Diseases & Pests —
Pest of the Month: Japanese Beetles Disease of the Month: Cedar-Apple and Rusts
by Heather Prince
emergence. Japanese beetle traps attract males via pheromones. Research has shown that traps attract more beetles to the area and actually increase damage.
Pest of the Month: Japanese Beetle
This pesky critter is usually cause for deep alarm by clients as the adult beetles emerge and begin to skeletonize leaves of many desirable plants. Adult beetles are metallic green with copper wing covers and a row of white spots just below the wing covers. Adults are typically active for about six weeks beginning in July. Mated females will burrow into wellJapanese Beetle watered turf and lay eggs that hatch into white grubs. The grubs will feed on turf grass roots, sometimes causing dieback in the fall. Adults skeletonize leaves and will also eat flowers such as roses and hibiscus. The adults visit a new host plant about every three days and can fly between ¾ and 1 ½ miles to forage. The good news is that Japanese beetles will rarely kill a plant. The damage is unsightly, but there are several strategies to reduce beetle populations.
Treatment:
Hawthorn rust
Once Japanese beetle larvae hatch from eggs in late July to early August, they need 11 inches of water through the fall before burrowing deeper into the soil for the winter. They tunnel downward when turf grass root zone temperatures drops to 60˚F. Thus, a summer into fall drought will impact populations. This also means that turf allowed to go dormant will be undesirable for beetles. Larvae overwinter in the top 11 inches of soil, so a deep, cold winter will also impact populations. Adults may be killed by carbaryl, cyfluthrin, permethrin, and other pyrethroid insecticidal sprays that will provide about two weeks of protection per application. Prized specimen trees such as lindens and cherries may be treated with a systemic insecticide containing imidacloprid applied as a drench in June. Be careful of the timing with lindens to avoid their flowering season as many pollinators, especially bees, forage on the flowers. You may also hand-pick beetles or knock them into a container of soapy water. You will see best results if more adults are killed in the first two weeks of
University of Illinois Extension Service https://web.extension.illinois.edu/state/ horticulture/index.php 217-333-0519 54
Disease of the Month: Cedar-Apple and Related Rusts
Cedar-apple, cedar-hawthorn, and cedar-quince rusts, also known as the Gymnosporangium rusts, are named after their hosts, and all have a similar lifecycle. Cedar-apple rust is the most common and is found on apples and crabapples. Leaf symptoms first appear in May and June as pale yellow spots that mature to orange. Infection may cause yellowing leaves and defoliation. Cedar-hawthorn rust can infect species in the rose family, but is particularly severe on hawthorns. The rust begins as yellow spots that mature to grey-brown lesions on the leaves. Leaves may turn bright yellow and drop. Cedar-quince rust is most noticeable on hawthorn, serviceberry, quince, and apple. This fungus targets stems, thorns, and fruits. Stems and thorns may become enlarged and deformed, while fruit is covered with fungal aecia and giving them a fringed appearance. Juniper is the alternate host for these rusts, so both hosts should be scouted for symptoms. These rust pathogens overwinter on Eastern red cedar and other Juniperus species as hard and pitted galls or spindle shaped swellings on young twigs.
Treatment:
It is easiest to control these rusts on the deciduous host plants. Apply a regular fungicide application of chlorothalonil, myclobutanil, potassium bicarbonate, or propiconazole beginning in spring when flower buds begin to open. Apply at the label-listed intervals until about two weeks after petal fall. If choosing a new tree for the landscape, look for disease resistant cultivars.
Additional resources:
The Morton Arboretum http://www.mortonarb.org/Plant Clinic: http://www.mortonarb.org/trees-plants/ tree-and-plant-advice/ 630-719-2424 The Landscape Contractor June 2019
Chicago Botanic Garden Plant Information Service: https://www.chicagobotanic.org/ plantinfoservice 847-835-0972