PLANT PROTECTION 1 – Pests, Diseases and Weeds

.
PLANT PROTECTION 1 – Pests, Diseases and Weeds
REPRODUCTION
Know when
weed seeds will
germinate and
the length of the
germination period
Caltrops
means many-pointed
Stipa
means stem-like
Weeds mainly reproduce by seeds. However, they may reproduce by other means,
eg stolons. Some weeds reproduce by more than one method. It is important to know
all the methods by which your weed reproduces.
SEEDS
RHIZOMES
STOLONS, RUNNERS
TUBERS, BULBS, CORMS
SUCKERS
OVERWINTERING,
OVERSUMMERING,
THE SEED BANK
SEED BANK
With poorly
competitive crops,
seedbank levels
can reach
10000 ryegrass seed/m 2
There can be
75000 seed/m 2 of
perennial veldt grass
after fire
ROOT PIECES
Skeleton weed is troublesome because it can reproduce freely from both seed and
pieces of underground stems. Tools and machinery used in cultivation cut up
underground stems encouraging development of more plants.
WEEDS ‘OVERWINTER’ IN MANY WAYS, eg
Contaminated produce and planting materials, eg stored grain, seed, bulbs, tubers.
As biennial and perennial weeds.
Weed seed and vegetative propagules, eg cuttings, bulbs, tubers.
Soil acts as the primary storage bank for vegetative propagules and seeds, eg
– Rhizomes, stolons, runners, tubers, bulbs, corms, suckers, root pieces.
– Roots may grow to a depth of more than 2 metres (inside back cover).
– Seed banks. refer to the existing seeds in soil. The weed seed bank is a reservoir of
weed seed in the soil or on the soil surface. Seed content of soil can be determined
and used to predict future weed problems in the field and aid in the development of
effective weed management systems. One broom plant can produce thousands of
seeds that remain viable for many years. Up to 15,000 seeds/square meter of Chilean
needle grass are found beneath infestations. New weed seeds are continually added
to the soil so weeds are never eliminated. The seed bank largely determines the
species composition and potential densities of weeds that subsequently develop with
crops during the growing season. Annual grasses are an exception as seeds of few
grass species persist for longer than 4 years. Poppy seeds persist for decades.
– Reducing the weed seedbank assists in the fight against herbicide resistance.
Researchers are focusing on ways to lower the numbers of seed in the soil, in an
effort to lessen dependence on herbicides.
Weed Seeds – Breaking the Bank www.grdc.com.au/
426 Weeds - Biology, classification and identification