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PRODUCTION GUIDELINES: MANAGING SPIDER MITES IN STRAWBERRIES PAGE 6 PRODUCTION GUIDELINES References MANAGING SPIDER MITES IN STRAWBERRIES Shaw, D.V., F.G. Zalom, and K.D. Larson. 2003. Relative differences in yield for strawberry FRANK ZALOM, DOUG SHAW, KIRK LARSON & PAT THOMPSON (Fragariaxananassa Duch.) genotypes are stable over differing levels of infestation by twospotted spi- dermites (Tetranychus urticae Koch.). J. Amer. Soc. Hort. Sci. 128(5): 678-681. Issue 7 May 2007 Walsh, D.B. and F.G. Zalom. 2002. Winter horticultural and agricultural mineral oil treatments for control of two-spotted spider mite on California strawberries. pp. 481-491, In A. Beattie, D, Watson, M. Mites in Strawberries Managing Spider The twospotted spider mite (Tetranychus Stevens, D. Rae and R. Spooner-Hart (eds.). Spray Oils Beyond 2000: Sustainable Pest and Disease urticae) is an annual pest of strawberries Management. Veritage Press. Lisarow, New South Wales, Australia. in all California growing regions. Less common is the carmine spider mite Walsh, D.B., F.G. Zalom, and D.V. Shaw. 1998. Interaction of the two spotted spider mite (Acari: (Tetranychus cinnabarinus) which is close- Tetranychidae) with yield of day-neutral strawberries in California. J. Econ. Entomol. 91(3): 678-685. ly related to the twospotted mite, but it seems to be occurring more frequently. Walsh, D.B., F.G. Zalom, N.C. Welch, C. Pickel, and D.V. Shaw. 1997. Pretransplant cold storage of Feeding by both spider mite species strawberries: effects on plant vigor, yield and spider mite (Acari: Tetranychidae) abundance. J. Econ. reduces plant vigor, resulting in decreased Entomol. 90(3): 818-823. fruit size and yield. Mite monitoring should occur regularly throughout the season. Contact Infomation Controls are usually needed every year to Frank Zalom Doug Shaw Kirk Larson Pat Thompson prevent substantial losses. Spider mites Department of Entomology, Department of Plant Department of Plant Department of Entomology, are best managed by using cultural prac- University of California, Sciences, University of Sciences, University of University of California, tices that favor vigorous plant growth, Davis California, Davis California, Davis Davis encouraging biological control and apply- [email protected] [email protected] [email protected] [email protected] ing selective yet effective acaricides when Ph: 530.752.0905 Ph: 949.857.0136 Ph: 530.752.0275 Ph: 530.752.3687 monitoring indicates they are needed. Figure 1. Twospotted spider mite eggs are spherical and pearly white in Some insecticides used to control lygus color. This photograph is by Jack Kelly Clark and is copyrighted by the Regents of the University of California. It is provided by the UC Statewide IPM Program bugs or other pests can destroy predator for use in this publication.) populations and cause secondary out- breaks of spider mites. Although these April 2007 Zalom, Shaw, Larson & Thompson April 2007 Zalom, Shaw, must often be used to maintain fruit yield and quality, it is a good practice to delay application of the most disruptive products until later in the season. Identification Spider mite eggs are laid on the under- sides of leaves and are spherical and col- orless when laid. Twospotted mite eggs become pearly white as hatch approaches (Figure 1), while carmine mite eggs become yellow to orange. Twospotted mite nymphs, adult males, and reproductive adult females are oval shaped and gener- ally off white to greenish in color (Figure 2) with one or more dark spots on each side of their bodies. Carmine mites are bright Figure 2. A twospotted spider mite adult female is oval shaped and red in color (Figure 3). Adult female generally yellow or greenish in color. with one or more dark spots on twospotted mites may enter a reproduc- each side of their body. (This photograph is by Jack Kelly Clark and is copy- tive diapause during the winter months in righted by the Regents of the University of California. It is provided by the UC Statewide IPM Program for use in this publication.) colder inland valleys, but they continue to mate and reproduce in coastal growing regions. Diapause is indicated by a change in color to bright orange. Take care to correctly identify these mites in the field. Twospotted mites in diapause and carmine mite may be mistaken for the preda- ceous mite Phytoseiulus persimilis (Figure 4), however, the predaceous mite can be distinguished from the two pest mites by its much faster movement. CALIFORNIA STRAWBERRY COMMISSION P.O. BOX 269 WATSONVILLE, CA 95077 PH: 831.724.1301 FAX: 831.724.5973 WWW.CALSTRAWBERRY.COM © 2007 CALIFORNIA STRAWBERRY COMMISSION PRODUCTION GUIDELINES: MANAGING SPIDER MITES IN STRAWBERRIES PAGE 2 PRODUCTION GUIDELINES: MANAGING SPIDER MITES IN STRAWBERRIES PAGE 5 Life History and Damage Other ways to delay resistance are to avoid Spider mite damage to strawberries unnecessary spraying, and treating only infested appears as stippling, scarring, and red- portions of the plantation which allows some sus- dening