Insect and Mite Pests of Strawberries

 
 
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  Aphid | Clipper weevil | Leaf rollers | Mites | Slugs | Spittle bug | Strawberry root weevil | Tarnished plant bug | Wasps/yellow jackets/hornets

An important part in the production of any fruit crop is to know what type of insects could cause production losses. A crop is at risk throughout the fruiting cycle. Insects can attack plants during flowering, fruit formation or just before harvest of the plump, juicy berries. A successful pest management program includes: insect identification; pest number and damage monitoring; what population numbers warrent control and knowing when the pest can be effectively controlled.

Aphid

Identification

  • the aphid is 1-3 mm long, soft-bodied and pear-shaped
  • main identifying feature: cornicles (tailpipes sticking out of the back end)
  • variety of colors: green, yellow, pink, white, bronze, dark-brown or black
  • adults can be winged or wingless

Green Peach Aphid

Life cycle
  • overwinters as egg on the host plant
  • hatchs into a "stem" mother and starts bearing live young; which, in turn, bear live young
  • each mature aphid can produce 50-100 offspring
  • 15-30 generations produced per season
  • aphids can reproduce either sexually or asexually, males are not produced until fall; mating occurs and either an egg or another stem mother is produced which lays the overwintering egg
  • moist, cool weather favors aphid outbreaks

Damage
  • feeding symptoms include: leaf discoloration, flattened appearance, shiny (from honey dew) and, in severe cases, wilted plants
  • produces a sticky substance called honey dew; makes the leaves and fruit sticky and can promote the growth of sooty mold fungi (not harmful to the plant but both can make the fruit unsalable)
  • it seldom causes much direct injury, unless present in large numbers
  • can transmit viral diseases

Monitoring
  • generally, they are found in clusters on the new growth, stems, buds or on underside of leaves
  • in young plants, aphids may cluster near the base of the plant
  • look for symptoms weekly
  • severe infestations are often visible from the edge of the field
  • economic threshold--30 aphids per plant
  • before spraying consider: weather conditions, presence and abundance of natural enemies, value and stage of the crop

Cultural control
  • start with clean stock
  • there are a wide range of natural predators: lady bugs, lace wings, and predatory wasps

Clipper Weevil

Identification
  • 2-3 mm long, dark reddish-brown weevil
  • it has rows of tiny pits and two small white spots with dark centers on its back
  • the long snout is about as long as the insect's body
  • the legless larva is 2 mm long, white to yellow white, thick bodied and curved

Life cycle
  • the female inserts a single egg inside an almost mature bud and then girdles the bud to prevent it from opening and exposing the larva
  • in 1 week, the egg hatches
  • adults emerge in late June; and, in few weeks, they seek a hibernation site, remaining there until the following spring

Damage
  • holes in flowers and petals
  • stems that are chewed or almost clipped through and left dangling
  • the dead straw-colored section is easy to see against the green of the plant

Monitoring
  • weekly checks beginning in May with the early-blooming varieties
  • first place to look--closest to woodlots and shelterbelts
  • economic threshold is one or two clipped buds per metre of strawberry row
  • more information on monitoring for the clipper weevil is described in the Ontario Ministry of Agriculture and Food,Agdex 232/620 Strawberry Clipper Weevil: A Major Pest of Strawberry.

Cultural control
  • minimize the amount of trash in the fields in mid to late summer
  • separate new plantings from old
  • vigorous tillage of old beds after the final harvest while the clippers are pupating will reduce the movement of clippers from infested fields to non-infested fields

Leaf Rollers

Identification
  • a diverse group of moths
  • the caterpillar is slender, green to brown, 12 mm long with dark-brown or black head
  • very active and moves backwards when disturbed

Life cycle
  • the eggs are laid on the strawberry leaves
  • larvae change from pale green to greyish brown as they mature
  • they pupate rolled in the leaf
  • could be 2 generations per year

Damage
  • holes are eaten in the leaves; later the leaves are folded in half and webbed together, causing the leaves to turn brown and die
  • the fruit is rarely attacked
  • damage is usually minimal
  • damage is most common on new plantings late in the season

