Pest Identification

• Grubs can be difficult to identify. They live in the soil eating roots, where their effects may not be visible until the damage has already been done. Spot grubs by looking for large, irregular patches where your grass has turned brown and can be peeled or dug up easily. Beetle eggs are usually laid in July, and do the most damage from August through October. After first frost they usually dig deeper into the ground, to reemerge in springtime. If you aren't sure whether grubs are your problem, dig up a core sample--a small section of soil and grass reaching a few inches beneath the surface. If you count more than five grubs, consider treating your lawn. If you count less than five grubs, beetles may not be your problem. In this case, milky spores will not be effective.
  
  

Function

• Milky spore disease is transmitted when grubs feed on the roots of treated grass. Infected grubs eventually die, transmitting billions of spores back into the soil. The disease then spreads to future generations of grubs. Nematodes, on the other hand, are microscopic worms that feed on larvae and pupae. They seek out and kill all the existing grubs in an area, then die off. Because they attack any type of grub, nematodes can also be used to control ants, fleas, flies, termites, caterpillars and even other worms.
  
  

Application

• Milky spores and nematodes are most effective in the fall, when grubs are close to the surface. However, they can be effective at any time of year when the ground is not frozen. Milky spores come in powder and granular form. Powder is applied once or twice, and granules are applied over two to three years. Nematodes are purchased in a liquid that can be sprayed on the lawn. Nematode application may need to be repeated in spring and fall if you have a serious grub problem.
  
  

Long-Term Effects

• Milky spore disease can take weeks to years to infect a population of grubs. However, the spores remain in the the soil, and can be effective for more than a decade, preventing any future infestations. Nematodes, on the other hand, will die out once they are finished consuming a population of grubs, and may die out in cold winters. They are not an effective long-term strategy, but are more effective in the short term. In either case, grass will not automatically regrow in damaged areas. You will need to re-seed those areas.
  
  

Considerations

• Avoid using chemical pesticides in conjunction with milky spores or nematodes. Milky spore disease requires living grubs to be effective. Nematodes can be harmed or killed by chemicals, including chemicals in the sprayer used for their application. Heavy rains can then wash the chemicals away, allowing healthy grubs to feed undisturbed in the fall. In addition, you should always avoid direct contact with even low-impact pesticides such as these. Even though they are plant-derived and much less harmful than chemicals, they may still have adverse effects in humans.