This is the time of the year a hemp grower should start to monitor for beet leafhopper (BLH) adult populations. BLH insects that vector (transmits from a diseased plant to a healthy plant) Beet curly top virus (BCTV) can infect a variety of agricultural crops including sugar beet, tomato, and hemp. Below is information focused on BLH adult monitoring and management tips. To know more about the epidemiology and symptoms of BCTV on hemp, check out Hemp (Cannabis sativa)- Beet Curly Top disease page from Pacific Northwest Disease Management Handbook.
In the fall, BLH adults overwinter in weedy habitats, and then during the spring and summer seasons, they migrate to crop fields and can transmit BCTV into hemp plants. Monitoring for the adults is particularly important if you experienced BCTV damage in hemp fields during previous years. In some situations, you may find BLH adults on hemp plants or in the surrounding landscape, but those plants may not be infected with BCTV and not show disease symptoms. Therefore, monitoring and testing the BLH adults for BCTV presence is important
Depending on the field size, 1-2 traps can be used to monitor the BLH adult population on hemp. A trap can be installed and mounted on a wooden stake, about 1-2 ft above ground level, and the trap can be secured with a binder clip (Figure 1A). Traps should be checked regularly, sticky cards changed every week, and fields monitored until mid-season.
Finding BLH adults on yellow sticky traps can be challenging. Yellow sticky traps are attractive to a variety of insects including flies, thrips, lygus bugs, and several leafhopper species (including BLH). In general, leafhopper adults are elongate in shape, narrowing from head to tail, their wings appear like a roof over the body while resting and the size ranges from 3-10 mm long. When compared with other leafhopper species, the BLH adult specifically does not have a dark spot on the head; the head is rounded in front; adults have two color forms that include light pale-yellow colored form and dark pale-colored forms (Figure 1B). A hand lens or stereo microscope is helpful when identifying the BLH adults on sticky traps.
You can also send insect samples to the OSU Plant Clinic for identification or contact your local OSU Extension Office/Research and Extension Center for other service sites for BLH identification and BCTV testing.
There is limited information on BLH and BCTV management on hemp. However, both the pest and the disease are not new, occurring in many other crops (e.g., sugar beet, tomato, and peppers); it is therefore applicable to explore the following strategies established for other crops until further research is conducted for the hemp production system.
- Avoiding transplanting very young hemp seedlings may help to minimize BCTV damage although the yield may be compromised. In other crops, the earlier that plant stages are infested with BLH that carries the virus, the greater BCTV damage to plants.
- Several weed species (such as Kochia, Russian thistle, bindweed, dandelion, and chicory) can be a breeding ground for the BLH and are hosts for BCTV. In spring and summer, the removal/control of weeds around hemp field edges may help to reduce the migration of local BCTV infected BLH populations to hemp plants.
- Removal of BCTV-infected hemp plants will help to reduce the spread of the virus to other hemp plants during the cropping season.
- Although no BLH pest control products tested on hemp, a Kaolin particle formulation (Surround® WP) is currently registered for use on hemp in Oregon and has shown to reduce BCTV incidence in chili pepper crop.