Scaling up on-farm drying equipment for Elderflower and other perennial herbs in the Upper Midwest.

Effects on Spotted Wing Drosophila 

As part of the grant project, Sharing Our Roots staff conducted both observational and trap based surveys of Spotted Wing Drosophila (SWD) in their elderberry field. Observations were collected weekly to coincide with existing harvest days throughout the normal harvest season in 2020, 2021, and 2022. Traps were used in 2021 only to allow for the positive ID of SWD as well as other drosophila species that were present. A summary of results is presented below followed by a brief analysis of trends.

2018: Suspected SWD first observed by staff in elderberry field. SWD was likely present prior to 2018 but no existing staff member was trained to ID the pest. Harvest had also previously been intermittent so effects on berry quality had not been significant to harvest yields. In 2018 there was a noticeable degradation of expected harvest quantity and quality when compared to published standards and yields by other growers. The berries were immediately frozen post harvest in accordance with Midwest Elderberry Coop standards but ultimately were unfit for sale. The primary concern was the flavor and sugar content appeared to have been heavily affected by SWD infestation.

2019: Due to the previous year's harvest failure the decision was made to not expend any staff time on harvesting berries for market. A small amount of the fruit was harvested as U-Pick by a handful of customers who were willing to sort the available fruit to maintain quality standards. As a result of this 2019 had the most significant infestation of SWD of any year from 2018 onwards. At any given time during the active fruiting season there was SWD present on each berry observed. SOR staff also constructed a small forced air dryer from plywood and a leaf blower as an initial test of drying elderflower. Weather conditions were highly favorable for SWD throughout the season. Ample rain and relative humidity fostered near perfect conditions for the lifecycle of SWD.

2020: In 2020 baseline monitoring of SWD was begun by SOR staff. The initial goal of monitoring was to positively identify SWD alongside other drosophila species. At a glance it can be difficult to distinguish between them and as the season progresses the prevalence of other drosophila species increases. The first field observation was conducted the same week as the first flower harvests; the last week of June. At that time no significant infestation was observed. At our site the majority of the harvestable flowers are available over a three to four week period. In that time roughly 60% of the harvestable flowers were removed completely from the field. The first observation of SWD came in mid-July and coincided with the beginning of fruit set in the elderberries. This observation indicates that early and timely harvest alone would not be sufficient in avoiding damage from SWD as the flies are appearing prior to any fruit becoming fully ripe. This is an issue unique to SWD as most other drosophila species would be unable to cause significant damage in unripe fruit. The presence of other host plants, including wild elderberries, in the immediate area of our farm allows for SWD to proliferate prior to the elderberry harvest. It did appear that as the season progressed the volume of SWD present began to decrease. Regular observations were not conducted after the commercial harvest period was over but field walks in late July and August saw fewer drosophila on the remaining crop. Environmental conditions and a reduction in host fruit are believed to have played a key role in a decrease in SWD present. A small flock of sheep was also allowed to graze the elderberry field after the harvest had been completed. The goal was to reduce low lying vegetation around the plants that various pests utilize.

2021: There was a significant reduction in SWD observed in the field in 2021. Traps showed an overall decrease in drosophila present, not just SWD throughout the season. Salt bath tests observed no drosophila larvae at the time of initial fruit set. A goal of harvesting 75% of the flowers was established at the beginning of the season and was nearly met. A handful of rows of elderberry were also removed prior to the start of the season. The goal of doing so was to increase airflow around individual plants and decrease the amount of vegetative habitat around the base of the plants. The low, moist, and stagnant area around the base of the plant is perfect habitat for SWD larvae and adult flies to reproduce. June 2021 also saw incredibly high temperatures. The two weeks leading up to the initial harvest had day time temperatures averaging over 90 degrees at the farm. SWD is highly sensitive to temperature for its breeding cycle. Roughly 70 degrees is the optimal breeding temperature and as temperatures increase above 90 degrees their ability to reproduce drops off significantly. The summer of 2021 also was at the beginning of a significant drought affecting both commercial crops as well as wild host species. This combination of environmental factors is likely the primary contributing factor to a reduction of SWD observed in the field. Starting a few weeks after the fruit set, evidence of SWD began to be visible. Most umbels had some evidence of fruit fly damage but not all berries appeared to be affected.

2022: A continued decrease in SWD presence was observed in the field. The entire crop appeared to be highly affected by the continued drought reducing the total number of flowers and the duration of plants setting new umbels. An interesting impact of the drought appeared to be an increase in early fruit termination. Many of the plants exhibited increased water stress that resulted in fruit being aborted prior to reaching full ripeness. Even the few berries that appeared to reach maturity had no sugar development and were smaller than previous years. The vast majority of the fruit in the field never made it to this stage though. As a result no SWD was observed in the field at any point in the season. As SWD specific traps were not utilized this year we do expect some flies were present, just not on the plants and berries observed. The total harvest of flowers appeared to be depressed throughout the season. Many plants will continually produce new flowers until August but very few did so in 2022. Anecdotally it appeared there was a 90% reduction in late season flowers compared to previous years. The impact of this on future years' SWD presence is not entirely known but we expect a continued suppression of SWD populations for the next few years as a result of this.

Dryer Description

The dryer is made up of a 20’ shipping container. We chose a used unit that was in near new condition with good working doors, intact air seals, and clean interior. To convert it to a dryer we added 6 one-way 4” air vents along the top of the walls of the container. These vents included bird screens to prevent pest intrusion. On the floor we installed a custom cut grain bin floor with 0.05” perforations. We also used the supplied floor support system though we would recommend having the floors cut to the width rather than the length of the dryer and simply using stand 2x6 framing lumber to support the floor. Or initial design utilized a transition to pull air from outside the container in through a hole that was added on the back wall of the container. The hole was cut such that the fan discharge was underneath the bin flooring. One of our major adjustments was to remove the transition, block the hole and move the fan inside the container. This eliminated the introduction of excessively moist air and significantly reduced the volume of the dryer from the outside. A dehumidifier was also added to reduce the interior humidity and help in the drying process. Various other shelves and bins were utilized to maximize the available space in the dryer.

