In the 1800s, commercial hop growing was well-established in the Northeast, but by the late 1920s, downy mildew, DM (Pseudoperonospora humuli) devastated the industry and drove hop production to the more arid Pacific Northwest, where commercial hop production in the US remains concentrated, with over 93% grown there (USDA, 2010), almost all using conventional methods.
A resurgence of hop growing in the Northeast has occurred, with over 300 acres strung in 2015 in Maine, New York, and Vermont (USA Hops, 2015). There is also a heightened interest in organic hop production since a 2013 National Organic Standards Board rule change requiring that all organic hops be used in USDA-certified organic beer (Turner, 2011).
One of the biggest challenges continuing to face east coast growers is effective control of DM, which thrives in moist environments typical here. Severe DM infections can result in total crop loss, and intermediate cases result in reduced yield and quality. Extension recommendations advise on best IPM strategies, including planting resistant cultivars and disease-free rootstock, hopyard sanitation, crowning to remove infected buds, hilling, using drip irrigation, stripping the lower bine, weed management, and fungicide.
Removal of new spring growth along with the top of the plant crown, a practice called “crowning”, helps to remove DM inoculum, and is standard in many areas of the US. However, the shorter growing season in the Northeast means there is less time for plants to reach the trellis. This trade-off was investigated in a 2015 crowning trial at UVM, where early crowning (pre-shoot emergence) positively impacted yield, though there was no impact on DM incidence and reduced yield when crowning occurred post-shoot emergence. It is unclear whether crowning is worth employing in our even shorter northern Maine climate.
Controlling weeds effectively also reduces DM incidence and increases hop yield. Using sheep to graze a hopyard can aid in weed management, sucker pruning, lower bine stripping, and some added soil fertility. In New Zealand, where the majority of the world’s organic hop crop is produced, using sheep that are removed for the last two weeks prior to harvest is a standard practice. Two complicating factors for US organic growers are: 1) the best OMRI-approved fungicides cannot be used since they are copper-based and toxic to sheep, and 2) sheep can generally not be used within certified-organic hops due to current rules that require a 90-day period between any manure application and harvest, though some growers have been granted exemptions and this rule may be updated (Sirrine, 2014).
Another option for weed control is organic herbicides that are effective for use around a perennial crop like hops. UVM trialed Avenger, a citrus-based concentrate that attacks the plant cuticle, which produced good results in weed reduction and increased hop yield (Darby, 2014); however, it is relatively expensive to use on a commercial scale and ineffective on established mature perennial weeds.
The common organic practice of mechanical cultivation requires precision, is time-consuming, and may not get at all weeds effectively.
In order to assess whether effective weed control significantly reduces DM presence and economic loss, we will compare the relative rate of DM infection at eight key points in growing season, from spring through harvest in two hop varieties (Centennial: susceptible to DM infection, and Cascade: moderately resistant) using three experimental treatments: 1) sheep-weeded hopyard with no copper but a Regalia biofungicide spray, 2) organic herbicide, also with a copper-based fungicide and Regalia , and 3) a control plot with no sheep or organic herbicide, but with hand-weeding and lower bine stripping, also with copper and Regalia. For a third hop variety, Nugget (susceptible to DM) we will compare the organic herbicide and control groups only. In addition to quantifying relative DM presence in each group, we will measure hop yield at harvest time, and quantify material and labor costs associated with each management practice to compute per acre costs, and assess the trade-offs of each practice.
In order to assess whether effective weed control and DM management practices significantly
reduce DM presence and economic loss, we will compare the relative rate of DM infection at four
key points in growing season, from spring through harvest in two hop varieties (Mt. Hood:
susceptible to DM infection, and Cascade: moderately resistant), crowned or not, using three
experimental treatments and control as each set of split plots: 1) sheep-weeded hopyard with no
fungicide, 2) organic herbicide plus fungicide, and 3) fungicide only, and 4) a control plot with no
sheep or organic herbicide. In addition to quantifying relative DM presence in each group, we will
measure hop yield at harvest time, and quantify material and labor costs associated with each
management practice to compute per acre costs, and assess the trade-offs of each practice. If
reduction of weeds and lower bine leaves effectively controls DM, then farmers could determine if
organic herbicide (expensive), or sheep (not allowed under organic certification) are worth
employing over less expensive cultivational practices alone, or in comparison to the environmental
concerns of copper-based fungicide. Thus, the solution may inform both organic certified and
non-certified hops farmers to maximize yield/profit with environmental concerns.
