Evaluating the Current Weed Community in Wild Blueberry Fields and IPM Strategies for Spreading Dogbane (Apocynum androsaemifolium)

Lowbush blueberry (Vaccinium angustifolium) is Maine’s third largest crop (USDA 2020 a). From 2017 – 2019 the three seasons yield average was 27,200 tons were harvested from 19,500 acres for a value of $22,468,000 (USDA 2020 c). Lowbush blueberries are managed on a two-year cycle. Every other year, lowbush blueberry fields are pruned to the ground either through the use of a tractor mounted flail mower or a prescribed burn (Yarborough 2009). Pruning is a necessary part of managing lowbush blueberries as the second-year growth produces the highest yield but steadily declines in subsequent years (Drummond et al. 2008; DeGomez 1988). This practice is not detrimental to the lowbush blueberry as approximately 70% of the plant grows underground (Drummond et al. 2008). After a prune, lowbush blueberries regrow for the following year in what is referred to as the “prune” year. Floral buds develop over the prune year and overwinter into the next year, referred to as the “crop” year (Yarborough 2009). In May of the crop year, the floral buds open into small-bell shaped flowers and remain open for three to four weeks. Lowbush blueberry flowers are typically not self-fertile and require the use of pollinators. Most farmers will supplement their pollination by renting commercial beehives, increasing the yield (Yarborough 2019). Berries form from the pollinated flowers by the end of July to August (Yarborough 2009). Harvests involve the use of either large mechanical harvesters or teams using hand rakes. Mechanical harvesters are the more common tool for harvesting, as they are used in 80% of the fields in Maine (Yarborough 2009). Farm crews remove debris from what was harvested, and berries are either sold fresh or delivered to one of many commercial freezers. Frozen berries are then packaged for the retail market or processed further into a range of value-added products (Calderwood and Tooley 2020). A common challenge for farmers is the presence of weeds within their fields. Weeds take up valuable shade, nutrients and space that would otherwise be utilized by the lowbush blueberry. Weeds can reduce yield, increase disease incidence and interfere with harvest operations. Up to 84% of yield can be lost because of weed cover (Yarborough 2009; Yarborough and Mara 1997). The moisture created by the additional canopy of weeds can increase the incidence of harmful diseases such as mummy berry (Monilinia vaccinii-corymbosi) (Drummond et al. 2012). Weeds can interfere with the efficiency of mechanical harvesters as they get caught within the harvested berries (Yarborough 2009). Despite these negative effects, there has not been a weed survey of lowbush blueberry fields in the state of Maine since 1980 (Yarborough and Marra 1997). Weed surveys are important for farmers to evaluate their current weed management strategies and to discover possible trends in the weed community. One of the most difficult weeds to manage within wild blueberry fields is spreading dogbane (Apocynum androsaemifolium). It resists at least six common herbicides (NBDAAF 2017) and can form dense patches through its rhizomes (Niering et al. 2001)