Now is the time to use preemergent
herbicides
Bill Sevier: Ask a Master Gardener
Saturday, February 13, 2016
Q: When is it time to use a preemergent
herbicide? J.T., Tulsa
A:
Preemergent herbicides
are helpful in preventing weed establishment. They are used in early spring
(mid-February through mid-March) to prevent crabgrass and other summer weeds.
They also are useful in the fall (mid-August through mid-September) to prevent
winter weeds such as henbit. Some of the herbicides will need a second
application in spring 60 days after the first for complete coverage of
crabgrass. The label on the product will indicate if this is needed.
Many people are reluctant to use herbicides of
any sort for weed control. That is a reasonable choice for those who are
willing to tolerate some weeds. If you have a well-established lawn, this may
prevent much of the weed invasion. A healthy thick lawn depends on good soil,
proper turfgrass for the area, adequate sunlight and supplemental irrigation.
Most lawns need some fertilizer, and there are organic and synthetic sources
available for nutrients.
Helpful lawn maintenance calendars for what to
do, what to use and when to do it for Bermuda and fescue lawns are available in
the turf section of the Master Gardener website.
Master Gardeners are often asked if there are
any “organic” preemergent herbicides, as opposed to commercial or “synthetic”
ones. Unfortunately, while there are other organic pesticides, there is no
effective organic preemergent herbicide.
Corn gluten is an organic sold as crabgrass
prevention. While some reports say that if applied during a narrow window in
spring, there may be some benefit; OSU turfgrass specialists cite studies that
show little benefit.
For those wishing to use a synthetic preemergent
herbicide, OSU has some recommendations. While there are several varieties of preemergents
available on the market to prevent weeds, especially crabgrass, OSU feels that
one of the many commercial brands containing either the chemicals dithiopyr,
pendimethalin or prodiamine are good choices. These preemergents cost a bit
more than other types but last a lot longer and, in many cases, can kill
crabgrass and other weeds after they have sprouted.
The labeled directions of these products must be
followed. These herbicides usually come on a dry particle such as fertilizer or
other inert material. They may also be found less often as liquids. They must
be washed onto the soil with at least ½ inch of water after application. After
washed onto the soil, they form a barrier for weed prevention, which may last
for months if undisturbed.
One of the benefits of these three products is
that they are not soluble in water and do not leach into groundwater or spread
from where they are applied. They are broken down in nature by sunlight and
soil microorganisms.
For more information or to ask a question about
gardening, contact the Master Gardeners at 918-746-3701 from 9 a.m.-4 p.m.
Garden tips
§ Most bare-rooted trees and shrubs should be
planted in February or March. The roots of these plants are easily damaged and
should never be left exposed to air. Plant them at the same depth as in the
nursery and make sure good root and soil contact is made by gentle tamping and
irrigation after planting.
§ Finish pruning shade trees, summer flowering
shrubs and hedges. Spring-blooming shrubs such as forsythia and azaleas may be
pruned immediately after flowering. Do not top trees or prune just for the sake
of pruning.
§ Dormant oil can still be applied to control
overwintering insects.
0 comments:
Post a Comment