PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Post-emergent, pre-emergent,
soil residual herbicides
Weed types
Annual and perennial herbaceous grass and broad
leaved weeds.
Herbicides
For effective herbicide application and to avoid poor
herbicide performance:
Select a registered herbicide to control the
weeds in the crop or situation in which the weeds
occur. Apply at right stage of crop and weed.
Apply the herbicide at the correct time, eg
– To control winter annual weeds apply March/April.
– To control summer annual weeds apply Sept/Oct.
Length of time between treatments can be
manipulated by careful attention to herbicide
selection for weed spectrum, application rates, weed
populations, uniform coverage and use of various
non-chemical methods, eg hand weeding.
Use appropriate application equipment,
techniques and rates, eg correct nozzles, distance
between nozzles, boom height, pressure and speed,
calibrate application equipment.
Add a wetting agent or other spray additive if
label recommendations indicate.
Apply during the correct weather before, during
and after application.
– Apply during favourable temperature and
moisture conditions that enable the herbicide to work.
– Temperature must not be too hot or too cold. Avoid
applications when weeds are stressed, eg hot weather.
– Irrigation and rainfall affects both post and preand
so reduces post-emergence herbicide
emergents. Drought reduces weed growth
performance. Rain following application results in
herbicide being washed of treated target weeds.
– Moist leaves absorb herbicide better than dry ones
so good soil moisture which leads to moist leaves
is paramount. If the foliage is not moist the product
fails to penetrate leaf hairs.
Plant injury (phytotoxicity).
– Many young plantings and new crops are very
sensitive to herbicides, eg new turf and roses < 2-3
years of age.
– With hormone herbicides select least volatile
formulations, ie sodium salts or amines of 2,4-D
instead of esters (page 460).
– Observe plant back times on the label.
Do not mow, graze or cultivate until after the
recommended time on the label. Allow time for postemergent
herbicides to be absorbed by the plant.
Table 76. Near desired plants. Some examples, the following is a guide only.
What to use?
NO RESIDUAL WEED CONTROL
Post-emergents are used for controlling emerged
weeds only, often described as knockdown herbicides.
Can be used around trees and shrubs, domestic paths
and fencelines. Follow label directions for application
around newly planted trees and shrubs.
Can be used as a directed spray.
Post-emergent (foliage-applied)
Non-selective post-emergents, eg
Group M, eg Glypho , Roundup (glyphosate)
Group N, eg Basta , Finale (glufosinate-ammonium)
Group L, eg SpraySeed , Tryquat (diquat + paraquat)
DANGEROUS POISON
When and how to apply?
Apply most post-emergents when weeds are young, weeds
are easier to kill and landscapes look better. For perennial
weeds the aim is to kill the plant’s underground parts.
Systemic herbicides move from foliage to roots.
Systemic foliage absorbed. Kills emerged weeds only, kills
roots. Do not disturb treated weeds by cultivation, grazing or
sowing for at least 1 day after treatment of annual weeds and
7 days for perennial weeds (check label for variations).
Contact (minor translocation) foliage herbicide. Burns
off parts of green plants contacted by spray. Many annual and
perennial broadleaved weeds and grasses, some perennial
weeds may regrow from roots.
Contact foliage herbicide. Kills emerged weeds only, does
not kill roots. Do not sow or cultivate for 1 hour after spraying
(check label for variations).
Fig. 251. Examples of herbicide damage. Left: Glyphosate injury to honeysuckle.
Centre: Glyphosate injury to roses. Right: Tryquat injury to tulip leaves. PhotoCIT, Canberra (P.W.Unger).
Weeds - Examples of weed situations 457