Development of pest and nutrient management strategies for hop production in the Northeast

2017 and 2018 Germplasm Results

In 2017, the germplasm lines appeared to differ in their susceptibility to pests (Figure 1). Although these data were not analyzed for statistical differences, it is worth noting the observed differences in pest populations across the varieties. Two-spotted spider mites were only observed on two of the varieties while HA and PLH were present on all varieties. The variety Wolcott 001 had the highest populations of PLH averaging 2 insects per leaf while the next highest variety, Wolcott 002, averaged only 0.5 insects per leaf. The highest HA populations were observed on the variety Morris which averaged about 4.5 aphids per leaf. As we continue the study, we plan to continue to measure the impacts of these various insects on hop quality and yields, and hope to observe any variations in cultivar susceptibility.

In 2018, we also experienced adverse reactions to a combination of pesticide applications which resulted in severe plant damage to a large portion of plants. Champ was sprayed at 2 lbs ac^-1 in conjunction with Regalia at 1qt ac^-1 diluted in 50 gal of water.  This resulted in severe leaf and cone damage, impacting the survival of a number of the wild hops (Figure 2). While each of the wild hop varieties were adversely affected by the combination of these two fungicides, the hops growing as part of our commercial variety trials showed no phytotoxic effect. This may indicate that these hop varieties are far more susceptible to phytotoxicity caused by certain types of fungicides.

Hop varieties also differed in yield and harvest characteristics (Table 2). While all plots were harvested at similar dry matter contents, the varieties Wolcott 001 and Northfield 001 were harvested one week earlier than the others suggesting faster maturation rates. The highest yields were obtained from the variety Morris, which produced approximately 456 lbs ac^-1. Although these data were not analyzed for statistical differences, it is interesting to note the observed differences in first year production across the varieties. Wolcott 001, although reaching maturity about 1 week earlier than the other varieties, produced less than 100 lbs ac^-1. Varieties Wolcott 002, Kingdom 001, Kingdom 002, Northfield 003, and Peacham 002 were not harvested.

Interestingly, the varieties Morris and Mount Toby produced relatively high yields but also exhibited severe cone browning and damage. We will continue to monitor these differences as plants are monitored in future years.

Table 2.  Harvest characteristics by variety.

+ Cones were also rated in browning severity on a 1-10 scale where 1 indicates low browning and 10 indicates severe browning.

Hop varieties also varied dramatically in acid content and oil profiles (Table 3 and Table 4). Wolcott 001 and Argyle had similar concentrations of alpha and beta acid while Morris had significantly more alpha acid than beta acid. The opposite was true for Peacham 001 and Northfield 001. Argyle and Peacham 001 also had about double the oil content of the other varieties.

Table 3. Wild hop variety acid content.

In addition to basic quality parameters, the varieties also differed in oil profile (Table 4). Argyle and Morris produced the highest alpha levels compared to the other varieties. Peacham produced the highest beta acid levels and total oil concentrations.

Table 4. Hop aromatic oil profiles.

Table 5 summarizes the aromatic oil profiles of the harvested varieties. Each harvested variety has distinct oil compositions, which has the potential for new uses or substitutions in the brewing process. Table 5 provides a brief sensory description of individual oil characteristics.

Table 5. Oil characteristics.

2019 Germplasm Study Results

The germplasm lines appeared to differ in their susceptibility to pests (Figure 2). Although these data were not analyzed for statistical differences, it is worth noting the observed differences in pest populations across the varieties. With the exceptionally dry and hot summer in 2018, we noticed much higher populations of two-spotted spider mites compared to other pests. This year, Peacham 002 had the highest levels of TSSM with an average of 4.15 TSSM per leaf whereas Mount Toby had the lowest with only 0.6 TSSM per leaf. Hop Aphids (HA) and Potato Leaf Hoppers (PLH) were both observed in very low numbers throughout the ten germplasm varieties with Wolcott 001 having the highest average of HA per leaf at 0.82 and Peacham 002 at 0.35 pests per leaf for PLH. As we continue the study, we plan to continue scouting germplasm varieties on a weekly basis and hope to observe any difference in cultivar susceptibility.

In 2018, we measured the height and side arm lengths of 6 bines out of the 14 bines present in each plot (Figure 3). The length of 4 side arms on each of the 6 bines was measured. Overall, Kingdom 001 had some of the smallest plants with the lowest average plant height and side arm length. Northfield 003 and Argyle had the greatest average bine height at 4.87 m and Peacham 002 had the greatest average side arm length at 58.2 cm.

