Our research on how cranberries respond to phytoplasma infection—and its effects on above- and belowground herbivores—was recently featured on the Theobald Smith Society’s website in the article When Plants Get Sick, Pests Thrive: The Unseen Battle in Cranberry Bogs

Phytoplasma infection, which causes false blossom disease in cranberries, is transmitted by the blunt-nosed leafhopper (Limotettix vaccinii). Our findings show that infection increases cranberry susceptibility to herbivores both above and below ground by increasing plant nutrient levels and suppressing plant defenses. This work highlights the complex—and often harmful—interactions among plants, pathogens, and insect herbivores in agricultural ecosystems.

By: James Shope and Cesar Rodriguez-Saona

As of June 23, Sparganothis fruitworm has accumulated 1,225 degree-days (DD) since the April 15 biofix, based on our degree-day model. This suggests that flight activity has surpassed 90%, with peak flight likely occurring around June 19, 2025. The model reflects average conditions across multiple beds, so some variation may occur depending on the variety. We will continue to provide updates as the season progresses. If needed, an insecticide application is recommended two weeks after peak trap catches—around July 3.

In collaboration with Washington State University and the Western IPM Center, we produced three YouTube videos focusing on blunt-nosed leafhoppers and false blossom disease.

Ben-Zvi, Y., Rodriguez-Saona, C., Kraft, L., Ben-Zvi, E. Blunt-nosed leafhoppers and cranberry false blossom disease: I. Biology and symptoms. Western IPM, extension video series. https://www.youtube.com/watch?v=nEujE6nNF58

Ben-Zvi, Y., Rodriguez-Saona, C., Kraft, L., Ben-Zvi, E. Blunt-nosed leafhoppers and cranberry false blossom disease: II. Grower interviews. Western IPM, extension video series. https://www.youtube.com/watch?v=Lpvwl9QzIEM

Ben-Zvi, Y., Rodriguez-Saona, C., Kraft, L., Ben-Zvi, E. Blunt-nosed leafhoppers and cranberry false blossom disease: III. Current research. Western IPM, extension video series. https://www.youtube.com/watch?v=9vh-eKUt_5U

New Jersey cranberry growers are increasingly concerned about the rising populations of blunt-nosed leafhoppers (BNLH). This increase is likely linked to shifts in pest management strategies, including the adoption of reduced-risk insecticides and reduced use of broad-spectrum products, as well as the expansion of high-yielding cranberry varieties. BNLH is particularly troubling 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.

Life Cycle

The blunt-nosed leafhopper (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 the course of about 2 months. Adults emerge in early July, peak in mid to late July, and decline by the first week of August. These 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 juices using their piercing-sucking mouthparts. While this direct feeding causes little visible damage, BNLH is an important pest because it serves as a vector for the phytoplasma that causes false blossom disease.

Management

At this time of year eggs should be hatching and early-instar nymphs should be active (Figure 2).

Here are some guidelines to consider when managing BNLH in cranberries:

Identify Infestation Sites: The key to effective BNLH control is identifying infestation sites. The most reliable method for monitoring this insect is by using 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.

Sweep net Monitoring: Perform sweep sets of 25 sweeps each. The recommended number of sweep sets is:

• 1 per 1–10 acres
• At least 10 sweep sets per 10–20 acres
• 1 sweep set per 2 acres for areas larger than 20 acres

Lack of Economic Thresholds: Establishing an economic threshold for BNLH is difficult, as the proportion of false blossom 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.

Control Measures: Control measures 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 the beds have not been treated for BNLH in the past 2–3 years, treatment should be considered.

Treatment Options: If treatment is necessary, consider the following options to manage BNLH:

• Timing: The best time for insecticide treatment is before bloom to target young nymphs.
• Insecticide Options:

Organophosphates: Diazinon (diazinon), Orthene (acephate)

Carbamates: Sevin (carbaryl)

Pyrethroids: Fanfare or Brigade (bifenthrin), Danitol (fenpropathrin)

Neonicotinoids: Assail (acetamiprid), Actara (thiamethoxam). Note: Use neonicotinoids with caution before bloom due to their potential negative effects on pollinators. These systemic insecticides can accumulate in pollen and nectar, posing a risk to bees.

Sulfoximine: Closer (sulfoxaflor). Although effective in small plot trials at the P.E. Marucci Center, more data are needed to confirm efficacy on larger commercial scales.

• Be aware that, while 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 prevent the development of resistance in BNLH populations.

The cranberry toad bug, Phylloscelis rubra (Figure 1), is a pest of concern to cranberry growers in New Jersey. A recent study demonstrated that even relatively low densities of this insect can cause significant injury to cranberries (Rodriguez-Saona et al., 2020. “Characterizing the Feeding Injury Caused by Phylloscelis rubra (Hemiptera: Dictyopharidae) to Cranberries,” Journal of Insect Science, 20(6), 37, https://doi.org/10.1093/jisesa/ieaa143). Thus, monitoring for this insect from now through mid-August is critical.

Life cycle. Cranberry toad bugs feed exclusively on cranberries. This insect has a single generation per year and overwinters as eggs. Nymphs appear from the end of June through early September, while adults are present from the end of July through October (harvest). Eggs are laid from the end of August through October.

Damage. Feeding damage can be noticed in two stages. First-stage feeding damage on vines causes the leaves on new growth to close in towards the branch. Second-stage feeding results in a color change in the new growth, turning it from reddish to brown. This damage can be seen from July until harvest and will cause the branches to die and the berries to shrivel up. Heavy infestations will result in dwarfed berries.

Management. To determine infestation, lightly sweep problematic beds; the bugs should be easy to catch in sweep nets as they are very active. Currently, no threshold has been established for this pest. Therefore, insecticide applications should be based on the relative number of bugs per sweep compared with other sites and the previous history of infestation. If needed, growers can use the following control options: Sevin (broad-spectrum carbamate), Diazinon (broad-spectrum organophosphate), Danitol or Fanfare (pyrethroids), and Actara or Assail (neonicotinoid insecticides, effective against piercing-sucking insects). If infestation is high, treatments should be applied now (early through mid-August) for best control.