Cooperative Extension Publications

By Lily Calderwood, Ph.D., wild blueberry specialist and associate professor of horticulture, University of Maine Cooperative Extension; Leala Machesney, Extension and research professional, University of Maine Cooperative Extension and Jordan Parks, wild blueberry research technician, University of Maine Cooperative Extension

For information about UMaine Extension programs and resources, visit extension.umaine.edu.
Find more of our publications and books at extension.umaine.edu/publications/.

Introduction

Weeds are a persistent management challenge in Maine wild blueberry (Vaccinium angustifolium) production. Weeds compete with wild blueberry plants for light, water, nutrients, and space. Weeds can grow over wild blueberry plants (Figure 1), shading them from light, and weed roots compete underground with wild blueberry rhizomes for nutrients. Shading or starvation can limit the formation of flower buds altogether, reducing wild blueberry yield. Additionally, the presence of weed stems and seeds in wild blueberry fields interferes with harvester mechanics and can cause rakes and harvesters to jam, slowing the harvest process. Weed debris in harvested fruit increases the amount of cleaning required along processing lines. From plant growth in the field to cleaning the final product, reducing the weed coverage in your wild blueberry field will improve efficiency on the farm.

Because wild blueberries are a perennial crop naturally occurring in fields and never planted, weed management cannot rely on practices such as crop rotation or frequent cultivation. Instead, successful weed management requires a long-term, integrated approach. Management strategies including regular field scouting, prevention of weed seed production, maintaining low soil pH, balanced nutrient management, spot and whole-field mulching, and timely mechanical or chemical control are necessary. By practicing a rotation of these weed management strategies and maintaining healthy blueberry plants with dense cover that can reduce initial weed establishment, you can greatly increase your wild blueberry yield and ensure your fields are productive for years to come.

What is a Weed?

In wild blueberry fields, a weed is any plant other than blueberry growing in the field that can interfere with harvest and processing and as a result, reduce economic yield. By this definition, wild blueberry weeds can be native or introduced species. Labeling a native species as a “weed” does not mean that it does not provide important ecosystem services or imply that these plants should be removed from non-blueberry field locations. Native Maine plants that can be considered weeds in wild blueberry systems include Yes, spreading dogbane (Apocynum androsaemifolium) (Figure 2), sheep laurel (Kalmia angustifolia), and bunchberry (Cornus canadensis) (Figure 3), among many others. Any plant labeled as a weed in wild blueberry fields has been shown to present significant economic challenges to wild blueberry growers and some management is required to protect the long-term health and productivity of wild blueberry fields.

It is important to note that the goal of successful weed management is never a field and field border completely free of all weeds. Complete eradication of weeds in wild blueberry fields is not only impractical, but impossible. Growers should always weigh the cost-benefit of managing weeds. Some weeds may be more competitive, or present greater harvesting and processing challenges, than other species. Weed management should be focused on the species that pose the greatest risk of competition and are present in the highest numbers. 

In addition to reducing wild blueberry vigor through competition for light, water, nutrients, and space, some weeds can also be hosts for insect and disease pests of wild blueberry. Knowing what weed species are host to which pests is a critical step in successful weed management. To correctly identify the weeds in your field and understand their life cycle, visit the Weed ID Tool on the UMaine Extension Wild Blueberry website.

Weed Life Cycles and Their Importance

Understanding the life cycle of a weed species is necessary for effective management in wild blueberry fields. Weeds are classified as annuals, biennials, or perennials. Each weed type requires a different management strategy.

Annual Weeds

Annual weeds complete their life cycle in a single growing season. They germinate from seed, grow, flower, produce seed, and die within one year. Summer annuals germinate in spring and produce seed by late summer or fall, while winter annuals germinate in late summer or fall and resume growth the following spring.

Because annual weeds rely entirely on seed production to persist, preventing seed set is one of the most effective management strategies. Timely mowing, hand-pulling weed shoots, or herbicide application before flowering can greatly reduce future infestations.

Examples of annual weeds in Maine wild blueberry fields include witch grass (Panicum capillare), common ragweed (Ambrosia artemisiifolia), and lambsquarters (Chenopodium album).

Biennial Weeds

Biennial weeds require two years to complete their life cycle. During the first year they form vegetative growth, often as a low rosette. In the second year they flower, produce seed, and die.

Management is most effective during the first-year rosette stage before the plant develops a flowering stalk. Mowing, hand-pulling, or herbicide applications before flowering are also effective strategies for these species. Once flowering begins, seed production can occur rapidly and many seeds can then enter the soil seed bank.

Examples of biennial weeds in Maine wild blueberry fields include wild carrot (Daucus carota) and common evening primrose (Oenothera biennis).

