Researching Maintenance

Grub-control timing Which grub-control product works best in October?-Michigan

A better question might be, "What time of year is best for grub-control applications?" By October, grubs may already be heading down to deeper soil in preparation for colder winter weather, and soil insecticides might not be able to penetrate deeply enough to provide effective control. However, even if that wasn't the case, grubs become larger later in the year and are somewhat more difficult to kill. Thus, it simply makes more sense to apply controls in July and August when newly hatched grubs are small and more susceptible to insecticides. In addition, you wouldn't really prevent much damage with an October application. By this time, grubs have already inflicted their damage for the season.

Most traditional grub-control products don't have enough residual to be effective when applied before grub larvae have hatched, so it's important to time applications correctly. This means late July to mid-August in many parts of the country, but this can vary. If you are unsure about the proper timing in your area, consult an extension specialist or other authority. Exceptions to this timing are imidacloprid (Bayer's Merit) and halofenozide (Rohmid's Mach 2). Both products have enough residual to provide good control throughout the summer when you apply them in May or June.

Taking these factors into account, you can see that anytime from May or June (for imidacloprid and halofenozide) through July and August (for most traditional grub controls) are the logical times to apply grub controls for effective results. October is less than ideal, regardless of the product.

Kentucky bluegrass for tees Is there a variety of Kentucky bluegrass suitable for the shorter height of cut of tees?-New York

Some superintendents mow tees under 0.5 inch. For these low heights, perennial ryegrass and creeping bentgrass are probably better choices. However, several Kentucky bluegrass varieties perform well in the range of 0.5 to 0.75 inch-an acceptable height for tees-so you do have some options.

To get good data on specific varieties, consult National Turfgrass Evaluation Program (NTEP) Kentucky-bluegrass-trial results. Dr. Robert Shearman, special projects coordinator for NTEP, notes that NTEP typically chooses a few trial sites to use fairway-type conditions such as shorter mowing height. Because superintendents often mow fairways and tees at about the same height (usually 0.625 to 0.75 inch), these trial results can be useful for you in selecting a good variety for tees. Look at the maintenance regimes listed in the NTEP reports to see which sites maintain their turf with fairway-type conditions. Then pay special attention to the performance of varieties at these sites.

One important difference between fairways and tees, according to Shearman, is that you need more aggressively spreading species on tees to help heal over divots. Shearman suggests looking at the sod-strength data in the NTEP reports. Rapid spreaders tend to be good sod-formers, so this data can be useful for selecting a tee variety.

You can obtain NTEP reports by accessing the NTEP website at or by writing to: National Turfgrass Evaluation Program Beltsville Agricultural Research Center-West Building 002, Room 013 Beltsville, MD 20705

No trivial matter How can I get seed that's free of Poa trivialis contamination?-Kansas

Poa trivialis (rough-stalk bluegrass) contamination is an increasingly serious problem in the turfgrass-seed industry. P. trivialis is a prevalent weed in some seed-growing areas, and its seed is so similar to that of Kentucky bluegrass that it is difficult to clean from seed lots. Thus, contaminated seed is making it to the end user and creating problems with turf quality. Even tiny amounts of contamination cause serious aesthetic problems because P. trivialis plants form conspicuous patches that contrast sharply with the surrounding turf. This creates major maintenance headaches, requiring turf managers to constantly rogue out P. trivialis patches and lawn-care contractors to perform "make-goods" for lawns established from contaminated seed. Unfortunately, no herbicide provides good selective control of P. trivialis in established turf.

Poa trivialis, which is a frequently used overseeding species, is classified as "other crop" on seed labels. Thus, even if a lab performing an analysis finds that P. trivialis is present, it doesn't end up recorded on the tag that the end-user sees. To make matters worse, it takes an experienced seed technician to tell the difference between Kentucky bluegrass and P. trivialis seed, and it's probable that some labs don't spot P. trivialis seed even when it's present.

What can the end user do about this? The first thing is to insist on a complete seed analysis. Seed suppliers should have at their disposal a seed analysis that lists everything in the seed, not just what you normally find on a seed tag. If your supplier is reluctant to provide this, you may want to seek another source of seed.

You also can ask for an additional analysis of a larger seed sample. Typical seed samples are small enough that they might not, by chance, contain any Poa trivialis seed, even though some small level of contamination may be present in the lot. A larger sample reduces the chance of this happening. However, this is only economical for larger seed purchasers such as golf courses and sod farms.

