Introduction to Insecticides. Kinds, Modes of Action

Transcription

1 Introduction to Insecticides Kinds, Modes of Action

2 Advantages of Insecticides Fast (compared to biocontrol) Generally reliable Flexible increase yield (PROFIT $$)

3 Potential Disadvantages of Insecticides Direct hazards to humans Perceived hazards, societal fears, litigation Pest resistance Adverse side effects on non-target organisms Pest resurgences; secondary pest outbreaks

4 Insecticide Toxicity (Direct Hazards to Humans)

5 LD 50 = Amount of pesticide required to kill 50% of the test animals under standard conditions Expressed as mg pesticide per kg of body weight Useful for comparing toxicity of different pesticides

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7 Remember: The lower the LD50, the more toxic the pesticide!!

8 Insecticide Toxicity - Oral - Dermal - Inhalation

9 Signal Words on Pesticide Labels Moderately Toxic Highly Toxic Slightly Toxic or Relatively Non-toxic

10 Human LD 50 Oral: 50 mg/kg or less; lethal dose of a few drops to teaspoon Dermal: 200 mg/kg or less Highly Toxic

11 Human LD 50 Oral: mg/kg; lethal dose of a teaspoon to a tablespoon Moderately Toxic Dermal: 200-2,000 mg/kg

12 Human LD 50 Slightly toxic Oral: 500-5,000 mg/kg; lethal dose of an ounce to a pint Slightly Toxic or Relatively Non-toxic Dermal: 2,000-20,000 mg/kg Low toxicity Oral: > 5,000 mg/kg Dermal: > 20,000 mg/kg (all compounds will have at least a caution)

13 Toxicity versus Hazard (Putting things into perspective)

14 What is it that is not poison? All things are poison and nothing is without poison. It is the dose only that makes a thing not a poison. Paracelsus, 1567

15 Substance LD50 for lab rat (mg/kg) Sucrose (table sugar) 29, saccahrin 14, Benlate (fungicide) 9, Vinegar 3, Sodium chloride (table salt) 3, Resmethrin (insecticide) 2, Malathion (insecticide) 1, Aspirin 1, Sevin (insecticide) Diazinon (insecticide) Caffeine Gasoline Nicotine LD50 for 150 pound Human (ounces)

16 Approximate lethal doses for naturally occurring toxins The amount of caffeine in 100 cups of strong coffee The amount of solanine in pounds of potatoes The amount of oxalic acid in pounds of spinach or rhubarb The amount of aspirin in 100 aspirin tablets The amount of hydrogen cyanide in 4 pounds of lima beans

17 Modes of action Chlorinated hydrocarbons Organophosphates Carbamates Pyrethroids Neonicotinoids (generalized pesticide groups) Insect Growth Regulators (IGR s)* Microbial insecticides* Horticultural Mineral Oils Inorganics (sulfur) * Multiple MOA s exist in these and other groups

18 Understanding the different pesticide classes and how they work is important Proper application Determining if an application was successful Choosing products that are most likely to control a pest without disrupting natural enemies when feasible

19 Chlorinated Hydrocarbons Examples: DDT, Chlordane, Dieldrin

20 DDT revolutionized pest control in the 1940 s Saved millions from insect-borne diseases such as malaria, typhus, during WWII Post-WWII Green Revolution

21 Chlorinated Hydrocarbons Less acutely toxic than compounds used before 1940s (e.g. lead arsenate) Cheap Broad spectrum; i.e. effective vs. a wide range of different pests, BUT. Highly persistent, residues detectable in soil for >10 years

22 Drawbacks of Chlorinated Hydrocarbons Stored in fatty tissues of vertebrates, excreted in milk (DDT) Biomagnification; adverse environmental effects Potential Carcinogenic Effects Pest resistance

23 Organophosphates Developed in Germany during WWII; spin-off of military nerve gas research Act as synaptic poisons, disrupting normal transmission of nervous impulses across synapses Contact poisons

24 Seta A Simple Nerve Pathway Muscle Sensory Neuron Motor Neuron Synapse

25 Seta Muscle Direction of impulse Acetylcholine is released to transmit impulse across the synapse

26 Seta Muscle Direction of impulse Impulse crosses over. Then, an enzyme called Cholinesterase clears the acetylcholine from the synapse

