Cover cropping and seasonal landscape fabric mulch for weed and mummy berry control in organic blueberries

Blue Dog Farm is a certified organic blueberry and raspberry farm in the Snoqualmie Valley near Carnation, Washington. The 50-acre farm includes 5.5 acres of blueberries and is owned and operated by Amy and Scott Turner. We propose to test a combination of summer cover cropping and winter landscape fabric cover to address some of the most pressing challenges to organic blueberry production in the Pacific Northwest: weed competition, mummy berry and sufficient nutrient supply. Through 12 years of experience, we have pioneered seasonal application of landscape fabric as a mummy berry and weed control strategy. With this grant, we will compare this strategy to hand-weeding and will also investigate including cover crops in the system for summer weed control and fertility. We will distribute our results widely through a field day, an article in a grower publication distributed throughout the Northwest and available online and a presentation at a regional conference. The blueberries at Blue Dog Farm are grown on fertile, floodplain soils with high organic matter that hold water a long time in the spring. We cannot use tractor-driven cultivators or mulchers early in the spring before annual and perennial weeds have emerged and taken over the four-foot wide mulched zone under the plants. Production suffers with strong weed pressure because shallow-rooted blueberries do not compete well. Historically, we have done a great deal of time-consuming and/or expensive hand-weeding at the same time that pruning needs to be done. Other methods of weed control that we have experimented with in the past include mulching with composted sawdust /horse manure, paper, cardboard, used burlap coffee sacks and weed fabric. The compost added organic matter and some fertility but did not hold back weeds into the spring and provided a nice habitat for new weed seed germination. Paper, cardboard and burlap biodegraded and were overtaken by weeds. The weed fabric held back the majority of the weeds but did not contribute to soil-building or fertility. We estimate that in some years mummy berry, Monilinia vacinii-corymbosi, reduced our crop yield by 30-50%. This problem only worsens over time if left to its own devices. Mummy berry overwinters in mummified berries. During spring, spores are released and are spread by rain and wind. The infection period ends after pollination, or mid-April in the Pacific Northwest. Deep mulching and scuffing under the plants are the main methods we have tried. We currently supply nutrients with compost and commercial organic fertilizer. Our compost is produced on-farm, with an aerated static pile using horse manure and bedding from neighbors. While we intend to continue the compost operation, availability of horse manure is unpredictable. We are interested in fitting cover crops into our perennial cropping system to assist in weed control and reduce the purchase of commercial organic fertilizers. With the resources from this Western SARE grant, we will test a system of covering and uncovering the beds under our blueberries with weed fabric cut to fit each row. In our experience, the weed fabric can be conserved from year to year, which reduces the annual cost of the program. The beds will be covered with weed fabric in the late fall over a light application of composted horse bedding. We hypothesize that the winter weed fabric will prevent the establishment of weeds that would need to be weeded out by hand from our wet spring ground. Furthermore, since the weed fabric would be applied after all leaves and mummified blueberries have fallen, we're anticipating that the majority of mummies (which serve to propagate the following season's disease) would be effectively covered. In the spring, once the danger of mummy berry infection has passed, we will remove the weed fabric,possibly graze chickens in the field to reduce slug eggs, and then plant a summer cover crop. Following harvest and the fall of any mummified berries, the cycle is completed by mowing or scything the cover crop, retaining as much as possible within the blueberry rows, adding a light mulch of composted horse bedding, fertilizing if necessary, and then covering under the plants once again with the retained strips of weed fabric. Over time, we hope that weed pressure, especially from deep rooted perennial weeds, will lessen and that by regularly covering mummy berries over the winter that disease can be managed at a tolerable level. We will evaluate seven types of cover crops for biomass production, weed suppression, nutrient addition, ease of management (e.g. will tolerate some foot traffic and can be kept below the level of the blueberry canopy) and ability to provide other benefits such as beneficial insect habitat or possibly seed or animal feed. We will monitor blueberry and cover crop nutrition with fall tissue testing and will evaluate mummy berry by counting primary and secondary infection among blossoms and young leaves and by counting infected berries.