Cranberry toad bugs (Figure 1) should be the last insect pest of concern this season. Growers should start monitoring for this insect from now until the end of July.

Figure 1. Toad bug nymph. Photo by Elvira de Lange

Life cycle. Toad bugs, Phylloscelis rubra (Hemiptera, Dictyopharidae), feed only on cranberries. This insect has a single generation per year. It overwinters as eggs. The nymphs appear by the end of June through early September; nymphal abundance peaks between last week in July and 1st week in August (Figure 2). The adults emerge from end of July through October (harvest) and eggs are laid from end of August through October (Figure 2). Figure 3 shows seasonal abundance of toad bug nymphs and adults in New Jersey cranberries based on sweep net samples.

Figure 2. Toad bug life cycle

Injury. Feeding injury can be noticed in two stages. First stage feeding injury on vines causes closing in (towards the branch) of the leaves on the new growth. Second stage feeding causes changed in color (reddish to brown) of new growth (Figure 4). The injury can be seen from July until harvest. This injury will cause dying of the branch and the berries to shrivel up (Figure 4). Heavy infestation will result in dwarfed berries.

Figure 3. Seasonal abundance of toad bugs in cranberry bogs

Figure 4. Toad bug injury to cranberries

Management. To determine infestation levels, lightly sweep problematic beds (bugs should be easy to catch in sweep nets as they are very active). There is currently no threshold established. Thus, insecticide applications should be based on the relative number of bugs per sweep compared with other sites and previous history of infestation. Currently, growers can use the following control options: Sevin 4F (carbamate), Diazinon, Imidan 70W (organophosphates), Actara or Assail 30SG (neonicotinoids). If infestation is high, treatments should be applied before the 1st week of August.

If needed, post-pollination sprays (particularly for Sparganothis fruitworm and spotted fireworm) should be applied as soon as bees are removed; ideally before 11 July. Sparganothis fruitworm is monitored with pheromone traps to assess adult flight pattern and their abundance. If you had high trap counts of this pest and have not used an insecticide treatment yet you should consider treating soon to prevent damage to berries. Your post-pollination options include Diazinon, Exirel, Altacor, or Delegate.

Root-feeding insects and use of Imidacloprid

If your cranberry beds have damage caused by root feeding insects, you should consider treatment with imidacloprid (Admire Pro and other generics) immediately after bees are removed (mid-July). Dead plant patches indicate the presence of root-feeding insects (Figure 1). Pull dead vines and search through the root zone and soil for grubs. Imidacloprid is labeled for the control of rootworm, root grub (Phyllophaga spp.) (Figure 2), and other scarabs in cranberries. 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. This insecticide can be applied by ground or by chemigation. Aerial application of this product is prohibited. Admire Pro has a long residual activity (> 100 days) as long as the insecticide is not directly exposed to the sun and 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. Irrigate target area with 0.1 to 0.3 inches before and after the application of imidacloprid. The pre-harvest interval is 30 days. Most scarab grubs in cranberries have multi-year life cycles; consequently, you may not be able to suppress a population of 2- and 3-year life cycle grubs with a single application. You may have to use imidacloprid two to three years in a row for most effective suppression. For this reason, it is useful to know what species you have before using imidacloprid. See “Cranberry Insects of the Northeast” (authors: Averill and Sylvia) for information on how to identify common grub species in cranberries.

Figure 1. Damage caused by Phyllophaga grubs

Figure 2. Phyllophaga grubs

Based on our degree-day (DD) model for Sparganothis fruitworm, first eggs hatched at about 895 DD (see chart). As of July 01, Sparganothis has accumulated 979 DD (using April15 as biofix). This indicates that eggs have started to hatch, and fruit will become susceptible to infestation. Most beds are close to the end of bloom. Thus, if trap counts have been high, then a post-bloom application might be necessary. Growers should consider treatment early next week (as soon as bees are removed) to prevent damage to berries. Optimal control will be achieved if insecticides are applied before 07 July. Your best post-bloom options are Diazinon, Exirel, Altacor, or Delegate.

Sparganothis fruitworm degree-day model

Based on our degree-day (DD) model for Sparganothis fruitworm, flight initiation and first eggs laid events are expected at around 596 and 681 DD, respectively (see chart). As of June 18, Sparganothis has accumulated 661 DD (using April 15 as biofix; a biofix more realistic to New Jersey practices). Based on the April 15 biofix, flight has been initiated and eggs should start to be laid soon. However, we do not expect peak flight and those eggs to start hatching until the end of next week. Larval injury to fruit usually begins after the eggs hatch. If treatment is required (based on pheromone trap counts), sprays should be done 10-14 days after peak moth captures, ca. 7-11 July. If Sparganothis pressure has been high, it may be advisable to treat 3 weeks after the moth flight began (i.e., around 1-4 July) and again 10 days later. When bees are present your option is to use an insect growth regulator such as Confirm or 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 too long to manage this pest. I will continue to provide weekly updates to see if these estimated dates change as the season progresses.

Sparganothis fruitworm degree-day model