GROWING An ongoing series provided by Oregon State University in collaboration with the United KNOWLEDGE States Department of Agriculture Series content is coordinated by Dr. Jay Pscheidt, professor of botany and in partnership with the and plant pathology at Oregon State University in Corvallis, Oregon. Oregon Association of Nurseries

Image 4 (above): Scout for European chafer grubs by digging a 1-foot long by 1-foot wide by 2-inch deep section of sod, the action threshold for high maintenance turf is 15–20 grubs per square foot. PHOTO BY ALEC KOWALEWSKI Protecting lawns against European chafer These control strategies can help mitigate damage to turfgrass

BY ALEC KOWALEWSKI, EMILY BRAITHWAITE AND CHAS SCHMID

HE EUROPEAN CHAFER (Amphimallon majale) is a ½-inch in length, larger than a Japanese (Popillia japon- beetle that feeds on turfgrass roots causing substantial ica), but smaller than a green June beetle ( nitida). This damage. In more recent years, this beetle has a light-brown or tan colored Tinvasive has been confirmed in the head, thorax, abdomen and wing covers Pacific Northwest and British Columbia. (Image 1). The insect’s eyes are dark-brown Populations have been observed as early as to black, and the wing covers have grooves 2015 in Portland, Oregon and Seattle and running the length of the insect. The abdo- Tacoma Washington areas. Their numbers men protrudes slightly beyond the wing cov- have been increasing ever since. ers at the rear end. The adult stage of this insect is short- Identification and life cycle lived, at one to two weeks. During this time, The adult European chafers can be Image 1: The adult European chafer is the adults find partners, mate, and then lay found above ground in late June and early about ½-inch long and has a light-brown eggs before dying. Each female European July. This thick-bodied beetle is about or tan colored body. PHOTO BY MICHAEL REDING chafer will lay 20–40 eggs, one at a

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Image 2: European chafer grubs are about 1 inch long and have a white C-shaped body with three pairs of legs. PHOTO BY DAVID CAPPAERT

time, in the top 2–4 inches of cycle. The pupae are just over moderately dry soil. The eggs ½-inch in length and stout with are one-tenth of an inch long, a light-brown appearance. In thick and white to a dull gray in late June and early July, adult appearance. Larva hatch from chafers emerge from the pupae these eggs about two weeks and leave the soil to complete after being laid. the life cycle. The larval stage of this insect lives underground from Damage late July to the following May Symptoms of chafer grub (11 months). This larva is a activity include localized patches large, C-shaped grub. Chafer of drought-stressed turf appear- grubs have a white body, light- ing in the spring and early sum- brown head, three pairs of light-brown ning toward the front of the grub. mer months. These patches of turf easily true legs, and a dark section at the end These grubs reach maximum length peel up from the soil because the grubs of the abdomen (Image 2). The European of one inch in the fall and cause the larg- have eaten the root system. At this stage, chafer raster pattern, which is used to dis- est amount of damage to the rooting insecticide applications will not make a tinguish between various species of white systems of grass plants in the subsequent difference because the root damage has grubs (European chafer, , spring. In May and early June, the chafer already been done. These areas often and June beetle), includes a Y-shaped anal larvae form pupae in preparation for the become desiccated during the summer slit and two rows of parallel spines run- transition to the adult stage of their life months, and will require replacement with

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34 SEPTEMBER 2020 DIGGERMAGAZINE.COM seed or sod. Skunks, and birds will often forage for the grubs in infested areas, damaging the turfgrass in the fall and following spring (Image 3).

Scouting Scouting for European chafer grubs should be done in the fall (September and October). To scout for these grubs, dig up a 1-foot long by 1-foot wide by 2-inch deep section of sod with a square end shovel. Flip the sod layer over and inspect the soil for grubs (Image 4). European chafer prefer dry, sunny turf areas with lit- tle irrigation. Sloped turfgrass areas prone to surface runoff will likely be drier than flat turf area, and consequently could have higher rates of chafer infestation. forging for grubs in the fall and spring are also a good indicator of infested turfgrass.

Preventive management The typical action threshold (pest population) that will cause damage if untreated is 5–10 grubs per square foot for low maintenance turf, and 15–20 grubs per square foot in high maintenance turf. Considering this, adequate implemen- tation of the primary cultural practices (mowing, fertilization and irrigation) is an important factor because this will increase resistance to damage. High-maintenance lawns in the Pacific Northwest should be mowed at 503-434-5525 least once a week to a height of 2–3 inch- 1726 SW Highway 18, McMinnville, OR 97218 • www.dstakemill.com es. To improve nutrient levels, grass clip- pings should be returned using a mulching mower. High-maintenance lawns should • Shipping Materials be fertilized twice in the spring and twice - Pallet repair boards, shipping gates, in the fall at 1 lb. N per 1,000 square tilt sticks. feet per application, totaling 4 lbs. N per • Custom Assembly 1,000 square feet annually. - Shipping racks, bare root Research has shown that frequent crates and nursery pallets. irrigation during late June and July can • Planting Stakes substantially mitigate pest populations. - Multiple sizes available It is speculated that the adult chafers • Treated Lumber prefer to lay their eggs in dry soil, rather - Multiple sizes available than moist soil. Frequent irrigation also improves turfgrass tolerance to root-feed- ing pests, such as the European chafer. Considering this, irrigation events Lumber Products for All Nursery Needs of ¼-inch deep, four times a week,

