Tank Mixing Revisited

research

Recent quantitative research takes a close look at what pesticide mixtures growers are currently adopting. While popular for its potential to improve pest control, growers should approach tank mixing with caution. By Raymond Cloyd

esticides — in this case, insecticides times added to tank mixtures to help manage and miticides — are used primarily plant diseases. to control arthropod pests encoun- There is relatively minimal information cur- tered in greenhouse production rently available on the effect of pesticide mix- systems. These include greenhouse tures in controlling arthropod pests typically Pwhitefl y, sweet potato whitefl y B biotype, green encountered in greenhouses. There is no data peach aphid, two-spotted spider mite, western or assessment pertaining to the types of pesti- fl ower thrips, American serpentine leafminer cide mixtures (two- and three-way combina- and citrus mealybug. tions) that greenhouse producers use to control However, federal rules and regulations, such arthropod pests. As such, we decided to survey as the Food Quality Protection Act (FQPA), and greenhouse producers at two conferences in manufacturers’ voluntary withdrawal or can- 2007 and one in 2008, during which the author cellations have resulted in the continual loss or gave presentations on the fundamentals of tank registration changes associated with “older” or mixing, to determine the most widely used pes- conventional, broad-spectrum pesticides, par- ticide mixtures among the participants. ticularly in the organophosphate and carbamate chemical classes. This has led to an increase in Survey Distribution and Completion the development and availability of alternative We distributed pesticide mixture evaluation pesticides that are more selective or control a nar- forms during three sessions at two conferences rower spectrum of arthropod pests compared to in 2007: The OFA Short Course on July 14, 2007, conventional pesticides. in Columbus, Ohio; and the Greenhouse Expe- Examples of alternative pesticide groupings rience Conference on Sept. 10, 2007, in Cleve- include insect growth regulators; insecticidal land. The forms also went out at the Society of soaps; horticultural oils; selective feeding inhibi- American Florists’ Conference on Pest and Dis- tors (blockers); microbial agents, such as benefi cial ease Management in Ornamentals on March 1, bacteria and fungi; and related micro-organisms 2008, in Atlanta. (e.g., spinosad). In addition to their selectivity, The evaluation forms were provided prior to many of these alternative pesticides are less toxic the start of each session and asked for the respon- to humans, leave minimal residues, are short-lived dents’ four most common pesticide mixtures, and in the environment and have minimal impact on for what specifi c insect or mite pests. There were natural enemies, including parasitoids and preda- approximately 200 participants in attendance for tors. Although the availability of pesticides that all three sessions, and although not all the par- demonstrate selectivity may be desirable, this ticipants in the three sessions were affi liated with presents a dilemma when dealing with multiple greenhouse production, a majority — greater than Growers mix a wide variety of pesticides in hopes of arthropod pest populations in greenhouses. 80 percent — were greenhouse producers. achieving success not found with separate applica- To regulate or control the myriad arthropod Partial results of the survey are summarized tions. (Photos: Raymond Cloyd) pests such as thrips, aphids, fungus gnats, leaf- in Table 1 (opposite) and represent the fi rst quan- miners, whitefl ies, mealybugs and spider mites titative assessment to determine the pesticide that feed on ornamental crops, greenhouse pro- mixtures conducted by greenhouse producers. ducers will mix together two or more pesticides, (A full version of the table is available at www. including conventional and alternative insecti- gpnmag.com.) cides or miticides, into a single spray solution, A total of 45 fully completed evaluation forms which expands the activity of the application. were assessed; although 12 of the evaluation As such, it may be necessary to tank mix two or forms did not contain the arthropod pests tar- more pesticides to obtain the same spectrum of geted for the specifi c pesticide mixtures, they control for multiple arthropod pests that a single were still included in the results. The evaluation broad-spectrum pesticide might provide. To fur- form specifi cally stipulated that only pesticide ther complicate matters, fungicides are some- mixtures involving insecticides and miticides be

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Top 25 Pesticide Mixtures from Survey Results

