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ENY602 2002 Florida Citrus Pest Management Guide: Spider Mites1 C.C. Childers, C.W. McCoy, H.N. Nigg, and P.A. Stansly2 1. This document is Fact Sheet ENY-602, part of the 2002 Florida Citrus Pest Management Guide, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Date printed: December 1995. Date revised: October 2001. For a copy of this handbook, request information on its purchase at your county extension office. Please visit the EDIS Web site at http://edis.ifas.ufl.edu. 2. C.C. Childers, professor, entomologist, Citrus REC, Lake Alfred, Florida; C.W. McCoy, professor, entomologist, Citrus REC, Lake Alfred, Florida; H.N. Nigg, professor, entomologist, Citrus REC, Lake Alfred, Florida; P.A. Stansly, professor, entomologist, Southwest Florida REC, Immokalee, Florida; Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 32611. The use of trade names in this publication is solely for the purpose of providing specific information. It is not a guarantee or warranty of the products named, and does not signify that they are approved to the exclusion of others of suitable composition. The Institute of Food and Agricultural Sciences is an equal opportunity/affirmative action employer authorized to provide research, educational information and other services only to individuals and institutions that function without regard to race, color, sex, age, handicap, or national origin. For information on obtaining other extension publications, contact your county Cooperative Extension Service office. Florida Cooperative Extension Service/Institute of Food and Agricultural Sciences/University of Florida/Christine Taylor Waddill, Dean. There are three species of spider mites that are potential pests on Florida citrus: Texas citrus mite, citrus red mite and six-spotted mite. The Texas citrus mite is the predominant species in most groves throughout the state. The citrus red mite is usually second in abundance, but in some grove and nursery operations it is the predominant species. The Texas citrus and citrus red mites occur on citrus throughout the year and usually are most abundant in groves between March and June. They are found most commonly on the upper leaf surface of recently mature flush, and all stages of the mites orient along the mid-vein. As populations increase, they move to leaf margins and fruit. The six-spotted mite is a very sporadic pest occurring in colonies on the lower leaf surface. This mite tends to be more abundant following cold winters, especially during December. Usually localized populations of this mite can be recognized by characteristic yellow blistering on mature leaves between March and May. Populations decline rapidly in June and remain very low through the remainder of the year. Spider mites feed primarily on mature leaves and differ from rust mites by feeding beneath the epidermal layer of cells. They are capable of removing cellular contents, causing cell destruction and reducing photosynthesis. Mesophyll collapse and leaf drop can result when trees are stressed by high spider mite infestations alone or in combination with sustained dry, windy conditions that may occur in the late fall, winter or early spring months. When populations of Texas citrus mite or citrus red mites are high they will also feed on developing fruit. Spider mites prefer dry weather and low relative humidities in the range of 30-60 percent and generally do not pose a sustained problem in the higher humidity conditions that occur between June and September. Populations of both Texas citrus and citrus red mites aggregate among leaves within and between citrus trees. A sampling method has been developed for Texas citrus and citrus red mites on Florida citrus. This method provides 25% or less error margins when motile mite densities (i.e. all stages except eggs) are above 2/leaf.
