News
Meeting the challenge of weed management in blueberry plantings

Controlling weeds in wild
blueberry plantings is becoming more difficult as herbicide tools
appear to be losing their effectiveness.

Controlling weeds in wild blueberry plantings is becoming more difficult as herbicide tools appear to be losing their effectiveness.

“The days when Velpar could control everything are going,” says Dr. Nathan Boyd, integrated weed management research chair with the Nova Scotia Agricultural College (NSAC).

Dave Yarborough, a University of Maine extension specialist, agrees, adding the last two years have seen poor control results from Velpar, most likely due to heavy rainfall and the high leaching effect of the chemical.

“We have used Velpar for too many years,” he explains. “We can’t expect to continue using it.”

He advises growers to rotate between herbicides but notes this can be a problem as there are few new emergence chemistries available for use.

In light of the limited herbicide choices available to blueberry producers, Dr. Boyd is urging growers to keep a close eye on plantings. Relying on only a few herbicide options usually results in a shift or change in the weed species infecting a planting, he says, adding it can also cause the development of herbicide resistance within weed populations. This results in overall weed numbers remaining constant or increasing, despite herbicide applications, he says.

“We need to get out in the field to see what is there,” says Dr. Boyd. “We will have to manage each field individually.”

Soil pH
Yarborough suggests that growers consider changing soil pH as an option in controlling weeds, adding that lower soil pH levels can increase herbicide toxicity and result in more effective weed control. He cites past cranberry research, which showed that soil acidification through a sulphur application can help to reduce weed competition.

Yarborough and his research associates have tested this idea by reducing soil pH in a test plot and using Sinbar and Velpar for weed control. Following several years of sulphur applications on the plot, the researchers observed reduced populations of both grass and broadleaf weed species. The greatest reduction in weeds was observed using 1,000 pounds of sulphur per acre, says Yarborough, adding the wild blueberry plantings remained healthy and maintained yields comparable to plantings in higher pH soils.

New weed controls
Professor Glen Sampson and his NSAC research team are also involved in blueberry weed control work. They are currently evaluating new controls, including non-chemical management, for possibly addition into an integrated weed control program.

“We have looked at a large number of grass and broadleaf herbicides,” he says, adding they are also evaluating soil applications of fatty acids and clove oil.

“The fact we are getting good results with alternative products indicates we should look at the timing of the application of these products,” he says, adding some herbicide alternatives work well early in the production cycle, but lose effectiveness later.

His team’s research is also looking at new herbicide products coming to the market, including Callisto, which is now registered for wild blueberries. Dr. Sampson says researchers are also getting good results with a Rimsulfuron/Mesotrione combination, while a mixture of Clethodim/Mesotrione has shown an 80 per cent control on grasses. A Mesotrione/ Callisto mix also appears promising as a grass control, he adds.

Dr. Sampson is also interested in researching the different ways weeds can infiltrate a field and how to deal with the primary seed sources.
“I would put more emphasis on the controlling that plant before it can produce that seed, or controlling the movement of seeds on equipment.”

Mechanical infiltration
Scott White, an NSAC graduate student, is currently involved in this type of research, observing the role blueberry harvesters can play in the dispersal of weed seeds. That role is obviously a major one – on one harvester alone, White found more than 500,000 broadleaf seeds and almost one million grass seeds.

It would appear that cleaning of the harvesters is required. This means more than just a hose down with the pressure washer. While White admits pressure washing can do a good job of cleaning machinery, seed counts can still exceed 20,000 seeds after a hosing.

Instead, the harvester should be sanitized. White recommends that growers concentrate on cleaning the belts, the bar around the rake and hydraulic pumps. To keep the harvester as clean as
possible, he suggests producers avoid harvesting in dense weed patches.