PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
NON-SYSTEMIC & SYSTEMIC HERBICIDES
Contact & translocated herbicides – Movement in weeds
NON-SYSTEMIC
HERBICIDES
Contact
NON-SYSTEMIC HERBICIDES are only active at the point of application
(leaves, stems, roots); they are not absorbed by the plant.
They are mostly applied to leaves and stems.
They often have no action through the soil.
Normally act rapidly, good coverage is necessary for maximum effectiveness.
Useful for controlling annual weeds and perennial weed seedlings with no
underground reserves of food or buds from which to regrow after treatment.
Contact herbicides may be either non-selective or selective.
NON-SYSTEMIC FOLIAGE, eg
Sprayseed , Tryquat (diquat + paraquat)
Basta , various (glufosinate-ammonium) -
slightly systemic
Contact action, perennial weeds may
regrow from tap roots, etc
SYSTEMIC
HERBICIDES
Translocated
SYSTEMIC HERBICIDES are applied to the leaves and stems of weeds, they
then enter the plant and move through the stems to the roots, eventually killing
the weed. Systemic herbicides may also be applied to the soil to control
germinating weed seeds (pre-emergent herbicides) or taken up by roots.
May either be non-selective or selective at normal dose rates.
Herbicides enter leaves through upper or lower leaf surfaces (lower surface is
more permeable). Entry is mostly via the cuticle but also occurs via the stomates.
Most effective against actively growing weeds which can circulate the
herbicide through the plant effectively.
Dosage rates must be low enough for absorption and maximum translocation
by the plant to take place. At excessively high dosage rates many systemic
herbicides are least effective, merely acting like a contact herbicide.
Mainly act slowly often taking several weeks for maximum effect.
Advantages of systemics.
– Whole plant surface need not be treated, eg may be applied as foliage, root and soil
or tree injection treatments. Active at sites remote from where they are applied.
– When applied to the soil, systemic herbicides dissolve in soil water and are taken
up by the roots. The soil must be kept moist for continued uptake.
– Once systemic herbicides have been absorbed by the foliage they cannot be washed
off by rain or irrigation. Allow sufficient time for absorption.
Disadvantages of systemics.
– Excessive residues may still occur unless withholding periods are observed or there
is excessive application.
– May control weeds more slowly than contact non-systemic contact pesticides.
SYSTEMIC FOLIAGE, eg
Roundup , Zero , various (glyphosate)
SYSTEMIC ROOTS, SOIL, eg
Diuron , various (diuron)
For perennial weeds
the aim is to kill the
parts.
442 Weeds - Integrated Weed Management