Hop varieties also differed in yield and harvest characteristics (Figure 4, Table 6). This year due to harvester constraints, the germplasm varieties had to be harvested on the same date instead of during ideal harvest periods based on aroma and dry matter. The plant yields are also for first year plants as the germplasm was once again propagated and replanted into a new hopyard. With these factors taken into consideration, Mount Toby showed highest first year yields at 370 lbs ac^-1 whereas Kingdom showed the lowest yields at 71 lbs ac^-1. Higher yields should be expected in subsequent years.

Table 6. 2019 Harvest characteristics by variety.

†Cones were also rated in browning severity on a 1-10 scale where 1 indicates low browning and 10 indicates severe browning.

In 2018, disease pressure was very low resulting in less browning throughout each of the ten harvested germplasm varieties. Despite having to harvest these wild hops at the same period, most fell within reasonable ranges if using dry matter as the sole means of determining harvest period.

Hop varieties varied dramatically in alpha and beta acids. In addition to varietal variability, hops also have potential to be influenced by various growing conditions such as fertility, temperatures, precipitation, disease pressure and many others, impacting their profiles.

Both Kingdom and Peacham samples showed some very close similarities this year in alpha and beta acids (Table 7). These two groups could be similar varieties as they were collected from similar areas, although genetic testing would need to be conducted to determine similarities or differences in the varieties.

Table 7. 2019 Wild hop variety brew quality.

This year we were also forced to switch labs, adding another variable into the equation making it difficult to compare between years as processes differed slightly. In addition to the switch, samples molded while in possession of Alliance Analytical and samples were not able to be run accurately for essential oil profiles.

In addition to lab difficulties, hops had to all be harvested at the same time in 2018. In 2017, Wolcott 001 and Argyle were harvested on 7-Sep, whereas Northfield 001, Morrisville 001, and Peacham 001 were all harvested a week later on 15-Sep. In 2018, all varieties were harvested on 5-Sep. In 2018, the hot and dry conditions from the season could have impacted the resin and oil profiles in addition to our necessity to harvest plants early this season. There is the potential that cones did not have the chance to fully develop resins or fully develop their essential oil profiles as a result of growing conditions or other circumstances. While we were able to have these samples analyzed for brew quality, samples did not have the chance to be accurately analyzed for essential oils and we were not able to compare these varieties with last years results.

2017 Crowning Study Results

Table 8. Temperature, precipitation from 2017.

In the 2017 growing season there were an accumulated 2411 Growing Degree Days (GDDs) this season, approximately 199 more than the historical 30-year average (Table 8). 2017 proved to be the wettest year throughout our five year study putting hops at a much higher risk for disease infection for a large portion of the growing season. During critical growth and development periods we experienced rain events averaging 7.39 inches above our 30-year averages despite having late summer months that began to taper off.

Table 9. Temperature, precipitation from 2018.

In the 2018 growing season there were an accumulated 2688 Growing Degree Days, 477 more than the historical 30-year average. 2018 was unusually hot and dry accumulating far less rain during the bulk of the growing season (May-Sep) than the average year. Hot and dry conditions impacted disease pressure and yields (Table 9).

2017

In 2017 we experienced well above normal precipitation which lead to very high disease pressure and incidence within the hop yard. Within this wet season, we continued to notice trends on the significant impact of crowning on cone weights, in addition to some less significant impacts on yield and cone disease severity (Table 10). Yield and cone weights were consistently impacted by crowning throughout the study to some effect, whereas other metrics may be influenced by growing conditions. Because of the wet season and high disease pressure, our sample size was significantly reduced and individual plants were analyzed within plot treatments as opposed to entire replicated plots, which could have potentially had an impact on results for the year.

Table 10 : 2017 Dry matter, yield, 100 cone weight, cone disease incidence, cone disease severity.

*Treatments with an asterisk are not significantly different than the top performer in bold.

Table 11 : 2018 Dry matter, yield, 100 cone weight, cone disease incidence, cone disease severity.

*Treatments with an asterisk are not significantly different than the top performer in bold.

 The flamed treatment, 11-May, yielded highest. While there was not a significant difference in yield between crowning and control treatments this year, crowning did have the lowest yield compared to control and flamed treatments. Flaming resulted in significantly smaller cone sizing on hop plants despite having highest yields in the 2018 trial (Table 11). 

