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.

Most beds are either out of bloom or should be coming out of bloom soon. If Sparganothis fruitworm trap counts have been high and you haven’t already treated, you should consider doing so in the next few days after honey bees are removed to prevent damage to berries. The best post-bloom treatment options are Diazinon, Intrepid, Altacor, or Delegate. All treatments for lepidopteran pests should be completed before the end of this week to avoid significant fruit injury. Additionally, please monitor the weather conditions, as there will be several rainy days this week.

Root-feeding Pests of Cranberries

If your beds show damage caused by root-feeding insects, you should consider treatment with Imidacloprid (e.g., Admire Pro, Alias 4F, Alias 2F) after bees are removed. The presence of root-feeding insects will be indicated by dead patches (see Picture 1). Pull up dead vines and search through the root zone and soil for grubs and worms. Imidacloprid (Admire Pro or other generic insecticides) is labeled for controlling cranberry rootworm, white grubs (Phyllophaga spp.), and other scarabs in cranberries.

White grubs, Phyllophaga spp. Several species of white grubs infest cranberries in New Jersey, with P. georgiana being the most abundant. These grubs are C-shaped and often found near bog margins.

The adults are reddish-brown and nocturnal. While the grubs attack cranberry roots, the adults have not been reported to feed on cranberries (see Picture 2 of grubs and adults in cranberries). The life cycles and abundance of white grub species in New Jersey are not well known. However, it is likely that Phyllophaga grubs have a 3-year life cycle based on previous reports and our observations. Eggs are laid in late June and July, hatching in July. First instars can be found in late July and August, turning into second instars by the end of August to September. The second instar grubs will overwinter. The following year, these grubs will feed until June and molt into third instars, which will overwinter again. In the subsequent year, the third instars will feed for a while before pupating in June. Pupation occurs in July-August, with adults appearing in the soil in August-September. These adults will remain in the soil and overwinter, emerging in June to mate and lay eggs, thus completing the cycle.

Cranberry rootworm (Chrysomelidae). Pupation starts in late May, with beetles emerging in early June. Adults (see Picture 3) are nocturnal and

hide in leaf litter, but can be easily picked up with a sweep net. Females feed on foliage before laying eggs. Young larvae feed on roots, with feeding continuing until October. In the fall, the mature larvae (see Picture 4) move down into the soil to overwinter. Holding water will delay the onset of pupation. The rootworm has a 1-year life cycle. Entomopathogenic nematodes (Heterorhabditis bacteriophora) can be used to control cranberry rootworm.

Use of Imidacloprid. If treatment is needed, use Imidacloprid (Admire Pro or other generic insecticides such as Alias 4F) to control white grubs and rootworms. Imidacloprid is most effective against early (1st-2nd instar) grubs and should be applied after bees are removed from the beds. Due to the 3-year life cycle of these pests, treatment should be continued for 2-3 consecutive years to ensure effective control. Imidacloprid, a neonicotinoid insecticide, is registered for use in cranberries against cranberry rootworm and scarab grubs. This insecticide acts as a contact and stomach poison, affecting the insect nervous system. It is highly systemic and toxic to honey bees, so it should only be used as a post-pollination insecticide. Imidacloprid can be applied by ground or by chemigation, but aerial application is prohibited. The insecticide has a long residual activity (over 100 days) as long as it is not directly exposed to the sun.

Based on our degree-day model, Sparganothis fruitworm has accumulated 1038 degree-days (DD) as of June 24, using April 15 as the biofix date. This indicates that peak flight activity should have occurred at the end of last week. Historically, we recommend insecticide applications 10-14 days after peak flight. This period will fall between mid- to the end of the first week in July.

Based on our degree-day model, Sparganothis fruitworm has accumulated 867 degree-days (DD) as of June 18, using April 15 as the biofix date. This indicates that flight activity has reached the 25% mark. We anticipate that peak flight will likely occur by the end of this week. This model uses averages across several beds, so there may be slight differences depending on the variety. We will continue to provide updates as the season progresses.