Effective use of alfalfa as a trap crop for potato leafhoppers in hops

View the project final report

• 2016 annual report

Commodities

• Agronomic: hops

Practices

• Crop Production: catch crops
• Education and Training: demonstration, extension, farmer to farmer, on-farm/ranch research
• Pest Management: cultural control, economic threshold, field monitoring/scouting, integrated pest management, trap crops

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, 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 the project will be 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.

BACKGROUND

There are now more than 350 acres of hops grown in the northeast region. At Four Star Farms in Northfield, Ma, my family and I currently have 17 harvested acres. Our production goal is to have 1800lbs/acre by 2018. We have been supplying more than a dozen breweries with local hops for the last 5 years years ­ this year’s crop sold out in under one week. Hops were a major crop in the northeast region from 1840­1940. We know that hops can be grown successfully here. Vermont hop production peaked in 1860 when more than 600,000 lbs of dried hops were produced (Kennedy, 1860). Western hop yield typically reaches 1500­2000 lbs/acre yet most northeastern growers currently yield below 1000 lbs/acre. Arthropods, diseases, and weeds are pest challenges on our farm. In particular, potato leafhopper (PLH), is not a problem in Western growing regions but it is a pest of significance in the northeast. Aside from two UVM Extension trials, there is very little information available for growers on PLH management tactics in hops. We are a conventionally managed farm that is looking for alternatives to pesticides. We have shifted to almost 100% chemical free weed control using tillage and hilling to replace pre­emergents and weekly burndown herbicide applications, and would like to continue that shift on our insect pest managment. PLH is native to the northeast and feeds on more than 200 broad leaf plants. This pest has been researched in other northeastern production systems including snap bean (Nault et al. 2004), alfalfa (Lamp et al. 2007), maple (Frank et al. 2007), and grape (Lenz et al. 2012).

PLH is a migratory pest that overwinters in the southeastern United States and is carried north on spring wind currents. Upon arrival, females feed and lay eggs in hop leaf and stem tissue. Adult females can arrive to northern New England anytime between May and August making it an unpredictable pest. Two- four generations of PLH have been observed on hop in northern New England. PLH was reported as a pest on hops in the 1940s (Magie 1944). Current research on this pest has just recently begun. In 2015, we observed a very high population of PLH and used two applications of Bifenthrin to reduce damage to our yield. In 2014 we hardly saw a single PLH in our hop yards. This trend was also observed in Vermont by the state wide scouting efforts conducted by UVM Extension. Pesticides are expensive and the products available for use against PLH would kill any natural enemy arthropods and pollinators present. In addition, other than parasitoid wasps, there are very few natural enemy arthropods that biologically keep PLH populations in check. Therefore, we are motivated to implement a cultural control method to manage this pest. The UVM Extension Northwest Crops and Soils Team presented the idea that alfalfa could be used as a trap crop for potato leafhopper.

PROJECT OBJECTIVE

At the beginning of any season we want to be ready to manage a large PLH population weather it comes or not. We propose to further study the efficacy of an alfalfa trap crop to manage PLH. While this project is of interest to our farm’s success, it is research that will benefit both organic and conventional hop growers across the northeast. We propose the following research questions. A. Does a 10ft wide alfalfa trap crop need to be sprayed with pesticide (Imidacloprid) to prevent the potato leafhopper (PLH) population from spilling over to hop plants? B. How close does the trap crop need to be to hop plants to remain effective?

PREVIOUS WORK

Work conducted by UVM Extension confirmed that PLH is a pest of hops. They measured net photosynthesis on first year hop leaves that were exposed to 3 adult PLH and not exposed to any PLH at Borderview Farm in Alburgh, VT. In the field, adult potato leafhoppers reduced photosynthesis of hop leaves by 32.7% (See Attachment "Figures"; Figure 1). “Healthy” leaves were not exposed to PLH. “Injured” leaves were exposed to 3 adult PLH. (Source: UVM Extension NWCS 2015) The research on potato leafhopper as a pest in northeastern hop production was conducted as part of a University of Vermont Ph.D. dissertation (Calderwood 2015) and NESARE graduate student grant (GNE12­033). In this study, a mowed grass drive row, un­mowed red clover, and a three species mix (red clover, common yarrow, and beebalm) were compared for their attraction to natural enemy arthropods in hopes of regulating pest populations on hop plants. The most significant finding was that the red clover treatment acted as a trap crop for potato leafhopper (See Attachment "Figures"; Figure 2). PLH is has been studied extensively as an economically damaging pest of alfalfa. Certain varieties of alfalfa are more susceptible to PLH feeding compared to others. A study conducted by Straub et al. (2013) showed that PLH preferred to feed on monocultures of alfalfa compared to mixed stands of alfalfa and clover. Anecdotally, growers have noticed that when alfalfa fields are cut for hay PLH migrate from this vegetation to nearby hop yards.

