Archives for May 2020

There is continued concern among New Jersey cranberry growers of increases in blunt-nosed leafhopper populations due to changes in pest management strategies (e.g., adoption of new reduced-risk products and decreased applications of broad-spectrum insecticides). Blunt-nosed leafhopper is of particular concern because they are vectors of false blossom disease.

Blunt-nosed leafhopper nymphs. Photo credit: Lindsay Wells-Hansen.

Life Cycle – The blunt-nosed leafhopper has one generation a year. Blunt-nosed leafhopper eggs overwinter and begin to hatch in early May. The nymphs (see Picture; small yellow-colored insects) will go through five instars in about a month. The adults begin to appear early in July and are most abundant in late July. Numbers of this species start to diminish by the first week in August. The adults have a characteristic blunt head and vary from light yellowish-gray to dark brown. Eggs are laid in August-September.

Damage – Nymphs and adults get their food by sucking the plant juices of the cranberry with their piercing-sucking mouthparts. This direct injury is, however, not noticeable. They are most important as vectors of false blossom disease.

Scouting and Control – The most important point in leafhopper control is locating the infestation. Monitoring for this insect is accomplished best with an insect sweep net. Nymphs can be monitored before bloom using sweep nets. 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. 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, and 1 sweep set per 2 acres for more than 20 acres. In cases of high blunt-nosed leafhopper numbers, we recommend application of a broad-spectrum insecticide, such as Lorsban. This time of the year (May 20-30) would be the period for pre-bloom applications. The neonicotinoids Actara and Assail are very effective against blunt-nosed leafhoppers and can be used to target the adults after bloom. There is no threshold so decisions should be made based on current numbers and prior infestation history. Broad-spectrum insecticides will disrupt biological control particularly the natural enemies (predators and parasitoids) of Sparganothis fruitworm, so their use should be minimized to areas of high blunt-nosed leafhopper populations.

Last year, the insecticide Exirel® (FMC Corporation) was registered for use in cranberries. The Exirel label includes the target pests: cherry fruitworm, cranberry fruitworm, blackheaded fireworm, and Sparganothis fruitworm. The active ingredient (a.i.) is cyantraniliprole. This insecticide belongs to a class of insecticides known as anthranilic diamides (similar to Altacor). This class of insecticides is particularly effective against lepidopteran pests but Exirel has broader insecticidal activity that includes flies, aphids, weevils, etc. After ingestion, anthranilic diamides work by impairing muscle contraction, resulting in feeding cessation, lethargy, and partial paralysis, eventually leading to the death of the insect.

Exirel is considered a reduced-risk insecticide and compatible with biological control and pollination. It should thus be considered as a new alternative when rotating insecticides with different modes of action for preventing the development of resistant populations.

Exirel has a 14-day pre-harvest interval (PHI) and a 12-hour re-entry interval (REI). A maximum of 0.4 lb a.i. can be applied per acre, which equates to three applications at the highest label rate (20.5 fl oz per acre).

Our previous work in laboratory and semi-field experiments has demonstrated that Exirel can provide similar, or sometimes even better, larval control as compared with other registered materials such as Intreprid, Delegate, and Altacor. I encourage growers to consider using Exirel as a pre- or post-bloom application for the control of lepidopteran pests. Because it is a new insecticide, we have limited (large-scale) field data, so I recommend growers to start by using Exirel in a few acreages and share their experiences with me.