PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Weed types
Annuals, eg annual ryegrass in field crops and winter
grass (Poa annua) in turf are arguably the most written
about annual grass weeds. Perennial grasses are
endless, eg couchgrass (Cynodon dactylon), various
tussock grasses in pasture and bushland.
Impacts
Water and nutrients are used up. Crop yields are
reduced, playing surfaces affected and native bushland
invaded by perennial grass weeds. Landscapes may be
affected aesthetically. Old clumps of unmown grass
weeds are a fire hazard in some areas.
Weed biology
‘Overwintering’ in seed banks, eg 10000 ryegrass
seed/m 2 and 75000 perennial veldt grass seed/m 2
have been found in WA after fire; perennial grasses also
as underground roots and other structures. It should be
possible to disrupt seed cycles of grass weeds, especially
for annual grasses, since seeds are not well adapted
for long term storage in the soil (up to 4 years). The
problem is there are so many seeds.
Methods of spread. Depending on the species, seed
may be spread by wind and water. Stolons and rhizomes
grow into adjacent areas. Seed, rhizomes, cut up root
pieces, bulbs, are spread by cultivation, in soil deliveries,
manure, compost, containers, road building materials.
Conditions favouring, depend on species, but seed
of some species in some areas will germinate at any
time of the year following rainfall. Poor pasture, bare turf.
Many grasses prefer open sunny sites and do not
establish or compete successfully in shade.
Management (IWM)
Are you a commercial grower or home gardener?
1. Obtain/prepare a plan that fits your situation.
Assess sites for weed control and soil type; plan a
possible program of control and maintenance.
2. Crop, region. Recognize variations. List the grass
weeds which are a problem.
3. Identification. Grasses are more difficult to identify
than broadleaved plants, there are many native grasses.
Be able to identify different growth stages of grass
weeds. Identifying and treating grasses at the correct
growth stage is essential for successful control. Consult a
diagnostic service if necessary (page xiv).
Grass weeds
4. Monitor/map weeds and/or their impact and record
results of any weed management programs (page 429).
5. Threshold. Have any thresholds been established? If
so, are they economic, fire, aesthetic, environmental?
6. Action. Take appropriate action when any threshold
is reached.
7. Evaluation. Review IWM program to see how well
it worked. Recommend improvements if needed.
Control methods
Correct timing is fundamental to successful grass weed
control - prevent seed set, reduce seed bank and kill
emerged weeds. In bush areas have enough resources
to control grass weeds following fire.
Cultural methods. After eradication from a flower
bed, maintain a suitable groundcover of plants or
mulch to prevent re-establishment of grass weeds.
Select couchgrass cultivars that do not ‘run’.
‘Tolerant crops’. Some ornamental crops, eg petunia,
have been genetically engineered (GE) to be resistant to
non-selective herbicides, eg glyphosate.
Plant quarantine. After eradication from a bed
minimize re-infestation by not introducing soil,
compost or containers infested with grass weed seeds,
stolons or rhizomes, bulbs.
Weed-tested seeds, soil etc. Ensure crop seed is
certified weed-free; tubestock and containers should
not contain weed seeds, rhizomes, etc.
Physical & mechanical methods. In small areas,
annual grass weeds may be pulled out before seed is
set. Perennial grass weeds may be dug out over a long
period of time to remove stolons and roots. Garden
beds may have an edging to keep out the stolons. A
ditch a few centimetres wide may be used in place of
an edging. Grass weeds may also be mown, slashed,
rolled or grazed before seed set.
Herbicides. Many herbicides are available to
control grass weeds, however, some grasses have
developed significant resistance to herbicides, eg
annual ryegrass (page 449). Slashing without followup
herbicide treatment may increase seed production
of some grasses, eg love grass. Herbicides must be
applied at the correct stage of weed growth. Selective
control of grass weeds is difficult (Table 79 below).
Table. 79. Grass weeds. - Selective control (commercial growers).
What to use?
When and how to use?
GRASS WEEDS IN BROADLEAVED CROPS eg perennial borders, vegetable & field crops
Post-emergents, eg
Group A, eg Fusilade (fluazifop-p)
Systemic, foliage-applied. Grass weeds in broadleaved
crops, garden beds. Soil residual for up to 4 months or longer.
Pre-emergents, eg
Soil residual
Group K, eg Devrinol (napropamide)
Most grasses, some broadleaved weeds in tomato, other crops.
GRASS WEEDS IN GRASS CROPS, eg cereal crops, pasture, turf
Post-emergents, eg
Group C, eg Tupersan (siduron)
Group I, eg Drive (quinclorac)
Plant growth regulator, eg SHORTstop Turf Growth
Regulator (paclobutrazol)
Pre-emergents, eg
Group D, eg Pre-M (pendimethalin + fertilizer),
Dimension (dithiopyr)
Group J, eg Tri-allate (tri-allate)
Group J, eg Exporsan (bensulide).
SPOT SPRAYING (DIRECTED SPRAY)
Post-emergents, eg
Group M, eg Roundup (glyphosate) - non-selective
Couch, kikuyu and summer grass in bent turf.
Summer grass, white clover, suppresses kikuyu in turf.
Suppression of winter grass and growth regulation in turf.
Soil residuals
Winter grass in many turf species.
Winter and summer grass in turf.
Wild oats and some broadleaved weeds in wheat, barley,
triticale and some broadleaved field crops.
Winter grass in certain turf species.
Systemic, foliage-applied.
Weeds - Examples of weed situations 461