Monitoring
  • start in the spring
  • look for the folded or rolled leaves, also discolored leaf areas showing some feeding damage
  • unroll leaves and look for small green caterpillars
  • if no caterpillar, then the insect is gone
  • economic threshold--spraying is seldom necessary as healthy strawberry plants have an abundance of leaves and the loss of a few leaves has little effect on fruit production

Cultural control
  • there are several natural predators and parasites that do keep the populations in check
  • spraying is difficult; as once the leaves are rolled, the insect is protected

Mites

Identification
  • the cyclamen mite (CM) is oval, semi-transparent,.25 mm long, shiny and light-green, amber or light tan colored, the nymphs are milky-white; the females are pale-brown
  • the spider mite (SM) is .5 mm, oval, greenish-yellow with 2 irregular dark spots on back

Spider Mite

Life cycle
  • CM overwinter as egg, nymph or adult on underside of leaf, close to the ground
  • CM lay eggs in dark moist places on the host plant (buds and leaf clusters), several generations can overlap
  • each female can produce up to 90 eggs; 80% develop into females
  • SM overwinter as adults
  • when the plant starts to grow, mites mate and lay eggs
  • the eggs hatch and begin to feed
  • there can be several generations overlapping
  • hot, dry weather favours population explosions of SM (depending on the species)

Damage
  • CM--feeding reduces vigour of plants
  • growth appears retarded, twisted, and distorted
  • stems and petioles of leaves remain short and do not elongate
  • high infestations cause new leaves to form a compact mass in crown centre
  • at this point, the leaves are usually brownish green
  • in high infestations, CM move out to feed on the flowers, causing flower death; fruits are small, dry and distorted, and the seeds stand out on the berry
  • symptoms are apparent, even at low population levels
  • SM feed on the leaf underside, preferring the young leaves in the crown
  • feeding damage causes yellow spots (mottling or stippling), leaf crinkling, browning and leaf curling
  • high populations will cause loss in plant vigor and fruit will not form

Monitoring
  • CM--check the midrib of leaflets where they join the petiole
  • economic threshold--10-15 mites per leaf, densities of 45-65 mites per leaf can reduce yield by 33%
  • SM--examine for webbing between or under the leaflets, damage shows up in dry areas of field
  • diagnostic tool--breathe on leaflets, this causes the mites to scurry about; or, tap the leaf over a white sheet of paper, making the pest visible
  • economic threshold is 5 mites per leaf before July 30

Cultural control
  • CM control is hard because the mites hide in closed leaf and flower clusters where the penetration of a pesticide is almost impossible
  • SM predators become established as a strawberry planting matures
  • irrigate regularly to avoid water stress on the plants
  • eliminate weeds that can also be hosts
  • cultivate in the fall to disturb the overwintering sites
  • SMs have naturally occurring predators

Slugs

Identification
  • slugs are 5-7 cm long, greyish, grey-brown or almost black in color, depending on the species and age of the gastropod
  • they hide during the heat of the day in moist-dark places like soil crevices, earthworm holes or under leaves

Life cycle
  • overwinters as adults in trash and leaf litter of hedge rows and windbreaks
  • slugs have both male and female sex organs (hermaphrodites)
  • mating usually takes place; but, under extreme situations, they can fertilize themselves
  • eggs are oval clear, cream or yellow, up to 3 mm long and are in batches of 20 or more
  • the eggs can lay dormant until sufficient moisture is available because they are protected by a jelly like substance
  • eggs can be produced at anytime during the growing season.

Damage
  • can be serious in wet areas or through out over-irrigated fields
  • most damaging to young plants, but can contaminate fruit by feces and slime
  • most pickers either will not pick or will toss away slug contaminated fruit
  • foraging is done in a relatively small area and they usually return to the same spot to hide during the day, unless this spot dries out
  • feeding produces large ragged holes; they rasp away the plant tissue, then suck up the residue
  • feeding is done at night, most active 2 hours after sunset to 2 hours before sunrise, especially when the temperature is below 23°C.