If you're purchasing smaller quantities that won't justify the cost of additional analysis, use Gold Tag seed. This is sod-quality seed that must undergo more stringent analysis than Blue Tag seed-it comes with a complete and specific list of everything found in the seed and must not contain any "other crop." It's more expensive, of course, but not as expensive as make-goods

No perfect solution to this problem exists, but it helps to be picky when choosing a supplier and purchasing seed. Some suppliers are taking steps-such as using growers in regions where little or no P. trivialis is present, seeking out experienced seed labs and taking larger samples for analysis-to ease the problem of P. trivialis contamination. Talk to your supplier about these issues. And if you aren't satisfied with what you get-including a full, complete analysis of the seed-go elsewhere.

Determining the nutritional status of trees is difficult. Do you use soil tests? Tissue analyses? Visual symptoms? Your conclusions could vary according to which criteria you use. To better understand this problem, researchers with the University of California Cooperative Extension examined the effects of nitrogen (N) fertilizer on the growth, appearance and tissue-N levels of two tree species: Chinese pistachio (Pistachia chinensis) and Valley oak (Quercus lobata).

To the oaks, the researchers applied 0.25 pound of N (in the form of ammonium sulfate) per inch of trunk diameter (dbh) to the soil surface and watered the fertilizer in. To the Chinese pistachios, the researchers supplied 4 pounds of N (also as ammonium sulfate) per 1,000 square feet to the soil surface within the dripline. Unfertilized trees served as controls.

After checking the trees 3, 9, 16 and 28 months after treatment, the researchers found no significant difference (in either species) in growth or tissue-N levels between the fertilized trees and the unfertilized controls. In addition, the researchers assessed tree health based on visual appearance before and after fertilizing and found no correlation between tissue-N levels and visual appearance. The healthiest looking trees did not consistently show higher N levels than trees exhibiting less vigor or what appeared to be N-deficiency symptoms.

The researchers note that tissue-N levels in the oaks (including the unfertilized specimens) were within ranges considered adequate for oaks. Therefore, the existing fertility of the soil was apparently adequate to supply the oaks with the N they needed, explaining why additional N did not result in increased tissue levels or growth. From this, the researchers concluded that specimens that rated poorly for visual appearance were exhibiting symptoms due to some factor other than N deficiency, although the symptoms resembled N deficiency. Although no published range of adequate tissue-N levels for Chinese pistachio exists, the researchers suggest that the situation was similar in that case-existing soil fertility was adequate. (Pre-treatment soil-N levels were 0.051 percent for the oaks and 0.1 percent for the Chinese pistachios.) With the pistachios, as with the oaks, visual appearance did not correlate with tissue-N levels.

The results of this study suggest that annual fertilizer applications to trees as "insurance" may be wasteful in many cases. Further, they imply that visual symptoms are not a reliable indicator of N needs because they may stem from factors other than N fertility, simply mimicking N-deficiency symptoms. The researchers suggest that more tree species commonly used in landscapes need study to determine adequate tissue-N ranges. (Currently, such information exists for only a relative few landscape species.) This would provide arborists with a quantitative method of evaluating tree fertility status.

As if we don't have enough reasons to hate imported fireants (IFAs), here's another. Texas Parks and Wildlife officials report that more than 20,000 trout are believed to have died this year as a result of eating IFAs. Steve Magnelia, a state fisheries biologist, explains that this is the fourth documented trout kill caused in this manner. The kills occur near San Antonio in the Guadalupe River, the southern-most trout fishery in the United States.

Apparently, when rains in late May and early June trigger massive mating flights of the winged forms of the IFA, many of the ants find their way to the river, where trout gorge on the insects. Dead trout examined by biologists had as many as 500 ants in their stomachs. According to Magnelia, it is not yet clear whether toxins absorbed through digestion kill the trout or whether the ants simply sting the fish as they're being swallowed. Entomologists working on the problem are trying to gain a better understanding of the toxin and its mode of activity.

Officials haven't decided how to deal with the problem. One possible solution is to delay stocking the river with fish until IFA flights are over (most of the casualties were small, recently stocked fish). Fortunately, the IFA flights are short-lived, and the trout kills end as soon as the flights are finished.

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