PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Broadleaved weeds
Weed types
Annual and perennial broadleaved weeds, eg
Annual, eg capeweed (Arctotheca calendula) and
Perennial, eg sheep sorrel (Rumex acetosella).
Spread
Depending on the species, methods of spread include:
By wind and water, eg seed, broken plant parts.
By cultivation, eg oxalis bulbs, root parts.
By growth of stolons on the soil surface.
In soil deliveries, manures, compost, containers as
seed, rhizomes, cut up root pieces, bulbs etc.
Management (IWM)
1. Access a plan that fits your situation.
2. Crop, region. There will be variations in activity
depending on the situation.
3. Identification of the weed(s) must be confirmed. Be
able to identify different growth stages of the weeds.
Consult a diagnostic service if necessary (page xiv).
Know their life cycle, method of spread, etc.
4. Monitor weeds and/or their impact, record results
(page 429). Know when seeds are going to germinate.
5. Threshold. How much weed infestation is acceptable?
Have any economic, environmental aesthetic? Do you
need to calculate your own threshold? There may be a
nil tolerance, eg turf playing fields.
6. Action. Take appropriate action when any threshold
is reached and follow through a maintenance program.
7. Evaluation. Review IWM program. Recommend
improvements if required.
Control methods
Cultural methods. After ‘eradication’ from a bed,
maintain suitable groundcover of plants, or mulch, to
prevent re-establishment of weeds. Consider edging
beds to keep out any stolons.
‘Tolerant crops’. Some crops have been genetically
engineered (GE), eg ornamentals (petunia), vegetables
(potato), field crops (canola, cotton, soybean) for
tolerance to non-selective herbicides, eg Roundup
Ready Cotton.
Plant quarantine. After removal from an area
avoid re-infestation by not introducing soil, compost
or containers infested with broadleaved weed seeds,
stolons or rhizomes, corms.
Weed-tested seeds, soil etc. Ensure crop seed is
certified weed-free; tubestock and containers should
not contain weed seeds, rhizomes, etc.
Physical & mechanical methods. Annual
broadleaved weeds may be hand pulled before seed is
set. Perennial broadleaved weeds may be dug out
diligently over time to remove most stolons and roots.
Cultivation can spread bulbs and root pieces, etc and
there is still a seed bank of weeds seeds in the soil.
Herbicides. Depending on the situation, annual
weeds can be controlled before they flower and set
seed, by foliar sprays of selective herbicides, or
directed sprays of non-selective herbicides. Preemergents
must be applied before seeds germinate
(page 458, Table 76). Many broadleaved weeds have
developed resistance to certain herbicides (page 449).
Table 78. Broadleaved weeds. - Selective control (mostly for commercial growers).
What to use?
BROADLEAVED WEEDS IN GRASS CROPS.
Post-emergents
Selective post-emergent hormone herbicides which do not
kill grasses have been available for years to control a wide range
of broadleaved weeds in turf, pastures and cereal crops. Some
are more effective at controlling some broad-leaved weeds than
others. Check label directions for the weeds in your crop.
Hormone-type herbicides
Group I, eg 2,4-D, MCPA, dicamba, clopyralid, mecoprop;
often formulated as mixtures, eg dicamba and MCPA
Pre-emergents, eg
Group B, eg Glean (chlorsulfuron)
When and how to use?
Hormone herbicide injury to crops eg cotton and grapes,
is not uncommon (Fig. 253). There are restrictions on
their use near grapevines. Some formulations are volatile
and may damage non-target plants. Hose jar applications to
garden lawns may damage surrounding broadleaved plants.
Systemic, foliage applied
Soil residual, mainly broadleaved weeds in cereal crops
(see also broadleaved weeds in turf, page 462).
BROADLEAVED WEEDS IN BROADLEAVED CROPS
Post-emergents,
Are available for a few crops.
Pre-emergents, eg
Group D, eg Dacthal (chlorthal), Surflan (oryzalin)
Group G, eg Ronstar (oxadiazon)
SPOT SPRAYING (DIRECTED FOLIAGE SPRAY)
Post emergent
Systemic.
Group M, eg Roundup (glyphosate) – Non-selective
Soil residuals
Certain broadleaved weeds (and grasses) in ornamentals,
eg roses, fruit, vegetables, nursery stock.
Fig. 253. Hormone herbicide injury. Left: Spindly tomato leaves. Centre and
right: Parallel leaf veins in plane tree and grape vine. Cotton and grapevines can be
severely damaged each year. PhotoNSW Dept of Industry and Investment. PhotoCIT, Canberra (P.W.Unger).
460 Weeds - Examples of weed situations