PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
TRUE
PARASITES
(contd)
Branched broomrape
is distinguished from
the common variety
by its typically
branched flowering
stems and often
bright blue flowers.
BROOMRAPES (Orobanche spp., Orobanchaceae). In Australia three species
are known to be present. O. cernua var. australiana, a native species that does
not attack crops, lesser broomrape (O. minor) which is a common minor weed
and branched broomrape (O. ramosa) which is under an eradication program.
Have no chlorophyll. Difficult to control
No true roots.
Annual flowering plant (occasionally biennial). Stems are erect, brownish,
and grow to about 20-40 cm high. Scale-like leaves, flowers inconspicuous.
By the time flowering stems emerge it is usually too late to save the crop.
Parasitic on the roots of broadleaved vegetable and field crops, eg clover,
legumes, ornamentals, eg gazania and some weeds, eg skeleton weed.
Spread interstate by travellers, via transport or other material. Seed is spread by
soil on machinery, contaminated soil, sand, animal manures, livestock through
the gut, wool, fur and in soil, manure attached to animals. To a lesser extent
by wind and flooding. Seeds are small, like dust. One broomrape plant can
produce up to 500,000 seeds with a dormancy of 10 years or more!
Broomrapes are serious weed pests of certain crops affecting yields, eg
canola, and can stain crops such as celery and cabbage. Ornamentals often
appear to be unaffected when only a few broomrape plants are present.
Broomrape stems range
from 20-40cm in height.
PhotoCIT, Canberra
(P.W.Unger).
INTEGRATED WEED MANAGEMENT (IWM)
MAIN STEPS
The National Branched
Broomrape Eradication
Program commenced
in 2000 to eradicate
branched broomrape
(Orobanche ramosa)
from South Australia.
CONTROL METHODS
Legislation
Cultural methods
Sanitation
Biological
Resistant varieties
Plant quarantine
Pest-tested material
Physical/mechanical
Pesticides
1. Plan ahead. Commercial growers should contact their local authority for
information on quarantine status and protocols for management of the parasitic plant
in question. Keep records of the crop, eg source of planting material, planting/sowing
dates, temperature, irrigation, fertilizers and pesticides. National Eradication
Programs are in place for some parasitic weeds, eg branched broomrape.
2. Crop, region. List parasitic plants which are likely to occur in your crop or region.
Some parasitic plants are declared noxious weeds only in some areas. Management
plans are available for some parasitic plants, eg broomrape, mistletoes.
3. Identification must be confirmed. Send specimens to a diagnostic service if
necessary (page xiv). Once identified obtain information on its life cycle, population
dynamics and likely impact on the crop and control. Obtain Fact Sheets.
4. Monitor. Know when, where, what and how to monitor. Early detection of a
parasitic plant in a crop assists control (page 429). Record results as recommended.
5. Threshold may be determined by legislation which may impose a nil tolerance or
specific threshold through Noxious Weed Acts, Seed Acts and Quarantine Acts. If
not you may need to work out your own threshold.
6. Action/control. There may be legislative requirements. Protocols are available
for the control of Orobanche ramosa in SA. Certified seed is available for some
crops. Use control measures strategically and early be it chemical or biological or
both and potential major weed problems may be avoided.
7. Evaluation. Continue monitoring after treatment. Review IWM program to see
how well it worked. Recommend improvements if required.
382 Parasitic flowering plants