Weed control in lawns
By: Sandy Feather
©2009
Penn State
Cooperative Extension
Q.
As a new homeowner, I have lots of questions about
lawn care. Most of my neighbors use a lawn service. I prefer not to
use a lot of pesticides but would still like my lawn to look nice.
It does have a lot of weeds, and I am willing to use some herbicides
to get them under control. Are there cultural practices that would
help keep it nice without constant spraying?
A.
Proper cultural management of your lawn will go a long way toward
improving its health and appearance without using a lot of
pesticides. You may need to make a few herbicide applications at
first to get the weeds under control. After that, you can control
the occasional weed by hand pulling or spot treating with a liquid
herbicide. Your best defense against weeds is a lush, thick lawn.
Late summer and early fall are excellent times to control many lawn
weeds, especially tough perennial weeds such as clover. At that time
of year, perennial plants are translocating the products of
photosynthesis to their roots for storage over the winter and absorb
herbicides readily. Tough customers such as clover and ground ivy
will require repeated applications.
Ground Ivy is a "tough customer"
While granular weed and feed products are useful, they have their
limitations. They must be applied to a lawn that is moist from dew
or rain so that the granules stick to the leaves of the weeds in
order for them to absorb the herbicide. And you cannot make a second
application of weed and feed to go after those tough weeds -- that
would be too much fertilizer in too short a time.
Liquid broadleaf weed killers allow more flexibility. If you have
weed and feed on hand and have not fertilized your lawn in six to
eight weeks, you can make the first application with it, then make
subsequent applications with a liquid.
Broadleaf weed killers typically include active ingredients such as
2,4-D, MCPP, MCPA, dicamba, carfentrazone and triclopyr. Active
ingredients are listed in fine print, usually on the lower left
corner of the pesticide label. They are generally sold as
combination products to take advantage of the synergistic effect of
these herbicides together. (If you have a lot of trees in your yard,
do not use products containing dicamba within their root zone, or
choose a product that does not contain dicamba.)
Violets are difficult to eliminate
They are available as ready-to-use hose end applicators or as
concentrates that you mix and apply with a pump sprayer. The pump
sprayer offers more control; hose end sprayers are convenient and
you do not have to measure and mix spray solutions. Whichever you
choose, always read and follow mixing and spraying directions
carefully. The label contains important information on using the
product for maximum safety and effectiveness.
If you choose a pump sprayer, reserve it strictly for spraying
herbicides; never use it to apply insecticides or fungicides to
plants that you value. Even if you clean it out, there may be enough
herbicide residue to damage them.
You may need two or three applications to get sufficient control of
tough-to-kill weeds. Check the label of the herbicide you are using
for suggested application intervals. Even though some of these weeds
seem indestructible, re-spray at the shortest recommended intervals
until you are satisfied.
Mowing practices
greatly determine the quality of lawns. Allowing a lawn to grow long
and then cutting it short is stressful to grass. It uses a
tremendous amount of its stored energy reserves to push out new
growth after such treatment. The general rule of thumb is not to
remove more than one-third of the leaf blade at one time.
Rather than mowing on a schedule -- say, every Saturday -- mow as
the grass's growth dictates. That may be twice a week during the
cooler weather in spring and fall or every few weeks during hot, dry
summer weather (especially if you do not water).
Most species of turfgrass should be cut at a height of 21/2-3
inches. There is a direct relationship between the height of cut and
the depth and extent of the root system. The longer the grass grows,
the more extensive its root system; the shorter you cut it, the less
root system it will have. Summer heat and drought are more stressful
for our cool-season grass species than winter cold. Keeping the
grass a little taller encourages an extensive root system that will
make your lawn more drought-tolerant. It also shades the soil,
moderating soil temperatures and helping to conserve soil moisture,
as well as shading out germinating weed seeds that try to become
established.
Be sure to sharpen your mower blade regularly. A sharp blade makes a
clean cut that the grass recovers from easily. Dull blades make
jagged wounds that are harder to heal. They can serve as a point of
entry for insect and disease problems.
How often you sharpen your mower blade depends on the size of your
lawn and the number of obstacles it is likely to encounter. Monthly
sharpening for large (or obstacle-filled) lawns is not unreasonable.
Small lawns can get by with once a year.
Crabgrass control
Ground ivy
Lawn Care
Advice
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