On many outdoor grown perennials and annuals, the warm, dry conditions are leading to continued problems with potato leafhoppers, thrips and spider mites. See previous messages for more information. But, we have been having heavy dews and humid conditions which can also promote many different leaf spots and blights.
Inspect Incoming Poinsettia Cuttings – carefully inspect poinsettia cuttings (by each batch, and variety) to insure that they are free of insects and diseases and are of the quality you expect.
Look for whitefly egg, nymphs and pupae on the underside of the leaves, especially the oldest bottom three leaves where most of the whitefly may be found. If possible, randomly inspect from 10 to 30% of the cuttings. Inspect each shipment and cultivar separately. Record which shipment or cultivar has whitefly and which stage is present.
Whitefly eggs and nymphs are very small, so a 10x handlens or hands-free optivisor is helpful. Patches of dried spray residue or dried latex might be confused with dusty appearance once sees near the whitefly eggs. See photo of sweet potato whitefly nymphs and eggs on the underside of the leaves.
Don’t assume that if you don’t see whitefly adults emerging from the shipping containers, that you are free of whitefly. Adults are less likely to be observed compared to the more sedentary stages.
Record which shipments and varieties may need follow-up treatments. For information on chemical control of whiteflies, including the highly resistant Q Biotype of the siverleaf whitefly see www.q-biotypewhiteflies.com .
Look for fungus gnat larvae and signs of their feeding damage (blunt root tips). Roots should be white and healthy with no signs of root rot disease.
Look for any angular leaf spots with a yellow halo, that may be indicate of a bacterial leaf disease. Leaves may also appear water soaked. Bacterial leaf diseases spread rapidly under warm conditions and over head watering.
http://www.negreenhouseupdate.info/index.php/search-form/341-poinsettia-xanthomonas-leaf-spot
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