Our experiment will be conducted within two sections of our 5-year old, 3-acre hopyard. We will quantify DM presence and hop yield in two varieties (Mount Hood: susceptible to DM infection, Cascade: moderately resistant) under three experimental treatments and one control: 1) organic herbicide, with copper-based fungicide and Regalia, 2) normal mechanical cultivation and hilling, with copper-based fungicide and Regalia, 3) a sheep-weeded hopyard with no fungicide, and 4) control group that is normally cultivated, but will not receive any additional weeding, bine stripping, or fungicide, with each group also 1) crowned in early spring or 2) not crowned. A split-plot design will be used with variety X crowning as the whole plot, and each of the 5 treatments assigned randomly to one split plot – across the rows within a variety (and crowned or not). Since rows are 250’ long, split plots will be roughly 50’ in length across multiple rows. All measurements will be taken from randomly selected plants in the middle 14’ of each split plot, which provides at least 18’ of buffer between split plots or edge. Where necessary, a backpack sprayer will be used instead of the tractor-mounted sprayer for more precise spraying to protect buffers. All rows are on the same soil type, CgB, and are similar in other environmental attributes.
In 2017, we will fence part of our west hopyard for sheep to control sucker growth, lower bine leaf stripping, and weeds between hop plants. A neighboring sheep farmer, William Jordan, will lease us 10-14 adult sheep to intensively enough graze this area. Mr. Jordan and Aroostook Hops will fence and move animals, and routinely check on the sheep and fencing. We will fence in experimental plots with ElectroNet 9/35/12, as well as corner support posts, an AC/DC IntelliShock10 energizer, and a ground rod (Premier 1 Supplies). A separate 75’ x 75’ area will be created using more permanent Permanet 10/48/6 fencing to move sheep out of the hopyard when needed for routine activities like spraying and harvesting, or to temporarily remove animals that may be problematic in the hopyard. This sheep-grazed hopyard will be sprayed with Regalia only and not copper.
The organic herbicide treatment will use the non-selective, post-emergent herbicide Avenger, with citrus-based d-limonene, which strips away the plant cuticle, causing dehydration and plant death. This herbicide will be applied three times throughout the growing season by backpack sprayer, on weeds that occur in the 3’ space between plants within rows, as well as the bottom 3’ of the hop bine to remove leaves. The first application will occur as soon as stringing is complete in late May (on weeds only), by the second or third week of June, and again in mid-July.
The crowning will be done in early spring (typically late April) just after snow has melted enough to crown the plants using a heavy duty Stihl combitool, with metal blade to cut into the plant and soil by roughly one inch.
The control plots will not have any fungicide, and will receive only standard mechanical cultivation and tilling at the edges of hills, and include both crowned and non-crowned plants.
We will compare the relative rate of DM infection at key points throughout the span of the growing season: 1) when shoots are emerged 6”, 2) when plants have reached the top of the trellis (18’ high), 3) pre-harvest, and 4) in the rhizosphere of the soil in October, after harvest.
Shoots will be collected when they are around 6 inches high. Sampling leaves will be done at the lower part of the plant where DM is most present, for both collection #2 and #3. Rhizosphere soil samples will be collected by taking a soil core containing root material, shaking off any excess, or bulk soil, and collecting the soil that remains on the root material. A sampling unit will consist of ten shoots/leaves/soil samples from two bines of two adjacent plants, and five replicate samples per group will be collected into Whirl-Pak sterile sample collection bags, placed on ice, then stored at -20C.
Hop DM presence and relative abundance will be quantified with qPCR to count the number of gene copies in a sample. Leaf samples will be homogenized, DNA will be extracted using a PowerPlant Pro DNA Isolation kit (No Bio Laboratories, Inc.), and qPCR will be done using AccuStart II Gel Track PCR Super Mix (Quanta Biosciences). The number of gene copies of hop downy mildew will allow us to determine if there are differences in abundance that can be attributed to treatment, time of harvest, or hop variety. Dr. Larry Feinstein, along with Jason, will conduct the laboratory work and Krista and Jason will analyze the data using ANOVA and summarize results.
Hops scouting will also be conducted on the same bines sampled for qPCR for DM, on the same day as leaves are collected. We will record presence or absence of DM per bine, number of basal spikes per bine, and percent of collected leaves showing evidence of DM. Weekly rainfall and temperature data will also be collected.
At harvest, the hop yield (grams) of 10 bines per treatment will be collected to compare yield to level of DM infection.
We successfully collected all field measures, as proposed, with the exception of measuring hops yield in Mt. Hood. The August drought combined with heavy hop aphid and potato leafhopper pressure decimated this variety. We did however measure the whole plants to salvage some data to compare treatments. Soil and plant samples are awaiting the laboratory assays, which we should complete in January. Afterward, data analyses and report-writing will be conducted. We will have results at this point.
No conclusions yet, except, anecdotally it was very clear that the sheep-grazed hops had much better plant health and vigor!
Education & Outreach Activities and Participation Summary
- MOFGA Aroostook Tour tour (June) – 30+ people with diverse constituency had a tour of our farm with discussion of organic hop farming generally, and discussion of the experiment and challenges of sheep in organic farms.
- Aroostook Hops Field Day (September) – 15 people had a tour of the farm, harvesting, oasting, pelletizing, and packaging operation.
- Guest lectures at UMaine-Presque Isle (2): Plant Biology course, and Agribusiness Management course.