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Conrad Bérubé island crop management email: uc779(at)freenet.victoria.bc.ca |
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Conrad Bérubé island crop management email: uc779(at)freenet.victoria.bc.ca |
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15 paces then drop unless plants are
particularly infested; inspect leaves for leps and aphids (5%
infestation is threshold for wooly aphid)
There are three generations per year of imported cabbage worm and diamond- back moth. Previous work on thresholds was done by Harcourt. .67 cabbage looper equivalents = 1 imported cabbage worm. 1 diamond-back moth = .2 cabbage looper equivalents. The idea is to use one model unit to simplify threshold calculations. .75 cabbage looper equivalents/plant (for at least fifty plants) is the threshold.
Threshold for cabbage and cauliflower is .25 cabbage looper equivalents during the heading to harvest stage. The disadvantages are that all insects on a whole plant must be counted which requires basic identifying skills.
Binomial model is presence/absence system that uses damage on plant as basic parameter (which has the advantages that less training is needed, less time to scout fields, more user-friendly). 303, 40-plant samples demonstrated that of 152 decision-events, in over 90% of cases the same decisions were reached using a 40% infestation threshold compared to .25 cabbage looper equivalents threshold. Further testing of the threshold criteria for both protocols revealed curves that were very similar and yields that exhibited no significant difference in harvest yields. There was a significant savings in labor in labor with presence/absence protocol (14 mins for 10 plants for cabbage looper equivalents model 8.7 minutes for binomial sampling).
Diamond-back moth and imported cabbage worm have high potential for biocontrol through a conservation approach. Dibema insularae is a very effective parasitoid for diamond-back moth. Cotesia, Pteromalius glomeratus, and Copidosoma (a polyembryonic egg-pupal parasitoid) are part of an effective parasitoid guild of imported cabbage worm. Trichogramma work on cabbage looper. A tachinid (Vorea boralis) pupates right on looper larva.
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