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Nursery & Forest
Volume 58 Number 8 Date 06/20/2013 STEM AND BULB NEMATODE - The DATCP Plant Industry Laboratory, UW-Madison and USDA ARS Nematologists have confirmed the first detection in Wisconsin of the stem and bulb nematode, Ditylenchus dipsaci, one of the most destructive plant parasitic nematodes in temperate regions of the world. The nematode was discovered in phlox 'Fireworks' in a Jefferson County greenhouse. Recent detections have also been reported from Missouri in phlox and Minnesota in garlic Ditylenchus dipsaci is a recognized pest of a wide range of root crops, ornamental and nursery plants, and some field crops, including alfalfa, apples, beans, carrots, oats, onion, garlic, peas, potatoes and strawberries. This species completes its life cycle in stems, bulbs and leaves of hosts, causing distortion and discoloration of shoots and rotting of bulbs, tubers and rhizomes. The photo below shows shortening, twisting and reddening of the infested phlox plant.Ditylenchus dipsaci should not be confused with the potato rot nematode, Ditylenchus destructor, a state quarantine pest which feeds below-ground in roots, tubers and rhizomes and cannot survive desiccation. Control of nematodes is often difficult and avoidance is the best strategy. The stem and bulb nematode can survive in dried plant debris, seed and in soil, so proper sanitation practices and removal of infected plant material is essential. The greenhouse in which the infested phlox plant was detected cooperated in removing all other phlox plants from sale and the out-of-state supplier also voluntarily pulled all implicated phlox. -- Anette Phibbs, DATCP Plant Pathologist VOLUTELLA BLIGHT - Symptoms of this potentially lethal disease were noted on pachysandra and boxwood at several garden centers in Jefferson and Racine counties. Volutella blight begins as small, water-soaked leaf lesions that eventually turn brownish-black and necrotic. Recommended controls include removal of diseased leaves, stems and debris, and thinning existing plantings to promote air flow. For severe infections, nursery operators should remove diseased plants and follow with one or more applications of a broad-spectrum fungicide. LABELING NURSERY STOCK - Recent inspections of nursery stock retailers found many instances of trees and shrubs that were incorrectly labeled or had unsuitable hardiness ratings for Wisconsin. For example, inspectors observed Yoshino Cherry, which is hardy to Zones 5-8, for sale in Zone 3 without the hardiness zone identified on the tag. It is illegal to sell or distribute plants that are insufficiently hardy and cannot survive or grow in Wisconsin. Retailers are required to provide signage or label woody landscape plants with the appropriate hardiness rating. Customers should carefully check labels and not presume all trees and shrubs offered for sale are adequately cold hardy for their area. PHOMOPSIS BLIGHT - This evergreen disease is reported to be infecting several varieties of juniper in Jefferson, Ozaukee, Sauk and Sheboygan counties. Plants with phomopsis blight develop yellow spots at the shoot tips of young needles that progress to the stems, causing gradual dieback of new growth and eventual death of the infected branch. Its occurrence can be reduced by pruning out symptomatic branches and twigs 4-6 inches below the diseased area, and disinfecting pruning shears between each cut. Maintaining adequate spacing and airflow between plantings will also help to prevent it from spreading. -- Liz Meils, DATCP Nursery Inspector GYPSY MOTH - Bacillus thuringiensis var. kurstaki (Btk) treatments were applied to approximately 1,540 acres in Bayfield, Douglas and Sawyer counties June 17-18, marking the completion of all Btk spraying in the state for the 2013 season. Mating disruption, or pheromone flake treatment, is scheduled to begin before the end of June in southwestern Wisconsin. The pheromone flakes are intended to interfere with population growth by disrupting gypsy moth mating. -- Rick Hummel, DATCP Gypsy Moth Program 
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