Insect and Mite Pests of Strawberries

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

• 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

• 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

• 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

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

• 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

• 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

• 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

• 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.

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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)

• 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

• 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

• 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 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

• 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.

• 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.

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

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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

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

• 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

• 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

• 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
  

• 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.

• 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

• 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

• 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

• 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)
  

• 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
  

• 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