If your beds have damage caused by root-feeding insects, you should consider treatment with Imidacloprid (e.g. Admire Pro, Alias 4F, Alias

Damage caused by root-feeding insects

2F) after bees are removed. Occurrence of root-feeding insects will manifest by the presence of dead patches (see picture). Pull dead vines and search through the root zone and soil for grubs and worms. 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 grub damage 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 instars, 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.

Phyllophaga life cycle

Cranberry rootworm (Chrysomelidae). Pupation starts in late May and beetles emerge in early June. Adults are nocturnal and hide in leaf litter. Adults can be easily picked up in a sweep net. Females feed on foliage before laying eggs. Young larvae will feed on roots, and feeding continues until October. The mature larvae 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 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.

As we approach the end of bloom, growers should consider the need for any post-bloom applications. The main pest targets for these applications are mainly Sparganothis fruitworm and spotted fireworm.

Sparganothis fruitworm (SPARG) – If your farm has high pheromone trap counts, you should consider managing this pest as soon as bees are removed. The timing for this 1st post-pollination spray is at 2 weeks after peak pheromone trap catches, which usually coincides with this time of the year.

Spotted fireworm (SFW) – SFW is one of the most important pests in New Jersey. Male SFW moth catches typically peak in the second through third week in June. Although trap catches give an indication of population size, these numbers not always correlate with numbers of egg masses. This insect becomes a problem in “weedy” beds because female moths lay their eggs predominantly on weeds. Thus, growers need to monitor for the presence of SFW egg masses on weeds (broadleaf species and grasses). Keeping beds clean from weeds will keep this insect under control. Egg masses should be hatching by now. SFW larvae from this generation feed on foliage as well as fruit.

Control Options – Insect Growth Regulators (IGRs) (e.g. Intrepid and Confirm) are effective against SPARG. Alternatively, if you have used IGRs intensively (e.g. last year and this year as a pre-bloom or bloom spray), and would like to rotate with other chemistries, you may want to use Altacor, Delegate, Exirel, or the broad-spectrum insecticides Diazinon or Lorsban. Broad-spectrum insecticides are also a choice if you have high blunt-nosed leafhopper populations because Intrepid, Delegate, and Altacor will have no effect against this insect. If you are an Ocean Spray (OS) grower please check restrictions on the use of these insecticides. Lorsban in particular can’t be used by OS growers after bloom due to MRLs for exporting cranberries. If you are an OS grower and want to use a post-bloom application to control SPARG then Delegate, Altacor, or Diazinon (no aerial application allowed) would be your options.

Blunt-nosed leafhoppers – The best timing for controlling blunt-nosed leafhoppers is before bloom when they are immatures. At this time

Table 1. Leafhopper control options

of the year, most of the population are adults and already laying eggs. If you did not spray before bloom and have a high leafhopper population, you may consider a post-bloom application to prevent from an increase in population size. You may also consider spraying next year to control for those immatures that will emerge from the already laid eggs. See Table for control options. Please check, especially for Ocean Spray growers, the restrictions based on maximum residue limits (MRLs).

Based on our degree-day (DD) model for Sparganothis fruitworm, peak flight and first eggs hatched events are expected at around 884 and

Sparganothis degree-day model benchmarks

895 DD, respectively (see chart). As of June 20, Sparganothis has accumulated 1022 DD (using March 1 as biofix) or 883 DD (using April 15 as biofix; a biofix more realistic to New Jersey practices). Based on the April 15 biofix, we are at peak flight activity and eggs should start hatching within the next few days. Larval injury to fruit usually begins after the eggs hatch. If treatment is required (based on pheromone trap counts), sprays should be applied two weeks after peak moth flight (i.e., 1st week in July) and/or earlier (i.e., next week) if populations are unusually high. When bees are present, your option is to use an insect growth regulator such as Intrepid. Our “standard” recommendation has been, however, to wait until bees are removed to apply an insecticide. Your post-bloom options include Diazinon, Altacor, Delegate, Exirel, or Intrepid. Timing of insecticide application is critical; so, if needed, do not wait longer than July 5 to manage this pest.

Cranberry beds are in bloom. If insects have been effectively managed prior to bloom, we recommend no sprays at this time. A reminder: when bees are present your only choices of insecticides are insect growth regulators (IGRs) such as Intrepid 2F or Bt products such as DiPel.

During bloom we recommend monitoring insect populations using pheromone traps. Pheromone traps should be used particularly to monitor activity of Sparganothis fruitworm and blackheaded fireworm, two key pests in New Jersey.

Sparganothis fruitworm– Adult flight should have started a few weeks ago and we will be at peak flight activity by next week (see DD model

Sparganothis fruitworm adult

below). Damage by the second generation larvae begins after the eggs hatch, usually 9-12 days after they are laid. These larvae will feed on foliage and fruit. Larvae will partially feed on berries, causes scoring of the fruit. However, particularly on Ben Lear, larvae may feed inside the fruit. Insecticide treatment should target small larvae. Pheromone traps can be utilized to time insecticides sprays. If treatment is required, sprays should be applied two weeks after peak moth flight and/or earlier if using an IGR. If trap counts indicate a low population that requires management, a single insecticide application may be made post-bloom. If trap counts are high, then an early application of an IGR may be used when the first eggs start to hatch. This would be followed by a second application soon after bloom. Your post-bloom options are Diazinon, Altacor, Delegate, Exirel, or Intrepid.

As indicated above, controlling fruitworm populations is often very difficult and many require multiple applications depending on pest pressure. Sparganothis fruitworm populations in Massachusetts are resistant to organophosphate insecticides (e.g. Diazinon, Lorsban). Thus, organophosphates should be used with care, i.e., always rotate insecticides with different modes of action. Organophosphate insecticides will also negatively affect natural enemy populations. Delegate, Altacor, and Exirel are insecticides belonging to relatively new modes of action; these are registered against fruitworms and can be used as an alternative to organophosphates post-bloom.

Degree-day model for Sparganothis fruitworm

The figure details life history benchmarks of interest for Sparganothis fruitworm and associated degree-day estimates from March 1(credit:

Sparganothis degree-day benchmarks

Elissa Chasen and Shawn Steffan, USDA-ARS and UW Entomology). Flight initiation is predicted around 595 DD, at a lower temperature threshold of 50°F. Based on this model Sparganothis fight was initiated in our region (Chatsworth, NJ) about a week ago. So far, we have accumulated (starting April 15) 688 DD, which means that egg laying has just started (depending on the DD accumulations specific to your farm); however, eggs are not expected to hatch until later this month. Also, a reminder that a single insecticide application aimed at Sparganothis larvae will likely have the greatest effect if it is timed between the beginning and the peak egg-hatch/larval-emergence, which is approximately 895-1,400 DD. I will keep you updated on these DD predictions as the season progresses.