PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
– Diseases
Dipel , (Bacillus thuringiensis (Bt), a
bacterium which produces a toxin that kills
caterpillars. It is marketed as an insecticide.
Small caterpillars are easier to kill.
Gemstar (Helicoverpa virus) may be applied
by commercial growers of cotton, sorghum,
chickpea. Slow-acting.
– Trapping moths
Moth attractants. Magnet (lure which is a
blend of plant volatiles attractive to insects and
feeding stimulants plus an insecticide sold
separately) attracts Helicoverpa moths which are
killed when they contact or ingest it, preventing
egg laying, reducing the need for insecticides.
Other products are being researched. Less than
2% of the crop area may need to be treated. Other
products are being researched for use in Australia,
eg BioATTRACTHeli (attractant which consists of
kairomones and sugar feeding stimulants) attracts
adult Helicoverpa, armyworm and certain other
moth pests; when combined with an insecticide
registered for that crop, reduces moth numbers.
Trap cropping is an option for area-wide
management of Helicoverpa on some crops,
eg cotton. Moths are attracted to particular
trap crops, eg chickpeas, where they can be
destroyed. Precise strategies depend on whether
the trapping is carried out in spring or summer.
Resistant/tolerant varieties.
Genetically engineered plants reduce the
need for spraying.
– Ingard cotton (Bt cotton), engineered to contain an
insect-specific toxin produced by Bt, was released in
1997. Helicoverpa caterpillars feeding on Ingard
cotton will die. Cotton varieties are now available
which not only incorporate the Bt genes but also genes
for herbicide resistance (Roundup Ready), and
resistance to Fusarium and other diseases (Bollgard II).
Beneficial insects, mammals and birds are not affected
and there has been a 50% reduction in pesticide use.
– Refuge crops are used in the cotton industry to help
prevent Helicoverpa resistance to Bt cotton
(genetically modified). Susceptible moths in these
refuge crops can mate with resistant moths from the Bt
cotton crop, diluting overall resistance levels. Refuge
crops can also support beneficial insects, and
secondary pests of cotton.
– Other hosts are being researched so that virus
particles can be synthesized in leaves to control
Helicoverpa spp.
Pest-tested planting material.
Seedlings and cuttings may carry eggs and very
small caterpillars, soil may support pupae.
Only plant pest-free seedling and cuttings.
Physical & mechanical methods.
Screen vents in greenhouses to exclude moths.
Cut off infested tops of corn cobs after harvest
before marketing.
Insecticides.
Helicoverpa Resistance Management
Strategies have been developed. Check label.
H. armigera has developed resistance to many
insecticides, eg carbamates, pyrethroids, etc.
– CropLife Australia Resistance Strategy. In
some areas certain insecticides may only be used at
certain times of the year on some crops.
– Despite increasing difficulty in managing
H. armigera with conventional chemical insecticides
due to resistance problems and the increasing
public concern about environment safety, chemical
insecticides continue to be the most widespread
commercially used method of controlling
Helicoverpa spp.
To preserve beneficial insects avoid using
insecticides early in the season or use selective
materials such as Bt.
Number and frequency of sprays depends on
duration and intensity of egg laying and weather,
particularly temperature.
Systemic insecticides are not particularly
effective against caterpillars.
Small caterpillars are easier to kill when using
Dipel . Where large caterpillars (> 13 mm long)
or large numbers of caterpillars are feeding
consider applying a synthetic insecticide.
Control Helicoverpa caterpillars when they are
about to emerge from the eggs (black-brown in
colour) before they can cause much damage.
Once they are sheltered they are difficult to
contact with insecticides.
Thorough spray penetration of foliage is
essential for good control.
Other research options under investigation
include applying semio-chemicals (behaviour
modifying chemicals) to cotton plant surfaces.
Improving the effectiveness of spray oils.
Table 8. Corn earworm – Some insecticides and bio-controls agents.
What to use?
FOLIAGE SPRAYS
Group 1A, eg carbaryl (not on food-producing plants in home gardens)
Group 1B, eg Rogor (dimethoate); Orthene , Tracer (acephate)
Group 3A, eg Cymbush (cypermethrin); Mavrik (taufluvalinate);
pyrethrins; Ambush (permethrin);
Baythroid , Bullock (alpha-cyfluthrin); Talstar
(bifenthrin); Decis (deltamethrin); Karate (lambdacyhalothrin)
Group 5, eg Entrust , Success , Tracer (spinosad)
Group 6, eg Affirm , Proclaim (emamectin)
Group 11, eg Dipel , Costar (Bacillus thuringiensis various
strains); INGARD cotton
Group 13, eg Secure (chlorfenapyr)
Group 19, eg Opal (amitraz)
Group 21B, eg Derris Dust (rotenone)
Group 22A, eg Steward (indoxacarb)
Group 28, eg Belt (flubendiamide )
Spray oils, eg Canopy (paraffinic oil)
Biocontrol agents, include Gemstar , Vivus (Helicoverpa
virus); see also Groups 5 and 11 above
House & Garden Sprays, eg bioallethrin, bioresmethrin
When and how to apply?
Steward (indoxacarb) may temporarily affect
beneficial insects but populations quickly recover.
Biocontrol agents can be used to kill caterpillars with
minimal impact on beneficial insects
88 Insects and allied pests - Lepidoptera (butterflies, moths)