Researching Maintenance

Oklahoma webworms Sod webworms have been a problem on some of my clients' lawns. However, I don't have time to monitor on a regular basis. Is there a preventive treatment for webworms?--Oklahoma

Preventive treatment is not a recommended practice for most pests, particularly when you would not ordinarily expect the pest to reach damaging levels. Dr. Ken Pinkston, a turfgrass specialist with the Oklahoma extension service, noted that sod webworms are not typically a serious problem in Oklahoma. However, that does not preclude damaging levels in certain areas.

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You can sometimes get a general idea of webworm levels just by "poking around" in the turf, looking for the silken webworm burrows in the thatch or the webworms themselves. However, a more precise way to monitor for the larvae is to flush the webworms out of the turf. Some authorities suggest using a dilute solution of pyrethrin (the equivalent of 1 tablespoon of 2-percent pyrethrin per gallon of water) sprinkled over the turf. This acts as an irritant and causes the webworms to emerge from their burrows. Then you count the webworms that emerge over the next several minutes.

Pinkston generally suggests a treatment threshold of 15 webworms per square yard. However, he notes that the level of infestation you can tolerate depends on the use of the turf or customer preferences. Several species of sod webworm occur in Oklahoma, and their generations do not coincide. Therefore, you should monitor for web- worm populations to determine whether treatment is necessary, based on infestation levels and how much damage you (or the client) can tolerate. In other words, you cannot (and should not) treat by the calendar when you have no reasonable basis for expecting a damaging level.

If you do decide to treat, effective treatment options include many traditional, widely available products. However, two new products that have recently received federal registration are worth your consideration: DowElanco's Conserve SC and RohMid's Mach 2. Both provide good control of webworms (and other pests) with minimal non-target effects. In fact, both of these materials have been registered as "reduced-risk" pesticides by the Environmental Protection Agency. Because some state registrations are pending, availability in 1997 may be delayed in some states.

New gasoline Are the new unleaded gasolines any good?--California

I assume you're referring to oxygenated gasoline, which is mandated in California and elsewhere and comprises an ever-increasing proportion of the gasoline sold in this country. Oxygenated gasolines were introduced in the 1980s to curb automobile emissions, especially carbon monoxide. They contain alcohol (ethanol) or ether (MTBE), which include oxygen in their chemical structure. This increases the overall oxygen content of the fuel--thus the term oxygenated--and helps gasoline produce less carbon monoxide when it burns.

Oxygenated fuels got a bad reputation soon after their introduction. They were reported to damage certain fuel-system materials, reduce lubrication in 2-stroke engines and to settle out in the bottom of gas tanks, among other problems.

Some of this was true and some not. In any case, much of the concern resulted from problems with methanol, which is no longer a common additive in oxygenated fuel. Another factor was the recommendation of many power-equipment manufacturers that oxygenated fuels not be used in their equipment. However, this mainly was due to manufacturers' lack of experience with these fuels. It was simply easier for them to tell users to avoid these fuels than to conduct the expensive testing necessary to formulate meaningful recommendations for their equipment.

Gasoline formulators now have much greater expertise with oxygenated fuels and, with the phase-out of methanol as an additive, the quality of oxygenated gasoline is now quite good. Plus, engine and after-market part manufacturers have upgraded their materials to be compatible with oxygenated fuels.

Oxygenated fuels now comprise a large portion of the gasoline sold in the United States, and manufacturers are adjusting to this fact, as well as gaining more experience with these fuels. Most manufacturers' owner-manual fuel recommendations now include oxygenated fuel (although many provide special instructions for its use). Some manuals do not mention oxygenated fuels at all, positively or negatively. Regardless of the logic manufacturers use, you should always follow their recommendations. Otherwise, you could void the equipment's warranty.

Late-season turf establishment When is the latest you can install warm-season turf in Zone 8?--Georgia

If you want to install warm-season sod in Zone 8 (which includes the southern half of Georgia), you can actually do so at any time of the year. However, Dr. Robert Carrow, a turfgrass specialist with the University of Georgia, warns that you run the risk of winter kill if you lay sod later than about the first of October. After this date, the turfgrass may not have enough growing time to become established. According to Carrow, if the turfgrass is not well-rooted, it is more susceptible to desiccation, which can be lethal to turfgrass plants during winter temperatures.