HARVEST TIMING

Table 12 shows a summary of the temperature, precipitation and growing degree day (GDD) summary. The 2017 growing season in Northfield, MA was fairly similar to Vermont growing conditions accumulating 2255 GDDs this season, 43 more than the historical 30-year average. Precipitation for the early part of the growing season was well above normal averages especially in May, where they experienced over 3” of rain above average.

Table 12. Temperature, precipitation and growing degree day summary. Northfield, MA, 2017.

Table 13 provides a summary of the analyzed oil characteristics and the aromatic qualities that they may contribute during the brewing process.

Table 13. Oil characteristics.

Harvest periods were broken down into early, normal, and late periods. The early period for Cascade was taken from 14-Aug through 21-Aug, normal harvest period is taken from 25-Aug through 5-Sep, and late harvest period is taken from 8-Sep through 18-Sep. Total analyzed oils for Cascade generally increased from early to late harvest periods, peaking during the late harvest period (Figure 3). The largest component was made up of myrcene which peaked during the normal harvest period and stayed relatively consistent through late harvest, as did caryophyllene. Whereas humulene and farnesene steadily increased as time went by. Cascade Alpha acids were consistent throughout the harvest and beta acids peaked slightly during the normal time period (Figure 4).  

The early period for Magnum was taken from 14-Aug through 21-Aug, normal harvest period was taken from 25-Aug through 5-Sep, and late harvest period was taken from 8-Sep through 18-Sep. Total analyzed oils for Magnum generally increased from early to late harvest periods, peaking during the late harvest period (Figure 5). As with Cascade, the largest component of the oil profile was made up of myrcene. In Magnum the myrcene and caryophyllene levels steadily increased as time went by, whereas humulene peaked in the normal harvest period. Magnum resin levels were relatively consistent, with a slight drop off for beta acids during the late harvest period (Figure 6).

The early period for Nugget was taken from 18-Aug through 28-Aug, normal harvest period was taken from 1-Sep through 11-Sep, and late harvest period was taken from 15-Sep through 22-Sep. Total analyzed oils increased over time peaking during the late harvest period (Figure 7). Myrcene showed a noticeable increase over the harvest period whereas humulene peaked during the normal harvest period for Nugget. Resins for Nugget had increasing levels over the tested period and peaked during the late harvest window (Figure 8).

The early period for Centennial was taken from 11-Aug through 18-Aug, normal harvest period was taken from 21-Aug through 28-Aug, and late harvest period was taken from 1-Sep through 8-Sep. Total analyzed oils for Centennial were highest during the early period and showed fluctuations throughout harvest periods (Figure 9). Resins showed similar fluctuations with peak concentrations of alpha and beta acids during the early harvest period (Figure 10).

The early period for Crystal was taken from 21-Aug through 1-Sep, normal harvest period was taken from 5-Sep through 15-Sep, and late harvest period was taken from 18-Sep through 29-Sep. Total analyzed oils increased over time once peaking during the late harvest period. While myrcene continued to develop over time and peaked with the total oils, humulene, caryophyllene and geraniol were highest during the early harvest period (Figure 11). While beta acids remained fairly consistent across harvest periods, alpha acids appear to have peaked in the late harvest period (Figure 12).

2018 Hop Harvest Timing Results

In 2018, we were required to switch labs for hop analysis. In past experiments, Alpha Analytics in Yakima, WA conducted hop oil analysis. Unfortunately, this lab stopped accepting samples in 2018. Hence, we were required to find another lab with the ability to test for essential oils and resins. The lab chosen for the project was Alliance Analytical Laboratories located in Coopersville, MI. Samples were shipped directly to the company and handling was unfortunately inadequate and led to samples becoming moldy. We were able to receive results for brew quality as this test was conducted prior to sample degradation.

Alpha acid, beta acid, cohumulone, colupulone, HIS, and moisture were measured for each harvest date (Table 14). Moisture was variable across all five samples and there was no significant difference between each of the harvest dates. While no statistical difference was noted between Early, Normal, and Late harvest dates, each date would have been deemed “ready to harvest” if using moisture as the sole means of determining harvest timing. Harvesting before aromas fully develop can result in lesser quality hops, making it important to use additional means of measuring hop readiness to determine ideal harvest windows.

