Nursery & Forest
Volume 52 Number 8 Date 06/15/2017
WEIR'S CUSHION RUST - This highly contagious fungal disease of spruce trees was observed by inspectors on Colorado blue spruce at a Lincoln County nursery. Needles infected with WCR develop yellow spots that produce pustules in spring which release bright-orange spores that infect new growth. Previously-infected needles turn brown and drop. A preventative approach using a fungicide containing at least 50% chlorothalonil applied before or shortly after bud break is recommended.
OAK GALLS - Nursery inspections in the past week found noxious oak gall and oak petiole gall wasp on oaks in Dane County. Galls are abnormal outgrowths of plant tissue caused by insects, fungi, bacteria, nematodes or mites. These growths may develop on any plant part, but most commonly occur on the branches and leaves. Although usually an aesthetic problem for larger oaks, some galls may pose a threat to smaller nursery trees. Most management recommendations emphasize pruning or removal of galls before wasp emergence in spring. Application of a systemic pesticide to control the adult stage may also be a viable option for severe cases.
FLETCHER SCALE - Arborvitae shrubs in a St. Croix County nursery were infested with this scale pest, which can cause yellowing, premature needle drop or branch dieback. The mobile crawlers, the life stage most susceptible to insecticidal control, should begin emerging soon. For severe infestations, horticultural oils or soaps, insect growth regulators, or conventional insecticides may be used as soon as the crawlers are noticed.
JAPANESE BEETLE - Beetle emergence was noted on June 10 in La Crosse County. Damage to fruit trees, ornamentals, nursery stock and field crops should be anticipated during the next two months, with peak activity occurring in mid-July. Populations of this invasive beetle are now established as far north as Barron County in northwestern Wisconsin and Oconto County in the northeast.
FOUR-LINED PLANT BUG - Adults of this insect have been observed on dogwood, hydrangea, viburnum and various perennials this month. Damage appears as small, round, sunken dark spots which may be mistaken for a leaf spot disease. The spots may become clear and after several weeks the affected tissue drops out leaving small holes. Both the adult and nymph stages can injure plants.
HOLLYHOCK SAWFLY - Severe defoliation of hollyhocks on a Monroe County farm was attributed to the tiny green and black larvae of this insect. The gregarious caterpillar-like worms feed in groups on the underside of hollyhock leaves, causing a lacy or skeletonized pattern of damage that can be misidentified as Japanese beetle defoliation. Chemical control with products containing Btk must be initiated as soon as the first holes appear on the lower leaves.
-- Shanon Hankin, DATCP Nursery Inspector