Weed control in low-input or organically grown wild lowbush blueberries

Weed control in low-input or organically grown wild lowbush blueberries

Summary

Wild blueberries (Vaccinium angustifolium) are a crop with significant cultural and historical significance to the northeast, but are facing considerable competition from Little Bluestem (Schizachyrium scoparius), a weed present throughout Maine and New Hampshire. Due to the nature of most wild blueberry fields (shallow, low fertility, sandy) using conventional herbicides is not a sustainable practice as it poses a significant risk to local water bodies and drinking water. We worked with 2 landowners who were facing significant Little Bluestem pressure to address these concerns using a sulfur treatment. We received overwhelming support from the two landowners who would prefer their land to be managed organically. Additionally the two farmers who manage and harvest the two properties were very interested in this project as they felt there were no options available to them. We were even given a donation for additional sulfur from one landowner to do more replication of the sulfur study in another field, due to their interest in this management.

We seek to measure any impact sulfur-controlled pH of soil along with Nitrogen fertilization has on weed pressure in blueberry plantints.

Objectives/Performance Targets

Two on-farm replicated trials were conducted in 2014 at two different low bush blueberry fields. There is significant weed pressure at both sites. On 6/10 and 6/16 plots were set up at each site. Plots measure 10 feet by 100 feet long and are replicated 4 times at each site. The four managements are low-pH, medium-pH, low-pH with nitrogen fertilizer, and control. Low-pH plots received enough sulfur to reduce the pH to 4.0 while 4.5 was the medium pH target. In June plots were set up, soil samples were taken, weed evaluation was done prior to sulfur application, and sulfur was applied. In October, plots were visited again and weed evaluation was done. We used a 2-foot square 5 times in each plot to measure weed size. We also rated the abundance (1=not severe, 10=very severe) in each plot during the spring (pre-management) and fall (post-management).

As this was a non-fruit year at both sites, we did not take foliar tissue analysis or record yield data on the blueberry crop. Both of these analyses will take place during the 2015 season.

Accomplishments/Milestones

• June 6/16: Plots laid out by extension specialists at two sites
  • Sulfur applied, & weed data collected throughout the 2014 season with assistance from growers. Yield, & plant tissue analyses was not taken in 2014 as it was a non-fruit year, but will be done in 2015
• September/October – numerous conversations with two growers about results of sulfur study
• October 10/16 – fall weed evaluation done
• December – presentation to landowner about 1^st year results

Comparing the spring and fall weed evaluation has shown some differences by management. While this was easy for us to note visually looking at the plots, the data shows the control plots (no management) have more weeds and they are of larger size. The plots receiving sulfur showed similar size & number of weeds in the fall as in the spring. Additionally, we noted an increase in vigor and productivity of weeds in the plots receiving nitrogen fertilizer in addition to lower pH. The weeds that received nitrogen looked healthier and were producing more seed heads. We understand sulfur will not kill the weeds outright, but are hoping this management will slow their development, especially production of vigorous and numerous seed heads. In year two we will continue to monitor weed development throughout the plots at both study areas.

We are also looking into sulfur application directly to little bluestem plants, as opposed to uniform (broadcast) application over the field as we did in the study. We believe direct application at a high rate of sulfur will be a more effective management tool and are interested in evaluating this method.

Impacts and Contributions/Outcomes

Collaborators: