Woody Ornamental Pest Update
Posted: May 20, 2011
I spoke too soon last week. The gloomy weather has returned, but I’ll look on the bright side (bad pun not intended) that all the rain sets up landscape and nursery plants for an easier summer than last year.
As I mentioned last week, the weather has been very conducive for early season plant pathogens. I have seen lots of bacterial problems. I have seen lilacs, viburnums, and Prunus with dark, angular leaf spots and/or ruined foliar buds with Psuedomonas syringae. Copper products (Camelot, Phyton 27, Kocide, Champion) have efficacy against bacterial diseases and some fungal ones too. They work best when applied preventatively, but you would have had to have known of a previous problem or been able to predict the prolonged wet weather. You may still want to apply if there is continued new growth and it doesn’t become drier. Another bacterial problem that has been quite active is fireblight (Erwinia amlyovora). Crabapple, hawthorn, cotoneaster, and many others are host plants. If possible, mechanical removal of symptomatic branches may be an option. Prune at least 8-12 inches below the visible damage margin. It is essential that pruning equipment is properly sanitized with either 70% alcohol or 10% bleach after every cut.