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OSU Organic Study Yielding Vital Information

Oregon State University Extension Berry Specialist Bernadine Strik applauds the blueberry industry when she thinks back to 2006 when the Oregon Blueberry Commission began funding a long-term study on organic blueberry production.

“They had the vision to support this project from the very beginning that allowed us to get this trial established,” Strik said. “Considering that 98 percent of the industry was conventional at the time, I think that shows quite the level of support.”

Since then, others have joined the OBC in supporting the study. “We’ve also had the Washington Blueberry Commission support this project and we’ve had federal funding, as well.

“These types of long-term studies cannot happen without this level of industry support,” Strik said.

Today, with nearly 20 percent of Oregon’s blueberry acres in organic production, the North Willamette Research and Extension Center study provides vital information on fertility, weed control, varietal selection and other management issues in organic systems.

Conventional growers are utilizing the information as well, Strik said.

Recently, Strik provided growers a report on how the trial’s two varieties, Duke and Liberty, are responding to raised beds and flat beds, to different mulches, different weed control tactics and to different fertilizer sources and rates.

First off, Strik said that plants in the raised beds consistently outperformed those in flat beds, to the tune of 28 percent greater cumulative yields from the second growing season (2008) through the eighth (2014).

Also Liberty has yielded 28 percent higher than Duke during that same period in the organic systems, and both cultivars have continued to show yield increases annually.

“There has been a steady progression in yields,” Strik said. “I’m not sure if we’ve flattened out yet.”

As for the different production systems’ effect on fruit quality, the effects appear very minor, she said.

Oregon State University Extension Berry Specialist Bernadine Strik

“The biggest effect on fruit quality -- the brix and firmness -- has been cultivar differences,” Strik said. “We’ve shown only minor effect when looking at fertilizer and mulch.

“To me, that is good news,” Strik said.

“It shows that if we are going with weed mat instead of organic mulch, there are not huge differences in firmness, which is something we have worried about as this industry tends to be shifting to weed mat,” she said.

In testing the different mulch treatments, Strik went with sawdust for the control, because most fields were in sawdust at the time the trial was initiated. She only used hand-weeding in the sawdust.

Her second treatment consisted of compost plus sawdust, a treatment she described as a “mulch sandwich.” She used herbicides approved in organic production in that treatment and, if they didn’t work, turned to hand weeding.

Weed mat, with sawdust around the planting hole, was the third treatment. She hand-weeded when needed in that treatment.

Trial results showed that the heaviest weed pressure was in the compost-plus-sawdust mixture. Also, when taking into account cost in labor hours in spot-treating and hand-weeding, labor costs were up 25 percent in that treatment compared to the sawdust treatment. And labor costs for weed control were significantly lower in the weed mat trial than in the other mulching treatments.

“It doesn’t take long to pay for the material cost of weed mat when you have this big of a difference in labor hours to hand weed,” Strik said. “Weed mat has turned out from a weed-management perspective to be by far the most economical method of weed control.”

One drawback in the weed-mat treatment was an increase in rodent pressure.

“Rodents like the protection offered by the weed mat, and this is something that does need to be addressed,” Strik said.

One potential solution is to leave open the weed mat when possible for predators.

Strik also advised growers to keep an eye on irrigation if switching to weed mat.

“If you’re switching to weed mat, (your irrigation needs) are going to be different potentially than they were with your organic mulches,” she said.

In general, the trial showed that cumulative water use in raised beds with weed mat was 50 percent higher than with organic mulch, she said.

In analyzing effects of different fertilizers and rates, Strik found that Duke was very finicky about which fertilizer source was used and at what rates, whereas Liberty reacted similar to both fertilizer sources tested and to different rates.

“Liberty didn’t care if we used a low rate of nitrogen or a high rate, or if we used feather meal or fish,” she said. “For Liberty, I would go the cheapest way.”

Duke, conversely, “didn’t like fish and it certainly didn’t like a high rate of fish.

“Duke is very finicky,” she said. “It is performing best when fertilized with a high rate of feather meal and weed mat.”

Overall, Strik said, researchers found a big difference in cumulative net returns when comparing the best to the worst treatments.

Researchers will be providing information on organic production systems, as well as the best options for conventional growers at the OSU Blueberry School, scheduled March 16-17 on the OSU campus in Corvallis. For more information on the school, go to

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