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 AFM 91-19/TM 5-629/NAVFAC MO-314
24 May 1989
7
in the soil may produce new plants for many
established roots are not seedlings and are more
years.
difficult to control. During their vegetative
stage, perennials are not very susceptible to
b. Biennials require two growing seasons to
herbicides because they are drawing on their
complete their reproductive cycle. The first
stored nutrients and not absorbing them from
year's growth is purely vegetative, with top
the surrounding environment. Control of peren-
growth usually confined to a rosette of leaves.
nials is best achieved during the bud and subse-
They are dormant during the winter and in the
quent regrowth stage. As the plant is actively
second season develop stalks with flowers and
setting buds in order to reproduce, its food
seeds. Because of this, they are easily confused
reserves are at their lowest levels, thus making it
with winter annuals, Because they reproduce
more susceptible to chemical control. Treatment
only by seed, they can be treated like annuals.
at the early flowering stage is generally as
Burdock, evening primrose, common mullein,
effective as during the bud stage, but, when
and wild carrot are examples of biennials.
perennials reach full flowering, control levels
decline drastically.
1-4. Perennial Plants:
e. Quackgrass, Canada thistle, Johnsongrass,
a. Perennials are plants that live more than 2
buttercup, and nutsedge are examples of peren-
years. Many have several means of reproduc-
nials that are difficult to control. Some herbi-
tion. In addition to reproducing by seed, they
cides, however, are effective even on these
may reproduce vegetatively with the aid of
hard-to-control perennials.
storage organs in the form of stolons (prostrate
aboveground stems), rhizomes (prostrate under-
Section C -- Characteristics of Herbicides and
ground stems), bulbs, corms, and storage roots.
Plant Growth Regulators
Food is stored in these organs by the plant, and
can be used when new growth occurs. New
shoots may come from buds that live on these
1-5. Common and Trade Names. Common
stored food reserves until the new plants become
names and designations of herbicides and
established. Unlike annuals, the top growth of
growth regulators used in this publication are
many perennials may be killed, and still the
those accepted or preferred by the Weed Science
plants can live and propagate by means of their
Society of America and the American National
belowground storage organs and dormant buds.
Standards Institute. Chemical names are those
b. To control a perennial plant's vegetative
preferred by Chemical Abstracts Service of the
reproduction, the plant's food reserves must be
American Chemical Society. Trademarks or
materially reduced, or its storage organs and
trade names used by the herbicide industry are
buds must be destroyed. The food the plant
cited for information only, and do not constitute
stores is the excess manufactured by the green
an endorsement over other products that may
leaves and stems, over and above what is neces-
have been omitted. Because many users of this
sary for growth. Therefore, if photosynthesis
publication will be more familiar with trade
can be prevented, the buildup of reserves will be
names than common names, an alphabetical list
curbed.
of trade names with a cross listing of common
names is given in attachment 2. Herbicides in
c. Cultural methods of control are designed to
other tables in this publication are alphabetized
allow new growth to use up the plant's food
by common name.
reserves. New shoots draw on stored food for
about 10 days after emerging. At this time the
top growth is killed. This is repeated until the
1-6. Active Chemical Content and Formula-
plant's food reserves are exhausted. The cultiva-
tions:
tion cycle usually takes 3 to 5 weeks, depending
a. The containers of all commercial herbicides
on the species and growing conditions, and the
have labels that state the amount of active
program often must be continued for at least
phytotoxic chemicals contained in the particular
two growing seasons.
product. This is expressed in pounds per gallon
d. Chemical control may also require repeated
for liquids and in percentage of active ingredi-
applications to deplete the plants supply of
ent, acid equivalent, or phenol equivalent for
nutrients. While perennials do have a seedling
granules and powders. Acid equivalent is com-
stage, and control is easiest at this point, most
monly used to express the active chemical in
are very inconspicuous, and accurate identifica-
herbicides derived from acids such as in di-
tion is difficult. Also, shoots that emerge from
camba; 2,4-D; glyphosate; and picloram. Phenol
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