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Nursery & Forest
Volume 61 Number 14 Date 08/04/2016 TWO-SPOTTED SPIDER MITE - Signs of spider mite damage have become apparent with the recent drier weather pattern and have been observed in several nurseries throughout the state. Inspectors are reporting mite damage to numerous perennials, especially bee balm and hollyhock. Although minor mite infestations can go unnoticed, heavier infestations are recognizable by the leaf stippling that develops on affected leaves. Examination of the leaf undersides with a hand lens may reveal fine webbing or the mites, which can be identified by the two dark lateral spots. Mite damage is likely to increase late in the season as plants experience heat or moisture stress. -- Timothy Allen, DATCP Nursery Inspector PINE LEAF ADELGID - The cone-shaped galls which form when needles are injured by adelgid feeding were observed in late July on black spruce trees in Chippewa County. This adelgid species alternates between black spruce and eastern white pine in Wisconsin. At this time of year empty galls are evident on black spruce, while the nymphs have migrated to eastern white pine to feed on the newer shoots. Damage to white pines can be significant and repeated attacks on white pine may cause mortality in low-vigor trees. High value white pine plantings adjacent to black spruce areas should be inspected to determine if control is warranted. Drooping or weeping pine shoots are an indicator of adelgid infestation. LIRULA NEEDLECAST - Spruce trees in a Pierce County nursery field were diagnosed with lirula needlecast, a common fungal disorder that causes second-year needles to turn brown. Lirula is easily identified by a single longitudinal row of black fruiting bodies or spores along the midrib on the undersides of dead needles. Environmental conditions that favor its development are high humidity, low temperatures and overcrowding or inadequate plant spacing. As with most fungal disorders, measures that increase air circulation are usually effective in preventing new infections. Properly timed fungicide treatments can help also reduce disease problems if cultural treatments are insufficient. SPRUCE NEEDLE RUST -Colorado blue spruce infected with spruce needle rust were found late last month in Pierce County. Spruce needle rust (SNR) can be identified now by the pale yellowish bands that surround new needles. As the season progresses, yellow-orange fruiting bodies or telia develop on new needles and eventually spread spores that infect new needles. Unlike many rusts, SNR is an autoecious rust which does not require an alternate host to propagate and spread from tree to tree. Needles infected from the previous year will turn black-brown and eventually drop. Heavily infected trees lose vigor and aesthetic appeal and may die if other stressors are also present. Mowing, pruning and other cultural practices that reduce humidity and improve air flow around trees can help minimize the occurrence and severity of this disease. Properly timed fungicide applications may be justified for severe cases. Spruce trees infected with SNR should not be offered for sale until they are treated and the rust disease controlled. SPRUCE NEEDLE MINER - The clusters of brown needles held together by webbing observed on Black Hills spruce in Pierce County were caused by this spruce pest. Spruce needle miner (SNM) larvae enter and hollow out needles that are at least one year old, then spin silk nests in early summer. The larvae tend to aggregate and feed gregariously. The partially grown larvae overwinter in the nests and pupate the following spring. Controls, if necessary, should be applied in early spring. -- Konnie Jerabek, DATCP Nursery Inspector EMERALD ASH BORER - Beetle emergence recently peaked along the eastern lakeshore counties and throughout the northern portions of the state. Meanwhile, the adult flight is subsiding across the remainder of Wisconsin. Mid-season monitoring of the nearly 800 EAB traps set in Wisconsin's non-quarantined counties has been completed and no trap captures have been reported as of August 3, although results are preliminary. By contrast, five new detections were confirmed in the last two weeks in the following counties with known EAB populations: Brown County (City of De Pere), Dodge County (City of Mayville), Richland County (Town of Akan), Sheboygan County (City of Plymouth), and Washington County (Village of Kewaskum). -- Renee Pinski, DATCP Forest Entomologist GYPSY MOTH - The moth flight and oviposition period are ending across southern Wisconsin. Approximately 5,382 traps (48%) of the DATCP trap set total have been checked to date and 21,511 male gypsy moth have been captured. Removal of gypsy moth pheromone traps in scheduled to begin on August 10 in areas south of Hwy 21. -- Nolan Stracke, Public Information Officer 
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