No. 9/August 24, 2020

White Grubs
White grub is a common name for the larvae of June beetles, chafers and Japanese beetles that feed on the roots of turfgrass. The grubs can be found in the first 8 inches of soil beneath turfgrass. They are white, C-shaped larvae, about 1 inch long and have 6 jointed legs attached close to their small brown head capsule. Excessive root feeding by white grubs can leave turfgrass poorly anchored to the soil and can result in brown patches in a lawn that can be pulled back like a rug. This can impact the aesthetics of a lawn and, in some cases, can make sports fields less safe for children and athletes.

Adult billbugs are small weevils, about 3/8 of an inch long. They can range from brown to black in coloration and have the distinct long snout and hard wing covers that are characteristic of weevils. Adult billbugs spend much of their time in the soil, feeding on grass roots. When they are above ground, they usually do not fly and may be seen walking along driveways and sidewalks. Because they do not fly, billbug damage usually does not spread to new areas.

Magnolia Scale
Magnolia scale (Neolecanium carnuparvum) is a pest of magnolia, including star, cucumbertree, saucer and lily magnolias in northern and central Illinois. This insect can produce a large amount of honeydew, making leaves and branches shiny and sticky. The honeydew can promote sooty mold growth on the affected area, turning leaves and branches dark gray or black. If large populations of scales are present, honeydew can also coat lawn furniture or cars below the magnolia tree causing additional nuisance.

Pigweeds (Amaranthus species) in the Landscape
Amaranthus species are commonly found in cultivated areas and landscape plantings throughout Illinois yet many are unfamiliar with them. The Midwest is home to several species including redroot pigweed (Amaranthus retroflexus), tall waterhemp (A. tuberculatus), Palmer amaranth (A. palmeri), tumble pigweed (A. albus), prostrate pigweed (A. blitoides), smooth (A. hybridus), spiny amaranth (A. spinosus), Powell amaranth (A. powellii), and others. All are similar in appearance with slight differences and cross-pollination can make identification quite difficult. All are summer annuals. In 2014, I warned landscapers and home gardeners about Palmer amaranth becoming a problem across the state in my article For the sake of brevity, I’ll limit our focus here primarily to redroot pigweed and make comparisons to similar species.

Tar Spots on Maple
Tar spots are now evident on many maple species. I recently traveled to northern Illinois where nearly every Norway maple that I came across had tar spot symptoms. Fungi in the genus Rhytisma cause this disease.

Gymnosporangium Rusts on Apples, Crabapples, and Hawthorns
Diane Plewa wrote about Pear Trellis Rust in Issue 8 of this newsletter. A few closely related rust diseases have also wreaked havoc on apples, crabapples, and hawthorns this growing season. I recently observed numerous hawthorns that were entirely defoliated by severe rust infections.