Saturday, June 8, 2013

Nasty critters in your backyard

By ecoRI.org News staff

KINGSTON — If it seems that every year you are battling a new pest or disease in your garden, you’re not alone.  According to Heather Faubert, who runs the Plant Protection Clinic at the University of Rhode Island, that trend is primarily due to the rapid transportation of plants around the country and the increasing frequency of extreme weather events.

To help local gardeners, landscapers and farmers become aware of what to be on the lookout for this year, here is a list of Faubert’s top three plant pests and diseases for 2013, along with a few honorable mentions:

Impatiens downy mildew. Impatiens are the top-selling annual bedding plant in the United States, because of their colorful flowers that bloom all summer and for 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, according to Faubert. Its spores become wind-borne, making it easy for it to spread.

“Early symptoms are mottled, down-curled leaves and, later, white spores on the underside of the leaves,” Faubert said. “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 buying the plants while the nursery industry searches for a variety that is resistant to the fungus. New Guinea impatiens, begonias and salvias are good alternatives, she said.

Crypt Gall Wasp
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 shouldn’t die after one year, but two or three years of defoliation could kill them. Faubert suggests waiting until the fall or winter when egg masses are easily visible on branches and pruning those branches.

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.


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