TRADE NAMES COMMON NAMES ARTHROPOD PEST(S) COUNT Two-Way Mixtures Avid + Talstar Abamectin + Bifenthrin Mites, whitefl ies, mealybugs and aphids 8 Avid + Conserve Abamectin + Spinosad Thrips, aphids, and spider mites 6 Avid + Ornazin/Azatin Abamectin + Azadirachtin Thrips, spider mites, aphids and whitefl ies 6 Orthene + Tame Acephate + Fenpropathrin Thrips, caterpillars, whitefl ies and aphids 6 Conserve + Endeavor Spinosad + Pymetrozine Aphids, thrips, and caterpillars 5 Conserve + Pedestal Spinosad + Novaluron Thrips 4 Avid + Endeavor Abamectin + Pymetrozine Aphids and mites 3 Conserve + Floramite Spinosad + Bifenazate Thrips and mites 3 Avid + Flagship Abamectin + Thiamethoxam Aphids, mites and whitefl ies 2 Avid + Floramite Abamectin + Bifenazate Thrips and mites 2 Avid + Marathon Abamectin + Imidacloprid 2 Avid + Mavrik Abamectin + Fluvalinate Aphids and mites 2 Avid + TetraSan Abamectin + Etoxazole Spider mites 2 Avid + Ultra-Fine Oil Abamectin + Paraffi nic oil Spider mites 2 Cleary’s 3336 + Subdue Thiophanate-methyl + Metalaxyl Pythium and thrips 2 Conserve + Flagship Spinosad + Thiamethoxam Aphids, whitefl ies and thrips 2 Conserve + Marathon II Spinosad + Imidacloprid 2 Enstar II + Mavrik Kinoprene + Fluvalinate Mites, aphids and mites 2 Hexygon + Pylon Hexythiazox + Chlorfenapyr Spider mites 2 Ornazin/Azatin + Talstar Azadirachtin + Bifenthrin Fungus gnats, shore fl ies and whitefl ies 2 Three-Way Mixtures Acephate + Azatin + Tame Acephate + Azadirachtin + Fenpropathrin 1 Avid + Azatin + Pipron Abamectin + Azadirachtin + Piperalin 1 Avid + Conserve + Decathlon Abamectin + Spinosad + Cyfl uthrin Thrips, mites and aphids 1 Avid + Conserve + MilStop/Compass Abamectin + Spinosad + 1 Potassium bicarbonate/Trifl oxystrobin Avid + Daconil + Marathon II Abamectin + Chlorothalonil + Imidacloprid 1 Common name = Active ingredient Neem oil = Clariﬁ ed hydrophobic extract of neem oil Btk = Bacillus thuringiensis spp.. kurstaki Lure = Attractant Adjuvant (spray) with the active ingredient: blend of polyether-polymethylsiloxane-copolymer and nonionic surfactant

Table 1. Results of pesticide mixture survey indicating two-, three- and four-way combinations used by the participants. Evaluation forms were distributed at two conferences in 2007 and one in 2008. Forty-fi ve of the 200 distributed surveys were returned. included, but 13 participants included pesticide chlorfenapyr (Pylon: OHP, Inc.) + acetamiprid and adult) they are most active on are presented mixtures with fungicides. The return rate of the (TriStar: Cleary Chemical Corp.) two-way mix- in Table 2 (page 24). A number of the miticide evaluation forms was 22.5 percent (45 out of 200), ture has been shown to provide 86 percent mor- tank mixtures listed in Table 1 were legitimate which may be considered a small sample size; tality of sweet potato whitefl y B biotype nymphs based on the life stage activity of the active however, the information gathered is useful in 14 days after application. ingredients: abamectin + etoxazole (TetraSan: determining the extent of what pesticide mix- All the commercially available miticides Valent U.S.A. Corp.), hexythiazox (Hexygon: tures are being used by greenhouse producers. labeled for use in greenhouses and the two- Gowan Co.) + chlorfenapyr, and abamectin spotted spider mite life stages (e.g., larva, nymph + clofentezine (Ovation: Scotts-Sierra Crop ➧ Survey Results The two-way tank mixture cited most often on the evaluation forms — a total of eight times Popular Pesticides — was the combination of abamectin (Avid: Syn- Abamectin and spinosad were the pesticides most often included in two-way (abamectin was cited 15 genta Professional Products) + bifenthrin (Tal- times, and spinosad was mentioned 17 times) and three-way (nine mentions for abamectin and seven for star: FMC Corp.) for control of mites, whitefl ies, spinosad) mixtures. mealybugs and aphids. The other two-way tank Both pesticides are labeled for control of Western fl ower thrips, one of the most important mixtures, cited six times by survey respondents, insect pests of greenhouses. In fact, after commercialization in 1998, spinosad is the pri- were abamectin + spinosad (Conserve: Dow mary pesticide used by greenhouse producers to control western fl ower thrips due to its AgroSciences); abamectin + azadirachtin (Azatin: effectiveness against this insect pest although there are now concerns OHP, Inc., and Ornazin: SePRO Corp.); and regarding resistance. Abamectin, which has been available since acephate (Orthene: Valent U.S.A. Corp.) + 1980, is commonly used by greenhouse producers to control the fenpropathrin (Tame: Valent U.S.A. Corp.). two-spotted spider mite, a major arthropod pest of greenhouses.

