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Grubs, Anyone?






The Japanese beetle grub is found east of the Mississippi. The adult beetle lays the eggs in the spring, the eggs hatch in the summer and the feeding begins in August and continues through October.


A weevil is a generic name applied to a family of beetles (Curculionidae) with down-curving snouts that are destructive to plant life. The larva of weevils are white grubs, a term descriptive of the shape the little buggers take upon being exposed to light.



They Like What Your Grass Likes!

The problem with grubs is they thrive in moist soils heavy with organic matter, and keeping the grass green is a function of keeping the soil moist and organically rich. However, the damage to the turf is mitigated by watering. The one thing you don’t want to do is keep the soil dry. It will make the grubs less happy and active, but the combination of grub damage and drought conditions will surely kill the grass.

The good news is that even if grubs have destroyed the grass roots, the grass can be successfully transplanted and recover if properly watered.1

White grubs are regional critters. The masked chafers are found west of the Mississippi, while the Japanese beetle is the concern for those east of the Big Muddy. Both species have the same life cycle: The adults lay the eggs in the spring, the eggs hatch in the summer and the feeding begins in August and continues through October--thus the name “fall grubs.“ Not all grubs follow this routine. Junebugs, a common grub throughout the U.S., has a different life cycle and does most of its damage in the summer.



Japanese Beetles

Ray Bond, the owner of Bond Nursery in Dallas, Tx., says Japanese Beetles have “two missions and desire in life--sex and food, in that order.” (Hmmm, just like people, except probably the reverse order.) They are known as “insect bulldozers,” and Bond estimates they are “probably the most destructive insect pest to the landscape in the eastern U.S.”






White grubs, the larval stage of the Curculionidae family of beetles, reside below the grass thatch and eat grass roots.


Rainfall in the late summer (and watering the grass, of course) keeps eggs and grubs from desiccating, but the female Japanese beetle knows to lay the eggs in moist areas. If the soil becomes too dry, the grubs will burrow deeper. The grubs don't venture more than 30 inches or so within turf or sod, but move considerably more in unplanted soil (up to 15 feet!). They generally spend the winter 2-6 inches below the surface, and become inactive if the soil temperature drops to 50?F.



Bio-Control

The superintendent needs to examine the grass closely to identify if there is root damage, otherwise the super may not notice a problem until the grass starts to die.

European starlings, grackles and crows particularly enjoy grubs on the menu, and will dip their bills into soil or turf to find them. Crows, however, will pull up bits of turf as they dig for their juicy morsels.1

“Bt” (Bacillus thuringiensis) is an effective biological control for Japanese beetle grubs (early fall) feeding near the surface. The Bt is applied to areas out of direct sun.1

Bacillus popilliae (milky spore) is also effective against Japanese beetle grubs.1 When the grub eats milky spore, its internal organs liquefy. The spore can remain in the soil for many years, although it may take several years for it to become effective.



Pesticides

As grubs tend to hang out below the thatch, pesticides may not easily reach them. Water in the turf will help deliver the pesticide to the grub, but repeated applications may be necessary due to the dilution of the pesticide. It is recommended to apply pesticides on wet turf and water again after spraying.2



Beetles do not damage turf, preferring to nibble on trees and shrubs, but in their formative period as little white grubs, they quite enjoy snacking on the roots of grasses. If you pull on the grass and it breaks away from the roots, that's evidence of the little terrors at work. The culprits are:1

  • Black turfgrass ataenius
  • Asiatic garden beetle
  • European chafer
  • Green June beetle
  • Japanese beetle
  • Northern masked chafer
  • Southern masked chafer
  • Oriental beetle
  • May beetles (aka Junebugs)


Bond recommends these chemicals for killing grubs:

  • Cythion 57% EC (malathion)
  • Dymet (20/10) EC (methoxyclor + diazinon)
  • Marlate 50% WP (methoxychlor)
  • Marlate 25% WP (methoxychlor)
  • Orthene 75 S (acephate)
  • Sevin 50% WP1
  • Tempo 20 WP (cyfluthrin) - Commercial use only
  • Diazinon

References
1. Bond, Ray. “Japanese Beetles: Insect Terrorists.”
2. Christians, Nick. Fundamentals of Turfgrass Management, 2004, John Wiley & Sons, Hoboken, New Jersey.



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May 26, 2019, 3:19 pm PDT

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