Adult and immature lace bugs feed on the undersides of leaves of deciduous trees and shrubs. Lace bug feeding can discolor leaves but does not normally affect the health of woody plants. Management is normally not necessary. Pesticides can be effective in reducing lace bug numbers if treatment is necessary.
Lace bugs feed on many trees and shrubs in Minnesota, especially hackberry, walnut, basswood, white oak, bur oak, willow, chokecherry, hawthorn, cotoneaster and amelanchier (juneberry/serviceberry). Lace bugs have two generations per growing season in Minnesota. They live through the winter, as adults on or near their host plants. They can be found in bark crevices and under leaves and other debris on the ground next to these plants.
In the spring, adults fly to plants and feed on newly-expanding leaves. Adults mate and lay tiny black eggs in small groups on the underside of the leaves. Eggs hatch into nymphs after about two weeks. Nymphs feed for about three to four weeks and mature into winged adults that lay additional eggs. Second-generation adults feed until late summer or fall.
Adults from the second generation overwinter and begin the cycle anew the following spring.
Adults and nymphs feed on the underside of leaves by inserting needle-like mouthparts into leaf tissue. This creates small, white or yellow mottled spots on the upper leaf surface.
Feeding damage is most noticeable in mid to late summer when populations are at their highest. Heavy feeding can cause severe leaf discoloration and premature leaf drop.
Healthy, mature trees and shrubs can tolerate damage by lace bugs. If feeding happens for several consecutive years, plant growth can be reduced in new transplants. Lace bug populations and the extent of damage vary from year to year.
Information source: University of Minnesota Extension
Information source: University of Minnesota Extension
Information source: University of Minnesota Extension
Bacterial leaf spot diseases often start as small dark brown to black spots with a halo of yellow tissue surrounding each spot. In some cases, the center of the leaf spot will dry up and fall out, giving the leaf a “shot hole” appearance. If weather conditions remain favorable for disease, some bacterial leaf spots will grow together creating large black blotches on leaves or turning leaves completely black. Shoots, buds, and flowers can also become black and blighted by bacterial leaf spot pathogens.
Information source: University of Minnesota Extension
Powdery mildew is a common fungal disease of trees and shrubs in Minnesota.
White to gray, powdery spots, blotches or felt-like mats form on leaves, stems, and buds of infected plants. The disease is often most severe on young leaves and green shoots. Powdery mildew does not cause significant damage to the health of the tree and does not require management. The disease can significantly affect the look of ornamental plants like roses and purple-leaved ninebark shrubs. Resistant varieties, cultural control practices, and fungicides can be used to manage powdery mildew.
White to gray powdery spots, blotches or felt-like mats forms on leaves, green stems, and buds. Infected plants may appear to be sprinkled with baby powder or covered in cobwebs. Young leaves, water sprouts, and green shoots are often most severely affected. Infected leaves may be cupped or twisted at the site of the infection. When severely infected, leaves may turn yellow and fall prematurely during the growing season. In some plants, leaves turn purple to red around the infection. In late summer or early fall, tiny round orange to black balls forms within white fungal mats.
Powdery mildew thrives in humid conditions but does not do well if leaves are wet from frequent rain or irrigation. In Minnesota, powdery mildew increases in the spring and fall, when cool nighttime temperatures are followed by warm daytime temperatures. It can be often found throughout the growing season. The disease is worse on shaded plants or plant parts with little air movement such as interior or lower branches.
Powdery mildew fungi create dark round resting structures that contain and protect spores through the winter. In spring, these resting structures break open, releasing spores that are spread by the wind. These spores start new infections on succulent, new growth. Some species of powdery mildew fungi survive the winter in infected buds. In spring, the young shoots growing from infected buds are covered with velvet-like white growth of powdery mildew. The powdery mildew fungus grows into the plant to steal nutrients. Powdery spores are produced in leaf spots throughout the growing season. Spores spread by wind and start new infections within the plant or in neighboring plants. Powdery mildew needs humid conditions to start new infections. The spread of the disease is reduced by rain or irrigation.
Water on the leaves prevents the light airy spores from moving on the wind.
Information source: University of Minnesota Extension
Information source: University of Minnesota Extension
