Researching Maintenance

Flaming mulch This year we applied hardwood mulch and Snapshot pre-emergent to two median strips. Not long after, we experienced fires, probably due to cigarette butts, at these locations. We never had fire problems before and didn't have any this year except where we applied the mulch and pre-emergent. Is it possible that the mulch or the combination of the mulch and herbicide could increase flammability? -- Maryland

Representatives of DowElanco assured me that Snapshot poses virtually no risk of increasing the flammability of mulch. However, a mulch's propensity to burn varies according to its content, so it's possible that this mulch was in some way different from mulch you've used previously.

Bob LaGasse of the National Bark and Soil Producers Association (Manassas, Va.) explains that cellulose ignites more easily than lignin. This means that wood (which is primarily cellulose) burns more easily than bark (which has a much higher lignin content). Because of this, mulch quality affects flammability -- so-called poor-grade mulch, which has high wood content, is more flammable than high-grade mulch. Specifying hardwood mulch doesn't ensure what's in it, beyond the fact that it came from hardwood trees. It could mostly be hardwood wood (poor grade) or hardwood bark (high grade). Obviously, then, it pays to inspect mulch before you accept it. LaGasse notes that according to his association's definitions, products defined specifically as bark mulch should contain at least 85 percent bark. Products defined simply as wood mulch may include wood or bark but usually consist of mostly wood.

LaGasse notes that fire retardants are available that you can spray on your mulch, although they tend to leach out over time. Still, they might be worth a try in areas that are especially prone to fires. LaGasse states that the ends of traffic medians near intersections burn more frequently due to stopped motorists who toss out cigarette butts as they wait.

Eliminating deer ticks What's a good method of eliminating deer ticks? -- Illinois

This is an increasingly important issue as new residential developments push into wooded areas, exposing more people to Lyme disease, which is transmitted by deer ticks. It's doubtful you can eliminate ticks from an area, but several strategies allow you to substantially reduce populations on a property.

One key is to reduce the numbers of tick hosts. Obviously, deer ticks feed on deer but also on other types of animals, such as rodents and birds. Therefore, if you make property less attractive to these kinds of wildlife, you should reduce the number of tick hosts present. Remove underbrush, logs, wood piles and brushy or weedy vegetation in or near homes or other areas of human activity. Deer fencing can help keep deer away (though many people object to this on residential sites for aesthetic reasons).

Some studies suggest that exposed open areas discourage ticks, perhaps because they are more prone to desiccation in such environments. Consistent with this, other research has shown that manicured lawns and landscapes harbor lower tick populations than property fringes near wooded or brushy areas. Therefore, expanding mowed or maintained areas around homes and other areas of human activity may reduce tick levels. Also, where rows of vegetation provide screening between properties, consider pruning up branches and replacing leaf litter (where ticks can hide) with mulch.

Several conventional pesticides effectively reduce tick numbers. One study obtained good results from carbaryl, chlorpyrifos and cyfluthrin. However, several other pesticides are registered for ticks, including bendiocarb, bifenthrin, diazinon, fluvalinate, lambda-cyhalothrin and permethrin. The particular material you use may not be as important as timing. A late-spring application substantially reduces immature ticks for the entire season. However, fall applications further reduce populations as well as their offspring the following spring.

Where ticks are prevalent, especially those that harbor Lyme disease, use all appropriate control measures. However, do not be lulled into a false sense of security. You can't entirely eliminate ticks, so you should be aware that the possibility of tick bites exists in any infested region.

Baseline temperature What is the baseline temperature for crabgrass and broadleaf weeds on Long Island? -- New York

As a general rule, 50 degrees F is considered the "default" baseline temperature for most organisms. This works well enough for most purposes, which is fortunate, because more precise baseline and degree-day information does not exist for most weeds.

Crabgrass is one exception. Dr. Michael Fidanza conducted research on crabgrass germination at the University of Maryland and used a baseline temperature of 54 degrees F (see "Use degree-days to predict crabgrass emergence," April 1997 Grounds Maintenance). With this starting point, Fidanza discovered that smooth crabgrass first germinated when an average of 57 degree-days had accumulated, with the first major emergence occurring at 185 degree-days. Fidanza suggests that crabgrass on Long Island should not behave significantly different from this but points out that geographic variation has not been investigated thoroughly.

