Archives for May 2021

Blunt-nosed leafhoppers (BNLH) continue to be an increasing threat to cranberries in NJ. BNLH has one generation a year. It overwinters as

Picture 1. BNLH nymph. Photo by Elvira de Lange.

eggs, which begin to hatch in early May. The nymphs (Picture 1) will go through five instars in about a month. The adults (Picture 2) begin to appear by the end of June and are most abundant in mid-July. Numbers of this species start to diminish by the end of July. The adults have a characteristic blunt head and vary from light yellowish-gray to dark brown. Eggs are laid in June-July. Nymphs and adults get their food by sucking the juices of the cranberry vines with their piercing-sucking mouthparts. This direct injury is, however, not noticeable. They are most important as vectors of false blossom disease (Picture 3). Typical disease symptoms include distinctive branching of the upright shoots (witches’ broom) and malformed flowers where flowers stand erect and petals are redder than normal.

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

1. The most important point in BNLH control is locating the sites of infestation. Monitoring for this insect is accomplished best with an insect sweep net. Nymphs should be monitored before bloom using sweep nets (this time of year). Nymphs before bloom are small; thus, you may need to freeze the samples (to kill them), and then count the number of nymphs under a microscope or using a magnifying lens.
2. To monitor, perform sweep sets of 25 sweeps each. The recommended number of sweep sets is: 1–3 sweep sets per 1–
   

   Picture 2. BNLH adult. Photo by Elvira de Lange.

   10 acres, at least 10 sweep sets per 10–20 acres, and 1 sweep set per 2 acres for more than 20 acres.

3. 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 do not 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.
4. Although they need to be tested, based on experience, I came up with the following tentative treatment thresholds: An average of 20 nymphs per sweep set if it is a new variety bed, bed with young plantings, and/or a bed that has a recent history of false blossom. Or, an average of 40 nymphs per sweep set if it is an older bed and older variety with no previous history of false blossom.
5. 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.
6. 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 increase.
   

   Picture 3. False blossom-infected cranberry vine.

7. 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.
8. 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).
9. Trials will be conducted this year at the Rutgers P.E. Marucci Center with existing and new insecticides against BNLH nymphs.