What’s Going on in the Fraser Valley's Strawberry Soils?

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Siva Sabaratnam, plant pathologist with the BC Ministry of Agriculture is seeing too many problems in strawberry fields lately. He recognizes that many of the issues involve soil-borne pathogens and wanted to take a closer look. In order to help strawberry growers understand what’s happening in their dirt, he presented his findings of the 20 strawberry fields studied at the late-January Pacific Agriculture Show in Abbotsford.

“We noticed a lot of issues in strawberries these days, especially with soil-borne pathogens,” Sabaratnam says. “So we did a survey.”

This survey is timely. There has been modest growth in the number of strawberry fields recently, with approximately 250 hectares (600 acres) currently in production in the Lower Mainland.

“We’re seeing interest because of the day-neutral [strawberries],” he adds.

The survey looked at fields in the Lower Mainland and on Vancouver Island (Abbotsford, Delta, Chilliwack, Langley, Saanich and Victoria) and included sampling and analysis (twice per field) as well as questions to growers about their management practices.

These fields consisted of three different kinds of production systems: bare soil (both with and without irrigation), raised beds (with black tarps, single or double-drip irrigation) and one greenhouse/polyhouse.

Soil-borne pathogens are challenging. They survive in soils for a long time and it can be very hard to identify and control them. Specifically, Sabaratnam points to black root rot, red stele root rot, wilt and crown rot as being a significant hassle.

“Fusarium [wilt] is one of the common ones you can see in the field most of the time. These pathogens are difficult to control because there is no one specific control for all of them,” he says. “The symptoms are very varied, there are a lot of different symptoms.”

One symptom he points to as being the most common is the dying of older leaves, with seemingly healthy new leaves which gradually also die off.

“The plant is going to die eventually,” says Sabaratnam.

Other symptoms include powdery mildew and the appearance of phosphorous, nitrogen and iron deficiency. Signs of mineral deficiencies can be particularly challenging because treating those deficiencies won’t eliminate the soil-borne pathogen causing the symptoms.

In the fields studied, about 25 per cent had Verticillium, 55 per cent had Rhizoctonia fragariea, 80 per cent had Fusarium, 25 per cent had Cylindrocarpon and five per cent had Phytophthora. Of the 20 fields, eight had three pathogens, the average. Other fields ranged from having just one pathogen up to five.

Of note was the fact that Rhizoctonia and Verticillium were quite often found together in one field. This is a concern to Sabaratnam because there are very few chemical controls. He noted that Quadris (azoxystrobin) and Scholar (fludioxonil) are licensed for use on Rhizoctonia.

When chemical controls are limited, management practices can’t be overlooked. Sabaratnam points to planting in a healthy (disease-free) site or at least rotating crops every three to five years. He also stresses the importance of pathogen-free stock.

“Clean and pathogen-free planting stock. I emphasize this because it is very difficult to screen some of the pathogens at the transplant stage,” he notes.

Sabaratnam also suggests planting resistant or tolerant varieties and considering pre-planting soil treatments such as soil amendments or fumigation.

Post-harvest field management is also important to reducing pathogen levels.

“This is really important,” he says. “To limit the impact next year.”

Taking care of strawberry fields often comes down to understanding what’s in the soil first. Growers will benefit from assessing their soil and considering what pathogens are in place in order to limit crop harvest impacts. ■