PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Weeds in flower plantings
Weed types
Many weed problems in flower beds are the result of
poor weed control in seed, seedling or cutting beds
prior to planting the crop. A wide range of annual and
perennial herbaceous grass and broadleaved weeds
must be identified to ensure that any herbicides
used will provide effective control. For example,
weeds poorly controlled by pre-emergent herbicides
such as clover and wireweed need to hand weeded to
prevent competition with annuals.
Impacts
Weeds reduce the aesthetic value of a display and
compete for water, light and nutrients and thereby
reduce plant vigour. Weeds look unsightly and
increase the incidence of disease and pests
(Forster 2008).
Management (IWM)
Are you a commercial grower or home gardener?
1. Prepare a management plan that fits your
situation and includes site assessment, source of
planting material (plant species selections), site
preparation and construction, planting and maintenance,
cleaning up the site.
2.Crop, region. Recognize variations depending on the
site, plants being grown etc. Select plant species suited
to site, season and climate, etc.
3. Identify likely weed problems - annual grasses, eg
annual rye grass (ARG), winter grass, wild oats, and
perennial grasses, eg couchgrass; annual
broadleaves, eg bitter cress, chickweeds, common
cotula, fat hen, perennial broadleaves, eg thistles,
wireweed, clover, and mustard weed. Obtain a Fact
Sheets for each one. Seek advice if unsure (page xiv).
4. Monitor weeds and their impact and record results (page
429). Begin by carrying out a weed risk assessment by
performing a weed seed germination test on the soil after
site preparation. After planting up, monitor flower beds
weekly for presence of weeds.
5. Threshold. How many weeds are acceptable? Have any
thresholds been established? If so, what are they,
economic, aesthetic, environmental? Do you need to
calculate your own threshold?
6. Action/Control. Take appropriate action when any
threshold is reached. Be careful in the selection of
herbicides.
7. Evaluation. Review IWM program and flower
species selection to see how well it worked.
Recommend improvements if needed.
Control methods
Cultural & Physical. Choose areas free of
perennial weeds. Beds must be properly prepared,
weed seeds allowed to germinate and any weeds which
develop must be controlled either by hand weeding,
cultivation or by herbicides (see below).
Weed mats or weed-free mulches of various types
prevent moisture loss, keep roots cool and discourage
annual weeds.
Resistant/tolerant varieties. Some crops have
been genetically engineered (GE), ie ornamentals, eg
petunia; to tolerate non-selective herbicides, eg
glyphosate.
Plant quarantine. Avoid introducing weedinfested
soil, mulch, planting material in tubes, pots,
etc. Try to prevent keep weeds in surrounding areas
from setting seed.
Disease-test planting material. Use if
available and considered necessary.
Physical & mechanical.
Hand weeding during flowering may disturb plantings
and damage roots.
Herbicides.
Post-emergents. Existing weeds can be sprayed
out with glyphosate after the weed seed germination
test has been done. Pedestrian paths can also be
sprayed with glyphosate, garden bed edges with
glufosinate-ammonium to keep weed free. Continue
weekly monitoring for weeds in flower beds –
weekly hand weed as required.
Pre-emergent herbicides. Select carefully to
ensure their effectiveness and least likelihood of
causing damage to plants. No pre-emergent
herbicide will control all weeds (page 458,
Table 76, Table 81 below).
Table 81. Weeds in flower plantings – Some herbicides
What to use?
NON-SELECTIVE PRE-PLANT POST-EMERGENTS
Group M, eg Roundup , Zero (glyphosate)
(systemic)
Group N, eg Basta (glufosinate-ammonium)
(partially systemic)
PRE-EMERGENTS
Group D, eg Dacthal (chlorthal-dimethyl),
Surflan (oryzalin)
Others
When and how to use?
Non-selective post-emergent herbicides may be used to kill
young emerged annual and perennial weeds in prepared planting
sites prior to planting. Check planting times. Where applicable
glufosinate-ammonium may be applied as a directed or shielded
spray along edges of garden beds and for inter-row weed control
after planting.
Treat immediately after planting out (page 458). Wide range of
weeds. Main use is over bulbs and annuals to control broadleaved
weeds such as chickweed, capeweed, wireweed, creeping oxalis
and fat hen.
Weeds - Examples of weed situations 463