Perennial Weeds

Perennial weeds survive for multiple years and often reproduce both by seed and vegetatively through rhizomes, stolons, bulbs, or roots. Many of the most difficult wild blueberry weeds are perennials because they can regrow even after top growth is removed. Wild blueberry is also a perennial, complicating how we can control perennial weeds. 

Repeated mowing, cutting, spot treatment, or long-term suppression strategies are often necessary to weaken perennial root reserves over time. Successful perennial weed management usually requires multiple years of consistent intervention.

Perennial weeds can be woody or herbaceous. Examples of woody wild blueberry weeds include wild raspberry and blackberries (Rubus spp.) and sweet fern (Comptonia peregrina) (Figure 3). Examples of herbaceous perennial weeds include red sorrel (Rumex acetosella), common St. Johnswort (Hypericum perforatum), and bracken fern (Pteridium aquilinum).

Integrated Weed Management

After you have positively identified what weed species are present in your field and which weeds pose the greatest production challenges, the next step is developing a plan to reduce the weed population in your field. Any plan for managing wild blueberry weeds must follow the principles of integrated weed management. 

Integrated weed management is the combination of cultural, mechanical, and when appropriate, chemical methods (pesticides) to reduce weed pressure while preserving crop health and mitigating environmental harm. The appropriate integrated weed management methods will depend on the specific weed species you are trying to manage. For example, although using sulfur to lower a field’s soil pH will work well for the management of nonnative fine-leaf sheep fescue (Festuca filiformis), it will not be an effective management strategy for native bunchberry, which is adapted to the same low pH, low fertility soils as wild blueberry.

Scouting and Weed Mapping

Regular scouting and annual weed mapping can help you track the weed pressure in your field and determine whether your management of weeds has been successful over time. 

Walking your fields and creating weed maps can be a useful exercise to learn the weed species and weed pressure in your field, which can help determine the herbicide costs by application area. For more information about how to use your smart phone to create an actionable weed map, read UMaine Extension Bulletin #2180, Weed Mapping Using Your Smartphone.

Cultural Weed Management

Cultural weed management is the act of making nonchemical production changes that reduce the vigor of weed species. These actions can be mechanical, such as hand-pulling weeds or flail mowing, or cultural methods to alter the growing environment to be less conducive to weed growth while being beneficial to wild blueberry health, such as reducing the soil pH.

Soil pH

Maintaining low soil pH is one of the most powerful cultural tools available in wild blueberry production for both organic and conventional production. Many competing weed species, especially grasses and certain broadleaf plants, are less tolerant of strongly acidic conditions.

Sulfur, applied as a soil amendment (Figure 4), is commonly used to lower soil pH. The amount of granular sulfur required depends on your field’s soil texture and organic matter, but as a general guideline, approximately 100 pounds of sulfur per acre will reduce soil pH by about 0.1 unit. Because sulfur must be biologically oxidized in the soil, pH changes occur gradually over two to three years.

Soil testing should be conducted every other year at the same time of year to monitor pH levels. Wild blueberries thrive in soils with a pH between approximately 4.0 and 4.5. Maintaining soil pH near 4.0 suppresses weed species very well without herbicide use, but reduces nutrient availability for blueberry plants. Alternatively, soil pH closer to 4.5 will be less effective for weed suppression but provide greater nutrient availability for wild blueberry plants. We recommend maintaining your field’s soil pH around 4.3 for increased weed suppression and moderate nutrient availability.

Although soil pH management as a cultural weed control method is vital for organic production, where organic herbicides show limited effectiveness, it is also an excellent tool for conventional growers to manage weeds in conjunction with herbicide applications aboveground.

Nutrient Management

Although fertilizing wild blueberry fields can increase plant yield, excessive fertilization, particularly nitrogen, can result in significant weed growth and reduce wild blueberry yields. If weed pressure in your field is high, you must reduce weeds before fertilizing. Otherwise, fertilizer will increase the vigor of not only wild blueberry plants, but weeds in the field, nullifying the benefits of fertilizer application. 

Take soil and leaf tissue samples and talk with UMaine experts to understand how to effectively fertilize your field. For more information about fertilizing organic and conventional wild blueberry fields, read UMaine Extension Bulletin #2383, Fertilizing Wild Blueberry Fields. For more information on taking leaf and soil samples, read UMaine Extension Bulletin #2382, Leaf and Soil Testing for Wild Blueberry Fields.

Mulch

Mulching is an effective cultural practice for reducing weed establishment and improving soil conditions. Wood chip mulch (Figure 5) can suppress weed germination by blocking light and creating a physical barrier. In addition to weed suppression, mulch moderates soil temperature, conserves moisture, and encourages wild blueberry rhizome spread. Mulch can also be an incredibly effective tool to manage and prevent soil erosion (Figure 6) by slowing the flow of water and holding soil in place.

