I'm confused.

Our university experts have recommended applying crabgrass pre-emergent herbicides or "preventers" when soil temperatures reach 50 to 55 degrees and stay there for a week or so.

This seems to correspond with the flowering of forsythia. However, other researchers report different optimum soil temperature for germination. Varying research indicates that peak germination occurs at 50 to 75 degrees. That's quite a range!

Some of this may be because of regional variations or the difference in crabgrass species, but it might also be because of germination conditions. Research at Cornell University and the University of Maryland indicates that crabgrass germinates later in dense turf when soil temperatures reach 73 degrees. They also found crabgrass germinates earlier in thin turf with gaps between plants. Apparently this allows the soil to warm up more quickly and most of the crabgrass will germinate sooner.

While interesting, does this mean lawn owners should change the timing of their crabgrass preventing chemical applications? Should they measure the soil temperatures before applying the chemicals. Not really. It's still best to apply "preventers" in early spring about the time forsythia starts to drop its blooms.

Of course, everyone is tempted to apply chemicals when forsythia starts to bloom, which will be soon. This is only a problem if you use a product that contains pre-emergent chemicals that aren't very persistent and don't last long in the soil. WSU recommends the pre-emergent herbicides of benefin, trifluralin and pendimethalin for crabgrass prevention.

Check the label of any product you apply to see how long it's supposed to be effective. Those with longer persistence are more forgiving if you apply them a little early, but those with only several weeks of efficacy may not last long enough if cooler weather returns and slows the germination process. Also, be sure to read the label regarding the rate of application and any other application directions, such as the need for watering right after application. If the product requires water for activation and you have no way of watering your lawn, it will not be effective. For good control, be sure to apply the material evenly at the recommended rate for good coverage.

Just last week, one of our WSU Master Gardeners was trying to help a friend understand the label of a particular crabgrass control product.

The Master Gardener called me, puzzled, because the product label seemed to indicate it was applied to crabgrass after emergence. He was unaware of home garden products available for killing crabgrass plants after they germinate or "post-emergence." Most of these materials contain MSMA (monosodium methanearsonate). While available to home gardeners, these organic "asenicals" must be applied early in the season when the crabgrass plant is small (only three to five leaves). They are not effective against larger, older grass plants -- and that's when most people notice their preventer didn't work.

-- IS IT REALLY CRABGRASS?

In our region, many homeowners mistakenly think they have a problem with crabgrass, an annual that comes up from seed every year. That's why "preventers" are applied in the spring. However, many folks actually have problems with Bermuda grass in their lawns. This tough warm-season perennial starts to grow from dormant roots, rhizomes and stolons after the weather warms up. If you think it's crabgrass, but it has tough wiry root and stems when you try to pull it up, it's probably Bermuda grass. We'll tackle its control another time.

* Marianne C. Ophardt is a horticulturist for the Washington State University Cooperative Extension Office in Benton County.