Dr. Cesar Rodriguez-Saona, Extension Specialist in Blueberry Entomology, Rutgers University

Dr. Yahel Ben-Zvi, Post-doctoral Researcher, Rutgers University

If needed, post-pollination sprays—particularly for Sparganothis fruitworm (Picture 1) and spotted fireworm (Picture 2)—should be applied as soon as bees are removed. Sparganothis fruitworm is monitored using pheromone traps to assess adult flight activity and abundance. If trap counts are high and no insecticide has yet been applied, treatment should be considered promptly to prevent berry damage.

Sparganothis fruitworm

Picture 1. Adult Sparganothis fruitworm

Where pheromone trap catches are high, management should begin soon after bee removal. The optimal timing for the first post-pollination spray is approximately two weeks after peak moth catch, which typically coincides with the 1^st-2^nd week in July.

Spotted fireworm

Spotted fireworm is one of the most important pests in New Jersey cranberry production. Male moth catches typically peak during the second to third week of June. While trap catches provide an indication of population levels, they do not always correlate well with egg mass abundance. This pest is particularly problematic in weedy beds, where females preferentially lay eggs on weeds, such as brier, red maple, redroot, and leatherleaf. For this reason, monitoring for egg masses on weeds is essential. Maintaining clean, weed-free beds is an important component of management. Egg masses are typically hatching at this time of year, and larvae from this generation will feed on both foliage and fruit.

Control options

Picture 2. Adult spotted fireworm

Insect growth regulators (IGRs), such as Intrepid, are effective against Sparganothis fruitworm and spotted fireworm. If IGRs have been used intensively (e.g., in pre-bloom or bloom applications over the past one to two seasons), rotation to alternative chemistries is recommended. Options include Altacor, Delegate, Exirel, or broad-spectrum insecticides such as Diazinon. Broad-spectrum materials may also be preferred where blunt-nosed leafhopper populations are high, since Intrepid, Delegate, and Altacor do not provide control of this pest.

Root-feeding insects and imidacloprid use

If cranberry beds show signs of damage from root-feeding insects, treatment with imidacloprid (e.g., Admire Pro and generics) should be considered immediately after bee removal (mid-July). Dead patches of vines are often indicative of root-feeding injury (Picture 3). Affected areas should be inspected by pulling dead vines and examining the root zone and surrounding soil for grubs.

Imidacloprid is labeled for control of rootworm (Picture 4), root grubs (Phyllophaga spp.), and other scarab beetles in cranberries. It acts as a contact and stomach poison affecting the insect nervous system and is highly systemic. Because it is highly toxic to honey bees, it must only be used post-pollination.

Picture 4. Larvae of cranberry rootworm

Since most scarab grubs in cranberries have multi-year life cycles, a single application may not fully suppress populations. In many cases, two to three consecutive years

Picture 3. Injury by root-feeding insects

of treatment are required for effective long-term control. Identifying the specific grub species present is therefore important prior to treatment.

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.