One approach is to monitor weed germination yourself and correlate your observations with published degree-day values (many extension offices publish this information) or monitor degree-days on your own. A weather station greatly eases this task. This should give you a rough, but useful, idea of when certain weeds germinate.

You also should realize that other "triggers" exist, such as soil moisture, soil-temperature extremes and exposure to light, that promote germination or, in some cases, prevent it. For example, U.S. Department of Agriculture scientists discovered that if temperatures within the top inch of soil reach 90 degrees F for even a single day in April, giant-foxtail seeds go dormant and do not germinate for the rest of the season. Dry soil conditions in spring induce season-long dormancy in pigweed. With variables such as these operating, weed germination is a complex process about which we have much to learn.

The lamentable performance of trees growing in urban settings is well-documented. For example, estimates place the life expectancy of a newly planted street tree at just 10 years. And while there is no shortage of possible reasons for this, researchers from Cornell University hypothesized that exploitable soil volume was a key factor in urban tree performance after transplanting.

To test their hypothesis, the researchers studied willow oaks, Quercus phellos, planted in sites representing various levels of cost, sophistication and soil volume. These ranged from the so-called "vault system" to tree beds in parking lots to trees growing in irrigated, fertilized lawn, with exploitable soil volumes ranging from about 10 cubic meters to "unlimited" (for trees growing in lawn areas). All the trees received good post-planting care from reputable professionals.

The researchers measured annual growth increments of the trees' trunks for up to 15 years and found, with one exception, that tree growth was similar regardless of soil volume. Even trees growing in lawn areas with no soil-volume restrictions did not outstrip those growing in more restricted sites. The one exception was the trees growing in irrigated, fertilized lawn: they significantly outperformed the others for as long as 7 years after transplanting. After that, however, their growth rate declined and was similar to that of other trees in the study at 15 years after transplanting.

The researchers also note that most of the trees they studied recovered well from transplant shock -- something you might not expect in stressful urban settings -- and resumed pre-transplant growth rates 2 to 3 years after transplanting. They attribute this, and the generally good performance of trees at most of the study sites, to the fact that all sites in the study were well-designed and -maintained.

Considering these results, it appears that all the study sites provided adequate soil volume for good tree performance for at least 15 years, the length of time encompassed by this study. The researchers stress that their results do not contradict observations of poor performance of most urban trees. Rather, they demonstrate the value of tree-health-based design and maintenance. After all, consider that standard sidewalk cutouts for street trees (which, remember, typically last only about 10 years) provide only about 1.4 cubic meters of rooting volume, compared to no less than 10 cubic meters of soil for the study trees. The researchers hope their results will encourage designers to use site specifications favorable to tree growth, and promote greater attention to proper planting and maintenance practices.

Anyone who must deal with kudzu welcomes any kind of help combating this undisputed champion of weeds. Even with herbicides, it's no easy task to eliminate kudzu, and attempts to exploit effective natural enemies have been fruitless. Thus, when someone noticed soybean loopers eating kudzu in Union, S.C., in 1995, scientists took note.

A curious aspect of this story is that the soybean loopers (as well as a few other native caterpillar species) were found to feed on kudzu only at this single location. North Carolina State University researcher Dr. David Orr began studying soybean loopers to discover why this was so. If some chemical attractant that stimulates feeding exists, perhaps it could be exploited to entice feeding on kudzu. This might result in the first viable biological control for kudzu.

To be effective against kudzu, the caterpillars would need to be aggressive feeders, causing enough defoliation to reduce kudzu's food reserves. This could suppress it's rampant growth or, ideally, kill plants outright. However, because loopers are pests of several agronomic crops, Orr has had to be cautious about releasing them. To satisfy the need for aggressive kudzu feeders that also do not devour desirable crops, Orr devised a clever solution: He infects the looper larvae with parasitic wasps that kill the caterpillars when they attempt to pupate. The infected loopers consume substantially greater amounts of foliage than normal loopers but cannot achieve adulthood and reproduce. Such infected loopers are not available commercially, and Orr is conducting further study to determine if they can be used on a wider scale. Field trials this year were "promising."

Meanwhile, soybean loopers were found feeding on kudzu in Alabama this year, suggesting that the loopers may be adapting to kudzu as a food source. Such a development would be a boon to grounds managers and farmers tired of fighting this seemingly unstoppable weed.

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