STEP 6 - Grubs ... and other pests
If you have a weed or pest breakout in your organic lawn, don't panic and reach for chemical pesticides (including insecticides, weed killers, and fungicides) as they will kill beneficial organisms in the soil and undo previous organic care benefits.
Remember with organic lawn care, the focus is always on building healthy lawn ecosystems and problem prevention. Rather than regarding weeds, insects, and diseases as problems that require an arsenal of chemical poisons to control, they instead should be seen as indicators of an underlying unhealthy condition in the plant or soil. If you only treat the symptom and not the cause, the symptoms will recur. The underlying cause is often related to turf management (for example improper mowing, watering, fertilization), or malnutrition of the soil and the plant.
Good organic practices always start with knowledge of the ecosystem you are seeking to manage. (Or if you prefer Sun Tzu's "The Art of War", the lesson is to know your enemy.) Grubs are probably the most common insect pest concern for Long Island lawns. Keen insight is gained from understanding that grubs are the larvae of beetles, and that adult female beetles are attracted a lawn to lay their eggs if the lawn provides a moist environment. The key to prevention therefore is to avoid overwatering, particularly in late spring and early summer when beetles are actively looking to lay their eggs. (Overwatering is a very common problem. We'll discuss watering in more detail in an upcoming post.)
It may not be possible, and fortunately it is not necessary to prevent all grubs from finding a home in your turf. The best way to prevent damage from insect pests is to first establish healthy turf, with a deep root system. If you follow the recommendations that we provided in previous tips in this series including mowing at 3 1/2", not over-fertilizing with quick release nitrogen, choosing a low maintenance blend of grass seed, and keeping the pH balance of your soil in the 6.0 to 6.5 range, you will have hardy turf with an extensive root system that can tolerate moderate feeding by insects.
Grubs live in the soil under grass and they eat roots. The damage they cause appears as patches of yellowed, thinning and wilted grass. An extensive infestation might cover most of a lawn and look like drought stress. One way to determine if you have grubs, is to try grabbing a handful of turf and if it comes up easily, as though it has hardly any roots holding it in place, then you likely have grubs. Other signs of a high grub population are crows gathering to peck and claw at your lawn, or lots of mole tunnels. Both crows and moles like to feed on grubs.
To confirm that you have a grub infestation and determine how bad it is, you can cut a patch of sod about one foot by one foot with a knife and lift it, and count how many grubs you find. You may be surprised to learn that healthy turf can easily handle a certain about of grub activity, that is why quantifying the number of grubs in the lawn is key to determining whether you have a more extreme infestation, that might require treatment. In the words of Al Lane, owner of Professional Turf and Tree Supply in Lindenhurst, Long Island: "After finding 6-8 larvae of the dirty white, 3/4" 'C' shaped Japanese beetle grubs in a square foot of your turf soil, it is time to apply a safe biological milky spore powder which provides 12-15 year control with only one application." (See photo.) A simple way to deal with grub damage is to rake away the dead grass, so birds can more easily get at the grubs. If you see any grubs while raking, pick them out by hand. Then re-seed the bare patches, put down a ¼ inch of compost, and water lightly to re-establish the grass.
Japanese beetle grubs can be controlled for years with milky spore, a disease that is specific to the Japanese beetle grub. Milky spore is an effective organic control because it is not a poison, it is specific to Japanese beetle grubs, and it does not present a threat to groundwater or human health. Follow the instructions on the package, and apply it when the soil is warm, over 55 degrees. It can take a couple of years for milky spore to become fully established and control the grubs. It is worthwhile, because the spores can lay dormant in your soil for years after that, and prevent future infestations. Milky spore is only effective against Japanese beetle grubs; milky spore will not affect other grubs. Identification therefore, is helpful. If you collect a grub or adult beetle, you can then contact the cooperative extension to help with identification, or you can compare it yourself to photos.
Many types of grubs, and other soil dwelling insect pests including chinch bug and webworm, can be controlled with beneficial nematodes. Nematodes are fast acting, but can be very delicate so they must be applied carefully, be sure to follow all instructions. The best time to apply nematodes to control grubs is in from the middle of August to the middle of September, when grubs are still young and small. Do not apply nematodes in direct sun or heat of the day. Water your lawn before and after application (the soil should be moist).
Organic controls for other lawn and yard insect pests:
Bt (bacillus thuringiensis) is a bacteria that controls caterpillar pests, including sod webworm. It has become a very common control used by organic farmers, and even golf course superintendents.
Insecticidal soaps (potassium salts of fatty acids), which disrupt cell membranes of insects, are particularly effective against soft-bodied insects and mites.
Vegetable-based horticultural oil kills mites, scales, and soft-bodied insects on trees, vegetables, and ornamental plants. Be sure to look for vegetable based oils (like canola oil) not petroleum.
- Link to Cornell Cooperative Extension of Suffolk's Horticulture Diagnostic Lab (Instructions for submitting samples under "Insect Identification Submission Form")
- A Grub's Life: Egg to Beetle (Cornell Cooperative Extension)
- White Grub Management in TurfGrass
- Northeast Organic Farming Association - Organic Land Care "Lawns: An Organic Approach to Grubs"
- Grub Damage? Try Beneficial Nematodes
- Beetle Identification from Maine State Government
Long Island Organic Landscapers
Although it's easy for the average homeowner to maintain their lawn organically, some may too busy and wish to hire a professional. In that case there are thousands of landscapers on Long Island to choose from, but only a small but growing number of experts who can maintain your lawn and landscape without the use of chemical pesticides. They can be found here.