Utah Pests News Winter 2009-10

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Tree Fruit and Landscape Pests to Watch For in Utah

APPLE CLEARWING

The apple clearwing (Synanthedon myopaeformis, related to the greater peachtree borer, S. exitiosa) was identified from a British Columbia orchard in 2005 as the first record in North America.  It was thought to have been introduced on infected planting stock from Europe.  In some orchards that were almost fully replanted, 95-100 percent of trees are infested.
 It has since been found in several other B.C. orchards and parts of northwestern Washington State.

The adult moths are metallic blue with an orange band.  They are attracted to the lure used for greater peachtree borer, and the Utah IPM program is watching for this pest.  Female moths lay eggs in spring on wounds, grafts, and pruning scars of apple trees, and the larvae spend two years in the cambium from the crown to the scaffold limbs.  As the bark dies over the feeding areas, it becomes loose and flaky.  Trees under drought stress are more susceptible to death.

SPOTTED WING DROSOPHILA

A vinegar fly pest was discovered feeding on Santa Cruz county, California strawberries and raspberries in fall 2008.  It was later identified as Drosophila suzukii, spotted wing drosophila (SWD).  The spring and summer of 2009 showed this pests’ true intentions, where, by the end of the season, it was found on nine hosts (strawberries, raspberries, blackberries, blueberries, table and wine grapes, cherries, plums, and peaches) in four states (CA, OR, and WA, and FL via a separate introduction) and B.C.  This Asian native was first described in Japan, and has been established in Hawaii since 1980.  It is one of only two of the 3,000 species of Drosophila (vinegar flies) that is known to be a plant pest.

The female penetrates the skin of ripening fruit, laying 2-3 eggs each time.  A single female can lay up to 350 eggs, and could potentially form 100,000,000 adults in just four weeks.  The larvae develop inside the fruit, and exit to pupate.  The feeding area becomes soft, brown and sunken. According to the original description, adults are most active at 68° F, and above 86° F, males become sterile.

Whether this pest could become established in Utah is unknown, but seasonal introductions are certainly a possibility.  A predictive model of establishment in the West shows that the northern Utah fruit growing region has been identified as “marginal” due to lack of moisture and temperature extremes.  The eggs, larvae, and adults cannot survive below freezing, and vinegar flies prefer humidity, dying within 24 hours in the absence of water.  If SWD were to become established in Utah, predictions show that emergence would begin around mid-June, and depending on location, it would have 1-7 generations per season.

Research is underway in CA-OR-WA to look at treatment options, pest biology, determining when fruits become susceptible to egg-laying, and monitoring options.  In Utah, we will monitor for this pest using yellow sticky traps and fruit inspections.

EUROPEAN GRAPEVINE MOTH

The first record of European grapevine moth in the U.S. was in the Napa Valley of California in October 2009.  It was introduced into Chile in 2008 and has since become a serious pest there. It is not predicted to be a threat in Utah, but residents should be aware of it, as it feeds on several hosts besides grapes, including blackberry, currant, cherry, peach, plum, and cucumber.  Larvae of spring and summer generations feed on flowers and leaves, while later generation larvae feed on and within the fruit, moving around in silken threads.

PINE WILT

Pine wilt is a disease caused by the pinewood nematode (Bursaphelenchus xylophilus).  The nematode is native to the U.S., but the disease has not been recorded in Utah.  It is a significant problem of pines in the Midwest where trees are killed within a few months.  Scotch pine is highly susceptible, and Austrian and 5-needled pines are somewhat susceptible.  The nematode is vectored from tree to tree by the pine sawyer beetle (Monochamus sp.).  Larvae of this beetle grow and develop in dead or dying trees, and if nematodes are present in the tree, they will enter the pupal chamber formed by the pine sawyer larva.  The emerging adult then transports tens of thousands of nematodes to healthy pine trees where it feeds on the outer bark tissue.  The nematodes enter the xylem vessels and multiply by the millions.  The only visible symptom is a rapid yellowing, then browning of the foliage.

PHYTOPHTHORA RAMORUM 

Phytophthora ramorum, which causes the disease sudden oak death, was discovered killing oak trees along the California coast in the mid-1990s.  It is a pathogen that thrives in cool, wet climates, but because several other Phytophthora species are able to cause plant disease in Utah, residents should be on the lookout.  Currently, there are over 75 hosts (click here for a full list) and symptoms vary from leaf blights (shown above on maple) to bleeding trunk cankers.

PHYTOPHTHORA BLEEDING CANKER

This disease occurs commonly in the east and in the Pacific Northwest, and rarely in Utah.  We are watching for this disease because in the last 7 years, many silver maples have been killed by bleeding canker, caused by Phytophthora citricola and P. cactorum, in northern Nevada.  Phytophthora bleeding canker is known to occur on a variety of hosts: maples, beech, birch, dogwood, elm, oaks, tulip-tree, willow, and some fruit trees.  This summer, the UPPDL identified bleeding canker on horsechestnut.

The primary spread of this pathogen to other parts of the country has occurred via transportation of nursery stock, wood, green waste, soil, etc. from infected areas.  To prevent spread, many counties of California and Oregon are quarantined while the remaining counties, and all of Washington, have transport restrictions. Even still, P. ramorum still pops up here and there, including a November 2009 identification in Maryland on a witch hazel shipped from Oregon.  With diligent inspections and eradication, P. ramorum has not become established anywhere except the regulated states.

Phytophthora is a fungus-relative that commonly causes crown and collar rot in Utah.  Spread of the pathogen to stems may be caused by rain splash, contaminated irrigation water, pruning, or any other physical transport.  The pathogen invades the bark and spreads in the cambium, killing tissue as it advances and staining it red-brown.  Most trees will ooze a tar-like sap from the infected area, which can range from a few inches to several feet long (shown above).  Usually cankers are found on the lower trunk, but can occur higher.


If you notice any of these pests, please do not hesitate to collect a sample for the UPPDL to diagnose.  It is very important to identify potential agricultural or landscape threats before they cause economic harm.  For information on collecting samples, go to: www.utahpests.usu.edu/uppdl, or call the Lab at 435-797-2435.


-Marion Murray, IPM Project Leader