Mulching can be integrated into fall management or prune-year activities, especially in areas with persistent weed pressure, poor blueberry cover, or in fields that have recently been de-rocked. For more detail on mulching wild blueberry fields, refer to UMaine Extension Bulletin #2179, Wood Chip Mulching in Wild Blueberry Fields.

Pruning

Pruning is a defining practice in wild blueberry production. Wild blueberry fields are pruned either by mowing or by prescribed burning. Both methods remove aboveground stems and reset the crop cycle.

Pruning influences weed dynamics significantly. Removing blueberry stems reduces immediate crop competition and exposes soil to light, which can stimulate weed germination. Therefore, prune-year management requires vigilance to prevent weeds from becoming established before blueberry regrowth forms a dense canopy.

Pruning should occur after harvesting plants and when they are dormant, typically after a frost event in fall or before spring growth resumes in late April. Proper pruning timing protects wild blueberry carbohydrate reserves and ensures vigorous regrowth, which enhances competitive suppression of weeds.

Burning

Research conducted in Nova Scotia indicates that 90% of witch grass, spreading dogbane, and meadow salsify (Tragopogon pratensis; also known as yellow salsify) seeds sitting on the soil surface were killed after exposure to direct flame (oil burning). Straw burning was not as effective as oil burning for killing weed seeds (White and Boyd 2016). A properly conducted burn consumes all blueberry and weed vegetation aboveground. Burning also consumes surface organic matter, which is a critical source of nutrients and water holding capacity. Therefore, it is important to consider the pros and cons of burning versus mowing as a pruning method. For more detail on how to effectively burn Maine wild blueberry fields, refer to UMaine Extension Bulletin #2096, Burning Wild Blueberry Land in Maine.

Mowing and Cutting

Pruning wild blueberry fields with a flail mower (Figure 7) may not reduce weed seed as effectively as burning fields, but mowing preserves more soil organic matter than burning. The residue left after mowing also helps to conserve soil moisture, moderate soil temperature, and protect the soil surface from wind and water erosion. Because mowing does not expose weed seeds and rhizomes to heat, some perennial weeds and grasses may recover more quickly. The combination of sulfur to reduce soil pH, herbicide application, and mowing can manage these weeds effectively.

Spot cutting or mowing weed patches repeatedly right before weeds flower can gradually reduce annual weed populations and weaken perennial species over time. Research conducted at UMaine found that cutting back saplings and woody weeds three times per season knocked weeds back significantly, slowly killing them (Drummond et al. 2012). To use this strategy, allow perennial weeds to grow almost to flower in the spring and cut them back to the soil surface. Repeat the process of allowing plants to grow and cutting them back to ground level three times a year. Growers find that cutting in May, June, and September provides effective perennial weed control and can be done in either the prune or crop production years.

Equipment Sanitation

Weed seeds, especially grass species, can be spread by harvesters as they move from field to field. Poverty oatgrass (Danthonia spicata) and fine-leaf sheep fescue produce thousands of small seeds that are easily transported on harvesting and pruning equipment and tractors (Boyd and White 2009). Consider power washing your equipment before use in a new field whenever practical to avoid spreading weed seeds, rhizome fragments, or diseases such as Valdensia leaf spot potentially present on weed species.

Hand-Pulling

Hand-pulling is a simple but effective weed management method for small infestations, isolated invasive weeds, or weeds growing in areas where mowing or herbicide applications are impractical. This method is particularly useful for weeds in bare spots, and new infestations along field edges before they spread throughout the field. Hand-pulling is labor-intensive and not practical for large infestations, but it remains an important part of integrated weed management because it allows growers to quickly target problem weeds and prevent further establishment.

Chemical Weed Management

Herbicides with U.S. Environmental Protection Agency (EPA) labels are used to chemically control weeds in conventional wild blueberry fields. Repeated use of herbicides with the same mode of action can select for resistant weeds, and as such, it is essential to rotate between herbicides with different modes of action. Once established, resistant populations are difficult and costly to control, and new herbicides must be developed to replace those no longer effective. Improper use of herbicides can also result in damage to wild blueberry plants, known as phytotoxicity (Figure 8). 

In organic fields, high concentration non-food-grade vinegar can be sprayed as a burn down herbicide. It will not kill the plants but knocks them back, similar to the action of cutting weeds above the blueberry canopy. This type of vinegar can be found at box stores and ranges from 30% to 45% vinegar, which can burn your skin. Diluting high concentration vinegar with water down to 20% will still burn down the tops of weeds.

Herbicides are an effective tool for weed management, but they should never be the only tool. In addition, spot treatments of herbicides (rather than broadcast applications across entire fields) and product rotation can reduce the potential development of herbicide-resistant weed populations. 

UMaine Extension releases an annual herbicide chart to help you identify useful chemistries and appropriate rotations. These charts are never a substitute for reading and complying with pesticide labels. You are required by law to fully read the labels of all pesticides you use. 