27 How Organophophates Kill The insecticide binds to the enzyme cholinesterase, deactivating it Without cholinesterase, the acetylcholine (transmitter substance) cannot be cleared from nerve synapses, so that the nerves keep firing Insect loses control of nervous system, with tremors, paralysis, death

28 Seta Muscle Direction of impulse With cholinesterase deactivated, acetylcholine cannot be cleared so the nerves keep firing

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30 Carbamates Same mode of action as organophosphates (i.e., synaptic poisons) Toxicity to vertebrates varies Highly toxic to all hymenoptera (parasitic wasps, bees, etc..) Contact poisons

31 Traditional Insecticides (Organophosphates & Carbamates) Broadly toxic Affect systems common to both insects and vertebrates; e.g. nervous system Risk to non-target organisms Secondary pest outbreaks Pest resurgences and resistance

32 Organophosphate and Carbamate insecticides used in Citrus Organophosphates Phosmet Imidan Dimethoate Dimethoate Chlorpyrifos Lorsban Carbamates Aldicarb Temik Carbaryl Sevin Oxamyl - Vydate Malathion Fyfanon Acephate Orthene Methidathion - Supracide

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34 Food Quality Protection Act (EPA, 1996)

35 EPA: Reduced-Risk Pesticides Reduced risk to human health Reduced risk to non-target organisms including fish, birds and natural enemies Reduce ground and surface water pollution Low use rate, low pesticide resistance potential

36 Pyrethroids High toxicity to insects, but low toxicity to mammals fast-acting moderately rapid degradation in the environment used at very low rates

37 Pyrethroids Target-selective for insect nerves (= low vertebrate toxicity) Cause rapid paralysis of insect nervous system by changing solubility of nerve cell membrane (disrupting closure of the sodium gates ) Axon poisons

38 Pyrethroids prevent ion channel closure; continued electrical impulse (rapid muscular paralysis) Na+ ions Axon nerve cell Electrical nerve impulse K+ ions

39 Pyrethroid insecticides Products labeled for use in FL citrus Fenpropathrin Danitol Zeta-cypermethrin - Mustang Bifenthrin Capture / Brigade

40 Despite their low mammalian toxicity, many pyrethroid insecticides are classified as Restricted Use because of their high toxicity to fish

41 Neonicotinoids (Chloronicotinyls) Agonist* which binds directly with the nicotinergic receptors in insects (like naturally occurring acetylcholine), causing a nerve impulse to be sent Not degraded rapidly by acetylcholinesterase, so the nerve system keeps firing *def: One that is engaged in a struggle

42 Chloronicotinyls block post-synaptic receptor sites for acetylcholine Acetyl choline released into synapse Imidacloprid blocking acetyl choline receptor Acetyl cholinesterase

43 Neonicotinoids ARE NOT CHOLINESTERASE INHIBITORS Blocks post-synaptic receptor sites for acetylcholine

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45 Neonicotinoids (Chloronicotinyls) Examples: Assail (acetamiprid), Admire and Provado (imidacloprid), Platinum and Actara (thiamethoxam), Belay (clothianidin)

46 Imidacloprid Toxicity & Mode of Action Imidacloprid was designed to take advantage of the differences in the binding properties of the nerve synapses of mammals and insects Although mammals have the same general group of receptors (nachr), there has shown to be a 1000x lower binding affinity for vertebrates than for insect receptors

47 Mode of Action of imidacloprid Excellent systemic performance Soil treatment can be the most consistent method of delivery Moves with the transpiration stream Moves across the leaf (translaminar) Both contact and ingestion routes, ingestion is best

48 Insect Growth Regulators (IGR S) Very target specific in mode of action Exploit an insect s developmental biology Chitin synthesis inhibitors Juvenile hormone mimics Reduced risk insecticides

49 Insect Growth Regulators (IGR S) Chitin synthesis inhibitors Buprofezin Applaud Diflubenzuron Micromite

50 Chitin synthesis inhibitors Affect the ability of insects to produce new exoskeletons when molting Typically slow acting Epicuticle Exocuticle Endocuticle Epidermis

