Effective use of alfalfa as a trap crop for potato leafhoppers in hops
Every year between May and August potato leaf hoppers (PLH) arrive in the northeast, carried by up from the south. While there has been research into their management on other crops produced in the northeast, until now, none has been conducted on hops in this region in the last half century. Over the last decade there has been a resurgence of hop production in the Northeast, and PLH have become a formidable challenge. There are crop protection tools available for the control of spider mites, but they are broad spectrum, harming both pollinators and beneficial predators important to the control of another major pest in hops, spider mites. The use of trap crops have been shown to be beneficial in the control of PLH in other crops, and there is a known preference for both alfalfa and clover over hops. Planting a trap crop amongst the hops has tradeoffs: it decreases airflow promoting hop downy mildew; provides a refuge for pests; and removes the ability to use tillage and hilling to control weeds and new hop shoots. This tillage is the only cost effective non chemical form of weed treatment we have.
A key portion of our project is at least two presentations to the hop industry at regional forums to share the results. This project will allow both organic and conventional hop farmers across the northeast to effectively implement a practice that will greatly reduces pesticide usage, while minimizing the trade offs from weed and hop downy mildew pressure.
We are working with various staff from the University of Vermont’s hops team, and with our technical adviser Lilly Calderwood to gather data, and review that data from the first year in an effort to refine our approach for the second year.
Four Star Farms has three hop yards in close proximity to each other . Hop Yard 1 is our oldest yard, and is roughly 3/4 of an acre. Its layout does not make it conducive for use in this study. Hop yard 2 is 6.5 acres, and is a few years younger (1/2 is 4 years old, 1/2 is 3 years old) and is more properly laid out for this work. Yard 3 is our largest at 10 acres, and youngest yard (most of the plants were planted in the spring of 2015.) It contains many of the same varieties, but will present a very different age class of plants, and is laid out in a manner conducive to this project.
METHODS UNDERTAKEN TO DATE: In the first year of this two year project we have monitored PLH in marginally established alfalfa trap crop treatments and on the hop plants. While sampling has already occurred and will be continuing in the second year of the project, the first year has been necessary to try and allow the alfalfa to establish. This first step has proved more challenging than anticipated – with vehicular traffic required over this establishing crop on a very regular basis, it has proven difficult.
Trap crop treatments were planted perpendicular to the hop rows on the north and south ends of our “Old” and “Young” hop yards. Our treatments were replicated 4 times and included: sprayed alfalfa trap crop, nonsprayed alfalfa trap crop, and no trap crop (mowed grass or tilled control). Four, 10ft wide and 220ft long blocks and four 10ft wide and 125ft long blocks of PLH susceptible alfalfa was planted at a thick stand seeding rate in early spring as soon as the ground thawed. Irregular early warmth followed by irregular late cold presented challenges for establishment. The alfalfa trap crop was not be mowed until after hops are harvested each year.
Starting on May 17th the hop yards were scouted weekly by Lily Calderwood & Four Star Staff – not only did they provide assistance but learned valuable scouting methods and protocols at the same time. PLH were scouted using sticky traps and a sweep net through mid August. Due to the planting of a large swath of potatoes directly adjacent to our hops, minimal scouting and agronomic practice tracking was added to make sure we were accounting for a huge PLH attractive crop planted directly next to the hops. The trap crop did not establish sufficiently to do sweep netting in the trap crop.
Hop plants were scouted using 3×5 unbaited yellow sticky cards. Two hop rows were randomly selected per trap crop treatment. Each row had 7 sticky cards placed at different distances from the treatments. One plant was randomly selected at 5ft, 20ft, 50ft from the end of each row. An additional plant was selected at 400ft in the middle of each row for a total of 7 sticky cards per row. One sticky card was placed in the center of each of the 84 total plants. Sticky cards were secured with clothes pinned to a piece of coir. The coir rope was tied to each of two climbing bines at a height of 8 ft in the canopy to hold the sticky card at that height.
As stated above, monitoring the PLH in the trap crop was challenging. We did however still gather incredible amounts of data relative to PLH in the hops, and how they changed versus activity in the neighboring potatoes, and in the hop yard itself.
Below are some general observations that we have been able to gather from the first year’s data:
No significant difference between the number of PLH when measured compared to the distance from the potatoes in either hop yard.
There was a significantly higher number of PLH in the south B yard for every variety when compared to the same variety in the C yard. PLH arrives from the south so it is not surprising that the southern side showed higher PLH numbers.
The B yard was surrounded by potato fields on 2 sides. The C yard had potato field adjacent to one side. When the potato was sprayed for PLH in June, PLH flew up, out of the potato and onto hop plants in both B and C yards. This resulted in a spike from around 5-10 mean PLH per sticky trap in all other weeks to well over 50 mean PLH per sticky trap the monitoring date following the adjacent spray event.
Preliminary, there was no difference in PLH across varieties.
We held a field day in partnership with UVM at the farm to discuss the project and publicize both NESARE and the work we were doing in August and had a very good turnout of growers and researchers. This project was just one of many issues and items addressed at that field day.
Senior Commercial Horticulture Educator
Cornell University Cooperative Extension
24 Martin Road
Voorheesville, NY 12186
Office Phone: (518) 765-3500