Monitoring
  • watch for slime trails and shredded leaves
  • they can be found resting or hiding when populations are high

Cultural control
  • predators--ducks, chickens, garter snakes, toads and salamanders
  • insect predators--ground beetles, soldier beetles, centipedes and rove beetles
  • prevention is the best method of control
  • limit excessive straw use, vigorous tilling at renovation also helps
  • avoid planting in perennially wet spots
  • clean equipment when moving from a slug infested area to a clean area
  • remove the organic litter on the soil surface of the shelter belts

Chemical control
  • chemical controls are available; slug baits have been somewhat successful--follow label directions
  • till headlands and inter-row areas

Spittle Bug

Identification
  • protects itself by covering its body with a white, frothy spit like substance
  • it is 1-2 cm or more and resembles a fat aphid
  • nymphs are white to lemon yellow
  • adults are greyish-brown, 6 mm long
  • it can hop and fly


Spittle Bug Masses

Life cycle
  • overwinters as an egg in masses of 2-30 on lower parts of crown
  • eggs hatch in May
  • nymphs take 5-8 weeks to reach adulthood
  • adults migrate in June and return in September and October to lay their eggs

Damage
  • nymphs pierce the plant stems and suck plant juice
  • feeds at the base of the plants and later moves up into the developing foliage
  • excessive feeding causes distortion of leaves, shortened fruit spurs and small berries
  • plants will recover after the bug moves on

Monitoring
  • every 2 weeks, randomly select five 2 ft2 areas per acre
  • look for characteristic spittle at the base of plants in the crown area
  • nymphs will be at base of plant, so spreading the plant is necessary
  • some studies indicate that pick-your-own customers are willing to accept a spittle mass of about 2 masses per 2 ft2 without complaints
  • aesthetic threshold 1 froth mass per square foot

Cultural control
  • fields that had been hay or pasture in the rotation are at a higher risk for spittle bugs
  • with good weed control, they are less likely to return in the fall
  • weed free planting
  • populations are higher in fields surrounded with grasses and broad leafed plants like golden rod

Chemical control
  • experience indicates that when chemicals are applied for the control of tarnished plant bug, the spittle bug is controlled
  • spittle acts as protective covering, making chemical control hard; especially, if the spray coverage is poor and low water volumes are used

Strawberry Root Weevil

Identification
  • adult are 5-8 mm long, usually black, but can be light to dark brown, hump-backed and hard-bodied
  • wing covers have rows of round punctures and it can not fly
  • it has a blunt snout
  • larvae are 6 mm long, legless grubs, pinkish-white with a C-shaped body and brown head

    Strawberry Root Weevil adult

    Strawberry Root Weevil larvae

Life cycle
  • overwinters as adults and larvae under soil trash and around the base of host plant
  • emerge in late spring and early summer
  • migrate, looking for food hosts to lay their eggs beside
  • also migrate in the fall looking for overwintering sites (that is when most of us see them)
  • no males are known, each female can lay 200-300 small white eggs in soil cracks
  • in 2-3 weeks the eggs hatch, larvae burrow into ground and begin feeding on host plant roots

Damage
  • adult feeding causes a notching on the leaves
  • does little harm to plant but indicates the pest is there
  • grub feeds on the rootlets and can burrow into the main root weakening the plant, predisposing it to disease and winter injury
  • injured plants may wilt and die during dry summer periods

Monitoring
  • inspect the field edges every week or two during July and August, look for the notched leaf margins
  • a sweep net will help to collect the weevils for identification
  • in the fall, check for larvae by collecting stressed plants; slit open the roots and check for tunneling and larvae

Cultural control
  • cultivated soil around the field perimeter creates a barrier
  • crop rotation
  • remember, they have to walk through the field

Tarnished Plant Bug

Identification
  • adults are 5-6 mm long, 2.5 mm wide and flattened, pale green to reddish-brown with a distinct triangle or "V" mark 1/3 way down back
  • they are difficult to see because they fly or move rapidly
  • young nymphs are dull blue-green; look similar to aphids, but move faster and lack cornicles