Several of the two-way mixtures with spinosad including spinosad The two-way tank mixtures of spinosad

+ pymetrozine (Endeavor: Syngenta + abamectin, spinosad + bifenazate (Floramite: OHP, Inc.), and W e spinosad + imidacloprid (Marathon II: OHP, Inc.) did not affect control s Professional Products); and spinosad t e r ip e of western fl ower thrips. n thr + novaluron (Pedestal: OHP, Inc.) were it fl ower r m cited fi ve and four times, respectively. The de spi Two-spotted www.gpnmag.com December 2008 GPN 25 research

Protection Co.) in Table 2. However, the fol- bifenazate + etoxazole, and hexythiazox + ture for control of thrips, which received two lowing miticide tank mixtures listed in Table 1 spiromesifen (Judo: OHP, Inc.) in Table 2. counts. Both are fungicides with no insecticidal were questionable because of similar life-stage One pesticide mixture that was diffi cult to activity. The four-way pesticide mixture of abam- activity of the active ingredients: fenpyroximate interpret was the thiophanate-methyl (Cleary’s ectin + spinosad + bifenazate + myclobutanil (Akari: SePRO Corp.) + clofentezine, fenpyroxi- 3336: Cleary Chemical Corp.) and metalaxyl (Eagle: Dow AgroSciences) was listed for control mate + etoxazole, abamectin + chlorfenapyr, (Subdue: Syngenta Professional Products) mix- of mites, aphids, thrips and powdery mildew. However, spinosad is not active on aphids or mites,and abamectin is labeled only for aphid Activity of Commercially Available Miticides suppression. A pesticide specifi cally labeled for and with demonstrated effi cacy on aphids Active Ingredient Trade Name Activity Type* Eggs Larvae Nymphs Adults should have been included in the mixture. Abamectin Avid T and C X X X Studies have evaluated the effect of tank mixing Acequinocyl Shuttle C X X X X pesticides on effi cacy against western fl ower Bifenazate Floramite C X X X X thrips, two-spotted spider mite and sweet potato Chlorfenapyr Pylon T and C X X X whitefl y B biotype. One study demonstrated that mixing the spinosad with other insecticides Clofentezine Ovation C X X X and miticides (imidacloprid, abamectin and Etoxazole TetraSan T and C X X X bifenazate) in two-, three- and four-way mixtures Fenbutatin-OxideProMite C X X X did not negatively affect the ability of spinosad to Fenpyroximate Akari C X X X X control western fl ower thrips. Another study eval- Hexythiazox Hexygon C X X X uated the effect of tank mixing the insecticides and miticides buprofezin (Talus: SePRO Corp.), Pyridaben Sanmite C X X X X acetamiprid, chlorfenapyr and bifenazate in two-, Spiromesifen Judo T and C X X X three- and four-way mixtures on the control of *Activity Type Codes: C = Contact, T = Translaminar two-spotted spider mite and sweet potato whitefl y B biotype. Overall, most of the tank mixtures did Table 2. Activity of commercially available miticides for use in greenhouses and the life stages of two-spotted spider mite, Tetrany- not affect control of either pest. However, the chus urticae, on which they are most effective. buprofezin + chlorfenapyr, and acetamiprid + ➧

