Research Update: Verdant spray oils

Mixing lime and fertilizer I have heard that lime and fertilizer should not be applied to turf at the same time but a few weeks apart because it could injure the turf. Is that true? If not, it would be good to know because it would save some travel time and labor.-New Jersey (via the internet)

Dr. Peter Landschoot, a turfgrass soil specialist at the Pennsylvania State University, states that as long as lime applications consist of appropriate types (agricultural ground or pelletized limestone) and amounts (under 100 pounds of lime per 1,000 square feet), little potential for burn or other problems exists, with or without a simultaneous fertilizer application. (Hydrated lime has a relatively high burn potential, but this is not the typical material you would use on turf.)

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As evidence of the harmlessness of fertilizer and lime going down at the same time, Landschoot observes that during lawn renovations, people often incorporate lime and fertilizers into the soil at the same time. Landschoot has never encountered a problem that resulted from such a combination.

Turf vs. shrubs Are turf or shrub beds more economical to maintain over the long run?-Idaho (via the internet)

Because so many variables come into play, it depends on how you maintain the turf and the shrub beds. Plus, each situation requires a different kind of maintenance. The difference is that turf requires more regular maintenance (mowing) than shrubs, and it's easy to confuse more often with just plain more. You often can ignore shrub plantings for many weeks without getting seriously behind, so they seem like they're low maintenance. However, think of the time it takes to prune a hedge well or apply a new layer of mulch around shrubs. Even if you only perform such tasks once or twice a year, they can take hours-enough time to have mown an equivalent area of turf many times.

That's another reason for confusion on this topic. Often, people mentally compare the amount of time they spend mowing turf with the time they spend maintaining shrubs. Period. They fail to consider that they're comparing an area of turf that is probably many times larger than the beds.

Maintenance standards for each type of site also make a difference. High-maintenance turf takes more effort than low-maintenance shrubs. Conversely, some shrub plantings require lavish attention to look their best. Thus, evaluating the comparative efficiency of turf and shrubs is highly site dependent.

Another factor to consider is installation cost. After all, if you installed a shrub planting with low maintenance in mind, you would have to purchase not only plants but also mulch and perhaps landscape fabric for weed suppression. This can be a rather costly initial outlay. A study performed by University of Tennessee researchers a few years ago calculated that just the annual earnings (at 6-percent interest) you would gain on the amount of money needed to install an acre planted this way would pay for contract mowing of the same amount of turf for an entire season. As this shows, there is more than one way to look at this problem, and turf often compares more favorably than people assume.

In need of a name When reseeding a lawn with a power slicer/seeder, what is the proper term for the debris the seeder kicks up when the blades verticut the turf? Would it be called dead grass, scum or thatch, and should it be raked up or left?-No city (via the internet)

This material actually includes several substances: dead and living grass, thatch and some soil. However, I can find no "official" name for it. Simply calling it thatch would probably be as useful as any other term.

Although you can get away with leaving it on the surface, especially if the "thatch" isn't too heavy, removing it allows greater light penetration, which will benefit seedlings. Plus, removing it provides a cleaner look. If the thatch is heavy, definitely remove it.

Horticultural oils were one of the primary pest-control tools of horticulturists early in this century. However, these formulations were known for their phytotoxic effects when used as verdant (foliar) sprays. Their use, then, was restricted to dormant applications. This may be why pest-control operators still primarily think of horticultural oils as dormant sprays (for which they are undeniably useful). However, many modern oils, unlike their predecessors, are more highly refined and less phytotoxic to foliage. In spite of this, verdant oil sprays are not widely used, apparently due to the lingering reputation of their less-refined ancestors.

To underscore the relative safety of modern oils, Dr. Fredric Miller, a researcher with the University of Illinois Cooperative Extension, studied the effects of verdant oil sprays on shade trees, woody shrubs and evergreen conifers (a total of 52 species and cultivars). Using a 2-percent mix of a 6E formulation of horticultural oil, Miller made three verdant applications to the plants: once each in June, July and August. Weather was fairly typical during this study. Miller then measured twig and leaf growth of treated and untreated plants, as well as phytotoxicity.

Not only did Miller find no phytotoxic effects, his results showed no inhibition of growth at all compared to the untreated control plants. Perhaps the only undesirable effect of the spray oil was that it eliminated the blue cast of Colorado blue spruce (about which oil labels typically warn). However, this research confirms that spray oils are a valuable option for controlling a variety of pests during the growing season, not just during dormancy.

(Editor's note: Not all horticultural oils are labeled for summer use. In addition, labels typically warn against use on plants under drought stress or during prolonged periods of high temperature or humidity.)

In 1996, Congress unanimously passed the Food Quality Protection Act (FQPA). This legislation, though well-meaning, has thrown the pesticide industry into disarray as it tries to meet the new FQPA requirements and understand its ramifications.

FQPA requires the Environmental Protection Agency (EPA) to consider what is known as aggregate risk. This means that all pesticides with a similar mode of action are to be grouped together when assessing potential exposure. For example, permissible exposure levels for any organophosphate (OP) pesticide depend on the combined potential exposure for all OPs.

Another aspect of FQPA is the use of default assumptions. This is especially critical because of the increased emphasis FQPA places on children's health. In lieu of data justifying some other position, a default 10-fold safety margin will be in effect to ensure the safety of infants and children. This means that manufacturers must lower acceptable exposure and residue limits by 90 percent in the absence of data indicating that not doing so would pose no unreasonable risk for children. It's likely that, for many pesticides, the 10-fold safety margins will be in effect simply because the data showing it's not needed doesn't exist, not because any real risk to children is actually occurring.

The trouble is that default assumptions allow a pesticide to exceed permissible exposure levels "on paper," regardless of the real exposures. Here's a hypothetical example: Let's say you test for pesticide residues on food and find none. And let's assume the limit of your analytical abilities is 2 parts per billion. EPA can (and will) assume that 1 part per billion exists, just to be safe. It could be (and often is) that virtually no residue is present. However, because the limits of your analytical abilities don't allow you to prove otherwise, EPA assumes a certain level is present. When you add up the assumed exposures from all sources (food, water, air, landscapes, etc.), it's quite possible to exceed the allowable level of exposure even if little or no actual exposure is occurring. That's the magic of assumptions and why cancellation of all OP registrations is one option EPA is considering. (As an aside, such assumptions are the basis of the much publicized report issued by the Environmental Working Group earlier this year, which erroneously concluded that our children were being regularly exposed to damaging levels of pesticides in foods.)

In some cases, manufacturers cannot economically justify funding more studies to support their products. In other cases, there simply hasn't been enough time to conduct the necessary research. However, some manufacturers are conducting the studies. For example, Dow AgroSciences, whose chlorpyrifos (Dursban) is an OP, believes it has adequate data to justify continued use of chlorpyrifos. However, thanks to aggregate risk, it is not up to Dow alone. Unfortunately, the policy of using aggregate risk has the effect of penalizing those manufacturers who are conducting the necessary research to support the registration of their products. The data gaps that exist for other OP products are filled with unrealistically high assumptions, which means that the aggregate exposure to OPs still exceeds allowable levels.

This situation is not what Congress envisioned when it passed FQPA. Industry groups are asking EPA to rely on science, not assumptions, to implement FQPA, and even Vice President Gore has asked that EPA's efforts be "guided by sound science and broad public participation." Let's hope that saner heads prevail. Otherwise, grounds-care professionals may find themselves without some of their most important chemical tools, perhaps as early as this year. OPs include such notable products as Dursban, Diazinon, Orthene, Dylox, Oftanol and malathion, among others.

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