Cranberry Insect Pests Commonly Encountered in Massachusetts

Insect Life Histories

Insects undergo change as they grow in a process called metamorphosis.  In complete metamorphosis, there are four stages: egg, larva, pupa, and adult (see Figure 1).  The larva bears no resemblance to the adult.  The pupa is an inactive stage where adult structures are formed.  Adults no longer molt or grow but they mate and reproduce.  Many cranberry insects, including black-headed fireworm and cranberry weevil undergo complete metamorphosis.

In gradual metamorphosis, there are only three stages: egg, nymph and adult (see Figure 2). Nymphs are the growth stage and their wings gradually develop.  Several pest species, including cranberry black bug and blunt-nosed leafhopper undergo gradual metamorphosis.

SPRING AND EARLY SEASON PESTS

Vaccinium SCALE (Diaspidiotus sp.) (and Dearness Scale, Latania Scale, etc.).

Vaccinium scale populations should be assessed in the spring.  There are two generations, one in spring, another in summer.  Treatment should only occur when the crawlers have been released (mid-June, mid-August) but care must be taken when bees are present.  

CRANBERRY WEEVIL (Anthonomus musculus)

Weevil Management: Cranberry weevil has developed sequential resistance to compounds over time. Use Avaunt (indoxacarb) if it still shows efficacy on your bogs; in the event of Avaunt failures, switch to Actara (thiamethoxam); in the event of Actara failures, switch to Fanfare (bifenthrin). For resistance management, if you have success with more than one compound, rotate them.

Action threshold is an average of 4.5 weevils in 25 sweeps for spring population, and 9 weevils in summer.  Summer feeding is not as damaging as spring feeding and egglaying.  Adult weevils are found throughout the growing season.  Sweep-net for weevil when warm, sunny, and calm.  Let net contents settle: weevils "play dead" when disturbed.  Do not count non-pest gray weevils.  Spring weevils move in from the woods and blueberry outside the bog; consult sweep records from previous years to determine invasion pattern.  Even if threshold is exceeded, sometimes it is advisable to wait 1-2 weeks in spring to treat.  Weevil numbers may continue to rise as more weevils move in.  However, waiting too long becomes risky if blossom buds have appeared and eggs are being laid.  Late water is not effective against weevil.  Early developing new hybrid cultivars may be infested by weevil earlier than heritage cultivars.  Sanded and new plantings are magnets for earliest weevil activity.

Blunt nosed LEAFHOPPER (Limotettix vaccinii)

This insect appears as a nymph (tiny green bug) in May and may be managed then.  This insect vectors false blossom disease.  Adults appear in July, and this timing could be a second window for treatment.  Any broad spectrum applications should keep populations in check.

Actara, Assail, and Cormoran were found to be effective in NJ screening trials. FIFRA 2(ee) recommendation based on efficacy in NJ.

Cranberry BLACK BUG  (Plagiognathus repetitus)

This insect appears as a nymph (tiny green bug) in May and should be managed then to avoid that year's crop loss.  Adults appear in July, and this timing and could be a second window for treatment.  Any broad spectrum application should keep populations in check.

CUTWORMS (BLOSSOMWORM, FALSE ARMYWORM), HUMPED GREEN FRUITWORM AND SPONGY MOTH

The action threshold for cutworms is an average of 4.5 larvae per 25 sweeps. Count all cutworms and spongy moths together.  Very young false armyworm caterpillars are whitish with black spots, each with a black spine.  These caterpillars tend to loop like spanworms but gradually drop this movement.  Early detection is important because they consume the terminal buds before new growth starts.  As cutworms get older, they will not be picked up in day sweeps.  

For spongy moth, check for patchy infestations and spot treat, i.e., along edges facing uplands with infested trees.  Larvae balloon in from trees.  Check previously infested areas - eggs can overwinter on flooded bogs. 