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chlorfenapyr + bifenazate tank mixtures resulted in lower sweet potato whitefl y B biotype nymphal mortal- ities (less than 38 percent) than the other tank mixtures. The survey results demonstrate that greenhouse producers mix together a diverse PATIO CONTAINERS group of pesticides. However, www.urban-gardener.net it is not known where or how greenhouse producers get the idea to use specifi c products in pesticide A “jar test” helps determine whether two pes- For the Retailer mixtures. Tank mixing pesticides is ticides are incompatible (evidenced by notice- popular because of the potential for able separation or layering) or compatible improved pest control. But although (evidenced by homogeneous appearance) Ideal for those who don’t have time for a tradi- there are benefi ts to tank mixing, tional garden. there are several issues — discussed not be mixed together in a spray below in more detail — that growers solution. Similarly, acephate and Great for small spaces on patios, decks, should consider beforehand. It also methiocarb (Mesurol: Gowan Co.), porches and balconies. is essential to consider why certain despite being in different chemical pesticides are being mixed together. classes (organophosphates and Floral selection to decorate the outdoor Greenhouse producers need to carbamates), have identical modes living area. develop tank mixtures based on the of activity. The active ingredient developmental life stage of each pes- blocks the action of acetylcholinest- Vegetables at the doorstep that are fresh ticide’s target pest. For example, tank erase (AChE), an enzyme that deac- and healthy. mixing two products that have miti- tivates acetylcholine (ACh), which cidal properties, such as abamectin is responsible for activating recep- + bifenazate, is not recommended tors that allow nerve signals to For the because both are active on the adult travel through the central nervous stage of the two-spotted spider mite system. The active ingredients in Wholesale Grower (Table 2). However, tank mixing both pesticides inhibit or block the abamectin with either clofentezine action of AChE by attaching to the or etoxazole is appropriate because enzyme. So, tank mixing these pes- Increased margins over traditional abamectin is primarily active on ticides should be avoided because garden bed plants. adults whereas clofentezine or etox- this exposes the insect pest popu- azole are active on the eggs, larvae lation to the same mode of action, Taps into the trends of home deco- and nymphs (Table 2). These tank which may result in the develop- rating and locally grown vegetables. mixtures target all life stages of the ment of resistance. This is referred two-spotted spider mite. to as cross-resistance. Offers opportunity for to sell to a new clientele. Considerations Beneﬁ ts of Tank Mixes for Tank Mixes Greenhouse producers often To purchase Urban A concern when tank mixing tank mix out of convenience — it Gardener growing kits, pesticides is the potential to is less time consuming, costly and increase the concentration of sur- labor intensive to mix together two contact one of these factants. Many pesticides already or more pesticides into a single approved Urban Gardener contain an adjuvant or surfactant spray solution and then perform Suppliers: as a component of the formulation. one application compared to two or However, at higher concentrations, more applications. Another reason surfactants may be harmful or phy- for tank mixing is the potential for 800-883-0234 totoxic to plants. As such, green- improved pest control or enhanced www.bfgsupply.com house producers need to be aware effectiveness. In fact, tank mixing of the consequences of increasing two pesticides may result in greater 978-851-4346 the surfactant concentration when mortality of arthropod pests than www.grifﬁns.com mixing pesticides. with separate applications. Another consideration is the Furthermore, tank mixtures need to tank mix pesticides with may be more effective on certain 800-253-0439 different modes of action. For developmental stages of arthropod www.mastertag.com example, although pyridaben (San- pests. This type of activity is often mite: Scotts-Sierra Crop Protection referred to as synergism or poten- Co.) and fenpyroximate are in dif- tiation. For example, tank mixing ferent chemical classes: pyridazi- two different insecticides may none and phenoxypyrazole, respec- result in higher mortality of insect tively. They have the same mode pests, such as western fl ower thrips The Urban Gardener logo is a registered trademark of Hubie Grown, LLC. of action: mitochondria electron and certain whitefl y species, than Urban Gardener Patio Containers are protected under patents transport inhibitors (METIs), which when the designated insecticides (D569, 302), (D569, 304), (D569, 303). disrupt the production of energy or are applied separately. Other US and international patents pending adenosine triphosphate (ATP). As In addition, insecticides con- ©2008 Hubie Grown LLC such, these two pesticides should taining the active ingredient ➧ Write in 703 28 GPN December 2008 www.gpnmag.com research

