Description of the Pest
Masked chafers are large C-shaped beetle larvae that feed on roots of turfgrass plants. These grubs are white, up to 1 inch (2.5 cm) in length, with dark translucent dorsal stripes, brown head capsules and legs, and a characteristic pattern of bristles on the underside of the posterior end of the abdomen (the raster). Masked chafers have a scattering of bristles, while less commonly encountered May or June beetles have two parallel rows of bristles. Masked chafers are larger than black turfgrass ataenius grubs and have a slight constriction at the forward portion of the abdomen, which helps distinguish them. Adult beetles are golden brown, hairy on the underside of the thorax, and have a darker brown head. Cyclocephala hirta is common throughout California; C. pasadenae is found in southern California. Both species complete one generation per year overwintering as mature larvae, which form earthen cells in soil where they pupate. Adult males are attracted to lights at night, mostly from mid-June through July.
All turfgrass species are susceptible to masked chafer damage. Damage is usually more serious on ryegrass and bluegrass turfgrasses, whereas fescues are somewhat less affected. Warm-season grasses tend to be the most tolerant of grub feeding.
Masked chafer grubs feed on roots, resulting in irregular dead patches. Symptoms resemble drought stress and persist even where there is sufficient irrigation. Grub activity can cause the ground to feel spongy; extensive root feeding sometimes allows the turf to be rolled back like a carpet. Most damage usually takes place in late summer or early fall. Digging by vertebrate predators, such as crows, raccoons, skunks, and coyotes, is a common indication of high grub populations. Damage becomes most apparent in late summer or fall.
For turfgrass infested with masked chafers, biological and cultural controls may help reduce their numbers. If monitoring indicates a need, treatment may be warranted. Commercially available parasitic nematodes are among the treatment options.
Tiphiid wasps are common parasites of masked chafers, but may not consistently be effective in reducing grub populations below damage thresholds. Milky spore (Paenibacillus spp.) organisms have been detected infecting masked chafers in California, but the milky spore pathogens infecting the larvae do not include the one that controls Japanese beetles and are not commercially available. Heterorhabditis bacteriophora are commercially available pathogenic nematodes that can effectively control masked chafers. Steinernema carpocapsae nematodes are not effective.
Establishing warm-season grasses may reduce white grub damage. Although not a reliable control method, thorough spike-aeration of turf also kills significant portions of white grub populations when they are feeding close to the soil surface.
Monitoring and Treatment Decisions
Carefully dig around roots of grass to detect white grubs. If the infestation is heavy, the turf may be loose and easy to roll back like a carpet. For more information on monitoring, see MONITORING AND TREATING INSECTS AND MITES. Threshold levels on golf greens are low; if you detect more than one grub per square foot on greens, treatment should be undertaken. In other turfgrass settings, up to six grubs per square foot can usually be tolerated.
Proper timing for insecticide treatments for white grubs is difficult. The most effective insecticides (imidacloprid, thiomethoxam) are most effective when applied preventively when adults are laying eggs and before damage is seen in summer. These treatments are usually effective but only a small percentage of turf in California is infested with white grubs in any year and requires treatment. Alternatively treatments can be applied when damaging levels of grubs are found later in the summer. Nematode treatments can be effective at this time. Other materials applied to control larvae include carbaryl.
Current chemical control options are most effective against early instar larvae (less than 0.5 inch long). Grubs may take up to 10 days to die following contact with an insecticide, so wait at least this long to evaluate insecticide efficacy. Adult activity generally occurs during the period from mid-June to July. Because applied insecticides bind to the leaf blades and thatch, remove thatch before and irrigate immediately following application to obtain good results.
|Common name||Amount per 1000 sq ft**||Ag Use
|(Example trade name)||(hours)||(hours)|
|Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Always read the label of the product being used.|
|(Acelepryn)||Label Rates||4||Until dry|
|(Acelepryn G)||Label Rates||4||After application complete|
|MODE-OF-ACTION GROUP NUMBER1: 28|
|COMMENTS: Applications should be made when adults are first observed in late spring, usually in May and June. Higher rates may be necessary when this window has passed.|
|(Merit 75 WP)||3–4 teaspoons (0.148–0.19 oz)||12||Until dry|
|(Merit 75 WSP)||1.6 oz (1 packet/8,250–11,000 sq ft)||12||Until dry|
|MODE-OF-ACTION GROUP NUMBER1: 4A|
|COMMENTS: Maximum of 1 application per year. Applications cannot exceed 8.6 oz/acre per year (0.19 oz/1000 sq ft). Optimum control will be achieved when applications are made before egg hatch followed by sufficient irrigation or rainfall. Applications should not be made when turfgrass areas are waterlogged or soil is saturated with water. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.|
|(Arena)||Label rates||12||Until dry|
|MODE-OF-ACTION GROUP NUMBER1: 4A|
|COMMENTS: Most effective if applied just before eggs laid. Toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.|
|(Meridian)||Label rates||12||Until dry|
|MODE-OF-ACTION GROUP NUMBER1: 4A|
|COMMENTS: Most effective if applied just before eggs laid. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.|
|E.||HETERORHABDITIS BACTERIOPHORA||25 million||NA||NA|
|COMMENTS: Apply in late spring or early summer before adults emerge, or early fall when most chafers are in the susceptible stages. Irrigate before and after applying nematodes. Store nematodes before use as directed. Apply to warm, moist, but not soggy soil. Several irrigations may be needed during 2 weeks after application to keep soil moist. Apply during cool time of day in hot areas.|
|(Sevin SL)||Label rates||12||Until dry|
|MODE-OF-ACTION GROUP NUMBER1: 1A|
|COMMENTS: For treatment of grubs. Nontarget effects likely on other soil-dwelling organisms. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.|
|**||Apply in 25 gal water/1000 sq ft|
|*||Permit required from county agricultural commissioner for purchase or use.|
|1||Rotate chemicals with a different mode-of-action group number, and do not use products with the same mode-of-action group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a group number of 1B; chemicals with a 1B group number should be alternated with chemicals that have a group number other than 1B. Mode-of-action group numbers are assigned by IRAC (Insecticide Resistance Action Committee).|
|‡||Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Agricultural use applies to sod farms and commercial seed production.|
|—||Indicates use is not listed on label.|