51 Insect Growth Regulators (IGR S) Juvenile Hormone Mimics Pyriproxyfen - Knack Fenoxycarb Award fire ant bait Methoprene Extinguish ant bait

52 Insect Growth Regulators (IGR S)

53 Insect Growth Regulators (IGR S) High levels of JH at the wrong time produce an additional larval stage (much larger) than then dies because it can t molt to the adult stage Additional larval stage

54 Microbial Insecticides - Commercial products containing pathogens or microbially-derived toxins that kill insects - mainly bacteria, nematodes, fungi, some viruses

55 Bacillus thuringiensis (Bt) Used since 1950 s to control leaf-eating caterpillars (Bt kurstaki strain) Produced commercially by fermentation Very low vertebrate toxicity Short-residual Works better against small larvae than vs. larger ones Must be ingested to kill

56 Bt crystal/spore complex releases toxins when they contact the high ph midgut of insects

57 Bt products registered for use in Citrus Agree B.t. aizawai strain GC-91 Biobit HP B.t. kurstaki strain ABTS-351 Condor B.t. kurstaki strain EG2348 Crymax - B.t. kurstaki strain EG7841 Deliver - B.t. kurstaki Dipel DF - B.t. kurstaki strain HO-1 Javelin WG - B.t. kurstaki Lepinox WDG - B.t. kurstaki strain EG7826 Xentari DF B.t. aizawai strain ABTS-1857 (all uses are for lepidopteran pests)

58 New strains of Bt are being developed that are active against insects other than Lepidoptera (e.g., mosquitoes, fungus gnats, Diaprepes root weevils) Bt for controlling mosquito larvae in ponds Bt for fungus gnat control in greenhouses

59 Other microbially based insecticides These are not traditionally what we think of as microbial pesticides, but they are toxins derived from microbes. Avermectin Agri-mek Spinosad Spintor, Entrust, GF- 120 fruit fly bait

60 Abamectin Agri-mek Antibiotic derived from Streptomyces avermitilis Inhibits nerve transmission in to the insect muscle Requires several days to kill Used in citrus for mites and leafminers

61 Spinosads Derived from the bacterium Saccharopolyspora spinosa Kills by primarily by ingestion, excitation of the insect nervous system Labeled for lepidopteran larvae, thrips and fruit fly baits

62 Horticultural Spray Oils - Highly refined petroleum-based oils - Clog pest s spiracles and suffocate - Useful vs. small or sedentary pests, e.g., aphids, scale insects, mites

63 Advantages: Horticultural Oils - non-toxic to vertebrates - no resistance potential Disadvantages: - must contact insect with spray - potential for phytotoxicity

64 Pesticide Resistance Management

65 Pesticide Resistance Management Use pesticides at labelled rates Rotate between pesticides with different modes of action Calibrate equipment for accurate application: use recommended spray volumes and pressures Use products less likely to harm natural enemy populations

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67 Insecticide Resistance Action Committee (IRAC) Fungicide Resistance Action Committee (FRAC) Herbicide Resistance Action Committee (HRAC)

68 Management of Asian citrus psyllid and Citrus Greening Disease

69 Management of Citrus Greening Disease The World s Experience Greening management must include: 1) propagation of clean nursery stock, 2) removal of infected trees in the field and 3) effective psyllid control

70 Difficulties Managing HLB Symptoms difficult to diagnose Resemble nutrient deficiencies Must use PCR for confirmation Latency period in plant of years from infection to first observation of symptoms

71 Asian Citrus Psyllid as a vector of greening disease The damage caused to new growth on young trees by psyllid feeding is of minor concern... Use of insecticides to manage psyllid populations is necessary to slow (not eliminate) the spread of greening disease in a grove once present.