SPANWORMS

(GREEN SPANWORM, BROWN SPANWORM, BIG CRANBERRY SPANWORM, WINTER MOTH)

Green spanworm caterpillars start to appear in early season sweeps. They pupate at the end of May and white/yellow moths can be seen flying close to the vines in June. The action threshold for spanworm is an average of 18 small larvae in 25 sweeps. Threshold may be lowered for large larvae. 

Brown spanworm larvae occur later but have been rare in recent years. 

Scout for winter moth much earlier than for other spanworms, as early as May 1. If you have a history of winter moth infestation, you may need to apply a prophylactic spray early in the season. Larvae balloon in from infested trees. Injury may be done to the developing buds before populations can be detected and impact yield.

BLACK-HEADED FIREWORM (Rhopobota naevana)

Watch out:  Fireworm can be a very serious problem! Start inspecting in early spring.  This pest is easy to manage if infestation is detected early. Larvae hatch in mid-May; even earlier in warm springs. Small larvae are hard to pick up and see in sweep net. Larvae do not grow bigger than 1/3 inch.

Second generation is active during bloom.  Use pheromone traps to time management of second generation. Black-headed fireworm moths are only 1/4" long and are black and gray; exclude larger, non-pest moth caught in traps.  For summer generation with Intrepid or Altacor, timing is 2 weeks after onset of moth flight (~6/20), and again 10 days later.  Do not use Diazinon, Orthene or Sevin during bloom; it is illegal and will interfere with pollination.

Infestations move rapidly!  Spring generation is a much easier target than the second generation (occurs during bloom).

YELLOW-HEADED FIREWORM  (Acleris minutum)

Orthene, Sevin, and spinosyn products (Delegate and Entrust) can be used as specified for black-headed fireworm (see previous page).  Intrepid and Diazinon, FIFRA 2(ee) recommendations, can be used as specified for black-headed fireworm.

Yellow-headed fireworm may appear on beds that are not completely flooded in the winter.  Eggs are laid in April and hatch in May.  Caterpillars are all yellow and are impossible to distinguish from Sparganothis. The yellow-headed fireworm pupa has a knob at its top, while Sparganothis pupae do not.  The overwintering moths are slate grey and the summer generation moths are bright yellow.

SPARGANOTHIS FRUITWORM (Sparganothis sulfureana)

Small Sparganothis caterpillars are picked up in the sweep net in mid-May.  Check for caterpillars in yellow loosestrife tips that have rolled leaves; this will give you an idea of the larva’s appearance so you can ID them in the net.  The 2nd generation in July feeds on both fruit and foliage.  With both generations, always target the small caterpillars.  Keep an eye on large-fruited cultivars, which tend to be hardest hit; Howes the least.  The 2nd generation caterpillars are difficult to manage because they feed inside large fruit.

Beginning in June, use pheromone traps to determine moth flight.  When managing 2nd generation population, you want to target caterpillars as they are hatching, not the adult moths.  If treating with growth regulator (Intrepid) or Altacor, apply insecticide 3 weeks after the moth flight begins, (~late June), and make at least one more application 10-14 days later.  When treating with Delegate, apply 10-14 days after peak moth captures (~mid-to-late July).

Sparganothis populations are resistant to the organophosphates, including Diazinon and Orthene.  Intrepid and Delegate are excellent alternatives.  Late water has not been shown to be effective against this insect, but it does synchronize moth emergence. 

CRANBERRY FRUITWORM (Acrobasis vaccinii) 

Moths fly in June. Females hold off laying eggs until pinheads have started to size up. Large-fruited cultivars are hard hit with early egglaying. Management of Howes should be later than all other varieties as berries are later to size up. A second peak of egglaying may occur at the end of July.

Late Water

Holding late water in the spring is an excellent cultural practice that severely reduces fruitworm when held for the full duration of 4 weeks. It is possible that sprays can be eliminated.

Early fruitworm spray options, when bloom is present (~6/20-7/10)

Later fruitworm options once bloom is complete 

All of these choices are toxic or highly toxic to bees and should not be applied to beds with bloom. Exception is Delegate (see caution above).