Cohumulone makes up a large percentage of total alpha acids and contributes to the bittering qualities of the hops after isomerization in the brewing process. Colupulone makes up a large percentage of total beta acids and would thus contribute largely to hop aromatics and later bitterness in beers after oxidization and conversion to hulupone. Cohumulone and colupulone are presented as a percentage of alpha and beta acids respectively. Cohumulone was highest in HD 4 and HD 3. Colupulone was highest in HD 3 with statistically similar levels shown in HD 4, HD 5, and HD 2.

Table 14. Brewing quality for Cascade hops harvested over a 5 week period in 2018.

Normal and Late harvest dates (HD 3, HD 4, and HD 5) had the highest percentage of alpha and beta acids compared to the earlier harvest dates (Figure 15 and 16). Major jumps in both alpha and beta acids occurred after Early harvest dates (HD 1 and HD 2). HD 3, HD 4, and HD 5 had the highest values for brewing qualities.

HSI measures the potential loss of alpha and beta acid over time; a lower number for HSI means less potential for loss. HSI can also be an indicator of handling and storage practices as the degradation of alpha and beta acids can be accelerated by increased temperatures, exposure to air, and exposure to light. Values for HSI less than 0.40 are generally acceptable but lower values below 0.30 are ideal. Our Normal harvest period (HD 3) also had the lowest HSI showing that resins would be most stable over time for this harvest date (Figure 17). The sample from HD 4 had the highest HSI and would be most subject to alpha and beta acid degradation. This sample may have been subject to improper handling. As a whole, Normal and Late harvest dates were all top performers in the trial and exhibited highest values for alpha acid, beta acid, cohumulone, and colupulone. Again due to laboratory error we were unable to test for changes in the hop oil profiles.

BENEFICIAL EXCLUSION STUDY

The open treatment would have allowed for natural enemies to prey on the hop pest populations whereas the excluded treatment would have kept natural predators away from the pests. Hence, it is expected that a decrease in pests in the open treatment would be a sign of predation due to populations of natural predators. An increase in pests in the open treatment may indicate an absence or low abundance of natural predators.

The Northfield, MA site showed very few significant differences in pest counts between open and excluded treatments for any of the sampling periods. There was a significant difference observed between open and excluded treatments for TSSM in June. There was an increase of 23.3 TSSM in the open treatment, whereas the exclusion treatment showed an increase of 6.40 (Figure 13).

In Starksboro there was no difference in TSSM counts for open and excluded treatments throughout the entire season, but there were some differences in June PLH and August HA counts. For June, there was an increase of 1.80 PLH in the open treatment and an increase of 5.20 for excluded treatment (Figure 14). The HA also showed significant differences in August with an increase of 1.20 for the open treatment, and an increase of 7.95 for excluded treatment (Figure 15).

The Alburgh site showed the most significant differences in pest counts when leaves were left open or excluded. In June there was a difference in TSSM, though very small, showing and increase of 0.25 for open treatments and a decrease of 0.20 for excluded treatments. In July, the HA showed a 4.10 increase for open and an 18.2 increase for the excluded treatment (Figure 16). In August we saw differences in both HA and TSSM. The HA had an increase of 2.35 for the open treatment whereas the excluded treatment had an increase of 49.1 (Figure 17). For TSSM there was an increase of 0.05 for the open treatment and an increase of 2.83 for the excluded treatment (Figure 18).

2019 & 2020 Hop Fertility Results

Within the trial, fertility rates appeared to have little to no impact on observed pests with the exceptions of hop aphids (Table 15). Aerial spikes were observed throughout the study yet fertility treatments appeared to have no impact on spike incidence when looking at nitrogen treatments alone. In general, hop aphids appeared to be present in much larger populations in 2019 compared to past years as a result of weather conditions favorable to aphids. The highest average population populations were observed on one of the higher nitrogen application treatments, 100_100 lbs N ac^-1 with an average of 6.65 aphids leaf^-1 compared to lowest populations observed on the 100_50 lbs N ac^-1  treatment at 2.17 aphids leaf^-1 and a trial average of 3.59 aphids leaf^-1. That being said there were also some “hot pockets” within the hop yard in which with some single leaf populations exceeded 100 aphids leaf^-1 and a number of weekly scouting populations exceeding some proposed action thresholds of 5-10 aphids leaf^-1.

Table 15. Average insect pest and disease scouting incidence for nitrogen fertility rates, Alburgh, VT 2019.

