By now the winter flood is off from most New Jersey cranberry beds. Once the water is removed, the vines will start to initiate bud break. From now until bloom, growers should scout their beds using sweep net sampling for lepidopteran pests (spongy (=gypsy) moth, blackheaded fireworm, spotted fireworm, Sparganothis fruitworm, and cranberry blossomworm), and blunt-nosed leafhoppers (Figure 1).
Figure 1. Spongy moth larva (A); Blackheaded fireworm larva (B); Sparganothis fruitworm larva (C), Spotted fireworm larva (D); Cranberry blossomworm larva (E); Blunt-nosed leafhopper nymph (F). Photo Credits: Elvira de Lange & Dan Schiffhauer.
Spongy moth – Although spongy moth numbers should have dropped compared to the last couple of years, we might see larvae still in places where high infestation occurred, particularly in beds near wooded areas. At this time of the year, the larvae are small (early instars). This insect has one generation a year and overwinters as eggs. Eggs hatch at this time of the year and 1st instars “balloon” on silken threads from infested trees onto nearby cranberry beds. Thus, spongy moths tend to be one of the earliest caterpillars to show up in cranberry beds, usually during the first week of May. The larvae are quite easy to detect by means of sweep net sampling and are easy to control with most of the insecticides at our disposal (see recommendations below).
Blackheaded fireworm – Blackheaded fireworm eggs overwinter on the bed and usually hatch by around mid-May. It is important to catch the first generation, if possible, because the second generation occurs during bloom and is typically much more destructive. Blackheaded fireworm larvae can be detected by sweep net sampling and it is a good idea to look along the edges of beds where vines first begin to grow. Remember: blackheaded fireworm is much easier to control if detected during the early part of the season.
Sparganothis fruitworm – This insect is a serious pest in most cranberry-growing states. It completes 2 generations a year and overwinters as an early-instar larva. The larvae from the 1st generation feed on foliage. In New Jersey, first generation adult moths emerge from mid-June through the first weeks in July; pheromone traps are commonly used to monitor adult flight and population size. The 2nd-generation eggs are laid on cranberry leaves, and larvae will feed on fruit.
Spotted fireworm – This insect overwinters as a 2nd instar larva and completes 2 generations a year. The larvae feed between uprights they have webbed together. First-generation larvae injure the foliage causing it to turn brown as if burned. In New Jersey, 1st-generation adult moths emerge the first week of June, followed by a 2nd-generation adult emergence in early August. Eggs are laid in masses on weedy hosts. The larvae from 2nd-generation adults emerge in mid-August and may feed on fruit. Populations of spotted fireworm are regulated by their natural enemies, particularly Trichogramma wasps that parasitize the eggs.
Cranberry blossomworm – Adults lay their eggs in October in cranberry beds. The eggs overwinter and hatch over a period of several weeks. Early instars can be found during the first week of May. Larvae go through 6 instars to complete their development. Because the first instars feed during the day (and at night), scouting can be done during the daytime using sweep nets to estimate larval abundance. Larvae turn nocturnal during the later instars and thus night sweeping (9 pm – 1 am) is recommended for sampling. Larvae complete their development by June-July. Older instars are very voracious and capable of destroying 100 blossoms within a 3-week period. There is a pre-pupal stage that lasts until the end of August and a pupal stage that lasts until October. Adults emerge from the end of August to the end of October.
Lepidopteran Pests Monitoring and Control – Use sweep netting for monitoring early lepidopteran pests (pre-bloom). A sweep set consists of 25 sweeps and 1 sweep set is recommended per acre (this may vary depending on the size of bogs). The action threshold for false armyworm, blossomworm, other cutworms, and spongy moth (we use a combined threshold from adding all these caterpillars per sweep set) is an average of 4.5 caterpillars in sets of 25 sweeps. For brown and green spanworms is an average of 18 per sweep set. The action threshold for blackheaded fireworm and Sparganothis fruitworm is an average of 1.5 per sweep set. We recommend the use of reduced-risk materials such as the insect growth regulator (IGR) Intrepid, the spinosyn insecticide Delegate, or any of the diamide insecticides Altacor, Exirel or Verdepryn if populations exceed action thresholds. These are reduced-risk, softer insecticides that are very effective against lepidopteran pests. Remember to rotate insecticides with different modes of action to prevent onset of insecticide-resistant pest populations.
Leafhoppers –There is continuing concern among New Jersey cranberry growers of a potential increase in leafhopper populations because of changes in pest management strategies (e.g., adoption of new reduced-risk products and decreased applications of broad-spectrum insecticides). The blunt-nosed leafhopper is of particular concern because this insect can transmit cranberry false blossom disease. This leafhopper has one generation a year. The adults are found in the highest numbers during July, although nymphs or adults may be found from the end of May until October. The eggs are laid in August-September and the overwintered eggs hatch in May or June. The nymphs go through 5 instars to complete their development.
Leafhopper Monitoring and Control: Leafhopper nymphs can be sampled using sweep nets (as described above for lepidopteran pests). 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. There is no established threshold based on sweep net counts because it varies depending on the age of beds, the variety, and/or with false blossom incidence. These decisions should be made by comparing current numbers with prior infestation history.
In cases of high numbers of blunt-nosed leafhopper nymphs, we recommend application of a broad-spectrum insecticide, such as Sevin, Diazinon (no aerial applications allowed), Fanfare, or Danitol. Broad-spectrum insecticides will disrupt biological control particularly the natural enemies (predators and parasitoids) of Sparganothis fruitworm, so their use should be restricted only to areas of high leafhopper populations.
