WHITE GRUB BIOLOGY AND MANAGEMENT STRATEGIES

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WHITE GRUB BIOLOGY AND MANAGEMENT STRATEGIES

• Dr. R. Chris Williamson
• Turf and Ornamental Specialist
• University of Wisconsin

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Understanding the BIOLOGY of an organism (insect,
pathogen, plant, etc.) is the KEY to successful
management!
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Japanese Beetles and May/June Beetles are the two
most important white grubs in Wisconsin!
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JAPANESE BEETLE ADULT
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MAY/JUNE BEETLE ADULTS
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Adults

• JAPANESE BEETLES
• Adults are broadly oval (longer than wide)
• 5/16-7/16 long (females are larger than males)
• Metallic green beetle with hard, coppery-brown
  wing covers

• MAY/JUNE BEETLES
• Medium to large sized
• 5/8-1 long (females are larger than males)
• Light-brown to reddish-brown to almost black

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White Grubs

• Larvae (a.k.a. grubs) are typical white grubs
  with three pairs of jointed legs and a
  yellowish-brown to brown head capsule
• They typically assume the C-shape position

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White Grubs

• Grubs have three immature life stages (instars)
• 1st instar larval stage
• 2nd instar larval stage
• 3rd instar larval stage
• Grubs develop (grow) via a process called molting
  which is regulated by insect growth hormones
  (IGRs)

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Japanese Beetle Biology

• Both the ADULTS and GRUBS cause serious damage to
  their respective plant parts
• Adults feed on gt300 species of plants
• Grubs do NOT discriminate food sources (roots)
• Only ONE generation per year

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May/June Beetle Biology

• Adults do NOT cause measurable damage
• Larvae cause serious damage to roots
• Grubs do NOT discriminate food sources (roots)
• Only ONE generation every three years

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JB uses a diversity of plant species and plant
parts for hosts
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Preferred Hosts of Japanese Beetle Aduts

• Linden
• Maple (Japanese and Norway)
• White Birch
• Apple/Crabapple (Malus spp.)
• Purple-leaf plant material
• Prunus spp. (Cherry, Plum, Peach, etc.)
• American and English Elm
• American Mountain Ash
• Roses

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Adult Behavior

• Adults are gregarious (aggregate)
• Adults prefer direct sunlight (full sun)
• Most active between 10 am 4 pm on Southern and
  Western exposures
• Feeding originates in the upper canopy of the
  tree
• Adults are not truly defoliators, they
  skeletonize within margins of leaf veins

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• JAPANESE BEETLE
• Females live for about 30-45 days
• Females mate multiple times
• Females lay up to 60 eggs (1-4 eggs each time)
• Eggs typically hatch in about 2-3 weeks once laid

• MAY/JUNE BEETLE
• Each female lays between 20-50 eggs in a lifetime
• Eggs hatch in 3-4 weeks

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Adult Behavior

• JAPANESE BEETLES
• Females prefer to lay eggs in moist, loamy soil
  covered with turf or mulch
• Females prefer to lay eggs low-cut (lt 1 ½) turf

• MAY/JUNE BEETLES
• Females are active at night
• Females prefer to lay egg in moist, loamy soil
  covered with turf

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Grub Behavior

• Young grubs begin feeding on roots and organic
  matter immediately after egg hatch
• As grubs grow and mature, they consume greater
  amounts of root tissue ultimately destroying the
  turf
• Once turf is damaged, it will roll-up like
  carpet
• Damaged areas also attract vertebrate pests such
  as skunks, raccoons, birds, etc.

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Larval damage
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Japanese Beetle Control Options

• Plant Resistance
• Biological
• Cultural (Mechanical/Physical)
• Chemical

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Plant Resistance

• Japanese Beetle Adults
• Resistant plant material (species and/or
  cultivars)

• White Grubs
• None available (No know resistance of roots)

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Biological Control Options

• Adults
• None available

• White Grubs
• Bacterial pathogens
• Milky spore
• Fungal pathogens
• Beauveria
• Metarrhizium
• Insect Parasitic Nematodes
• Parasitoids
• Tiphia wasps

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Cultural Control Options

• Japanese Beetle Adults
• Physical removal and exclusion (not practical for
  large properties)
• Trapping
• NOT effective!!

• White Grubs
• Withhold irrigation during adult activity
• Raise cutting height (gt3 inches)
• Irrigate and fertilize turf after grub damage to
  help promote recovery

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Two Approaches to Chemical Control

• PREVENTATIVE and CURATIVE chemical control
  options are available for Japanese Beetle ADULTS
  and White GRUBS

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Chemical Control Options

• PREVENTATIVE
• Proactive
• Prior to infestation
• Insurance, protection similar to fungicide
  treatments

• CURATIVE
• Reactionary
• Corrective
• Response to pest infestation and damage

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Japanese Beetle Adults Preventative Chemical
Control Options

• Systemic insecticide treatments applied to the
  plant material as a soil drench or injection near
  drip-line or basal area of plant
• Merit (imidacloprid)
• Preceding fall (mid-Sept.-Oct.) for larger trees
  (gt 15 ft)
• Spring for smaller trees (lt 15 ft)

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Japanese Beetle Adults Curative Chemical Control
Options

• Contact insecticides applied to adults
• Most effective when applied when beetles are
  active (between 10 4)
• Trans-laminar (tissue penetrating) insecticides
  applied to foliage (isolated translocation)

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Viable Insecticides

• Merit (imidacloprid), trans-laminar
• Sevin (carbaryl)
• DeltaGard (deltamethrin), deterrent
• Scimitar (lambda-cyhalothrin)
• Talstar (bifenthrin)
• Tempo (cyfluthrin)
• Astro (permethrin)

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Regardless of the control product or approach
(preventative or curative), ALL grub control
treatments MUST be watered-in with sufficient
irrigation or rainfall!
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White Grubs Curative Chemical Control Options

• Applied once grubs are present
• Keep in mind Larger grubs are often more
  difficult to control!
• Short-residual activity (lt10 days)
• Only two registered products are suggested
• Dylox (trichlorfon)
• Sevin (carbaryl)

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White Grubs Preventative Chemical Control Options

• Must be applied BEFORE or at egg hatch!
• May be applied in late-May, June, or July
• Long-residual activity (gt120 days)
• Will NOT control larger grubs (2nd/3rd instars)!
• Merit (imidacloprid)
• Mach 2 (halofenozide)

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Example Comparison Between Preventative and
Curative Control Products

• PREVENTATIVE
• Merit (imidacloprid)
• 0.3 ai/A
• LD50 2591
• gt 120 day residual activity
• Relatively narrow spectrum product
• Developed in late 1980s

• CURATIVE
• Dylox (trichlorofon)
• 8.0 ai/A
• LD50 395
• gt 10 day residual activity
• Broad spectrum product
• Developed in WW II era