Recent weed survey can benefit wild blueberry growers
/by Hugh Lyu
Lowbush blueberries (Vaccinium angustifolium Ait.) are an economically important fruit crop in Canada, and Nova Scotia is one of the most important production regions. Weed management in this perennial monoculture is difficult, and weeds contribute to a significant variation in annual yields.
Weed surveys provide the quantitative information on weed community composition required for developing sustainable integrated weed management strategies. From the early 1980s to the early 2000s, the number of weed species in lowbush blueberry fields doubled to more than 200. However, the quantitative data on recent shifts in the weed flora of lowbush blueberry fields has been lacking.
From 2017 to 2019, a weed survey project was conducted by a Dalhousie University Faculty of Agriculture vegetation management research team led by me when I was a graduate student, assistant professor Dr. Scott White, and summer research assistant Lienna Hoeg.
A total of 165 bearing-year lowbush blueberry fields were surveyed from 2017 to 2019, within which approximately 211 weed species were identified. Most weed species were herbaceous perennials (89 species) and woody perennials (49 species), followed by annual broadleaf weeds (24 species) and perennial grass weeds (20 species).
The remaining flora consisted of a range of ferns, biennials, sedges, rushes, and orchids.
The 10 most common weed species were Red sorrel (Rumex acetosella L.), Poverty oat grass (Danthonia spicata L.), Haircap moss (Polytrichum commune Hedw.), Hair fescue (Festuca filiformis Pourr.), Narrow-leaved goldenrod (Euthamia graminifolia (L) Nutt.), Rough hair grass (Agrostis hyemalis (Walter) B.S.P.), Woolly panicum (Dichanthelium acuminatum Ell.), Cow wheat (Melampyrum lineare Desr.), bunchberry (Cornus canadensis L.), and Yellow hawkweed (Hieracium caespitosum Dumort).
Red sorrel is well adapted to lowbush blueberry fields. Although competitive interactions between Red sorrel and lowbush blueberries have not been fully investigated, several issues associated with this weed species suggest that the development of sustainable Red sorrel management strategies should be developed.
The continued spread of Red sorrel, combined with the dramatic increase in the occurrence of Hair fescue and other weeds lacking wind-borne seeds, also highlights the need for the lowbush blueberry industry to take the movement of weed seeds on machinery seriously. The discovery and registration of new herbicides will not keep pace with the development and subsequent spread of resistant weed biotypes if the equipment is not cleaned or approaches to harvesting are not altered.
After the 10 most abundant weeds, other weed species are less common, but they have the potential to develop into management challenges and become problematic. Those weed species are herbaceous perennial weeds such as Common St. John’s wort (Hypericum perforatum L.), Spreading dogbane (Apocynum androsaemifolium L.), and Downy goldenrod (Solidago puberula Nutt.), as well as woody perennials, perennial grasses and sedges, and rushes.
The data, for example, shows a large increase in the occurrence of St. John’s wort, indicating that a spot treatment or other management strategies should be developed for this weed species.
One of the more important aspects of the weed survey data is that, if truly committed to a proactive approach to weed management, the Nova Scotia lowbush blueberry industry now has the opportunity to develop solutions for serious weeds before they become widespread and more difficult to manage.
Management strategies should be developed for some weeds that currently have low occurrence but high potential to become problematic. They include the perennial grass Red fescue (Festuca rubra L.), the woody shrub Glossy buckthorn (Frangula alnus Mill.), and the annual plants American burnweed (Erechtites hieraciifolius (L.) Raf. ex DC.) and Canada fleabane (Erigeron canadensis (L.) Cronquist).
The data, for example, shows that Red fescue is gradually increasing in occurrence. Although not as common as Hair fescue, Red fescue is arguably a more problematic fescue as it is also tolerant to many herbicides but spreads by rhizomes rather than relying exclusively on the seed. Established plants, therefore, will quickly colonize blueberry fields as few growers will likely invest in the Pronamide applications required to control initial infestations.
Glossy buckthorn currently occurs in only 1.2 percent of fields, but it spreads aggressively by animal-mediated dispersal of fruit and seeds, and is an incredibly problematic invasive plant. The time to develop an appropriate spot treatment and strategy for dealing with sporadic plants is now so that large populations that can’t be controlled do not become established.
Similarly, American burnweed and Canada fleabane occur in relatively few fields but have the inherent capacity to quickly become a problem. Growers are already asking about these and other weeds of low occurrence on the list, indicating that it is only a matter of time before some of these become more widespread and difficult to manage. Results are guiding future research priorities for weed management in lowbush blueberry fields.
(Hugh Lyu is a wild blueberry specialist with Nova Scotia’s Perennia Food and Agriculture Inc.)
