Sparganothis Fruitworm Degree-Day Update: as of July 07, 2021

Based on our degree-day (DD) model for Sparganothis fruitworm, the window for egg hatch is between 895 and 1,890 DD (see chart). As of July 07, Sparganothis has accumulated 1,251 DD (using April 15 as biofix). This indicates that most eggs should have hatched by now and fruit is susceptible to infestation. Most beds are out of bloom (early varieties) or should be coming out of bloom. If trap counts have been high and you have not done so already, then you should consider treatment in the next few days to prevent damage to berries. Your best post-bloom options are Diazinon, Intrepid, Altacor, or Delegate. All treatments for lepidopteran pests should be done before the end of this week to avoid substantial injury to fruit.

Sparganothis fruitworm DD model

Root-feeding Pests of Cranberries

If your beds have damage caused by root-feeding insects, you should consider treatment with Imidacloprid (e.g. Admire Pro, Alias 4F, Alias 2F) after bees are removed. Occurrence of root-feeding insects will manifest by the presence of dead patches (see picture). Pulling dead vines and searching through the root zone and soil are needed to reveal the presence of larvae. Admire Pro (imidacloprid) is labeled for the control of cranberry rootworm, white grubs (Phyllophaga spp.), and other scarabs in cranberries.

White grubs, Phyllophaga spp. There are several species of white grubs that infest cranberries in New Jersey, the most abundant being P. georgiana. Grubs are C-shaped and often found near bog margins. Adults are reddish brown and nocturnal. Grubs attack the cranberry roots; adults have not been reported to feed on cranberries. See pictures of grubs and adults in cranberries. The life cycles and abundance of white grub species in New Jersey is not well known. Most likely, Phyllophaga grubs have a 3-year life cycle (based on previous reports and our own observations). Eggs are laid in late-June and July, and will hatch in July. First instars can be found in late-July and August and turn into second instars by the end of August-September. The second instar grubs will overwinter. These grubs will feed the following year until June and molt to third insta

Cranberry Rootworm Injury

rs, which will overwinter. The following year, the third instars will feed for some time and then begin to pupate in June. Pupation will take place in July-August. Adults will appear in the soil in August-September. Adults will remain in the soil and overwinter. They will emerge in June, mate, and begin to lay eggs, completing the cycle.

Cranberry rootworm (Chrysomelidae). Pupation starts in late May and beetles emerge in early June. Adults (see picture) are nocturnal and hide in leaf litter. Adults can be easily picked up in a

Phyllophaga developmental stages

sweep net. Females feed on foliage before laying eggs. Young larvae will feed on roots, and feeding continues until October. The mature larvae (see picture) move down the soil in the fall to overwinter. Holding of the water will delay onset of pupation. 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 works best against early- (1st-2nd) instar grubs. Imidacloprid should be used after bees are taken out of beds. Because of the 3-year life cycle, treatment should be continued for 2-3 consecutive years to ensure control. Imidacloprid (active ingredient) is a neonicotinoid insecticide registered for use in cranberries against cranberry rootworm and scarab grubs. This insecticide is a contact and stomach poison that affects the insect

Cranberry Rootworm Adult

Cranberry Rootworm Larvae

nervous system. It is highly systemic and toxic to honey bees; therefore, can be used only as a post-pollination insecticide. Imidacloprid can be applied by ground or by chemigation. Aerial application of this product is prohibited. Imidacloprid has a long residual activity (> 100 days) as long as the insecticide is not directly exposed to the sun. Admire Pro can be used at 7-14 fl oz/acre. A maximum of 14 fl oz of Admire Pro can be used per acre per season. The PHI is 30 days.

Based on our degree-day (DD) model for Sparganothis fruitworm, first eggs hatch at about 895 DD (see chart). As of June 27, Sparganothis has accumulated 991.5 DD (using April 15 as biofix). This indicates that eggs have started to hatch, and fruit will become susceptible to infestation since larval injury to fruit usually begins after the eggs hatch. According to our model, peak flight should have occurred about a week ago (around June 20). Insecticide applications are usually recommended 10-14 days after peak flight (i.e., June 30-July 4). Most beds should be close to the end of bloom. If trap counts have been high, growers should consider treatment by the end of next week (depending on the variety and time of winter flood removal) to prevent damage to berries. If spraying when bees are present, your option is to use an insect growth regulator (IGR), such as Confirm or Intrepid, or the diamide Altacor. Our “standard” recommendation has been, however, to wait until bees are removed to apply an insecticide. Your post-bloom options include the organophosphate Diazinon, the diamides Altacor, Verdepryn, or Exirel, the spinosyn Delegate, or the IGR Intrepid. Timing of insecticide application is critical; so, if needed, do not wait too long to manage this pest.

Degree-day model for Sparganothis fruitworm

Based on our degree-day model for Sparganothis fruitworm, flight initiation is expected at around 596 DD (see chart). As of June 06, Sparganothis has accumulated 706 DD (using March 1 as biofix; based on Wisconsin conditions) or 554 DD (using April 15 as biofix; a more realistic biofix based on the time when winter flood is removed from New Jersey beds). This indicates that flight activity has likely just started or will start in the next few days. Growers are advised to place pheromone traps for monitoring this pest as soon as possible if they haven’t done so already.

Degree-day model for Sparganothis fruitworm

Based on our degree-day model for Sparganothis fruitworm, flight initiation is expected at around 596 DD (see chart). As of May 30, Sparganothis has accumulated 607 DD (using March 1 as biofix) or 455 DD (using April 15 as biofix; a more realistic biofix based on the time when winter water was removed from most NJ beds). The later biofix indicates that flight activity will start very soon, i.e., within a week from now. Thus, growers are advised to place pheromone traps for monitoring this pest this coming week.

Degree-day model for Sparganothis fruitworm