of the leaves and calyx. ceptible individuals to survive. Applications of Twospotted mite feeding is particularly pyrethroid insecticides used for control of other damaging during the first 4 to 5 months pest species are known to create twospotted mite following transplanting in late summer or outbreaks, so it is best to delay their use until fall when yield loss is detectable at infes- later in the season if possible. For best residual tation levels exceeding one mite per control using acaricides such as mite growth reg- leaflet (Walsh et al. 1998). Early season ulators that affect only eggs (ovicides) and imma- mite feeding substantially reduces fruit ture stages, the products should be applied when number per plant and overall plantation adult populations are relatively low and when yield, and treatment is recommended females present are already laying eggs. These when an average of 5 mites per mid-tier products can control larger populations as well leaflet is found. Summer transplants have but their effect may not be immediately apparent. a higher threshold of 10 mites per mid-tier Products that target all motile stages can be used leaflet during this same period. Plants are at any time, but as for any acaricide they will work Figure 7. The predatory mite Neoseiulus californicus, occurs nat- urally in many coastal production regions. (This photograph is by less sensitive to mite feeding after initial Figure 3. A carmine spider mite is bright red in color. (This photograph is best when applied before mite densities reach out- by Jack Kelly Clark and is copyrighted by the Regents of the University of Jack Kelly Clark and is copyrighted by the Regents of the University of fruit set, and can tolerate densities of 15 California. It is provided by the UC Statewide IPM Program for use in this publi- break levels. Good underleaf coverage is essential California. It is provided by the UC Statewide IPM Program for use in this to 20 mites per mid-tier leaflet at this time. cation.) for best control and this can best be achieved with publication.) Plants that sustain infestations of greater high (200 gpa) volume, directed nozzles and high than 75 mites per leaflet may become pressure. There are several products available for organic strawberry production which are fairly effective severely weakened and appear stunted, for control, but because they lack the residual activity of most conventional acaricides repeated applica- dry and red in coloration. Treatment tions may be necessary to achieve control, and good underleaf coverage is especially important. Products thresholds vary somewhat depending on recommended change over time, so it is a good idea to refer to University of California Publication 3339, overall plant vigor, cultivar and yield Pest Management Guidelines: Strawberries (www.ipm.ucdavis.edu/PMG/r734300111.html) for current potential. information. Spider mites remain active on strawber- Biological Control ries and other hosts all winter in coastal Predator mites such as Phytoseiulus persimilis, Galendromus occidentalis, and Neoseiulus californicus are growing regions. Twospotted mites have commercially available for release although experimental results demonstrating their efficacy on strawber- a broad crop and weed host range, and ries is limited. The information provided below thus largely represents a compilation of theory as well as can be blown from place to place by the experiences from greenhouses and other crops or localities, and must be interpreted with some caution. wind. Therefore, new strawberry plantings can be quickly invaded and densities build Of the commercially available predatory mites, P. persimilis is the most commonly applied. It is an aggres- rapidly when conditions are favorable. The sive feeder that multiplies and spreads rapidly. However, because they eat only mites, P. persimilis will greatest twospotted mite densities are leave the field if spider mite densities become too low to sustain the predator population. N. californicus often observed around the fruiting peak of (Figure 7) has a broader host range and will also feed on certain small insects such as thrips as well as the first crop. This peak is typically fol- Figure 4. The predatory mite Phytoseiulus persimilis, with a two-spotted pollen, but its reproductive rate and searching ability is somewhat less than P. persimilis. It is also more lowed by a rapid, natural decline in mite mite adult and eggs. (This photograph is by Jack Kelly Clark and is copyright- suited to warmer and drier conditions. N. californicus are less likely to move from strawberry fields when density when the plant enters a vegetative ed by the Regents of the University of California. It is provided by the UC spider mite populations decline. P. persimilis and N. californicus are established in many coastal produc- Statewide IPM Program for use in this publication.) growth cycle. Twospotted mite densities tion regions including Oxnard-Ventura and Watsonville, and can move on their own into strawberry fields often increase again later in summer.