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 24
AFM 91-19 / TM 5-629 / NAVFAC MO-314
24 May 1989
Chapter 4
WEED CONTROL IN IMPROVED GROUNDS-TURF AND HORTICULTURAL PLANTINGS
Section A -- Controlling Weeds in Turf
grade sulfur may be used to lower the soil pH,
but, if misapplied, it can injure turfgrasses.
4-1. The Importance of Good Cultural Prac-
Other treatments include using ferric sulfate and
tices:
acidifying nitrogen fertilizers, such as ammo-
a. The best defense against weeds is a dense,
nium sulfate, to prevent iron chlorosis by allow-
vigorously growing turf. Weeds have difficulty
ing nutrient release during cool soil conditions.
gaining a foothold in good turf. To grow dense,
Obtain advice from the county agricultural ex-
vigorous turf, it is necessary to have the best
tension agent on the treatment to be used.
varieties of adapted grass species, good soil
conditions, correct soil acidity, proper fertiliza-
4-3. Fertilizing Turf. Nitrogen is the nutrient
tion, proper watering, correct mowing, and con-
most often needed in turf. It and the two more
trol of weeds, insects, diseases, and nematodes.
common fertilizer elements, phosphorus and po-
b. Weeds can become a problem if the turf is
tassium, should be in good supply when the turf
weakened or partially lost because of mechanical
is growing most rapidly. Fertilizing should be
disturbances, excessive use, drought, or poor soil
based on the results of soil testing. The Cooper-
conditions. Also, some weed species are particu-
ative Agricultural Extension Service will make
larly strong competitors.
the analyses and recommend soil treatments.
c. The first step in weed control is to correct
a. In the northern temperate climate, fertilize
any improper cultural practices that are causing
cool-season grasses most heavily in the fall.
thin, weedy turf. Turf maintenance practices
Fertilize less, if at all, in early spring. In
vary with climate, soil type and condition, turf
cool-season grass turf, nitrogen levels in the soil
species, and management objectives. The instal-
should be declining before periods of expected
lation land management plan and the county
hot or dry weather. Nitrogen is seldom used in
Agricultural Extension Service should be con-
the summer. Annual rates of application range
from 2 to 5 lb of nitrogen per 1000 ft2.
sulted for appropriate local practices.
b. Fertilize warm-season grasses much as ber-
mudagrass, zoysiagrass, and St. Augustinegrass
4-2. Adjusting Soil pH. A pH in the range of
with nitrogen during the spring and summer.
6.0 to 7.0 is considered best for turf grass
Use annual rates of 1 or 2 lb of nitrogen on
because it provides the most favorable nutrient
zoysiagrass and 2 to 5 lb per 1000 ft2 on St.
availability and microbial activity.
Augustinegrass and bermudagrass.
a. In acidic soils in the eastern United States
c. Take extra precautions in applying
there is frequently a need to apply ground
fertilizer-herbicide "weed and feed" mixtures.
agricultural limestone. Soil pH and the amount
Don't overtreat by making a second or third trip
of lime needed should be determined by soil
around trees and shrubs to give them an extra
tests. In areas of higher rainfall, acid sandy soils
feeding of fertilizer. Such extra trips can apply
generally require applications of about 25-50 lb
too much herbicide and injure or kill the trees
and shrubs. Do not use fertilizer-herbicide mix-
annually and clay soils require heavier applica-
tures each time the grass needs fertilizer.
tions of about 50-100 lb per 1000 ft2 annually
until the soil pH rises to about 6.5. Therefore,
4-4. Watering Turf. Proper watering is impor-
apply lime every 2 to 3 years based on soil test
tant in maintaining high quality turf.
recommendations. Lime may be applied at any
a. Watering must be frequent enough to en-
season, but late fall or winter is the best time.
sure proper soil moisture. Sandy soils have low
The rain and snow that fall after application will
moisture-holding capacity and require frequent
carry the lime into the soil before spring and
summer, when the greatest growth of turf oc-
watering. Clay soils retain more water, and
therefore, should be watered less frequently but
curs.
in larger amounts. Do not water grass unless it
b. In areas having soils with a high pH,
chlorosis of turf may be a problem. Chlorosis is
shows signs of wilt. Then apply enough water,
characterized by a yellowish appearance caused
usually about an inch, to wet the soil 6 inches or
by a deficiency of chlorophyll. Agricultural
more deep.
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