PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
WHEN CAN HERBICIDES BE APPLIED – STAGE OF CROP GROWTH.
Timing is all important, otherwise significant crop damage may occur and weeds may not
be controlled (check keys and books describing the growth stages of crops).
FALLOW PERIOD
WEEDS IN THE FALLOW PERIODS between crops may decrease stored soil
moisture, carry over diseases and insect pests to affect subsequent crops and increase
the viable weed seed content of the soil. These weeds may be controlled mechanically
or chemically after the weeds had germinated.
PRE-PLANT,
PRE-SOWING
If residuals are
used ensure they
do not affect the
subsequent crop,
emerging crops
must be tolerant
AT PLANTING
POST-PLANT
HERBICIDES
Specific examples
have been given but
always follow label
instructions before
using herbicides in
any particular
setting
PRE-SOWING APPLICATIONS are made to assist seed bed preparation or to kill
weeds that would otherwise have germinated with the crop.
Non-selective systemic foliage herbicides can be applied prior to
planting or sowing the crop, eg Roundup (glyphosate).
Herbicides that require deep physical incorporation into soil can only be applied
before the crop is sown, later incorporation would damage the crop.
Herbicides that are incorporated into the soil by rainfall or irrigation may be
applied either before or after the crop is planted.
PRE-EMERGENCE HERBICIDES may be applied at planting, eg Dacthal
(chlorthal).
Herbicides are applied after the crop has been planted. The crop must be tolerant, but
it may be only tolerant at certain stages.
PRE-EMERGENCE CROP AND
PRE- EMERGENCE WEED
The herbicide is applied before either the
crop or weeds have emerged from the soil.
Examples include:
Dacthal (chlorthal)
simazine (in lupins)
PRE - EMERGENCE CROP AND
POST- EMERGENCE WEED
Non-selective contact or translocated
herbicides are applied before the crop has
emerged but after weed seedlings have
emerged from the soil, eg
atrazine
POST - EMERGENCE CROP AND
PRE - EMERGENCE WEED
The herbicide is applied after the crop has
emerged but before the weeds have
emerged. Examples include:
Tramat (ethofumesate)
POST- EMERGENCE CROP AND
POST- EMERGENCE WEED
A selective herbicide is applied after both
the crop and the weeds have emerged through
the soil. Crop is unharmed. Examples include:
Fusilade (fluazifop-p)
MCPA
PERENNIAL CROPS
Non-selective post-emergent herbicides
must be applied as directed sprays, eg
amongst trees and shrubs, roses, fruit trees
and vines, where weeds to be controlled have
emerged. Pre-emergent herbicides can
be applied as directed sprays before weeds
have emerged.
FOLLOW UP
TREATMENTS
This is critical when controlling many perennial weeds, eg
Nutgrass has underground nutlets, onion weed and three-cornered garlic have
underground bulbs. Couchgrass produces stolons and rhizomes. Months after
treatment with glyphosate, small leaves will emerge and follow up applications are
needed. It is important not to let these plants flower and seed.
Woody weeds such as gorse may require further treatments to control regrowth
and seedlings.
446 Weeds - Integrated Weed Management