To help local gardeners, landscapers and farmers become aware of what to be on the lookout for in 2013, Faubert has provided this list of the top three plant pests and diseases of the year (along with a few honorable mentions):
Impatiens downy mildew: Impatiens are the top-selling annual bedding plant in the U.S. due to their colorful flowers that bloom all summer and their ability to fill in large spaces in the landscape. But this is not the year to plant them — few garden centers even have them available – due to a fungus called impatiens downy mildew.
First discovered in a few greenhouses in 2004, it made its way to the landscape in six states in 2011 and arrived in almost every other state in the nation last year. Its spores become windborne, making it easy for it to move from one area to the next.
“Early symptoms are mottled, down-curled leaves and, later, white spores on the underside of the leaves,” said Faubert. “Then they just die. There may be a few leaves at the top, but the rest of the plant defoliates and dies.”
Little can be done to protect impatiens from downy mildew, so Faubert suggests gardeners avoid purchasing the plants while the nursery industry searches for a variety that is resistant to the fungus. She says New Guinea impatiens, begonias, and salvias are good alternatives.
Crypt gall wasp: Red and black oak trees with sagging leaves and a thin canopy may be struggling to combat this new invasive insect pest that appeared on Cape Cod last year and has been found in southern Rhode Island. The crypt gall wasp lays its eggs in the new growth of oaks and stunts their further growth.
In the 1990s, the pests built up a large population on Long Island, but didn’t cause many trees to die, and the wasps declined sharply after about a decade. But landscapers on Cape Cod are concerned the infestation there is severe and many trees will be lost.
Faubert said affected trees can be injected with an insecticide to kill the insects, but it is an expensive process and may not be worthwhile except on particularly treasured trees.
Viburnum leaf beetle: This invasive European insect was found in New York in 1996 and was discovered in Warwick, Kingston, Charlestown and Glocester last week. Faubert believes that the viburnum leaf beetle is probably in every community in Rhode Island, where it defoliates the leaves of many species of viburnum shrubs.
The beetle’s eggs hatch in early May, whereupon they feed on viburnum leaves until early June, and the adults feed on the leaves from July until the first frost. “Unlike most pest insects that feed on a plant either as larva or as an adult, this one feeds on viburnum during both stages, so it could shorten the plant’s life all the more quickly,” Faubert said.
Shrubs should not die after one year, but two or three years of defoliation could kill them. So Faubert suggests waiting until the fall or winter when egg masses are easily visible on branches and pruning those branches. An insecticide can also be sprayed on the leaves to kill the insects during the growing season.
In addition to these pests and diseases, Faubert encourages Rhode Islanders to be watchful for a fungal disease that is killing mature Colorado blue spruce trees; a scale insect whose excrement on oak trees becomes covered in black sooty mold; boxwood blight, a fungal disease that defoliates boxwood trees; and a Japanese fruit fly that lays its eggs in small wild and cultivated berries.
Those seeking diagnosis of plant diseases and pests may deliver or mail samples to the URI Plant Protection Clinic at the Mallon Outreach Center, 3 East Alumni Ave., Kingston, RI 02881. Insects should be placed in a small container such as a prescription bottle and wrapped to protect it from breakage in the mail. Fresh plant specimens should be placed in a plastic bag and mailed in a padded mailer. Various stages of a plant’s decline should be included (not just dead samples). A $10 fee per specimen must accompany all samples. For additional information, call 401-874-2900.