†Within a column treatments marked with the same letter were statistically similar (p=0.10). Top performers are in bold.

‡LSD –Least significant difference at p=0.10.

¥NS –No significant difference between treatments

Throughout the growing period, plots were sampled every other week for leaf petiole nitrates from 13-Jun to 31-Jul (Table 16). Collected petiole samples were analyzed on-farm for nitrates and sent out for total nitrogen. Basic guidelines have been proposed for determining plant nitrogen requirements yet there are no current recommendations based on these in-field nitrate readings. Collected leaf petiole samples may fall into three categories including Low: 0-6000ppm, Normal: 6000-10,000ppm, and High: 10,000+ppm.

Throughout the sampling period (2-Jul through 31-Jul), treatment differences between petiole nitrates were significant within the 16-Jul and 31-Jul sampling dates. Most notably the 100 lbs N ac^-1 treatment (lowest in the study) was significantly lower than the other treatments in these two dates, whereas those receiving a minimum 50 lbs N ac^-1 extra, were sustaining similar levels of petiole nitrates. Overall nitrate levels followed decreasing trends over the course of the sampling period with highest values observed in 200 and 250 lbs N ac^-1 treatments.

Total percent N followed similar trends over time, but some more consistent differences were observed between application rates. The 250 lbs N ac^-1 treatments was consistently the highest percentage total nitrogen and the 100 lbs N ac^-1 treatment was consistently the lowest percent total nitrogen. While the differences were slight between equal total nitrogen treatments (at the 150 and 200 lb rates), those receiving higher summer application totals appeared to have slightly higher total nitrogen within petioles. Application rates over 200 lbs N ac^-1 did not further increase % N concentrations in the petioles.

Table 16. Leaf petiole nitrates and total nitrogen over sampling period, Alburgh, VT, 2019.

†Within a column treatments marked with the same letter were statistically similar (p=0.10). Top performers are in bold.

‡LSD –Least significant difference at p=0.10.

¥NS –No significant difference between treatments

Whole bines were processed for nutrient analysis (Table 17). There was a significant difference across treatments for percent N, potassium, phosphorus, magnesium, manganese, iron, and zinc. Nitrogen, magnesium and manganese all showed increasing plant concentration trends with increased N rates from 100 lbs N ac^-1 to 250 N ac^-1. Peak whole plant N and magnesium concentrations were observed at the highest 250 N ac^-1 rate whereas manganese concentrations peaked at the 200 N ac^-1 rate (50_100 N ac^-1 treatment). Conversely, phosphorus and potassium showed peak values at lower N application rates and lower concentrations at higher N application rates. In most cases nutrient concentrations were maximized at 150 lbs N ac^-1.  A number of these factors may have been impacted by soil available nutrients as well as changes in pH that may have resulted from the increasing rate of fertilizer within the trial. Nitrogen management of soil is closely linked to the plant uptake of a wide number of nutrients. The trial results indicated that application of N can help to improve the availability and subsequent uptake of other essential nutrients.

  Table 17. Whole plant nutrients at harvest, Alburgh, VT, 2019

†Within a column treatments marked with the same letter were statistically similar (p=0.10). Top performers are in bold.

‡LSD –Least significant difference at p=0.10.

¥NS –No significant difference between treatments

At harvest 100 cone weight, diseased cone percentages, disease severity, harvest dry matter, and yields were recorded (Table 18). There was no difference across treatments for 100 cone weights or yields, however there were significant differences in the percentage of diseased cones, disease severity, and harvest dry matter. Disease was least prevalent in the 100_100 lbs N ac^-1 (200 lbs total N ac^-1) treatment at 54.5% and with a relatively low disease severity rating at 2.63. It also appeared that, with equal total nitrogen application rates, higher amounts of nitrogen applied in the summer months during the vegetative period may increase chance of disease and the severity. This can be seen specifically when comparing the 200 lbs N ac^-1   treatments with lowest severity in the 100_100 lbs N ac^-1 treatment and highest severity in the 50_100 lbs N ac^-1 treatment. Yields did not appear to be impacted by fertility rates within the trial for this growing seasons conditions, but highest yield was observed with the 100_150 lbs N ac^-1 treatment with a trial average of 901 lbs ac^-1.

Table 18. Fertility trial yields and cone quality, Alburgh, VT 2019.

