সার্চ করুন
সার্চ করুন
Crocidolomia is a genus of moths of the family Crambidae.Common Name:
English: Croci, Cabbagehead Caterpillar (CHC), Larger Cabbage WebwormSpanish: Croci, Gusano de la Cabeza del Repollo (GCR), Gusano Tejedor Grande del Repollo
Scientific Name:
Crocidolomia binotalis [Zeller] (Lepidoptera: Pyralidae)
Geographic Distribution:
Highland tropics of the Old World. Principally: Australia
(Queensland), India, Indonesia, Taiwan, Thailand, Malagasy Republic,
Mauritius, Philippines, South Africa. Croci has only been found in
tropical and subtropical regions.
Recognition and Diagnosis:Caterpillar
Adult Moth
Eggs
Damage and Importance:
Until the advent of synthetic insecticides Croci was considered
the foremost pest of crucifers in the Old World. Even a single larva
will destroy an entire plant by feeding on its growing center. Larvae
are extremely mobile and can easily travel 2 or more meters to reach a
preferred host plant. Also, as soon as larvae have begun boring into a
cabbage head they are protected from contact with insecticides. In the
Old World, Croci is a devastating pest of cabbage, particularly where
efforts are made to reduce dependence on bi-weekly pesticide
applications.
ControlManagement Strategies:
Sampling and economic thresholds:
For approximately the first 70 days from cabbage planting (or 40 days
from
transplant) monitoring for Croci damage is quick, effective, and
essential
for determining appropriate pest management action. After this time,
when the cabbage plant is larger and structurally complex it becomes too
difficult to detect Croci and sampling becomes much less effective.
Where to sample:During the first 40 days from
transplant, Croci can be effectively monitored by looking for the
window-like leaf damage created by the early larval instars. This must
be carried out twice weekly in order to detect the larvae before they
move towards the growing center of the plant.
Economic threshold: During the first 40 days after
transplant, Croci can be monitored and groups of young larvae can be
killed by hand or spot-sprayed with products based on Bacillus thuringiensis
(Bt). This method is time efficient while Croci densities remain below
15%. If the percentage of plants infested with Croci exceeds 15% it
becomes more efficient to spray the entire field.
After the first 40 days from transplant, monitoring is no longer
sufficiently effective. Cabbage must be sprayed routinely twice each week.
Biological Control:
Several Hymenopteran larval parasitoids have been identified for Croci,
but none has demonstrated greater than a 7% parasitization rate. The
first egg parasitoids were discovered in 1995, but these two species of
Trichogramma have not yet been identified.
Current IPM Practices:
Planting seasonIt is preferable to plant cabbage during the rainy season when Croci populations are reduced.Hand removal of egg masses and early instarsSuccess in locating egg masses and larval groups entirely depends on
plant architecture. During the first 40 days after cabbage transplant,
while leaves are still open and relatively few, the window-like patches
created by the gregarious early Croci instars are easily detected and
squashed. During this time it takes one person less than 3 hours per
2000 plants to monitor and remove larval groups by hand. This can be
done twice each week, as larvae will not have dispersed from their
aggregation within the time between monitoring. For some farmers the
time necessary to do this during the first 28 days may be more than
seems worthwhile given the usually low (~3%) Croci densities. They may
prefer to monitor against a surprisingly high infestation only once each
week.By 40 days after transplant the time required for hand monitoring
increases significantly and accuracy of detection decreases
dramatically. Even with meticulous efforts at least 20% of a cabbage
crop can be ruined by Croci.Spot spraying Twice weekly spot spraying of Bt on only those cabbage plants with
visible Croci is an effective means of control until 40 days after
transplant and until pest densities reach 15%. Backpack sprayers that
deliver a fine mist must be used since coverage with hand held spray
bottles is not adequate.After 40 days after transplant, monitoring and spot-spraying are no
longer effective since Croci become too difficult to to detect. It is
best to spray twice weekly with Bt.Trap CroppingSome trap cropping experiments have proved very successful. In India
15 rows of cabbage were successfully intercropped with Indian Mustard
(planted 12 days prior and 25 days post cabbage transplant).
Chemical strategies:
Pesticide recommendations and consideration of resistanceCroci has not demonstrated resistance to any of the insecticides
employed for its management. The focus of the problem is assuring
contact with larvae before they begin boring into the cabbagehead center
where they are inaccessible. This leads to bi-weekly spray programs.
While this strategy very effectively manages Croci, it cannot be
considered isolated from the Diamondback moth pest complex of which it
is part. Bi-weekly spray programs easily encourage evolution of
pesticide [even Bt] resistance in DBM. In addition, in many highland
areas of Asia, Diadegma semiclausem [Hymenoptera: Chalcididae], a
larval parasitoid, has proven to provide very effective control of
Diamondback moth. Spraying against Croci decimates the D. semiclausem population.Spray techniquesUse of spreader stickers is recommended to increase spray coverage
on the waxy surface of cabbage leaves. Croci early instars will be found
on the underside of leaves so it is important to spray the underside of
leaf surfaces thoroughly. Hydraulic nozzles and those producing fine
spray mist provide the best coverage
1. Use resistant varieties 2. At seedbed and transplanting, handpick and destroy egg masses 3. Raise level of irrigation water periodically to submerge the eggs deposited on the lower parts of the plant 4. Before transplanting, cut the leaf-top to reduce carry-over of eggs from the seedbed to the field 5. Ensure proper timing of planting and synchronous planting, harvest crops at ground level to remove the larvae in stubble, remove stubble and volunteer rice, plow and flood the field 6. Encourage biological control agents: braconid, eulophid, mymarid, scelionid, chalcid, pteromalid and trichogrammatid wasps, ants, lady beetles, staphylinid beetles, gryllid, green meadow grasshopper, and mirid, phorid and platystomatid flies, bethylid, braconid, elasmid, eulophid, eurytomid and ichneumonid wasps, carabid and lady bird beetles, chloropid fly, gerrid and pentatomid bugs, ants, and mites, earwigs, bird, asilid fly, vespid wasp, dragonflies, damselflies, and spiders Bacteria and fungi also infect the larvae: mermithid nematode, chalcid, elasmid and eulophid 7. Apply nitrogen fertilizer in split following the recommended rate and time of application.