Blunt-nosed leafhoppers (BNLH) continue to be an increasing threat to cranberries in NJ. This insect pest has also the potential to affect other cranberry-producing states. Here I put together some guidelines to consider when managing BNLH in cranberries:
1. A challenge for managing BNLH is the fact that they vector a phytoplasma that causes false blossom disease. For this reason it is difficult to establish economic thresholds for this pest because we don’t know the proportion of individuals that are infected in the population. Moreover, this proportion can vary depending on the variety. For instance, we have observed higher incidence of infection in the newer varieties even when populations of leafhoppers are low.
2. As an IPM practice, we recommend to monitor BNLH populations before bloom using a sweep net.
3. If BNLH populations are increasing compared to previous years and the beds have not been treated for BNLH for 2-3 years, growers should consider treatment.
4. If growers have treated for BNLH in the previous year and populations are low (average of less than 10-20 BNLH per sweep set), there is no need to treat again. Keep a record of the BNLH numbers and check those same beds again the following year to see if the numbers have increased.
5. In most cases, there is no need to apply broad-spectrum insecticides (organophosphates, carbamates) to control BNLH for two or more consecutive years. These insecticides will disrupt the biological control of other pests such as Sparganothis fruitworm and therefore cause increases in insecticide use.
6. If treatment is necessary, we have limited options to manage BNLH. The best timing for insecticide treatment is before bloom to target the young nymphs. We recommend the use of organophosphates such as Lorsban (chlorpyrifos) and Diazinon (diazinon), and carbamates like Sevin (carbaryl). The neonicotinoid Assail (acetamiprid) also works well against nymphs but we do not recommend the use of neonicotinoids before bloom due to potential negative effects on bees-neonicotinoids are systemic insecticides that can accumulate in the pollen and nectar. A new registered insecticide, Closer (sulfoxaflor), is also effective against BNLH nymphs. Although Closer has a similar mode of action as the neonicotinoids, it belongs to a different class of insecticides. Closer use is prohibited during bloom (between 3 days prior to bloom and until after petal fall). Ocean Spray growers need to check restrictions on use of these insecticides prior to application.
7. Last year, we (in collaboration with James Polashock, USDA-ARS) tested whether we could increase the cranberry’s own immune defenses to combat disease infection. In greenhouse studies (Fig. 1), we treated phytoplasma-infected cranberries with commercial products that elicit defenses in plants against diseases. Unfortunately, these treatments were unsuccessful at reducing the phytoplasma and, even worse, they made the cranberries more susceptible to BNLH and caterpillars.
Fig. 1. Greenhouse study on the effects of elicitors of plant defenses on cranberry-phytoplasma-insect interactions
8. We have observed that phytoplasma infection makes the cranberry root system weaker. Thus, applying stresses to infected cranberries such as sanding or herbicides could prevent them from growing and potentially cause their death. Greenhouse and field studies in collaboration with Thierry Besancon (Rutgers U.), James Polashock (USDA-ARS), Dan Schiffhauer and Lindsay Wells-Hansen (Ocean Spray) are underway to test this concept.
