|Small Fruit Industry|
The Washington processed red raspberry industry is worth about $60 million annually. Growers, however, struggle to control root diseases that can cause up to a 12% loss in fruit production.
In order to identify the most common soilborne pathogens responsible for root disease, we conducted the first large scale, multi-pathogen disease survey for this industry. Our results showed that Phytophthora rubi was the most common pathogen causing severe root disease. However, damage was more frequently observed when three different soilborne pathogens occurred together: P. rubi, Verticillium dahliae, and Pratylenchus penetrans (the root lesion nematode). This suggests that a soilborne disease complex is at play.
We then established a number of grower field trials to improve disease control and discovered that while the industry standard fumigant treatment was effective against the root lesion nematode, it did not adequately suppress fungal pathogens like P. rubi and V. dahliae.
Since then, we have demonstrated that bed fumigation and covering fumigated soil with plastic film can reduce fumigant use by up to 80% while increasing disease control efficacy against soilborne pathogens.
100% loss due to Phytophthora root rot in a 5 acre field of red raspberry.
We developed alternative, nonchemical methods for controlling Phytophthora root rot for the $320 million PNW blueberry industry.
We identified cultivars of northern highbush blueberry that were more resistant to the root rot pathogen, P. cinnamomi. We also discovered that reducing soil moisture with microsprinklers or by placing drip lines further from plant crown reduced root rot compared to irrigation methods that increased soil moisture (geotextile tape and narrow drip line placement). Sawdust mulch reduced infection by lowering soil temperatures, while the warmer temperatures under black weed mat increased infection. Lastly, a gypsum soil amendment was effective, especially when combined with wide drip line placement.
However, none of the nonchemical methods were as effective as fungicides. Therefore, fungicides may provide much needed control during field establishment if there is high disease pressure.
Together, these methods can be used in an integrated pest management system for reducing root rot damage. If adopted, these disease control strategies could save growers up to $2 million/year in lost revenues.
Healthy plant of blueberry 'Draper' (left) compared to a plant with root rot (right).