72 Insecticide Use for Psyllid Control Brazil: varying success using 6 to 26 applications per season (Belasque et al. 2008) Asia: worst-case situations up to 52 applications per year (Beattie and Holford 2008) Florida: much variation; on average 8 to 12 applications per year

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74 Psyllid Control in Florida What hasn t worked use of selective insecticides targeting immature psyllids (IGR s, etc ) diflubenzuron, fenpyroximate, petroleum oil, abamectin, etc targeting psyllid populations on new flush lengthy periods of new citrus flush allowed psyllid populations to continue to increase when adults were not controlled

75 Psyllid Control in Florida What does work Applications of broad-spectrum insecticide made to target adults prior to new flush Florida citrus growers now averaging 6-8+ broad-spectrum insecticide applications per season for psyllid control fenpropathrin, imidacloprid, chlorpyrifos, carbaryl, dimethoate, phosmet, etc estimated costs for psyllid control $300 / A

76 Psyllid / HLB Management Repeated use of insecticides is not a long-term solution for Florida growers High cost of applications Disruption of established biocontrol agents of other potentially important pests Pesticide resistance likely

77 Current Problems Managing Asian citrus psyllid Easy to kill Hard to control!!!

78 Primary reasons for repeated applications? Short residual of pesticide control Foliar applied insecticides Psyllid movement behavior

79 ACP Caging Study > 60% survival following exposure 12 DAT

80 Psyllid Movement Boina et al Environ. Entomol. 38: ACP movement between adjacent groves (3 days) ~ 100m Protein marker 1 Protein marker 2

81 Psyllid Movement Boina et al Environ. Entomol. 38: ACP movement between adjacent groves (3 days) ~ 100m 12% 20% 88% 80% Protein marker 1 Protein marker 2

82 Reasons for failed control? Collectively, these results explain how the lack of residual control combined with psyllid movement can result in the need for frequent repeated insecticide applications.

83 Citrus IPM Where s it headed? Traditional IPM Practices: Biological Control Pest Population Monitoring Cultural Practices Judicious Use of Pesticides

84 Biological Control There are numerous natural enemies of psyllids present that suppress psyllid populations, especially in the summer and fall Use of broad spectrum foliar insecticides will present a problem in maintaining populations of the natural enemies of psyllids and other potential pest species

85 Insect-vectored pathogen in a perennial crop

86 Insect-vectored pathogen in a perennial crop Biological control has never been successful in controlling an insect vector of plant disease especially in a perennial crop! low/no threshold for pest (vector) presence crop continually exposed to threat over multiple years cant plow under the crop and start over next year

87 Biological Control Prospects? Broad-spectrum insecticide use cant last forever we hope Novel solutions to reduce reliance on pesticides Resistant trees? Organic Groves If they survive biocontrol will be important to help maintain populations at reduced levels than left uncontrolled Urban / Dooryard Environments Little acceptance of pesticide use Biocontrol may help reduce threats to commercial citrus coming from these areas

88 Psyllid Monitoring

89 Feasibility of pesticide applications based on psyllid scouting? Psyllid populations can explode seemingly overnight High number of offspring Short generation time neighboring grove effects (psyllid movement) Lack of effective action thresholds (spray-based monitoring)

90 Psyllid Monitoring Where psyllid and HLB are established, psyllid monitoring has limited value Small citrus acreage may be able to time applications based on monitoring Large citrus acreage difficult to detect and respond in a timely manner Both calendar-based sprays and cleanup sprays based on scouting will likely be required

91 Cultural Practices Ongoing research: Flush management factor that promote / limit new leaf growth Altering host plant suitability changing plant nutritional status Host plant resistance identification of psyllid resistant cultivars and incorporate into breeding program

92 Use of Pesticides

93 Pesticide Application Methods Trade-offs in level of control provided Aerial applications poor inside coverage of canopy Low volume no residual effects; most product lost to drift Airblast slow and expensive; allows psyllid recolonization

94 Dormant Sprays First use of dormant sprays in Florida citrus for citrus rust mites!!! Where a preventive schedule has been followed, control has been more effective than where a corrective schedule has been followed the period of control was longer when targeting low populations than when treatment was delayed until a medium to heavy pest infestation had developed W. L. Thompson 1948, Entomologist, Lake Alfred

95 Dormant Sprays FL growers often make 2 dormant sprays for psyllid 1 st immediately after fall flush period Control adults that developed during fall flush period 2 nd just prior to early spring flush Ensure no adults present to reproduce on new flush Dormant sprays important to help keep psyllids low through bloom

96 Foliar Insecticides for Psyllid Control in Florida use of broad-spectrum insecticides targeting adult psyllids fenpropathrin, imidacloprid, chlorpyrifos, carbaryl, dimethoate, etc start with winter dormant sprays to minimize psyllid population growth on spring flush Additional broad-spectrum sprays prior to new flush throughout the year Most growers in FL have best success using monthly sprays

