Clean Plants vs. HSVd
What is HSVd and why is it important?
HSVd or hop stunt viroid is a pathogen impacting yields worldwide. Not only does it stunt growth and reduce yields, but it is also easily transmissible between plants.
The virus spreads when an infected plant is introduced to a field. Once there, it can infect other plants through sap transfers. Replacing all potentially infected plants is the only known way to prevent further HSVd infections as it cannot be treated.
What does this study look at?
When planting or replanting a field, growers have the opportunity to purchase ‘certified clean planting stock’ (CPS). Supported by the National Clean Plant Network, hop bines can be purchased from Clean Plant Centers (such as one at Washington State University) where cultivars are tested for viruses, including HSVd. While purchasing plant stock known to be virus free reduces the risk of introducing the virus to your fields, it is more expensive than purchasing noncertified clean planting stock (NCPS).
Hops plant with hop stunt viroid leaf symptoms. Photo courtesy D. H. Gent, USDA-ARS
This study aimed to answer two main questions:
At what level of yield loss due to HSVd do the benefits of using CPS make up for the increased planting cost compared to planting NCPS?
At what level of yield loss due to HSVd does it make sense for a grower to replant everything with CPS?
To answer these questions, costs and revenues are estimated for a one-acre plot of both alpha and aroma hops over a six-year period. These values are adjusted to represent the net present value (NPV) to include the value of future hops profits when making planting decisions. Crop budgets from Washington State University are used to calculate these values. We consider the costs incurred during production and assume the farm is already established and no new land, machinery, or trellising systems needs to be purchased.
Four scenarios are considered:
Scenario 1 (Baseline): NCPS is used and there is no yield reduction due to HSVd
Scenario 2 (CPS): CPS is used and there is no yield reduction due to HSVd
Scenario 3 (HSVd present): NCPS is used and there is HSVd present which led to yield reductions. Reductions of 5%, 10%, 15%, and 20% are modeled.
Scenario 4 (Replanting): NCPS are initially planted with HSVd present. The level of yield reductions is the same as scenario 3. In this scenario, the field is replanted with CPS. This scenario also estimates at what percent of yield loss a grower should replant the field with CPS.
As seen in the table 1, if there is no HSVd present over the 6-year period, returns are higher when planting NCPS since the CPS costs 50% more. Scenario three demonstrates that if HSVd is in your field, a yield loss between 5%-20% can impact your ability to turn a profit over a six-year timespan.
Table 2 shows the potential economic benefit of planting CPS compared to various yield losses due to planting NCPS. At 5% yield loss, the returns are higher by planting NCPS. But at higher yield losses, the NPV of planting CPM can have economic benefits. At a 20% yield loss, planting CPM provides $6,188 higher returns over the 6-year period for aroma hops and $5,555 for alpha hops. If the impact on yield is more than 6% for aroma or 7% for alpha, then there would be higher returns if CPS is used instead of NCPS.
Scenario 4 explored what level of yield loss by year 3 is needed to justify replanting with CPS. For aroma hops, a loss of at least 35% of the yield by year 3 is needed for the NPV to be higher by replanting. Alpha hops need a 36% yield loss to justify replanting in year 3.
This work provides information to better understand how it could be impacting potential profits depending on what is being seen in your field. This information can help you make decisions and better understand when planting certified clean plant stock makes sense in your operation.
Galinato, S.P. and Tozer, R. 2015 Estimated Cost of Establishing and Producing Hops in the Pacific Northwest. Washington State University Extension.
Davis, T.J., Gómez, M.I., Harper, S.J. and Twomey, M. 2021. The Economic Impact of Hop Stunt Viroid and Certified Clean Planting Materials. HortScience, 56(12), pp.1471-1475.
Davis, T.J., Gómez, M.I., Harper, S.J. and Twomey, M. 2020. Potential Economic Benefits of Using Certified Clean Hop Plants vs. Hop Stunt Viroid Disease. Cornell University