The Wellesley Pesticide Awareness Campaign’s phone line at the Natural Resources Commission has been very busy these last few weeks with residents calling for information on organic lawn care.
We appreciate the great interest in non-toxic lawn care techniques and plan to answer some of the more frequently asked questions here in the Townsman.
By all accounts, it appears that Wellesley’s number one most popular lawn problem this spring is grubs, followed a close second by crabgrass.
The April 26 issue of the Townsman carried our article on non-toxic control of crabgrass (which can be viewed on our Web site www.ci.wellesley.ma.us/nrc/pesticide). Now that this summer-like weather has the soil warmed up, it’s time to use some of our biological friends to help us keep the grubs under control.
I have to admit, I had never heard about grubs as a lawn problem until I moved to Wellesley. Where I used to live, lawns were just the mown areas of a yard, otherwise left to their own devices, and grubs never established themselves as a pest.
In Wellesley, however, so many lawns have been heavily treated with chemical fertilizers and pesticides, have shallow roots, and/or have no species diversity that grubs can do tremendous damage in a single season.
This article is written using up-to-date information obtained from several organic land care professionals, Priscilla Williams and Mike Nadeau of our partner organization, the Northeast Organic Farming Association, and Peter Wild of Boston Tree Preservation.
Grub damage appears as brown patches of grass and bare soil in the spring, when the rest of the lawn begins to green up. These areas may be a sign that grubs (beetle larvae) have been feeding on the grasses in your lawn, literally pulling them out by their roots. Another sign of grub activity may be crows gathering on the lawn to tear up small patches or mole tunneling. Moles are voracious eaters of grubs and will quickly excavate large areas in search of their prey. To verify grubs as the culprits, pull up the dead grass and look in the soil beneath.
There will be no roots on the grass, and in the soil you will be able to easily find the grubs themselves, about one inch long, white, with a dark head and small legs near the head. At this point, you may start to encounter feelings of anger and disgust, but, wait — don’t reach for those chemicals!
This year, try an organic approach to this problem. When the soil warms up to 55 degrees, milky spore bacteria (Bacillus popilliae) may be applied for safe, long-term control of the white Japanese and oriental beetle grubs.
While it may take two to three years to achieve complete control, milky spore is worth using due to its simple application method and effective long-term results. The spores multiply inside the grubs, and when the current infestation subsides, the spores lie dormant in the soil for up to 15 years, waiting to attack subsequent grub populations.
Be sure to follow the label instructions regarding application rate. It is most important to apply the milky spore powder on an overcast day and to water it in well to the lawn and surrounding garden bed areas where beetles have been a problem.
For short-term, fairly fast-acting control of Japanese beetle grubs, try Heterorhabditis bacteriophora. This is a beneficial nematode, a microscopic soil organism, that attacks deep-dwelling lethargic white grubs. Apply this in the late afternoon and water in thoroughly so they don’t have a chance to dry out. Researchers are still exploring the use of other beneficial nematodes which show promise for control of other grub species in lawns.
Biological control of grubs will keep the populations in check. It is important to realize that your lawn can tolerate up to 12 grubs per square foot without showing signs of damage. In fact, at this low level, grubs can actually be considered a beneficial insect as they aerate your soil, recycle plant matter, and excrete nutrients. The holes dug by skunks in search of grubs are also beneficial, have you noticed that they are about the same size as the holes intentionally made in athletic fields by mechanical aerators?
When renovating a lawn, select insect and disease-resistant cultivars of turf grass as a preventative strategy. These include fescues, ryes, and some bluegrasses. Develop the practice of watering deeply (1 inch of water collected in a cup) and infrequently, to encourage deep root growth. Consider developing some species diversity by allowing low growing plants like clover to have a place in your lawn.
Nature itself often can keep grub populations in check. A dry summer can kill thousands of grubs.
The adult beetles themselves can be handpicked to keep the adult population under control if there are a limited number of plants being attacked. This is easiest to do in the early morning or late afternoon when the adult beetles are more dormant — you can just push them off the leaves. Use a drop of biodegradable soap in a jar of water to collect the feeding adults. Contrary to some traditions, there is no need to use oil or kerosene in the jar. Once they have died in the soapy water, just dump the whole jar in your trash, or better yet, your compost pile.
Milky spore powder can be purchased at the Needham Garden Center, 53R Chestnut St., Needham. Wellesley residents who mention this article will receive a 10 percent discount on the purchase of this and other organic gardening supplies. Order the beneficial nematodes from The Green Spot, Ltd., (603) 942-8925, or BioLogic Supply Company, (717) 349-2789. Another good source of highly virulent milky spore is Doom™ from Fairfax Biological Laboratory, Inc., Electronic Road, P.O. Box 300, Clinton Corners, NY 12514; 845-266-3705.
Sarah Little is Wellesley’s Pesticide Awareness Coordinator