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98 Importance of Young Tree Protection

99 Young tree care Young trees crucial to ensuring future citrus production Perhaps more important than control of psyllids on mature trees at least in FL now Rely primarily on soil-applied systemic neonicotinoid insecticides imidacloprid, thiamethoxam and clothianidin

100 Application of systemic neonicotinoids

101 Soil-applied neonicotinoids Provide protection from both psyllids and leafminer Provide 6+ weeks of protection Must be applied 2 weeks prior to flush Can be applied to trees up to 9 in height but you have to increase product rate with increasing tree size

102 Soil-applied systemic insecticides Yearly Rate Limits Admire Pro (imidacloprid) 14 fl oz / A (0.5 lb a.i.) Platinum 75 SG (thiamethoxam) 3.67 oz / A (0.172 lb a.i.) Belay 50 WDG (clothianidin) 12.8 fl oz / A (0.4 lb a.i.)

103 Rate per acre (single application) (based on 140 trees / A) New Reset (2-3 height) 1-2 yrs (3-5 height) 3-5+ yrs (5-9 height) Admire Pro 4.6F 3.5 fl oz (4 apps) 7 fl oz (2 apps) 14 fl oz (1 app) Platinum 75 SG oz (2 apps) oz (2 apps) 3.67 oz (1 app) Belay 50 WDG 3.2 fl oz (4 apps) 3.2 fl oz (4 apps) 6.4 fl oz (2 apps)* * Currently Belay can only be applied to nonbearing trees Rate per tree New Reset (2-3 height) 1-2 yrs (3-5 height) 3-5+ yrs (5-9 height) Admire Pro 4.6F fl oz 0.05 fl oz 0.1 fl oz Platinum 75 SG oz oz oz Belay 50 WDG fl oz fl oz fl oz

104 Tree size Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Reset (<3 ) 1-2 yr (3-5 ) 3-5 yr (5-9 ) bearing Season-long ACP control (foliar applications to prevent pesticide resistance to neonics shown in orange) P A A B B A A P P A B B B B A P P A A A= Admire (imidacloprid); B=Belay (clothianidin); P=Platinum (thiamethoxam); Products are positioned for use at certain times of the year based on water solubility and likelihood for significant rain events.

105 Value of Insecticide Applications Population suppression vs. prevention of pathogen transmission

106 Can we protect trees from becoming HLB-infected? Kill psyllids before they infect a tree with the HLB bacteria

107 Candidatus Liberibacter asiaticus Causal agent of HLB Gram-negative bacteria Phloem-limited bacterium

108 How insecticides affect transmission Factors influencing feeding behaviors Plant surface exploration Labial dabbing Test probing Probing of extended duration Chemical stimuli affect these steps influencing transmission Transmission can be disrupted as a result of lethal or sublethal effects of insecticides

109 Feeding Behavior Assessment Electrical Penetration Graph Feeding? Or not Feeding?

110 Psyllid behaviors Probing behaviors Stylet penetration into plant Phloem penetration Phloem salivation Phloem ingestion Xylem ingestion Non-probing behaviors Walking Standing still/jumping off plant

111 Waveform correlations Top Bottom Pathway or stylet penetration C Phloem penetration D Bottom Top Phloem salivation - E1 Phloem ingestion - E2 Bonani et al 2010

112 Waveform correlations Top Bottom Non probing/non walking - z Xylem ingestion - G Non probing/walking - np Bonani et al 2010

113 EPG Assessment of psyllid feeding

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115 EPG Analysis of ACP Feeding Behavior Can insecticides prevent pathogen transmission from occurring? (untreated)

116 Results of EPG Studies to Date Product evaluated Active ingredient Application method Duration of psyllid feeding disruption Admire Pro 4.6F imidacloprid Soil drench At least 6 weeks* Platinum 75 SG thiamethoxam Soil drench At least 6 weeks* Belay 50 WDG clothianidin Soil drench At least 6 weeks* Provado 1.6 F imidacloprid Foliar applied 3 weeks Danitol 2.4 EC fenpropathrin Foliar applied 2-3 weeks Lorsban Advanced chlorpyrifos Foliar applied 24 hours Delegate WG spinetoram Foliar applied 24 hours Movento MPC spirotetramat Foliar applied none *no evaluations of the soil-applied neonicotinoids have been made beyond 6 weeks. The primary benefit of foliar insecticide use is ACP population suppression