Botanical Drying time and yield results.

2020

In 2020 we did not collect significant harvest or drying time records. Our primarily goal was to run small batches of a variety of products through the dryer to observe what happened with each. We watched temperature and humidity most closely and used that insight to make changes for the 2021 season

2021

Expected drying time and fresh-to-dry ratio varied significantly between different crops. The chart below shows the recorded fresh and dry yields for each of the crops monitored for the project in 2021. Both Red Clover and Feverfew were excluded from the average ratio as records were incomplete for both these crops. The dry yield figures also include shrinkage from the final sifting stage of the crop. This step was primarily to remove stems and foreign material from the crops where needed. Some crops needed no removal of stems as the entire plant was marketable thus increasing the ratio. 

Environmental factors like humidity at harvest, wind speed, temperature, and time of day all also contributed to yield ratios and drying time but are not effectively captured in the data. Harvest time and duration was primarily affected by staff availability and not optimum timing for maximum yield. Harvest technique also played a role in the ratio but that information was not recorded as part of this grant.

Each crop was harvested an average of 12 times throughout the season suggesting that a variety of environmental conditions were experienced during harvest. The only conditions that were never experienced was during or immediately after a rain event. Plants were checked to confirm no surface moisture was present prior to harvest.

Most crops on average had dried to storage safe moisture contents within 48hrs of entering the dryer. As the ambient temperature increased throughout the season the drying times fell to as little as 24 hrs for light and thin crops while climbing to three to five days as temperatures decreased in the fall. The key factor in preventing damage to the crops was humidity fluctuations in the dryer itself. Our initial dryer design that we used in 2020 was pulling air in from outside the container 24/7 but for 2021 we altered the dryer configuration to recirculate the air already in the dryer.

2021 Harvest Data

2022

In 2022 Sharing Our Roots began the process of transitioning their botanical production to one of the farmers participating in their land access program. Delanie Harrman of So Below Apothecary, who previously had worked for Sharing Our Roots Farm, assumed production and drying responsibility for the existing botanicals on-site as well as introducing new crops as part of her business. Included is a summary of her 2022 season including information about dryer management, observations, and harvest dry down ratios.

General Overview

In 2022, I grew over 18 varieties of aromatic and medicinal botanicals to dry in Sharing Our Roots custom dryer.  Overall, the dryer worked well to dry the botanicals just as it did last year and I would recommend this set up to botanical farmers. However, I identified three major improvements that could be made to the dryer, which are maintaining consistent temperature, lowering humidity, and organization. Below I will also include proposed solutions for 2023 to increase drying efficiency and yield. 

Temperature

The dryer was operated from June 3, 2022 through October 15, 2022, and outside temperatures ranged from 30°F - 94°F.  Inside the dryer would average 7 degrees higher than the outside temp, but this could be lower if there were consecutive cloudy days, and higher for intense sunny days.

The first, and biggest, issue faced this year was the temperature of the dryer.  Temperature fluctuations would speed up or slow down the drying process by several days, leading to an unreliable harvesting schedule.

The dryer worked best when outside temperatures reached at least 78°F, and higher temperatures resulted in faster drying, improving overall yield. In southern Minnesota, this gave me about 3 months of ideal drying time, but the season in which to harvest botanicals can last around 5 months.  

I found the majority of botanicals I grew this year dried best at  90°F - 95°F. At this temperature, the color and aroma stayed intact, and they dried quickly.  A small heater in the dryer would help maintain consistent temperatures throughout the season, and add season extension to include early season botanicals (eg. dandelion greens and flowers, stinging nettle) and frost hardy herbs (eg. calendula, mint).  This year we experienced an early frost, and everything that was in the dryer was lost due to inefficient temperatures outside, and this could have been easily prevented with a sufficient heater.

Humidity

To control humidity within the dryer, a dehumidifier was run continuously, set at 30% humidity.  A hose was installed in the dehumidifier so it could run at all times, without the need to empty it.  Impacts on the humidity in the dryer included rain and general humid weather, but nothing incredibly significant.  The biggest impact was created by fresh plant material placed in the dryer, which would spike the humidity.  

Organization

This year the dryer was fit with two different types of shelving on which to dry botanicals.  One side was lined with bread racks, used to dry flowers and botanicals with low water content, such as calendula, elderflower, and echinacea leaf/flower.  The bread trays were 6” deep, so a single layer of flowers lined the bottom of each tray to promote air flow.

The other side of the dryer was fitted with three 48” NSF food safe epoxy wire shelving.  The individual shelves were spaced 15” apart to accommodate large botanicals.  Herbs with a high water or essential oil content, such as anise hyssop, tulsi, and sage, were evenly layered 3”-8” thick when fresh on the racks.  As the botanicals shrunk during dry down, they were spread out again to promote faster dry time.

Both shelving systems worked well when used as outlined above.   The bread racks were especially nice as they kept all the botanicals fairly confined. There was minimal loss in terms of plant material falling to the floor and becoming contaminated with other plant material.  

The epoxy shelves resulted in some loss of plant material, as the space between the wire allowed material to drop to the floor.  Though the floor under the racks is also a food safe space, this year I dried a different species of botanicals on each of the racks, and all three botanicals would fall to the floor, mix together, and contaminate one another.  

Next year I will do a big harvest of one botanical species to fill the epoxy racks with at a time, so that way I can also utilize the floor space under the racks and increase my yield. 

Botanical Drying Results