By: Yahel Ben-Zvi and Cesar Rodriguez-Saona

Rutgers P.E. Marucci Center

New Jersey cranberry growers are increasingly concerned about rising populations of the blunt-nosed leafhopper (BNLH). This increase is likely associated with shifts in pest management strategies, including the adoption of reduced-risk insecticides and decreased use of broad-spectrum products, as well as the expansion of high-yielding cranberry varieties. BNLH is particularly problematic because it transmits a phytoplasma—a type of bacterium that causes false blossom disease (Figure 1). Symptoms of this disease include stunted growth, deformed and sterile flowers that point upward, and a characteristic branching of upright shoots known as witches’ broom.

Figure 1. Cranberry false blossom disease symptoms in mid-May. Note the clustered branching of ‘witches’ broom’, erect and sterile flower buds, and more redness in the leaves. Photo by Yahel Ben-Zvi.

Life Cycle

BNLH has one generation per year (Figure 2). Its eggs overwinter embedded in cranberry stems and begin hatching in early May. Nymphs pass through five instars over approximately two months. Adults emerge in early July, peak in mid- to late July, and decline by the first week of August (Figure 3). Adults are characterized by their distinctive blunt heads and vary in color from light yellowish-gray to dark brown. Egg laying occurs between July and August.

Damage

Nymphs and adults feed on cranberry plant sap using their piercing-sucking mouthparts. Although direct feeding causes little visible damage, BNLH is an important pest because it serves as a vector of the phytoplasma that causes false blossom disease.

Management

At this time of year, early-instar nymphs should be active (Figure 2). Here are some guidelines to consider when managing BNLH in cranberries:

1. Identify Infestation Sites: The key to effective BNLH control is identifying infestation sites. The most reliable method for monitoring this insect is the use of a sweep net. Before bloom, use sweep nets to collect nymphs. Because nymphs are small and difficult to see, bag and freeze the samples to kill them, then count the nymphs using a microscope or magnifying lens.
2. Sweep Net Monitoring: Perform sweep sets consisting of 25 sweeps each. The recommended number of sweep sets is:
   • 1 per acre
     

     Figure 2. An early-instar blunt-nosed leafhopper nymph in mid-May. Photo by Yahel Ben-Zvi.

   • At least 10 sweep sets for 10–20 acres
   • 1 sweep set per 2 acres for areas larger than 20 acres
3. Lack of Economic Thresholds: Establishing an economic threshold for BNLH is difficult because the proportion of phytoplasma-infected individuals within BNLH populations is unknown and may vary by cranberry variety and location. Notably, higher infection rates have been observed in newer varieties, even when BNLH populations are low.
4. Control Measures: Management decisions should be based on BNLH population trends relative to previous years, the history of insecticide applications, and the cranberry variety grown. If BNLH populations are increasing compared to prior seasons and beds have not been treated for BNLH during the past 2–3 years, treatment should be considered.
5. Treatment Options: If treatment is necessary, consider the following options for managing BNLH:
   • Timing: The best time for insecticide applications is before bloom to target young nymphs.
   • Insecticide Options:
     • Organophosphates: Diazinon (diazinon), Orthene (acephate)
     • Carbamates: Sevin (carbaryl)
     • Pyrethroids: Fanfare or Brigade (bifenthrin), Danitol (fenpropathrin)
       

       Figure 3. Life cycle of the blunt-nosed leafhopper. Drawing by Lindsay Lindhult.

     • Neonicotinoids: Assail (acetamiprid), Actara (thiamethoxam)
       Note: Use neonicotinoids with caution before bloom because of their potential negative effects on pollinators. These systemic insecticides can accumulate in pollen and nectar, posing risks to bees.
     • Sulfoximines: Transform (sulfoxaflor). Although effective in small-plot trials at the P.E. Marucci Center, additional data are needed to confirm efficacy at larger commercial scales.
   • Although not scientifically proven, there are claims that Orthene and Sevin may reduce pollinator activity by repelling bees.
   • Rotate insecticides with different modes of action to help prevent the development of resistance in pest populations.