PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
CULTURAL
METHODS
(contd)
Know conditions
and practices
which encourage
weed seed
germination
CROP ROTATION.
Crop rotations are designed to control weeds, some pests and diseases,
and to retain and build up soil fertility and structure.
Appropriate crop bed preparation after a rotation, prior to planting.
Intercropping, eg companion crop, undersowing, hedges, brassicas crops, wind
breaks, permaculture systems.
Green manure crops, living mulch, grazing, cash crop sequence, fallowing.
Organic matter or green manure crops must be allowed to decay and organisms can
destroy weeds seedlings. Brassicas can suppress weeds.
Crop rotations, seedbank monitoring and careful management have
allowed farmers to contain the seedbank of herbicide-resistant ryegrass to
manageable levels, ie to less than 1000/m 2 (from highs of 10000/m 2 ) (page 426).
Why reduce the weed seed bank in the target area over time?
By maintaining a falling trend in the size of the seedbank (page 426), there are fewer
weeds to be sprayed, weed control methods are more effective and there is reduced
the risk of developing herbicide resistance (page 450).
What can you do?
Prevent introduction of viable weed seed from external sources, eg control weeds in
surrounding areas before they set seed, do not introduce infested soil, seed, etc.
Prevent established weeds in the target area from setting seed, eg control weed
seedlings, eg rogue, mow, spray, when weed populations are low and before seed set.
Practice recommended crop competition, crop rotation, etc.
Practice seedbank monitoring.
Follow specific guidelines produced by CropLife Australia and GRDC and follow
resistance management strategies on herbicide labels.
CropLife Australia www.croplifeaustralia.org.au/
Weed Seeds – Breaking the Bank www.grdc.com.au/
CULTIVATION.
Reasons for cultivation – weed control
– ‘Tickle’ or shallow cultivation promotes earlier and more uniform germination
of certain weed seeds by placing seed in a better physical position in the soil, eg
contact with moisture, protection from drying out, prior to sowing the crop. These
germinating weeds can then be controlled either by further cultivation, herbicides,
etc. However, some weeds, eg radish, germinate sporadically so that late
germinations flushes can be difficult to control.
– A naturally occurring germination stimulant, karrikinolide is being trialed to
reduce the extent to which cultivation is used to stimulate weed emergence and
improve the sustainability of minimum tillage farming systems. Karrikinolide
promotes weed seed germination so they can be controlled by fewer herbicide or
other treatments.
– Pre-sowing cultivation (or herbicide application) effectively controls young weed
seedlings and annual weeds that have been allowed to develop (see above), reducing
weed infestations in new plantings. The smaller the weeds at cultivation the more
rapidly, efficiently and cheaply, they are destroyed. Cultivation kills weeds by
burying shoots to prevent re-growth, roots and shoots exposed to air dry out and die.
More effective if carried out on warm days.
– Cultivation can be used to control weeds during a fallow, ie the non-crop
period. Traditionally fallow management is based on clean cultivation.
– Cultivation at the correct time prevents existing weeds from seeding and
exhausts food reserves of perennial weeds through repeated disturbance.
– Cultivate only as needed to limit soil disturbance and to keep weeds from
competing with the crop or from setting seed. Soil disturbance can dramatically
reduce the effectiveness of pre-emergents.
– Cultivation also aids moisture and nutrition retention.
Disadvantages of cultivation.
– If soil is too wet or too dry, cultivation can exacerbate rain and wind erosion.
– Frequent cultivation reduces organic matter, adversely affecting soil structure.
– Cultivation can damage crop roots and must be > 30 cm from tree stems.
– Weeds with hard underground parts or deep roots may form more shoots.
– Perennial weeds may remain alive buried in soil for some time and may be redistributed,
eg corms, cut up root pieces. Roots of perennial weeds which produce
suckers may require herbicide treatment to stop regrowth from their roots.
CONSERVATION TILLAGE (CT).
CT is aimed primarily at soil conservation and the need to conserve moisture to
sustain productivity. CT eliminates some or all operations involving soil disturbance.
In CT systems, post-emergent herbicides have largely replaced cultivation for
weed control; modified implements allow sowing into stubble/uncultivated soil and
more compacted seedbeds. In conventional crop production systems herbicides
supplement tillage. As tillage is reduced the diversity of weeds may decrease but
the numbers of these weeds surviving may increase.
In no-till systems up to 70% of weed seed is on the soil surface and may be
taken by ants and other predators, some will be decayed by fungi and other microorganisms
but some still remains. If stubble remains on the surface then conditions
remain favourable for germination. These can be controlled with herbicides or
suppressed by mowing, slashing or heavy grazing (page 438).
Weeds - Integrated Weed Management 433