METHODS

Four Star Farms has three hop yards in close proximity to each other (see Sheet "layout of current hopyard" of File "Schematic of Project"). 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. Overall Methods: We propose a two year project to monitor PLH in alfalfa trap crop treatments and on hop plants. Sampling will occur in both years of the project but the first year will allow the alfalfa to establish. We also believe this should be a two year project because the PLH population size and arrival date are unpredictable. Trap crop treatments will be planted perpindicular to the hop rows on the north and south ends of our “Old” and “Young” hop yards. Our treatments will be replicated 4 times and include: 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 (see attachment "schematic of project") of PLH susceptible alfalfa will be planted at a thick stand seeding rate in early spring as soon as the ground thaws. We will use susceptible variety “Vernal” or “Oneida VR” in our trial to allow for the most PLH feeding possible. Control plots will be mowed or tilled throughout the season. Alfalfa trap crops will not be mowed until after hops are harvested each year. Potato Leafhopper Monitoring: Hop yards will be scouted weekly by Lily Calderwood who is the IPM Specialist for the UVM Extension NWCS Team. Four Star staff will assist and learn the scouting methods and protocls at the same time. PLH will be scouted using sticky traps and a sweep net from the first week in June through the end of August for a total of 12 collection dates. Once hops are harvested in any yard, scouting will end. Trap crop alfalfa vegetation and controls will be scouted using the sweep net technique. Five sweeps will be taken while zig zagging through each plot. The number of leafhoppers/net will be counted in the field and recorded. The University of Minnesota and Cornell University have put together economic threshold levels for PLH in alfalfa by crop height. We will use their suggested thresholds in making a spray decision in the sprayed trap crop treatment plots. For example, taking 5 sweeps in 3 inch tall alfalfa, it is recommended to spray pesticide if 13 adults are counted. Imidacloprid will be sprayed with an air blast sprayer at a time that wind speed is less than 3mph to reduce the risk of insecticide drift into other treatment plots. The non­ sprayed alfalfa plots will be monitored using the same sweep net technique and the number of leafhoppers/net will be recorded. Hop plants will be scouted using 3x5 un­baited yellow sticky cards. Two hop rows will be randomly selected per trap crop treatment. Each row will have 7 sticky cards placed at different distances from the treatments. One plant will be randomly selected at 5ft, 20ft, 50ft from the end of each row. An additional plant will be selected at 400ft in the middle of each row for a total of 7 sticky cards per row. One sticky card will be placed in the center of each of the 84 total plants. Sticky cards will be secured with clothes pinned to a piece of coir. The coir rope will be 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 each plant is visited, Just before hops are harvested, we will take a 100 cone sample from each scouted hop plant. This sample will be weighed and dried to give us a measure of PLH damage impact on yield.

TIMELINE AND OUTREACH

2016 March: buy materials and seed April/May: plant alfalfa June: PLH scouting begins July: field day on pest management tactics on our farm in hops, PLH scouting continues August: PLH scouting continues until hops are ready to harvest August/September: side are yield and quality samples taken September: mow alfalfa for the winter December: attend the Cornell NY Hop Conference February: present project at UVM Hop Conference 2017: March: set up materials and seed April/May: check on alfalfa stand June: PLH scouting begins July: field day on pest management tactics on our farm in hops, PLH scouting continues, You­Tube video is shot of the project in process and posted online August: PLH scouting continues until hops are ready to harvest August/September: side are yield and quality samples taken December: attend/present at the Cornell NY Hop Conference; Supplement the previous video with conclusions February: present project at UVM Hop Conference