Features Agronomy
Nematode shows promise against grubs

This year marks the 10th anniversary of Ontario’s cosmetic pesticide ban, and some lawn care professionals are still lamenting that they can no longer use some of the pest control products they once took for granted.

Most, however, have adapted to the rules and regulations enacted in 2009 that outlawed several effective weed and insect controls. They have since come to terms with the legal means available to them to keep weeds and insects in check, including the use of organic and natural products.

A natural control method that has helped lawn care professionals succeed in their battle against grubs is beneficial nematodes. Prior to the ban, lawn professionals could apply Bayer’s Merit to keep grubs in check, but it’s a product that has long been removed from their toolboxes.

Lawn care professionals attending the Ontario Turfgrass Symposium in February at the University of Guelph were given a refresher on pest insects, their egg-laying habits, when they are most problematic and the means to control them naturally, including rates, application methods and timing. Sharing their insights were Ken Pavely and Richard Reed of Lawn Life Natural Turf Products.

They outlined the effectiveness of the Steinernema scarabaei nematode that was new to the North American market last year. Commercially produced, it is highly pathogenic to several species of white grubs. Discovered about 15 years ago at Rutgers University, the nematode offers 75 to 95 per cent control on the grubs of third instar Japanese beetle, Oriental beetle and European chafer. Lawn Life has exclusive rights to the Steinernema scarabaei product for the Canadian turfgrass market.

The scarabaei is a bigger, more aggressive species of nematode that is raised on a live host (the Gaillardia moth). The symbiosis makes the nematode healthier and stronger.

The adult European chafer is typically in flight the first week of July with hatching taking place about the first week of August. Because they prefer moist conditions to lay their eggs, homeowners who water their lawns regularly could face a dilemma. Heavy watering in late June or early July can effectively drown large populations of chinch bug nymphs but will create ideal egg-laying conditions for the chafer.

Reed said chinch bugs tend to prefer Kentucky bluegrass, suggesting such lawns overseeded with ryegrass or fescue can be an effective deterrent. Chinch bugs also prefer high light intensity. A correlation exists among the thickness of thatch, mowing height and insect pressure.

Resurgence of Japanese beetle
Pavely said there has been a notable resurgence of Japanese beetle in Ontario. At a trial conducted last September at a golf course north of Toronto, in which the soil temperature was about 15 degrees Celsius, grubs numbered about 40 per square foot in places, making for a heavy infestation. Compounding the problem was wide spread digging of the turf by animals that took place a couple of weeks before an application of scarabaei was made.

Curative synthetic treatments had been applied, but with only limited success. It neither slowed down the development of the grubs nor the amount of animal digging.

Nematodes were applied on 1,000 square feet of fairway, using a boom sprayer.

Thirteen days after treatment, the first stage of infection in beetle grubs usually takes place. For three to four days, depending on soil temperatures, white grubs will turn yellow and become sluggish. Sixty per cent of the grubs in the treated area were alive, but had turned yellow. The remaining 40 per cent were dead and were either copper or black in colour.

Once the infection stage is reached, the grubs turn yellow and are dying before they turn black. Pavely said it’s difficult to get a handle on the precise number of grubs killed because once they turn black “they pretty much disintegrate.” The nematode releases bacteria inside the grub, killing it, and then multiplies to bolster the amount of control.

Twenty-one days after treatment, roots had significantly rebounded, turf health had improved, and there was no further sign of animal digging in the treated areas. Soil temperatures had cooled to about seven or eight degrees, causing the nematodes to become inactive.

Because of the persistence of the scarabaei, it is expected their activity will resume this spring once soil temperatures warm up, Pavely said.

He noted Japanese beetle grubs were “nasty” 10 to 15 years ago, “and they’re still carrying people’s turf away.”

Like the European chafer, the Japanese beetle seems to have followed the general route of Highway 401 in an eastward direction where it is now present in Ottawa, Montreal and Quebec City.

The scarabaei nematode was discovered in New Jersey and is the only product registered for use in Ontario for grub control in lawn care. Reed said diaphragm pumps are effective in applying nematodes because they are less damaging to them as opposed to piston pumps and roller pumps that are known to cause damage. The higher the water output, the better, he said, suggesting at least two gallons per 1,000 square feet.

“Keep your pressure down so you have less chance of damaging them,” Reed said. “The key is watering before and having good soil moisture and then watering immediately after.”

Split applications
Reed said some theory suggests making split applications because eggs will hatch at different times during a hot, dry summer.

“If you put all your eggs in one basket and get out there early in August and treat all your lawns, and some of the eggs hatch a little later, you may get better control with a split app.”

Rainy days, either in the early morning or evening, are an ideal time for application. Staying away from ultra-violet light when applying nematodes is critical, Reed said, acknowledging tests are being conducted on UV inhibitors. Conditions in August can often be too dry, making September a better option.

Various turf management practices can either help to prevent a grub problem or may help rectify one. Maintaining a higher mowing height will result in deeper roots. Less damage will occur when there is more root mass. When turf is high and thick, it’s more difficult for beetles to get down and lay their eggs.

Aeration and slit seeding can damage grubs. In the United States and Europe, verti-cut machines have successfully damaged grubs. Aeration and slit seeding also allow nematodes to more easily penetrate the thatch layer to reach the soil profile.

Nematodes prefer loamy soil that is moist as well as a healthy soil with good organic matter and a large earthworm population. Nematodes will hitchhike onto worms, allowing them to move further distances.

Pavely said it is preferable to wait until soil temperatures fall into the 12 to 15-degree range before putting down nematodes. The timing of application, however, must be done before grubs begin to pupate because nematodes will not be able to penetrate their exterior shell.

He said studies have shown that high amounts of nitrogen will increase the number of surface insects. More will breed and more will survive. High potassium levels are detrimental to a lot of insects.

Options for grub control are currently limited, Pavely said, but he hinted new technologies are “coming down the road.”