†Within a column treatments marked with the same letter were statistically similar (p=0.10). Top performers are in bold.

‡LSD –Least significant difference at p=0.10.

¥NS –No significant difference between treatments

€Cones were rated in browning severity on a 1-10 scale where 1 indicates low browning and 10 indicates severe browning.

Higher rates of nitrogen also appeared to have some impact on hop resins (Table 19). Highest values for both alpha and beta acids were seen at the lowest nitrogen rate with 8.90% alpha acid and 3.62% beta acid. The lowest values were observed that the highest nitrogen rate at 7.37% alpha acid and 2.98% beta acid. It should be noted that alpha and beta acids did not differ statistically between 100 and 150 lbs N ac^-1 application rate. Essentially indicating that rates over 200 lbs N ac^-1 might actually depress quality of the hops. The various nitrogen application rates appeared to have no impact on hop storage index (HSI).

Table 19. Fertility trial brew quality, Alburgh, VT, 2019.

†Within a column treatments marked with the same letter were statistically similar (p=0.10). Top performers are in bold.

‡LSD –Least significant difference at p=0.10.

¥NS –No significant difference between treatments.

Table 20 shows a summary of the temperature, precipitation and growing degree-day (GDD) summary. In the 2020 growing season, there were an accumulated 2544 GDDs, 66 more than the historical 30-year average with greatest deviations from the norm occurring in July, 121 GDD’s above average. The 2020 growing season experienced a dry summer with well below average precipitation occurring during the months of May and June. Supplemental irrigation was applied to plants at a rate of 4500 gal ac^-1, however drier summer months and limited well capacity resulted limited the ability to provide adequate water to the crop.

Table 20. Temperature, precipitation and growing degree day summary, Alburgh, VT, 2020.

Based on weather data from a Davis Instruments Vantage Pro2 with WeatherLink data logger. Historical averages are for 30 years of NOAA data (1981-2010) from Burlington, VT. (http://www.nrcc.cornell.edu/page_nowdata.html).

Pest and disease

Within the trial, fertility rates appeared to have little to no impact on observed pests with the exceptions of hop aphids in the Centennial variety (Table 21). No treatment differences were observed for the Cascade variety for pests. Hop aphid populations were highest in the 50/150 lbs N ac^-1 treatment at 3.06 aphids per leaf. All N rates either higher or lower had significantly lower HA compared to the 50/150 N treatment rate.  The two-spotted spider mite (TSSM) and potato leaf hopper (PLH) populations were not impacted by the fertility treatments. In general, populations of HA were lower than previous years and much higher levels of TSSM populations. Populations of TSSM peaked in the hundreds per leaf prior to miticide application in the summer largely as a result of ideal hot and dry conditions conducive to TSSM outbreaks. Weekly basal and aerial downy mildew spikes developing during the scouting period were not impacted by fertility treatments for either variety.

Table 21. Average insect pest and disease scouting incidence for nitrogen fertility rates on Centennial hops, Alburgh, VT, 2020.

HA= hop aphid. PLH = Potato leaf hopper. TSSM = two-spotted spider mites.

†Within a column treatments marked with the same letter were statistically similar (p=0.10). Top performers are in bold.

‡LSD –Least significant difference at p=0.10.

¥NS –No significant difference between treatments.

Tissue analysis

Whole bines were processed for nutrient analysis (Tables 22 & 23). For the Cascade variety, N rate treatments were statistically different in phosphorus, manganese, and iron concentrations across treatments. For Centennial, treatment differences were observed in nitrogen, potassium, phosphorus, calcium, manganese, and iron. Highest nitrogen and manganese concentrations were observed in the 100/150 lbs N ac^-1 treatment for Centennial at 2.44% and 72.8ppm respectively. Total plant nitrogen decreased with each tier of down to the lowest value observed at 2.01% for the 100 lbs N ac^-1 treatment with manganese following some similar general trends. Other macronutrients such as potassium and phosphorus were highest in the Centennial hops at the lowest Nitrogen application rates whereas others showed peak tissue concentrations for mid-range total nitrogen treatments such as iron and calcium. Cascade hops appeared to have a visible decline in plant growth and quality from year two to year three (2020). This became much more apparent as normal side arm initiation occurred in the Centennial hops and the Cascade hops failed to develop side arms with much smaller hop clusters borne directly from the main bines. Nitrogen management of soil is closely linked to the plant uptake of a wide number of nutrients. The trial results (specifically for the Centennial variety) indicated that application of N can help to improve the availability and subsequent uptake of other essential nutrients, but highest rates may reduce the uptake of some.