Weed wiping is another common method of spot herbicide application for certain wild blueberry weed species, such as spreading dogbane. Weed wipers are purchased as a tractor or all-terrain vehicle (ATV) attachment. The benefits of weed wiping are reduced drift due to physical contact with weeds allowing for more control and therefore less risk of blueberry phytotoxicity. Weed wiping does require more labor than broadcast applications, but a more targeted approach is essential for difficult weeds that grow in patches, such as spreading dogbane and sheep laurel.

Seasonal Weed Management Strategies

Weed management strategies must change throughout the year because weed growth, blueberry development, and management goals vary by season. Weed susceptibility to management varies throughout their life cycle, and blueberry plants compete differently with weeds depending on whether the field is in the prune year or crop year.

Spring

In spring of the crop year, weed control focuses on early emerging annuals and perennials before flowering. Rapid blueberry canopy development is desirable to shade the soil and suppress weed germination. Pre-emergent herbicides and sulfur are applied in the spring of the prune year. Early intervention is especially important because blueberries have not yet formed a competitive canopy and even ground coverage is important for sulfur and some herbicides. Spring is also an excellent time to walk your fields and create weed maps of emerging weed patches.

Summer

During summer, weed management emphasis lies in preventing seed production. Weed whacking or weed wiping above the blueberry canopy before they flower reduces weed seed additions to the soil seed bank. Repeated removal of weed tops can also be effective at weakening root reserves.

Summer management must be timed carefully in crop years to avoid interfering with pollination or harvest operations. Weed wiping with herbicides is allowed only in the prune year.

Fall

Fall weed management is particularly important and historically underused. After harvest, many weeds continue to grow and set seed due to the warmer weather we now experience through October. Left unmanaged, these seeds fall to the soil and increase future weed pressure. Fall is also a critical period because many perennial weeds move carbohydrates and nutrients into underground roots and rhizomes in preparation for winter dormancy. Management during this period can weaken perennial weeds before the following growing season.

Postharvest mowing or cutting should occur before weeds set mature seed. Removing flowering stalks before seed maturation helps reduce additions to the soil seed bank and lowers future infestations. Fall is also an excellent time for sulfur application to adjust soil pH. 

Herbicide application in the fall depends on the EPA label, which is written for each specific chemistry. While weeds are still green, herbicides will be absorbed into leaf tissue. Herbicides used to control fine-leaf sheep fescue are effective in the fall under specific conditions outlined on the label. Fine-leaf sheep fescue also thrives in higher pH wild blueberry soils (where soil pH is above 4.5) and often becomes more problematic where blueberry cover is thin (Figure 9). Because of this, fall sulfur applications are one of the most effective long-term cultural management tools for suppressing this weed.

Conclusion

Weed management in Maine wild blueberry production is a complex, multiyear process that must be integrated with soil pH control, nutrient management, pruning strategy, herbicide rotation, and seasonal timing. Maintaining acidic soil conditions, promoting vigorous blueberry growth, preventing weed seed production, and applying mechanical or chemical controls strategically are all essential components.

Organic systems depend heavily on ecological approaches such as sulfur application, mulching, burning, and repeated cutting. Conventional systems must guard against herbicide resistance through rotation and integration of nonchemical methods.

Fall weed management deserves particular emphasis because it reduces future seed banks and improves spring conditions. By approaching weed control as a year-round, integrated process, growers can sustain productive, resilient wild blueberry fields for many years to come.

References

Boyd, Nathan S., and Scott White. 2009. “Impact of Wild Blueberry Harvesters on Weed Seed Dispersal Within and Between Fields.” Weed Science 57 (5): 541–46. https://doi.org/10.1614/ws-08-156.1 

Drummond, Frank, John M. Smagula, David Yarborough, and Seanna Annis, S. 2012. “Organic Lowbush Blueberry Research and Extension in Maine.” International Journal of Fruit Science 12 (1–3): 216–31. https://doi.org/10.1080/15538362.2011.619132

White, Scott N., and Nathan S. Boyd. 2016. “Effect of Dry Heat, Direct Flame, and Straw Burning on Seed Germination of Weed Species Found in Lowbush Blueberry Fields.” Weed Technology 30 (1): 263–70. https://doi.org/10.1614/wt-d-15-00103.1

---

Information in this publication is provided purely for educational purposes. No responsibility is assumed for any problems associated with the use of products or services mentioned. No endorsement of products or companies is intended, nor is criticism of unnamed products or companies implied.

© 2026

Call 800.287.0274 (in Maine), or 207.581.3188, for information on publications and program offerings from University of Maine Cooperative Extension, or visit extension.umaine.edu.

University of Maine Cooperative Extension is an equal opportunity institution and provider committed to nondiscrimination. For more information, visit extension.umaine.edu/nondiscrimination.