Tarnished Plant Bug

Life cycle
  • adults overwinter under debris or plant cover along fence lines
  • in spring, they feed on early growing plants, mate and migrate to crops suitable for feeding
  • egg laying may be as early as mid-May (south) to mid-June (Peace country)
  • nymphs develop into adults in 12-34 days depending on the temperatures; the hotter the weather, the faster they develop
  • they are strong flyers

Damage
  • TPB punctures the plant tissue and sucks the juice when feeding
  • TPB punctures the seeds (usually in one area on the berry)
  • those seeds punctured abort and the hormone production of these seeds stops, as a result, the tissue around that area stops growing causing "cat facing" or "button berries" or "apical seediness"
  • hollow seeds (turn a brown color) distinguish TPB damage from poor pollination
  • generally, the earlier the feeding takes place, the more severe the fruit deformation
  • one nymph per inflorescence can result in 20-30% of the fruit being injured
Monitoring
  • tap a flower or a fruit cluster into a colored dish (any color other than white or green); the dish needs to be deep enough to allow for the insects to be trapped, but shallow enough to allow for inspection
  • how to monitor--tap 3 flower clusters into dish from 5 different locations in the field
  • if there are .5 nymphs per cluster, then it is time to spray
  • another method of monitoring for the TPB is described in the Ontario Ministry of Agriculture and Food Tarnished Plant Bug: A Major Pest of Strawberry Agdex 232/620.

Cultural control
  • get rid of weeds in and near strawberry plantings
  • mow permanent sod in the fall to prevent overwintering sites
  • the TPB moves into the berry crop when alfalfa fields near strawberry fields are cut

Wasps/Yellow jackets/Hornets

Identification
  • Yellow jackets and Hornets belong to the family of Wasps
  • Hornets are black with yellowish white markings and approximately 19 mm long
  • Yellow jackets are smaller and black with bright yellow markings
  • wasps are hunters and are useful in controlling caterpillars and flies, but they can become pests in the berry fields

Life cycle
  • warm, dry springs produce larger wasp problems in August than do wet, cool springs
  • in spring, a fertilized queen emerges from hibernation
  • she chooses a good nesting spot which could be in a hole in the ground (a mouse burrow), a tree branch, bush, under the eaves or in the walls of a building
  • the nest is built by chewing wood fibres into a pulpy mass
  • the queen lays eggs which hatch into legless, blind larvae
  • larvae last 2 weeks, then pupate
  • in 3 weeks, adult females emerge and begin to tend the queen
  • in August, male and new queen cells are produced
  • in early fall, the males and new queens emerge; mating takes place on the wing
  • males die and fertilized queens overwinter in protected sites like stumps or hollow logs
  • the old nest is abandoned and never used again

Damage
  • wasps are attracted to the ripe or injured fruit as a source of sugar and moisture
  • they can be dangerous to pickers because they sting, which is painful, and some people are allergic to the venom (which could result in death)
Cultural control
  • prompt harvesting of ripe berries and clean picking practices
  • hang a piece of meat or fish over a bucket of water with detergent in it, wasps will take a mouthful and fall into the water and drown
  • a 2 litre soda bottle with about 5 cm of soda left in the bottom attracts wasps into bottle
  • a basin with a few inches of water and syrup (like pancake) in it will attract the insect and it drowns in the water
  • set the nest on fire with a torch
  • knock the nest into a sack and burn it
  • carry out control methods after dusk, after the wasps have settled for the night
  • wear protective clothes (coveralls, gloves and hat netting with ends tucked into the collar)
  • if necessary to use a light, do not hold the flashlight, set it to the side and shine the light on nest
Chemical control
  • spray insecticide into the entrance of the nest, do this after dark
  • for ground nests, stuff insecticide soaked cotton or steel wool into the nest entrance
 
 
 
 
For more information about the content of this document, contact Shelley Barkley.
This information published to the web on November 27, 2001.
Last Reviewed/Revised on November 24, 2008.