Table 22. Cascade whole plant nutrient analysis at harvest, Alburgh, VT, 2020.

†Within a column treatments marked with the same letter were statistically similar (p=0.10). Top performers are in bold.

‡LSD –Least significant difference at p=0.10.

¥NS –No significant difference between treatments

Table 23. Centennial whole plant nutrient analysis at harvest, Alburgh, VT, 2020.

†Within a column treatments marked with the same letter were statistically similar (p=0.10). Top performers are in bold.

‡LSD –Least significant difference at p=0.10.

¥NS –No significant difference between treatments

Yields and cone quality

At harvest, 100 cone weight, diseased cone percentages, disease severity, harvest dry matter, and yields were recorded (Table 24 and 25). For both the Cascade and Centennial hops, there was no difference across treatments for bine weight or 100 cone weights within variety. For the Cascade hops, significant differences were only observed in the percentage of diseased cones with the highest percentage observed (79.3%) in the 100/50 lbs N ac^-1 treatment. It’s also worth noting that, overall, the percentage of diseased cones for the Cascade hops (69.5% average) was much higher than the Centennial average (29.9% average) in addition to greater disease severity by 1.67 points on the given 1-10 scale. More treatment differences were observed within the Centennial hops including diseased cones, disease severity, harvest dry matter, and yields (Table 25). Within the variety, harvest dry matter was highest for the 50/150 lbs N ac^-1 treatment though was statistically similar to all other treatments receiving summer applied nitrogen applications. Similarly, highest yields in the Centennial hops were seen in the 50/150 lbs N ac^-1 treatment and was statistically similar to the 100/50, 50/100, and 100/100 lbs N ac^-1 treatments.

Table 24. Cascade yields and cone quality, Alburgh, VT 2020.

†Within a column treatments marked with the same letter were statistically similar (p=0.10). Top performers are in bold.

‡LSD –Least significant difference at p=0.10.

¥NS –No significant difference between treatments

€Cones were rated in browning severity on a 1-10 scale where 1 indicates low browning and 10 indicates severe browning.

Table 25. Centennial yields and cone quality, Alburgh, VT 2020.

†Within a column treatments marked with the same letter were statistically similar (p=0.10). Top performers are in bold.

‡LSD –Least significant difference at p=0.10.

¥NS –No significant difference between treatments

€Cones were rated in browning severity on a 1-10 scale where 1 indicates low browning and 10 indicates severe browning.

Brew quality

Higher rates of nitrogen appeared to have a negative impact on the brew quality of the Cascade cones for hop storage index (HIS) (Table 26). Values below 0.300 for HSI are considered to be of good quality with those reaching higher values above 0.400 becoming of questionable or poor quality. Highest observed values for HSI were seen at the 100/100 lbs N ac^-1 treatment at 0.639 (poor quality) compared and was statistically similar to all other treatments receiving summer nitrogen with the lowest value observed in the 100 lbs N ac^-1 treatment at 0.212. Beta acids were lowest at the 100/150 lbs N ac^-1 treatment (250 lbs N total) at 1.87%. While differences in alpha acids were not significantly different, there are some observable differences between the highest nitrogen rates which were around 4% alpha acids and the lower nitrogen rates which were closer to 5-6%. This may also correspond to the higher HSI values observed in those treatments receiving higher nitrogen applications for Cascade. For the Centennial hops, HSI did not appear to be impacted by nitrogen fertility treatments with all values falling with acceptable or good quality ranges and relatively consistent observed values for alpha acids (Table 27). Beta acids in the Centennials once again varied with the highest 100/150 lbs N ac^-1 treatment showing lowest overall beta acid percentage and all other treatments having statistically similar values.

Table 26. Cascade fertility trial brew quality, Alburgh, VT, 2020.

†Within a column treatments marked with the same letter were statistically similar (p=0.10). Top performers are in bold.

‡LSD –Least significant difference at p=0.10.

¥NS –No significant difference between treatments.

Table 27. Centennial fertility trial brew quality, Alburgh, VT, 2020.

†Within a column treatments marked with the same letter were statistically similar (p=0.10). Top performers are in bold.

‡LSD –Least significant difference at p=0.10.

¥NS –No significant difference between treatments.