Soil Feeders - May June Beetle

MAY/JUNE BEETLES (MIJB)
aka: May Beetle, June Beetle, Junebug
scientific name: Phyllophaga spp.

FIELD KEYS
Hosts: Most grass species
Site symptoms: Turf wilting under heat stress despite adequate available moisture. Turf is unresponsive to fertilizer applications. Wilted turf turns off color and dies in irregular patches to large uniform areas. Removed dead or wilted turf reveals grubs feeding at soil - thatch interface down to 2-inch soil depth.
Plant symptoms: Above ground plant structure shows no obvious damage or other symptoms. Root system shows much damage from the crown down to a 2-inch depth from grub feeding.
Site keys: Sunny locations with consistent soil moisture and moderate soil temperatures.

SPECIMEN ID
Immatures are typical six-legged white grubs with tan heads that range in size from 1/4 inch for newly hatched first instars to 1 1/2 inch fully-grown, third instars. Adults are 3/8 to 1-inch light to dark brown beetles.

SCOUTING TIPS
Despite the large number of Phyllophaga spp. comprising M/JB, they all have a similar growth pattern - the majority of time is spent as 3rd instar grubs. Adult flights begin when evening temperatures are greater than 60°F. Adult numbers can be monitored with light traps and grub sampling should begin about four weeks after adult numbers peak. New adult emergence for different species may occur sequentially, so do a consistent job of classifying which species is seen when. Most M/JB species have multi-year life cycles. Vulnerable sites with infestation history should be sampled in May (second year grub) or August (first year grub) to avoid damage.

CONTROL STRATEGIES
Cultural: Where possible limit supplemental watering for about 4 weeks at vulnerable sites (to increase egg and first instar mortality) starting when adult flights peak. Increase drainage at wet sites and manage turf for maximum root production.
Chemical: Because of the number of different species and different life cycles involved in M/JB, it is important to correlate the data about grub populations with observed damage to develop a decision-making matrix. Or, consider making control applications to asymptomatic sites when grub sampling indicates that the per square foot grub population has reached 5-10. At more vulnerable or low maintenance sites, applications may need to begin once grubs populations reach 3-4 per square foot.

Growth stages: egg - grub (three instars)* - pupa - adult
* - treatable stages

Life cycle: 1 to 4 year life cycle
Sequence: grub - pupa - adult - egg - grub