Date of Award

Winter 12-2021

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)


Plant, Soil, and Environmental Sciences


Lily Calderwood

Second Committee Member

Ellen Mallory

Third Committee Member

Yongjiang Zhang


Wild blueberry (Vaccinium angustifolium Aiton.) cropping systems are considered resilient to environmental changes due to ecological and genetic diversity within each field. However, wild blueberries can be sensitive to weather fluctuations that cause extreme temperature or moisture regimes. Climate change in Maine is represented by increasing rates of warming temperatures, more intense precipitation events, and more frequent atmospheric “blocking” patterns. Warming temperatures result in the northward expansion of pest ranges and altered growing seasons. More extreme rainfall events lead to damaged plantings and soil erosion. Atmospheric blocking leads to an increased likelihood of heat waves and drought. Two experiments were conducted over one production cycle to identify potential management strategies that can help wild blueberry growers mitigate drought and pest challenges in Maine.

The purpose of the first experiment was to determine the effect of wood mulch particle size on wild blueberry soil, plant growth, pest pressure and yield. Four mulch treatments representing four different particle sizes were applied at a thickness of 1.27 cm in an organic wild blueberry field in Stockton Springs, ME. Treatments from smallest to largest were sawdust, shavings, bark mulch and wood chips. No mulch treatment retained significantly more soil moisture than the control. All mulch treatments significantly reduced disease compared to the control in year one. Sawdust and shaving treatments, the two smallest particle sizes, resulted in the greatest yield. These results indicated that wild blueberry growers should consider smaller particle sizes rather than the traditional wood chip mulch when choosing a mulch type to apply.

The purpose of the second experiment was to measure the effect of diammonium phosphate (DAP) fertilizer application on a more recent pest of wild blueberry, the blueberry gall midge (Dasineura oxycoccana Johnson). This pest has been observed in high densities where there were high soil and foliar nutrient levels in both wild blueberry and cranberry (Vaccinium macrocarpon Aiton.) systems. This study was conducted in two conventional wild blueberry fields in Jonesboro and Washington, ME. The effects of treatment combinations of DAP application with galling on wild blueberry soils, plant growth and yield were recorded. Gall density was significantly greater in fertilized plots during the prune year in Jonesboro and both years in Washington. Foliar percent nitrogen and phosphorus had a significant positive linear relationship with gall density. Stems with galls and without DAP applied were significantly shorter and had fewer buds per stem compared to fertilized stems without galls at both sites. Stems without galls and with DAP applied had the greatest number of buds, flowers, and berries per stem at the Washington site. Mean stem height and total yield at this site were greater in fertilizer treatments even when galling was present. It is important for growers applying fertilizers to monitor field infestation levels due to our findings that DAP fertilizer impacted the economic thresholds for this pest and DAP fertilizer combined with galling impacted blueberry development and yield.

Both studies provide essential information for wild blueberry growers to make more informed management decisions when the effects of climate change make such decisions increasingly difficult as weather trends become more unpredictable.