By: Eddie Ayers, County Extension Agent
Late summer/early fall is an excellent time for you to survey or map the weeds in your pastures, hay
fields, orchards, and lawns, but it’s not the best time to spray. The majority of weeds growing in early fall
are usually summer annuals and summer perennials. Many people want to control summer annual weeds
that are present, but treatments now are usually unsuccessful. Your time would be better spent mapping
out your control strategy for next year.
Herbicides are usually more effective on weeds that are young and actively growing. The large size of
summer weeds makes them easy to identify for mapping out heavy infestations or "hot spots." Knowing
which weeds might be causing a problem and their location in the field allows you to develop a control
strategy for next year’s summer weeds.
For example, with fall here, many pastures are turning a brilliant shade of yellow. This is usually from a
problem weed called bitter sneezeweed but it could also be ragweed. Late summer or fall is not the
preferred time to control bitter sneezeweed or ragweed. Instead, controlling them in the seedling stage of
growth is cheaper and more effective but this is determined by scouting your lawn or pasture now.
Remember that proper identification is critical. A heavy frost is probably the best control for summer
annuals in the fall, but if you want to control them from spring thru summer, make notes now.
The key to low cost weed control is to match the most cost effective herbicide to the weed problem and
then apply the herbicide at the correct time of the year. The correct identification is needed so that you
can apply the correct herbicide. Keep in mind that there are two basic categories of herbicides. The two
categories are pre-emergence and post-emergence.
A pre-emergent herbicide is applied before the weed appears. This also means before the seed
germinates. If you plan to use a pre-emergent herbicide, it is extremely important to know what weeds
you had this year because chances are those are the weeds you will have next year. You can however
apply a pre-emergent now for winter weeds. One tool to keep in mind is the UGA weather network found
at www.georgiaweather.net which will give you soil temperatures so you can determine if it’s warm
enough for a seed to germinate. In the spring seeds usually germinate when the soil temperature is around
A post-emergent herbicide works after the weed has germinated, but you need to apply it early in the
growth cycle as the weed is easier to kill when it is small. There are exceptions, but in general, late May
and early June are the preferred times to control summer annuals. Most weeds will be in the seedling to
early vegetative growth stage at this time and will be more susceptible to control by the herbicide. For
winter weeds November is a good time to apply a post-emergent.
For more information, contact me in the Gilmer County UGA Extension office.
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