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Image 3: Skunks and other animals will forage for European chafer grubs in infested areas damaging the turfgrass, David Smitley, 2018. PHOTO COURTESY OF OREGON STATE UNIVERSITY

totaling 1-inch per week are suggested for high maintenance lawns in the Pacific Northwest. An August and September application of parasitic nematodes (Heterorhabditis bacteriophora) is sug- gested, however data on the effectiveness of this control method is minimal. Similar to insecticides, biological control agents typically need to be applied annually when managing insect populations.

Insecticides be observed when treatments are made Effective preventative insecticides Before considering insecticides, while the larvae are young, also known as with relatively low (mammals and always evaluate chafer grub populations. early instar, grubs in the fall. fish) toxicity levels include chlorantranilip- If the action threshold of 5–10 grubs per Spring scouting and insecticide applica- role, thiamethoxam, clothianidin, and imi- square foot for low maintenance turf, and tions will likely not prevent drought-related dacloprid. Chlorantraniliprole is the only 15–20 grubs per square foot in high main- turfgrass damage in the summer months insecticide listed that has a low bee toxic- tenance turf is not reached, an insecticide because the root system has already been ity. To protect pollinators, the remaining application will not provide any benefit. compromised. In the spring months, the products should not be applied to turf- If insecticides are going to be applied for fully developed, or late instar grubs, are also grass adjacent to blooming plants. These control of this insect, the best results will resistant to some insecticides. preventative products should be applied

36 SEPTEMBER 2020 DIGGERMAGAZINE.COM early in the chafers’ life cycle in July and August. Late applications of these prod- ucts will not provide effective control. Effective curative insecticides include thiamethoxam, trichlorfon , and carbaryl, but all have relatively high animal toxic- MARKETPLACE ity levels to mammals, fish and bees. These curative products are highly toxic to bees and should not be applied to turfgrass adja- Supplies for Small Growers B&B Spruce 4 to 24 feet cent to flowering plants. Curative insecticides SEED STARTING - Pots Trays Inserts Chamaecyparis • Fir • Pine should be applied in the fall in September Plug Trays Japanese Maple • Poodle Pine and October. Spring application of any insec- ______Cut Christmas Trees ticide will provide limited control. Labels - large variety size, color & shape of blank plant pot & row markers At this time, the larva are at their ______final instar, making them more resistant to Weed control, fertilizer, tapes & ties, the insecticides. The larva have also been watering, and more feeding on the turfgrass roots since the ______http://www.AAA-mercantile.shop fall, causing a significant amount of dam- http://stores.ebay.com/AAA-Mercantile (503) 630-4349 age going into the spring months. http://www.amazon.com/shops/AAAmercantile FAX (503) 630-7542 MARKETPLACE Enter promo code DIGGER for a 10% discount PO Box 598 – Estacada, OR 97023 Conclusion for a limited time at AAA-mercantile.shop European chafer populations are growing in the Pacific Northwest, and this insect is particularly damaging to turfgrass areas that receive minimal irrigation lev- Schurter els. Regular irrigation during the summer months, combined with frequent mowing Nursery and fertilization, will increase the action Arborvitae–Emerald green threshold for European chafer to 15–20 Virescens grubs per square feet. Boxwood If these populations are observed Japanese Maples during scouting, preventative insecticides Otto Luyken can be made in July and August, while Skip Laurel curative insecticides can be applied in September and October. Curative insec- Various sizes & Varieties ticides that effectively control European 503-932-8006 chafers are more toxic to animals and pol- linators than the preventative insecticides, so curative applications should be used as Motz & Son Nursery a last resort. Spring insecticide applica- HOSTETLER SHADE & FLOWERING TREES tions will have minimal effects because the FRUIT TREES FARM DRAINAGE damage has likely already been done and Dwarf, Semi-Dwarf & Standard 503-266-3584 should be avoided. COMBINATION FRUIT TREES (4 in 1) • Plastic Tubing 3"-24" • Laser Grade Semi-Dwarf & Standard Control • Open Ditch for Buried ESPALIER APPLES Alec Kowalewski, associate professor Irrigation • Plows and Trenches • Semi-Dwarf, Combination & One Variety and turfgrass specialist at Oregon State Pot-n-Pot Drainage • Oldest Drainage WALNUTS & FILBERTS Firm in Oregon • Newest Subsurface University (OSU), can be reached at DECIDUOUS SHRUBS Irrigation Techniques [email protected]. Emily www.motzandson.com Materials and Braithwaite is a faculty research assistant 11445 N.W. Skyline Blvd. Technical at OSU. Chas Schmidt, Ph.D. is a turf- Portland, Oregon 97231 Phone 503-645-1342 Assistance grass research assistant. Canby, OR Available WHOLESALE GROWERS FAX 503-645-6856

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