Joan Swenson: Pre-emergent herbicide a magic elixir for gardeners
| Thursday, Jan 29 2009 06:23 PM
Last Updated Friday, Mar 27 2009 01:31 PM
I pulled out my hand-cranked dry chemical applicator last weekend and did a rapid run around the back lawn and the side yard where we have fruit trees. In less than 30 minutes, I’d taken care of preventing a lot of irritating crabgrass and spotted spurge plants that were moments away from sprouting.
Sunday is the Super Bowl and while I have no interest in football, it has been a helpful date to remember to put down pre-emergent herbicide. However, given the warm weather we have had in January and headlines I saw a week ago that seasons are changing earlier, one might think about putting down pre-emergent on New Year’s Day instead. The Rule of the Super Bowl could become The Rule of New Year’s Day.
Soil temperatures typically begin rising in February — Feb. 15 is the end of the frost season in our areas — so be sure you have your pre-emergent down before the middle of the month. You will not notice the germination of small crabgrass and spurge seeds until it’s too late to treat and then you will have to either spray with post-emergent weed sprays or pull weeds. It may be necessary to apply pre-emergent again in late spring to prevent summer breakouts of weeds.
When buying a pre-emergent, check the sacks of pre-emergents at the nursery and read the labels to see that they control crabgrass and spurge. According to the University of California, chemicals that prevent crabgrass from sprouting include benefin, bensulide, DCPA, dithiopyr, oryzalin, oxadiazon, pendimethalin, prodiamine, and trifluralin. And if you are late in applying your pre-emergent, post-emergent applications of products containing MSMA can help control crabgrass. For spurge, the UC says that products containing DCPA, isoxaben, pendimethalin, oryzalin, and trifluralin plus benefin, and oryzalin plus benefin are helpful.
I had a sack of Amaze granules, which contains the trademark chemicals Balan (benefin) and Surflan (oryzalin), left over from a couple of years ago. Since benefin and oryzalin are recommended for crabgrass and spurge, it was effective at keeping down the summer weeds in lawn and open areas.
Read the product label for application amounts and watering directions. Pre-emergents need to be watered in to be effective. Some need to be watered in immediately, but with others you have a two- or three-week time frame and rain may do the job for you. When I put down the pre-emergent granules, it was under dark skies and I was hoping for rain.
Be sure you do not apply pre-emergents in locations were you plan to plant anything from seed, such as vegetables.
Some weed problems are the result of overwatering, particularly crabgrass. Excessive, regular watering encourages this lush, shallow-rooted weed to thrive. Starve it of water and it will shrivel and go away. The same is not so true with spurge, which grows a deep tap root. Once it gets established in an open, sunny area, a spurge plant seems capable of living on the tiniest bit of water in the most miserable heat. But spurge may be outsmarted, too, if you have it in a lawn. Taller lawn heights shade the soil and reduce spurge as a problem. Spurge needs lots of sun, which is why you see it grow poorly — reaching weakly for sunlight — in shady areas.