azadirachtin and the insect-killing or benefi cial penetrate the insect. The insect sheds off the spore, vents pesticides from mixing together properly fungus Beauveria bassiana (BotaniGard: BioWorks; forming conidia along with the old skin. However, in a spray solution. This may result in either a a n d N a t u r a l i s : O H P, I n c .) a p p e a r t o b e m o r e e f f e c t i v e tank mixing azadirachtin with B. bassiana may decrease in effectiveness or phytotoxicity. Incom- when tank mixed together compared to individual result in synergism or enhanced effi cacy because patibility may be due to the chemical or physical applications. It has been hypoth- azadirachtin, an insect growth regulator, may nature of the pesticides, impurities in the water, esized that azadirachtin may actu- slow down the molting process, thus allowing the water temperature or the types of formulations ally “stress” insects, thus enhancing insect-killing fungus to penetrate the target insect mixed together. the effi cacy of the benefi cial fungus. For example, pest and initiate an infection. To determine compatibility between two during the summer months, insect pests such as (or more) pesticides, conduct a “jar test.” This thrips and aphids molt or shed their skins (cuti- Concerns Related to Tank Mixes involves making a small sample of the spray cles) so rapidly that benefi cial fungi are unable to Just as synergism improves the effi cacy of two solution and placing into an empty jar or other or more pesticides, the opposite — referred to as container, and allowing the solution to sit for antagonism — may occur. Antagonism is when approximately 15 minutes. If the pesticides are mixing two or more pesticides reduces effec- not compatible, there may be a noticeable sepa- tiveness of the mixture compared to if applied ration or layering, or precipitates such as fl akes separately. In other words, the mixture is less or crystals may form. However, if the materials effective, based on percent mortality, than indi- are compatible, the solution may appear homo- vidual applications of each pesticide. It appears geneous or resemble milk. It is important to that azadirachtin may actually be toxic to certain understand that this procedure only determines benefi cial fungi, thus resulting in antagonism. compatibility, not synergism or antagonism. In addition to a reduction in effectiveness, there A concern often affi liated with tank mixing is also the potential for plant injury or phyto- pesticides is the prospect of resistance. Although toxicity. Greenhouse producers need to read this is still not well understood, there is specu- the label before tank mixing pesticides because lation that applying two or more pesticides at labels, in general, state which products can and different intervals has the same advantages as a Tank mixing pesticides is a convenient option for many cannot be mixed together. pesticide mixture. However, this is not entirely growers: It’s less expensive and requires less labor than sepa- Another issue associated with tank mixing true, as each individual arthropod pest in the rate pesticide applications. is incompatibility, a physical condition that pre- population does not receive a lethal dose or ➧ Cart-Mart DEALS ON WHEELS

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concentration of each pesticide, population, and it may be more depends on a number of factors; and as a result resistance may diffi cult for individuals in the pop- one of the most important is pre- evolve more rapidly than with a ulation to develop resistance to vious exposure to either similar or pesticide mixture. The mecha- several modes of action simultane- different modes of action. nisms required to resist each ously. However, it should be noted material in the mixture may not that the ability of arthropod pest In Conclusion be present in the arthropod pest populations to evolve resistance It is apparent from the survey

Though tank mixing can improve pest control, it can also lead to incompatibility or even phytotoxicity in a grower’s crops.

results that many different pesticide mixtures are being used by greenhouse producers. However, tank mixing has both positive and negative attributes. Although greenhouse producers commonly mix pesticides to reduce labor costs associated with spray applications and potentially improve control of arthropod pests (synergism), they need to be cautious when tank mixing to avoid problems associated with antagonism, incompatibility and phytotoxicity. Additionally, greenhouse producers may not be aware of which pesticide mixtures are compatible. Although pesticide labels often state whether certain pesticides can be mixed, not all combinations can be evaluated. Because tank mixing will likely continue to increase, further research is needed to assess pesticide mixtures, using the survey results, that are either synergistic or antagonistic so that greenhouse producers can speed up the process of deciding which pesticide mixtures to use and which to avoid.

Acknowledgements Double the Fun The author is grateful to the OFA — an Association of Floriculture with the latest addition to our Professionals (Columbus, Ohio), Ball Publishing (Batavia, Ill.) and the Society of American Florists (Alexandria, Va.) for making it pos- sible to conduct the survey during

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