2002 Florida Citrus Pest Management Guide: Spider Mites 2 The sample unit is a mature leaf immediately behind flush leaves. Figure 1 shows the optimum number of sample areas within a 10-acre block of orange trees when using 1, 5 or 10 trees per area and collecting either 4 or 8 leaves per tree. For example, if you look at 1 tree/acre then it is necessary to look at over 10 sample areas within a 10-acre block to achieve accuracy. If you examine 5 or 10 trees/area, then only 4 or 5 areas need to be examined. As mite densities increase above 2/leaf the optimal number of sample areas declines below 5. Table 1 provides examples of different sample sizes at different control thresholds. Figure 1. Optimum number of sample areas/10 acres. When the control threshold is increased from 5 to 10 mites/leaf, there are corresponding reductions in the amount of sampling required within a 1 or 10-acre block. At weekly or biweekly intervals during periods of spider mite activity, collect either one leaf per quadrant (i.e., N, S, E, W) (4 leaves/tree) on each tree per sample area or two leaves per quadrant (8 leaves/tree). Sampling consistency is important since spider mite numbers can increase on one quadrant of a tree. Place leaves from individual trees into labeled paper bags and then into a cold ice chest for examination under a stereomicroscope OR examine individual leaves in the field with a stereomicroscope or 10X hand lens. If one motile stage of a Texas citrus or citrus red mite is present on either the upper or lower leaf surface, then the leaf is infested. A good relationship was found between the average number of Texas citrus mites or citrus red mites and the percentage of leaves infested across 10-acre blocks of young orange trees. For example, an average of 5 motile spider mites/leaf equaled 70-80% infestation levels. This constitutes a treatment threshold for processing fruit. Lower infestation levels should be tolerated in blocks destined for fresh market and especially when spider mites are in association with citrus rust mites. Spider mites are suppressed to low densities by several species of predacious mites, insects, and entomopathogens in some groves. However, when populations averaging 5 to 10 motile spider mites per leaf develop between September and May it would be reasonable to apply a miticide, especially if the trees are stressed. However, infestations comprised predominantly of adults, particularly males, are in decline and would not require control. Adult mites are recognized by their large size relative to immatures and females distinguished by their round shape and shorter legs compared to males. Need for controlling spider mites is based on temperature and humidity conditions, spider mite population levels, tree vigor and time of the year. Petroleum oil provides some ovicidal activity against spider mite eggs. None of the other miticides provide ovicidal activity, and their residual activity must be sufficiently long-lasting to kill subsequently emerging larvae. Recommended Chemical Controls READ THE LABEL. See Table 2. Rates for pesticides are given as the maximum amount required to treat mature citrus trees unless otherwise noted. To treat smaller trees with commercial application equipment including handguns, mix the per acre rate for mature trees in 250 gallons of water. Calibrate and arrange nozzles to deliver thorough distribution and treat as many acres as this volume of spray allows. TO MINIMIZE RISK OF RESISTANCE DO NOT APPLY A SPECIFIC MITICIDE MORE THAN ONCE PER ACRE PER SEASON OTHER THAN PETROLEUM OIL.
2002 Florida Citrus Pest Management Guide: Spider Mites 3 Table 1. Control thresholds and appropriate sample sizes for 10 acres. If the control threshold is: Sample size (Sample trees should be uniformly scattered across a 10-acre block. Do not sample adjacent trees.) 5 mites/leaf Examine 4 leaves/tree from 6 trees/area from 4 areas/10 acres = 96 leaves on 24 trees/10 acres 8 mites/leaf Examine 4 leaves/tree from 6 trees/area from 3 areas/10 acres = 72 leaves on 18 trees/10 acres 10 mites/leaf Examine 4 leaves/tree from 5 trees/area from 2 areas/10 acres = 40 leaves on 10 trees/10 acres 15 mites/leaf Examine 4 leaves/tree from 4 trees/area from 2 areas/10 acres = 32 leaves on 8 trees/10 acres Table 2. Recommended Chemical Controls for Spider Mites. Pesticide Mature Trees Rate/Acre1 Comments Other Pests Controlled Comite 6.55 EC 3 pt Leaf distortion and/or fruit spotting may occur when used in the spring or it may occur if tank mixed with oil or applied within 2 weeks prior to or following an oil application. Do not use in spray solution above pH 10. Citrus rust mite Kelthane MF 6 pt Applicators must be in an approved cab or cockpit. Do not use in spray solutions above pH 7. Citrus rust mite Nexter 75 WP 6.6 oz Numerous use restrictions; see product label prior to use. Tank mixing with oil or copper results in reduced residual activity. Citrus rust mite, false spider mite Petroleum Oil 97+% (FC 435-66, FC 455-88, or FC 470-01) 5 gal See comments under Citrus Rust Mites, Table 1. Do not apply when temperatures exceed 94F. FC 470-01 has not been evaluated for effects on fruit coloring or ripening. These oils are more likely to be phytotoxic than lighter oils. Citrus rust mite, whitefly, scale, greasy spot, sooty mold Vendex 50 WP 2 lb Tank mixing with oil or copper results in reduced residual activity. Do not apply at rates greater than 20 oz/500 gal to fruit less than one inch in diameter within 10 days of an oil spray. Citrus rust mite 1 Lower rates may be used on smaller trees. Do not use less than minimum label rate.