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Seasonal Strawberry Pests in Florida

The mild weather of Florida’s fall and winter sustain the nation’s second largest strawberry production.  That positive condition, unfortunately, is suitable to several arthropod pests.  As soon as transplanting irrigation is turned off and strawberry plants are established, growers must scout fields once or twice each week to assess the status of pests such as spider mites, worms, aphids, thrips, cyclamen mites and sap beetles.  Our ability to recognize these pests and their damage is important in determining successful control methods.

1. Spider mites.  The twospotted spider mite, Tetranychus urticae, is the most significant arthropod pest in strawberry. It attacks strawberry plants in nurseries, greenhouses, and open fields. The twospotted spider mite feed on the sap of the leaves causing chlorosis (Fig. 1).  As few as 10 or even less mites per leaflet can cause economic losses. They disperse easily by either walking from leaflet to leaflet or by wind through their spider web-like system (Fig. 2). They develop through an incomplete metamorphosis including egg, nymphs, and adult (Fig. 3).

Control. Traditionally, control strategies for twospotted spider mite require several applications of miticides during the production season.  In many cases, miticides are applied when about 5% of the leaflets possess one or more spider mites.  As a biological control method, the predatory mites Phytoseiulus persimilis has been released in the Plant City area and they can provide excellent season-long control. They can be introduced in the field as early as when strawberries are being transplanted.  Neoseiulus californicus has been used successfully in North Florida production. 

There is a second spider mite of moderate concern occasionally in Florida.  The tumid mite, Tetranychus tumidus, is a dark red to purplish, robust mite (Fig. 4). The injury inflicted to strawberry plants resembles the damage caused by the twospotted spider mite.  The tumid mite and the twospotted spider mite co-exist in the strawberry crop.  In some instances, tumid mite densities have been higher than densities of the twospotted spider mite.  Control of this pest is somewhat easier to accomplish than is that of the twospotted spider mite.  In general, miticides that control twospotted spider mite will control the tumid mite.  Some broad-spectrum insecticides, such as methomyl, kill the tumid mite but do not control twospotted spider mite.  Accordingly, applications of such broad-spectrum insecticides may render the tumid mite unnoticeable.  

2.  Lepidopterous Larvae (worms). Two species of worms can cause early losses in Florida: the fall armyworm (Fig. 5) and southern armyworm (Fig. 6). These worms are the immature stage of moths and develop through a complete metamorphosis including egg, plant eating larvae (worms), hidden and resting pupae, and the night flying adult moth stage.  Larvae feed on young strawberry leaflets and buds as they develop. Dark, small fecal pellets on the tops of the leaves or on the plastic mulch indicate larval feeding (Fig. 7).

Control. Scouting should be performed once or twice per week, particularly during the early season, to check for young leaves with holes and missing margins. Several products are available to control these worms, some of which are biologically based and very compatible with biological control of spider mites.

3. Aphids.  There are two species of aphids found in Florida strawberries, the strawberry root aphid (Aphids forbesi), and the cotton aphid (also known as the melon aphid) (Aphis gossypii). Aphids may be green, black, brown, or some other color depending on the sap color of the host plant. These slow-moving insects with pear-shaped bodies range from 1/16 to 1/8 inch long. Only a few aphids have wings but all have a pair of cornicles or “exhaust pipes”, one on each side of the rear end (Fig. 8).  Aphids are sucking insects that feed by thrusting their long beaks into the plant tissue and can cause wrinkling of the leaves that can reduce photosynthesis (Fig. 9). They remove great quantities of sap then excrete the sticky, sugary excess as "honeydew".

Control. Well established strawberry plants can tolerate low (1-5 aphids per leaflet) to medium (10-15 aphids per leaflet) levels of aphids. Usually parasitic wasps, predators, and diseases that contribute to aphid control can be found in the field.  Several insecticides are available to control aphids when necessary.

4. Thrips.  Flower thrips are slender and very small (about 0.03 inch long). Adults have four feathery wings and vary from yellow to dark brown (Fig. 10); nymphs are pale and without wings. Nymphs and adult thrips can injure the plant by rasping the plant tissues and sucking the exuding sap. Thrips feeding on strawberry blossoms cause the stigmas and anthers to turn brown and abort prematurely (Fig. 11).

Control.  To sample thrips, randomly collect flower blossoms and slap blossoms onto white paper or “huff” air at your lips onto the flowers to cause the thrips to run about.  Flower thrips rarely cause economic damage at low population densities. Sprays (compatible and incompatible with biological control) are available to control excessive thrips.

5. Cyclamen Mites. This cyclamen mite, Polyphagotarsonemus latus (Fig. 12), can be a very serious pest in Florida. Infested strawberry leaves are small, chlorotic, highly wrinkled, thickened, and possess short petioles. Runners often have numerous small "thorns" rather than a smooth texture. Additional symptoms include dark brown, dry flowers, russeted berries, and poorly developed root systems. In general, plants look stunted and produce late (Fig.13).  Widespread infestations in Florida strawberry fields occur only occasionally and usually are related to an infested northern nursery.  Cyclamen mites can be found in the crevices of leaf wrinkles, on unopened and opened flowers, on newly formed fruit and in the plant bud.  This pest, once introduced into fields in Florida, can move along runners to infest neighboring plants or can be carried by bees, other insects, birds, field workers or machinery to infest other fields. The movement of mites along the soil or on plastic mulch is not likely since the mite requires the humid environment of plant surfaces.

Control.  Control strategies should be directed toward preventing an outbreak through the use of plants certified to be free of the pest. To prevent significant losses from cyclamen mites established in a fruiting crop in Florida, it is important to detect the infestation before plant growth has been affected significantly. A regular program of crop scouting should insure the earliest detection of this pest.  Several miticides are available to control cyclamen mites on strawberries, but none provide the rapid control that is desired. High volumes of spray preparations, perhaps 400 gallons per acre, are favored for miticides to contact the mites deep in the plant bud.

6. Sap Beetles.  Sap beetles feed on flowers, fruits, sap, fungi, stored products, and decaying and fermenting plant tissues from diverse trees and crops including strawberries. They work in association with yeasts and other fungi causing the fermentation of infested fruit (Fig. 14).  Their main impact, though, is the presence of the larvae or adults among the packed fruit. Sap beetles develop through a complete metamorphosis: eggs, larvae, pupae, and adults (Fig. 15).  Sap beetles fly into strawberry fields from wooded areas or citrus orchards about the time when temperatures exceed 60⁰F in the late winter. In managing this pest, it is important to pick berries before they become overripe, remove all damaged or overripe fruit from the field, especially in warm weather or at least place them into row middles where they can decompose more quickly.  Several insecticides are available to control sap beetles but most are hazardous to P. persimilis predator mites.

Other problematic insects and mites can occur on Florida strawberries and from time-to-time reduce yields.  The above, however, are the ones normally encountered and the ones for which growers should be best schooled.  Keen attention to these pests can go a long way toward experiencing a successful year of strawberry production.

Web links 

http://creatures.ifas.ufl.edu/
http://strawberry.ifas.ufl.edu/
http://www.hos.ufl.edu/protectedag/

Silvia I. Rondon¹, James F. Price², and Daniel J. Cantliffe^1
1Horticultural Sciences Department, ²Gulf Coast and Research Education Center
Vegetarian 05-02