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Nursery & Forest
Volume 60 Number 20 Date 12/03/2015


TAR SPOT - This common leaf disorder of maples was especially prevalent this season. The raised, black tar-like lesions which characterize tar spot are generally associated with wet weather during the period of maple leaf expansion in spring. Heavy infection may cause early leaf drop but long-term damage is rare. Raking and destroying leaves in fall is the most effective management practice.

BOXWOOD BLIGHT - Eight suspect boxwood blight samples, four boxwoods and four pachysandras, were tested by the Plant Industry Laboratory in 2015. None were found to be positive for boxwood blight. All four were instead infected with the more common Volutella blight.

NR 40 INVASIVE SPECIES RULE - Rule violations increased considerably in 2015 following the enactment of revisions involving the addition of 70 prohibited and restricted plant species in May. DATCP inspectors documented violations at 43 locations this season, compared to 13 locations in 2014 and 19 in 2013. Nursery operators and brokers still unfamiliar with the Chapter NR 40 rule changes can find a complete list of regulated species at: http://dnr.wi.gov/topic/Invasives/documents/Nursery_plantlist.pdf.

FOLIAR NEMATODE - An increasingly common and serious problem in the nursery industry, foliar nematode was detected this year in seven plant samples, on the hosts anemone, hosta, and toad lily. DATCP enforces zero tolerance to foliar nematodes in production nurseries and recommends that any nematode occurrence be thoroughly cleaned and disinfested. Diseased plants and old foliage should be destroyed.

SUDDEN OAK DEATH - One rhododendron sample tested negative for this regulated disease. The sample was a "trace-forward" from a nursery confirmed to have plants infected with Phytophthora ramorum, the plant pathogen known to cause sudden oak death (SOD). As of December 2015, SOD has never been detected in the state.

DAYLILY LEAFMINER - Reported for the first time in Wisconsin in 2014, the daylily leafminer (DLM) was observed to have overwintered successfully and has been found in the landscape. The larvae of this insect feed between the upper and lower leaf surfaces, creating long, white mines that run parallel to leaf veins. Infested daylilies are not killed by DLM, but usually are unmarketable. Removal and destruction of mined leaves is advised to reduce the spread of this new exotic pest.

-- Ellen Natzke, DATCP Nursery Inspector


SURVEY OF VIRUSES IN ORNAMENTALS - Nursery inspectors submitted 150 virus-symptomatic plant samples from 50 producers and retailers to the Plant Industry Laboratory for diagnosis this spring. Plants representing 14 genera were tested for up to 12 host-appropriate viruses. Seventy-five of the samples (50%) were infected with at least one virus. Tobacco rattle virus was the most common, with 44 of 85 samples testing positive (52%), followed by the potyvirus group in 15 of 30 samples (50%). Tomato chlorotic dwarf viroid was diagnosed in 10 of 42 samples (24%), impatiens necrotic spot virus was found in six of 41 begonia samples (15%), and cucumber mosaic virus was found in two of 45 samples (4%). Seven of twelve hosta samples were positive for hosta virus X and a single dahlia sample was infected with dahlia common mosaic caulimovirus.

TOMATO CHLOROTIC DWARF VIROID - Laboratory analysis of 42 petunia samples from seven greenhouses and retailers found 10 (24%) to be positive for this emerging disease of greenhouse-produced tomatoes that can be carried in symptomless petunias. Although several petunia varieties including "Peppy Red", "Johnny Flame", "Queen Bee", "Supertunia", "Sweetunia", and "Royal Velvet" were tested, TCDVd was traced to only a single variety: "Peppy Lavender." None of the infected petunias had visible disease symptoms. All "Peppy Lavender" plants were removed from sale and destroyed.

-- Anette Phibbs, DATCP Plant Pathologist


WALNUT TWIG BEETLE - A trapping survey for this insect component of the thousand cankers disease (TCD) complex was conducted for the fourth consecutive year. The survey included 37 pheromone-baited funnel traps, set at seven municipal brush disposal sites and 11 sawmills in Buffalo, Chippewa, Crawford, Dane, Grant, La Crosse, Langlade, Manitowoc, Richland, Sauk, Shawano, Trempealeau and Waupaca counties. Approximately half of the trap collection samples have been processed as of December 3, and to date, no walnut twig beetles have been found.

EMERALD ASH BORER - Continuing survey work for EAB resulted in 39 new detections in 2015. Beetles were captured on four traps and infested trees were identified at 35 new municipal sites. Most of this year's detections were in the southeastern part of the state where EAB was first discovered in 2008.

The 2015 Wisconsin EAB trapping survey consisted of 934 baited traps, 888 purple panel traps and 46 green multi-funnel traps, set across 47 counties. The green funnel traps used for the first time this season have been shown to perform better than the purple prism traps in low EAB-density areas. Four purple traps, one each in Crawford, Grant, Lafayette and Marquette counties, and one green funnel trap in Richland County, captured EAB adults.

Emerald ash borer infestations are now known to occur in nearly half of the state's 72 counties. The Wisconsin EAB quarantine also includes the counties of Iowa, Juneau, Kewaunee and Manitowoc, for a total of 39 counties.

MOUNTAIN PINE BEETLE - Survey work to detect the mountain pine beetle, the tiny bark-boring insect responsible for killing pine trees over millions of acres in the Western U.S. and Canada in the last decade, was carried out for the second year in a row. Twelve multi-funnel traps were placed at eight forest products facilities in Barron, Brown, Dunn, Forest, La Crosse, Marathon, Portage and Price counties. Sample screening is still under way, but results have been negative so far.

-- Renee Pinski, DATCP Forest Entomologist


GYPSY MOTH - One additional county was added to the state gypsy moth quarantine this year. Taylor County was officially quarantined on March 16, joining most of eastern and central Wisconsin which are considered generally infested. Taylor County was the 50th Wisconsin county to be quarantined for gypsy moth.

-- Tim Allen, DATCP Nursery Inspector