Important general considerations for cranberry fruitworm management:

1. Target only eggs. They are inside the berry calyx. Early larvae in fruit cover entrance with white silk.
2. Do not treat in attempt to control caterpillars in the fruit or expect that you can manage them as they move between fruit. Research shows that sprays made after caterpillars have entered fruit are wasteful and minimally effective.
3. Red berries indicate a missed treatment; caterpillars are protected now and feeding inside the berry.
4. Today, fruitworm populations may be very low on bogs that have had well-timed Altacor sprays; thus, the need for a series of three sprays like the old days may not be cost effective. (See Option 2 below where presence of an infestation is used to trigger a spray).
5. To truly estimate how big a cranberry fruitworm infestation is on a bog, sampling of berries must be random (close your eyes when your reach for a berry). Collect berries across the whole bog.
6. Use magnification when assessing eggs. Look at eggs carefully to be sure they are alive. As you move into the season, many eggs are dead or parasitized. Do not count these.
7. Be careful that you do not count newly settled Vaccinium scale; crawlers like to settle inside of the berry calyx and form a waxy cover that can be mistaken for a fruitworm egg.
8. Consider two possible approaches to managing fruitworm:
   • 1) A prophylactic option based on plant development where you spray and assume there is fruitworm pressure present.
   • 2) A sampling program searching for eggs in berry calyx to determine if or when treatments are triggered.

OPTION 1: USING PLANT DEVELOPMENT TO TIME EARLY FRUITWORM MANAGEMENT

1st treatment
Calculate % out of bloom (% flowers that have lost petals or become pinheads/fruits) 

To properly time your first spray, calculate the % out-of-bloom every few  days as pinheads start to form, usually around the end of June.  You are trying to accurately assess when 50% OOB occurs and to estimate the onset of berry development.  For each acre of bog, randomly collect 10 uprights and record the number of flower buds, flowers, pinheads, and fruit.    

Calculate using the following: 

2nd treatment
Apply about 10 days after 1st treatment.

3rd treatment
Sample berries and check for eggs to trigger this spray. Keep in mind that we may see a second peak of activity in late July.

One week after your 2nd treatment, inspect 50 randomly picked berries/A (with a minimum of 200 berries per piece, no matter how small piece is) for viable eggs. Follow guidelines in table below to determine necessity of additional sprays.  If egg numbers trigger a spray, spray ASAP.  If no egg is found, repeat berry inspection process every 3-4 days until Aug. 15 or longer if eggs are still being detected. 

OPTION 2: SCOUTING FOR FRUITWORM EGGS TO DETERMINE NEED FOR TREATMENT

Starting after 50% out-of-bloom when berries have enlarged, inspect 50 randomly picked berries/A (with a minimum of 200 berries per piece, no matter how small piece is) for viable eggs. Follow guidelines in table below to determine necessity of sprays to avoid a projected 3% infestation of fruit.  If egg numbers trigger a spray, spray ASAP.  If no egg is found, repeat berry inspection process every 3-4 days until Aug. 15 or longer if eggs are still being detected. 

CRANBERRY FLEA BEETLE (Systena frontalis)

Adult flea beetles are active in late July through September.  Beetles and their feeding injury are very patchy, often in areas of lush vine.  High levels of beetle feeding can impact bud development for the following year.  Firm thresholds have not been quantified, but sweep net counts of 15 per 25 sweeps on average over all acreage is the trigger to consider management.  

GOLDEN CASEBEARER (Triachus vacuus)

A tiny new beetle appeared in the last decade that causes feeding injury in June and July, showing as discrete brown areas and bloom damage. If beetles can be detected before bloom, a spray could be applied to manage them.  Larvae feed on detritus on the bog floor and cannot be targeted.

CRANBERRY TIPWORM (Dasineura oxycoccana)

Early season tipworm injury often is high, but good vine health enhances rebudding.  Appearance of injury does not mean that insects are still present.  Only very late-season injury, which is rare, appears to consistently reduce yield.  Stressful vine conditions in the year of injury may also result in yield reduction.  Diazinon is labeled for tipworm, but control is very poor.  
Sprays are strongly discouraged for this insect.