advise against it.

Another option (for lines only) is the time-honored practice of "burning" turf with a contact herbicide. Depending on the use of the field, this may or may not be acceptable, but it certainly saves labor compared to repeated paint applications.

2,4-D residual Will glyphosate plus 2,4-D applied to ivy and kudzu vines leave any residual in the soil?-Georgia

Glyphosate adsorbs to mineral particles so tightly that it is inactivated as soon as it comes in contact with soil. Thus, for practical purposes, it leaves no active soil residual.

In general, 2,4-D is not particularly persistent in the environment. It breaks down fairly rapidly in soil, mainly through microbial activity, and it also photodegrades when exposed to sunlight. Therefore, residual levels drop within a short time. However, the rate at which 2,4-D degrades depends on several environmental factors that affect microbial activity and varies considerably. Further, what you consider to be a safe level depends on what, if anything, you intend to plant after treatment.

Seedlings always are more susceptible than established plants and demand a greater interval after application for seeding safely. Some agricultural labels recommend waiting 15 to 30 days after a 2,4-D application before planting soybeans-a fairly sensitive species. Many broadleaf herbicides that include 2,4-D registered for use in turf areas recommend waiting 3 to 4 weeks before seeding a treated area with turfgrass.

Obviously, rate makes a difference. The higher the rate you apply to soil, the longer you will need to wait before planting seed there. If you are treating above-ground vines, most of your spray should land on the treated foliage, not the soil surface. Thus, you probably are not talking about a high dose reaching the soil. Considering this and the label information mentioned above, an interval of about a month should pose little risk for most landscape purposes.

Last year, Grounds Maintenance reported on a study at Colorado State University in which researchers compared the water-use rates of turf and certain ground covers. We received numerous inquiries regarding this study, so we thought readers would be interested in a similar study undertaken at the University of Nevada.

Researchers there compared the water use of three species of ornamental trees (desert willow, Argentine mesquite and Southern live oak) with that of tall fescue and bermudagrass (overseeded with ryegrass). Researchers made the comparison by matching turf area to tree basal canopy area (the "footprint" of the tree's canopy if you were looking down on it).

Fertility and water availability are important factors determining how much water plants use. To take these into account, the researchers used various levels of fertility and irrigation. They grew the trees in containers (lysimeters) so they could measure water use by weight, and they estimated turf water use by using evapotranspiration equations and crop coefficients.

In general, the tall fescue used considerably more water than the bermudagrass. Thus, the researchers suggest that specifications aimed at water conservation would do better to recommend bermudagrass over tall fescue.

More to the point of the study, however, were the tree-to-turf water-use ratios. The trees that received water in excess of their evapotranspiration used an average of 2.1 (oak), 1.9 (mesquite) and 2.4 (desert willow) times as much water as bermudagrass maintained under low fertility. The investigators felt this was a useful comparison because it represented a typical Las Vegas landscape-low-fertility bermudagrass lawns, some trees and poor irrigation management. They admit that other comparisons would have resulted in ratios more favorable to trees, but in nearly all cases, turf (both species) used less water than the trees.

It's clear from this study (and others) that plants (turf and ornamentals) use more water if you give them more to use. Conversely, they conserve when conditions become dry. Similar to the Colorado State study, water use of the trees varied-between species and according to water availability. For example, oak trees consumed twice as much water at the high irrigation rate compared to the low irrigation rate. Thus, the researchers suggest that proper water management is an important factor in lowering landscape water use.

The perception that ornamentals always are water-conserving choices for landscapes is erroneous. Thus, merely restricting turf won't necessarily result in water savings. According to the researchers, a more rational approach to water conservation would be allocating water based on the size of each landscape. With this as a starting point, designers could specify species and amounts of both turf and ornamentals appropriate to the available water.

You sometimes see figures for the acreage of turf grown in the United States. Home lawns are of particular interest because of their economic and environmental impact-they comprise the largest segment of turf in this country. Estimates of home-lawn acreage include: * 23.2 million acres (from an unpublished DPRA Inc. report) * Between 20.2 and 24.2 million acres (from The Lawn Institute).

However, it might surprise you to know that no one has ever conducted a nationwide survey specifically to determine home-lawn acreage. So how do we know how much turf is out there? The short answer is: We don't, at least not with certainty. Existing estimates are derived from data collected for other purposes.

A pilot project under way at the Environmental Protection Agency to estimate the benefits of turfgrass insecticides necessitated a closer examination of home-lawn acreage. Therefore, two EPA economists connected with this study conducted an analysis of their own to obtain a closer estimate of turfgrass acreage.

With data drawn from the 1990 U.S. Census, Federal Housing Administration figures and the various available state surveys, the investigators created their own estimate of home-lawn acreage. Their conclusion: Total U.S. home-lawn acreage lies somewhere between 14 and 26 million acres, with a conservative estimate of 17.7 million acres.

If you divide this by the number of single-family housing units with lawn (62.9 million, according to the 1990 U.S. Census), you get an average of 0.28 acres of lawn per home-around 12,200 square feet. However, the numbers argue against applying averages to specific situations. Clear regional differences are apparent in the figures. For example, four arid-climate states-Arizona, California, Nevada and New Mexico-averaged 0.12 acre (about 5,200 square feet) per home lawn. At the other end of the spectrum, the Northeastern states of Maine, New Hampshire and Vermont averaged 0.46 acre (about 20,000 square feet) per lawn, and four Southeastern states-Alabama, Georgia, North Carolina and South Carolina-averaged 0.47 acre per lawn.

The researchers concede that their estimates possess the same weakness as previous estimates-they are not the result of a national study designed specifically to estimate turfgrass area. This emphasizes the need for such a study.

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