Carrow further states that in Zone 8 you should plant seed, sprigs or stolons by mid-September at the latest, though doing so earlier--June and July are the best months--will give the turfgrass a much better chance to develop and harden off adequately before winter sets in.

Unlike cool-season turfgrasses, it is best to install warm-season species during late spring and summer, when they subsequently will have plenty of warm growing conditions. Thus, these guidelines tell you what you can get away with--not what is ideal.

Hydrophilic polymers (HPs) are organic substances that attract and hold water. Commercial products using such materials have been available for many years and have helped gardeners, for example, lower the watering requirements of container plants. Another possible use for HPs is in flower beds for the purpose of reducing irrigation requirements. Any product that reduces the amount of irrigation necessary could decrease water and labor costs. Texas A&M researchers in El Paso undertook a study to determine if this was the case with Hps.

The researchers incorporated various amounts of HP into plots in which they grew petunias, marigolds and vincas, representing low, moderate and high drought tolerance, respectively. HP application rates were 0, 25, 50, 70 and 100 pounds per 1,000 square feet. The researchers recorded flowering levels, soil moisture, soil temperatures and, when the experiment was terminated, dry weights for the harvested bedding plants.

Not surprisingly, the researchers found higher moisture levels in plots treated with HPs (even though most differences were not statistically significant). Did this translate into better plant performance? In the case of petunias, flowering and dry plant weights were significantly greater for the three highest HP rates. However, the vincas and marigolds showed mixed results, exhibiting increased flowering or dry weights in some instances, but not consistently.

The researchers discovered another possible benefit of incorporating HPs into bedding soil: smaller soil-temperature fluctuations. Extreme soil temperatures can have negative effects on plant growth, so this could be an important benefit. However, the researchers also saw a down side to the use of HPs. During the trials, unusually wet weather occurred, and the HP-treated soils remained excessively wet, to the detriment of the bedding plants.

The researchers sum up their results by suggesting that drought-susceptible bedding plants in dry conditions could benefit from incorporated HPs. However, they also point out that the potential for saturated soil may increase with the use of HPs, which could be problematic on wet sites or in regions where rainy weather can be persistent.

Crabgrass control is one of the most regularly performed pest-control functions in which lawn-care servicers engage. Thus, any strategy that reduces the input of labor and materials required for crabgrass control holds great potential value for the lawn-care industry. To this end, a University of Georgia researcher has been investigating the effectiveness of tank-mixing two herbicides commonly used for crabgrass control: MSMA (a post-emergent) and dithiopyr (a pre-emergent with early post-emergence activity on crabgrass in the two- to three-leaf stage).

In experiments he conducted on common bermudagrass in 1995 and 1996, the Georgia researcher applied dithiopyr and MSMA sequentially (in February and June, respectively), and together as a tank-mix in early May, when crabgrass was in the two- to three-leaf stage. In addition, the researcher used various application rates of both MSMA and dithiopyr. Thus, he created various combinations using sequential and tank-mix applications with several rates of each chemical. He rated the level of weed infestation and defined acceptable control as better than 80 percent.

He applied dithiopyr to some plots in February of each year. In 1995, this provided good control throughout the season. In 1996, however, the control provided by this single application was inadequate. Likewise, MSMA alone provided good control one year but not the other. By contrast, in both years, sequential applications--which included both the early dithiopyr treatment as well as the June MSMA treatment--provided good control (with half-rate dithiopyr and full-rate MSMA).

In addition, the researcher found that dithiopyr at one-half the label-recommended rate (0.25 pound per acre) tank-mixed with MSMA (at one-half and full rate) consistently provided acceptable crabgrass control through summer after the early May application. Similar tank mixes, but with only one-fourth the recommended rate of dithiopyr (0.12 pound per acre), provided marginal (73 to 91 percent) control through summer.

Both the sequential and tank-mixed applications of MSMA and dithiopyr controlled crabgrass effectively. An advantage of sequential applications is that you avoid having to use MSMA applications if the pre-emergent's control holds through the summer. Conversely, the advantages of tank-mixing--such as reduced labor and materials, and consistent season-long control--make this an attractive option, even though you apply MSMA regardless of whether it would eventually be necessary.

The sequential application of MSMA in June consistently caused greater injury to the bermudagrass turf than the tank-mix applications, which occurred in May. This apparently was due to the higher temperatures of the later application dates. However, the researcher noted that injury to the bermudagrass, due to the MSMA, was temporary (as noted on MSMA labels).

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