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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. Managing Spider Mites in Strawberries 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 outbreaks of spider mites. Although these

April 2007 Zalom, Shaw, Larson & Thompson 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 generally 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 predaceous 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.

Plant Vigor and Varietal Susceptibility Strawberry plant vigor during the first 4 months following fall transplant is key for spider mite management since more vigorous plants can withstand more mite feeding. Factors influencing plant vigor include vernalization, soil preparation, soil fumigation, polyethylene plastic mulch and proper irrigation to prevent water stress. Vernalization is particularly important for mite management. Nursery loca- tion, preharvest chilling, nursery harvest date and length of pretransplant supplemental cold storage can all affect a plant’s vernalization. Plants with low amounts of chilling have low vigor and will often develop intolerable mite infestations (Walsh et al. 1997). Excessive chilling will promote increased vigor and reduced mite abundance, but other production factors can be adversely affected (i.e., delayed flowering, large plant size, increased vegetative runner production). Be sure transplants have received adequate chilling for the specific variety. Road dust and water stress also promote mite infestations. Strawberry cultivars vary in susceptibility to spider mite infestation and tolerance of feeding. Day-neutral cultivars tend to develop greater spider mite densities than do short-day cultivars. When transplant- ed in summer, short-day cultivars are relatively tolerant of Figure 5. A mid-tier leaflet is chosen for determining mite feeding. Although there are no resistant or tolerant spider mite densities. (This photograph is by Jack Kelly strawberry varieties (Shaw et al. 2003), more recent Clark and is copyrighted by the Regents of the University of University of California varieties tend to develop lower spi- California. It is provided by the UC Statewide IPM Program for use in this publication.) der mite densities than did older varieties such as ‘Selva’ (Figure 6).

Acaricides Acaricides are important to spider mite management, but to use them effectively it is important to know about their mode of action and specific activity. Until recently, acaricides registered for strawberries were limited to abamectin (Agri-mek), and older products such as dicofol (e.g Kelthane) and fenbutatin oxide (Vendex) . Most twospotted mite populations are resistant to dicofol and fenbutatin oxide except for certain central valley areas, so their utility is limited. Paired applications (7 to 10 days apart) of abamectin have been the mainstay of mite control for most strawberry growers for the last decade, and fortu- nately this acaricide fared well in spite of the intense pressure from its annual use. Mineral Figure 6. A University of California variety comparison. The severely oils can be effective in controlling overwinter- mite damaged plots in the foreground are planted with the day-neutral ing spider mites (Walsh and Zalom 2002), variety ‘Selva’. but they have not been widely used because of concerns for phytotoxicity when applied at warm temperatures. Do not apply oil from peak bloom through fruiting or when air temperatures are expected to exceed 75°F within several days following application. PRODUCTION GUIDELINES: MANAGING SPIDER MITES IN STRAWBERRIES PAGE 4

Recently, a number of new products have been registered for use on strawberries, which represent a number of distinct modes of action (Table 1). This has been important because having several effective products to choose from enables the grower to alternate acaricides that have different modes of action, thereby reducing development of resistance to a specific chemical. The Insecticide Resistance Action Committee (IRAC), an inter-company group formed in 1984 to provide insecticide and acaricide resistance management strategies, endorses this approach.

Table 1. Mode of action classification of acaricides registered on strawberries.

Primary Target Target Life Stages Product Chemical Manufacturer Site of Action

Agri-merk Abamectin Syngenta Crop Protection, Inc. Chloride channel activators (GABA All motile stages agonist)

Kanemite Acequinocyl Arysta LifeScience North Site III election transport inhibitor All motile stages America U.S.A.

Acramite Bifenazate Chemtura Corp. Neuroative (unknown mode of Ovicide, all motile stages action)

Kelthane, generics3 Dicofol DowAgro Sciences LLC, Gowan Site II electron transport inhibior All motile stages Co., Makhteshim Agan of North America, Inc. Zeal Etoxazole Valent Agricultural Products, Inc. Unknown mode of action (mite Ovicide and larvicide (mite growth regulator) Groups 10A and growth regulator) 10B) Vendex3 Fenbatatin E.I de Pont de Nemours and Co. Oxidative phosphorylation All motile stages Oxide inhibitor/uncoupler

Savey Hexythiazox Gowan Co. Unknown mode of action (mite Ovicide and larvicide (mite growth regulator) Groups 10A and growth regulator) 10B Omite1 Propargite Chemtura Corp. Inhibition of Magnesium stimulated All motile stages ATPase

Oberon Spiromesifen Bayer CropScience Inhibition of Magnesium stimulated Ovicide, all motile stages ATPase

Ecotrol2 Rosemary + EcoSMART Technologies, Inc. Botanical All motile stages Peppermint Oils

GC Mite2 Cottonseed JH Biotech Inc. Botanical All motile stages +Clove + Garlic Oils Omni Supreme4 Horticultural Helena CHemical Co. Mineral oil All motile stages Mineral Oil

Organic JMS Style Paraffinic Oil JMS Flower Farms, Inc. Mineral oil All motile stages Oil2, 4

1 Only for use in strawberry nurseries. 2 Acceptable for organic production. 2 Widespread resistance has been reported to this product in coastal growing areas. 4 Oils may burn strawberry plants under warm temperature conditions. 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. A that are infested with spider mites. A number of factors affect predatory mite survival including pesticide small peak is often seen in the fall on summer-planted strawberries. applications, weather conditions, lack of food, dust and even the quality of the predator mite released. If predatory mite releases are attempted, make them early in the season before spider mite populations Monitoring begin to build or following winter spider mite sprays intended to reduce overwintering populations. Begin monitoring mid-tier leaflets (Figure 5) during the critical period between when the field is trans- Predatory mite releases will always be ineffective when spider mite densities are high. Suggested release planted and the first fruit appear. Mid-tier leaflets are those which are neither from old nor new leaves. rates of 2 to 3 predators per plant on average are common, and are made as a single large release or as Examine the undersurface with a hand lens to count the mites or use a mite-brushing machine. 2 or 3 smaller releases. Make sure that pesticide residues are below lethal levels before considering a Randomly sample 10 mid-tier leaflets per acre in larger fields, and 5 mid-tier leaflets per acre in small release. Lethal residues can easily last from 4 to 37 days or more depending on the product applied. It is fields. When using a mite-brushing machine, the leaflets from each acre can be brushed as one sam- especially important to monitor fields on a regular basis if predatory mites are released to determine if spi- ple. der mite densities remain below economically injurious levels. Be prepared to apply the more selective acaricides such as abamectin, acequinocyl, bifenezate, or spiromesifen. 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. Managing Spider MitesinStrawberries 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 outbreaks of spider mites. Although these

April 2007Zalom,Shaw, Larson&Thompson 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.