117 ACP control on young trees (foliar applications to prevent pesticide resistance to neonics shown in orange) Tree size Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Reset (<3 ) 1-2 yr (3-5 ) 3-5 yr (5-9 ) bearing P A A B B A A P P A B B B B A P P A A A= Admire (imidacloprid); B=Belay (clothianidin); P=Platinum (thiamethoxam); Products are positioned for use at certain times of the year based on water solubility and likelihood for significant rain events.

118 Value of Insecticide Applications Soil-applied neonicotinoids can reduce the likelihood of young trees from becoming HLB infected Reduction in psyllid populations Minimize chances for pathogen transmission through reduction in phloem feeding behaviors

119 Value of Insecticide Applications Foliar-applied insecticides provide population suppression but are not likely to provide much benefit in terms of preventing pathogen transmission (via disruption of psyllid feeding) Rotation of foliar products will be important to help prevent resistance to neonicotinoids used extensively in young tree plantings

120 Tree size Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Reset (<3 ) 1-2 yr (3-5 ) 3-5 yr (5-9 ) bearing Season-long ACP control (foliar applications to prevent pesticide resistance to neonics shown in orange) P A A B B A A P P A B B B B A P P A A A= Admire (imidacloprid); B=Belay (clothianidin); P=Platinum (thiamethoxam); Products are positioned for use at certain times of the year based on water solubility and likelihood for significant rain events.

121 Improving Protection of Mature Trees? Since foliar insecticides are not likely to prevent mature trees from becoming HLB infected How can we improve psyllid control on mature trees?

122 Area-wide ACP control programs Coordinated effort Simultaneous treatment of groves in a large area Delay psyllid recolonization of groves Goals: Greater reduction in overall psyllid populations Reduce the need for frequent reapplication of pesticides

123 Basis of Area-wide Control (Knipling 1979) Basic Principle of Total Population Control: Uniform suppressive pressure applied against the total population of the pest over a period of generations will achieve greater suppression than a higher level of control on most, but not all, of the population each generation

124 Key Features Grove-by-Grove Approach Targeting portion of population Refugia left for immigrants (reapplication of insecticides) Pests with limited mobility Low value crop with medium to high pest tolerance Reactive approach to pest presence Area-Wide Approach Targeting entire population No refugia for immigrants (reduction in insecticide use) High pest mobility High value crop with low pest tolerance Proactive approach to pest presence Complicates pesticide resistance management Facilitates pesticide resistance management (Summarized from: Hendrichs et al. 2007)

125 Area-wide Control Recommendation of National Academies of Science Development of Citrus Health Management Areas (CHMAs) Facilitate the coordination of psyllid control and other HLB management practices Best chance for surviving HLB until more long-term sustainable solutions developed Thus far Florida has only adopted coordinated psyllid control efforts

126 38 CHMAs statewide 486,079 acres (commercial citrus)

127 CHMA approach to psyllid management Coordinate timing of pesticide applications Reduce overall psyllid populations Cut down on cost and number of pesticide applications needed to stay productive Coordinate mode of actions used Managing pesticide resistance by minimizing repeated exposure to same MOA

128 Results to Date Psyllid populations are decreasing where coordinated applications have been implemented.

129 Central Highlands 17/27 CHMA Total blocks = 423 7,919 grove acres Blocks sampled = % of CHMA scouted In 62% (54/87) of the blocks sampled, no psyllids were found

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133 CHMA website ( Facilitate communication between growers Reference point for information of upcoming CHMA events Tool to convince non-participants to join the effort Demonstration of benefit (psyllid scouting reports) Educate growers (absentee growers)

134 Developing a comprehensive pest management program Psyllids/HLB are the primary focus of current pest management programs There are still other pests requiring management Rust mites Leafminer Weevils Other site specific pests

135 Developing a Management Strategy Multi-targeting of pests use of one pesticide application to control several pests simultaneously planning ahead to reduce insecticide inputs

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