Phytophthora the Abundance of Weevil Populations and Their Damage to Trees Varies Regionally
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The HLB Era: “manageable problems have become intolerable” Larry Duncan CREC D. abbreviatus Citrus root weevil refers to a complex of species. Diaprepes abbreviatus is the most damaging to citrus, but blue green weevils (Pachnaeus litus) are abundant and damaging in some parts of Florida. P. litus Little leaf notcher (Artipus floridanus) is not thought to be economically important. A newly introduced species, Sri Lanka weevil (Myllocerus undatus) looks similar to little leaf notcher and its economic importance is unknown. A. floridanus M. undatus Diaprepes abbreviatus life cycle Eggs Adults Neonates Pupae Larvae + Phytophthora The abundance of weevil populations and their damage to trees varies regionally 0.6 0.25 Weevils are occasional Flatwoods -1 Ridge 0.20 and sporadic pests on week 0.5 -1 0.15 the central ridge -1 0.10 0.4 0.05 Weevils are major and Weevils trap Weevils week 0.00 chronic pests in the -1 Lake DeSotoHendry Polk 1Polk 2 0.3 Indian River flatwoods 0.2 Consequently, another consideration is that Weevils trap Weevils 0.1 weevil management should be considered 0.0 to be habitat specific M J J A S O N D J F M AM J J A S O N D J F M AM J J A S O N 2001 2002 2003 Futch et al., Fla. St. Hort. Proc. 2004 Typical seasonal pattern of adult weevil abundance in citrus orchards In this Polk County grove, weevils emerged from soil in April-May each year (with a 2nd Fall emergence in one year). The timing varies from grove to grove. So monitoring weevil abundance is another important managemet tactic. Adult weevil management should be coordinated to follow peak adult emergence by treating with adulticides and ovicides. Duncan et al., 2001, Environmental Entomology Citrus root weevils Why so hard to manage? Basically… Modern pesticides have little residual activity Different weevil stages live in both the tree canopy and the soil. They serve as source of new individuals to replace those killed by management practices Damage to roots is cumulative. Yearly damage by just a few larvae eventually kills trees. The fact that weevils comprise part of a pest-disease complex is the basis for an important management tactic… While there are currently no rootstocks that are resistant or tolerant to weevils, they do exist for Phytophthora control. Diaprepes- Phytophthora complex evident on the sour orange trees, but not the Swingle citrumelo resets, in this DeSoto County grove. Symptoms of the pest-disease complex on roots of sour orange Rootstocks for central ridge (Phytophthora nicotianae) Swingle citrumello Carrizo citrange C-35 C-32 Rootstocks for flatwoods (Phytophthora palmivora) Cleopatra mandarin US-802 US-897 Relationship Between Tree Decline and Phytophthora Incidence Chemical Treatment, r2 = 0.78 Cleo 60 No Treatment, r2 = 0.65 50 40 C-22 C-32 30 Cleo 20 Swingle C-35 C-22 10 C-32 C-35 Percent Tree decline Percent Tree 0 Swingle 10 15 20 25 30 35 40 45 50 Percent Phytophthora Incidence Plot I, Treated, 2005 C22 C35 Swingle C32 Cleo Plot 2, Untreated, 2005 C32 C22 Swingle Cleo C35 Weevil management Rootstocks Regional considerations Cultural practices Soil drainage pH Physical barriers Insecticides (monitoring weevil abundance ) EPNs Management of soilborne insects Diaprepes Task Force website has biliography of all research papers, general information and dichotomous management key for 8 common grove situations Management of soilborne insects Each of 8 common scenarios provides links to resources from which recommendations were derived Management of soilborne insects Each of 8 common scenarios provides links to resources from which recommendations were derived Cultural practices Soil drainage is critically important because weevil abundance and therefore root damage is greatest in wet soil. Trees stressed by wet soil are less tolerant of weevil damage. Some natural enemies of weevils are less abundant in wet soil. S. diaprepesi H. indica EPNs EPNs Low area of Diaprepes- infested grove Campos-Herrera et al., 2013 Soil Biology and Biochemistry Cultural practices Low pH High pH Soil pH is critically important because many rootstocks are less tolerant of stress in 1.0 ) high pH soil (>6.5) and 3 0.8 because some important 0.6 natural enemies of 0.4 weevils are intolerant 0.2 of high pH soil. (mg/cm density root Fibrous 0.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 Soil pH Graham et al., 2013. Plant Disease Low300 pH High pH Cultural practices Raised natural pH 250 Soil pH is critically pH 5.5 important because some 200 pH 7.0 entomopathogenic 150 nematodes are intolerant of 100 high pH soil, whereas some 50 plant parasitic nematodes 0 are favored by high pH. 180 Steinernema diaprepesi Reduced natural pH 1200 160 140 1000 soil 120 -3 800 100 Recovered IJ 80 600 60 400 40 200 20 Citrus nemas x 100 cm Citrus x nemas 0 0 Ck Ad Ca Control Biocontrol Manure Low pH Treatment Cultural Practices Landscape fabric can be installed as a barrier to prevent larvae from entering soil and adults from exiting soil McKenzie et al. 2001 Duncan et al 2008 The integrity of these Neonate barriers was maintained for 5- larva 6 years. Herbicide savings equaled the fabric cost. Typical effect of landscape fabric mulch on tree growth 3500 Bare soil Landscape fabric In an experiment measuring 3000 Culture P=0.001 effects of Advanced Citrus Mulch P=0.001 CxM P=0.79 Production System (ACPS) versus conventional citriculture (CC), we also installed landscape 2500 fabric under some trees. ACPS trees were 25% larger than CC trees, but only 9% 2000 larger than mulched CC trees. Trunk cross-sectional area (mm) area cross-sectional Trunk 0 Mulched ACPS trees were 35% Conventional ACPS larger than conventional trees. Particle film of kaolin clay These trees are the same age! How does it work? Lab studies @ Optimum T and % RH Photosynthesis rate does not increase beyond 1/3 full sunlight – light is not limiting Syvertsen & Albrigo 1980 + 9o June Citrus leaves in sun can be as much as 9-10oC higher temperature than ambient. Most o fruit trees regulate Mar. + 5 their temperatures to not exceed ambient. But citrus evolved as an understory plant in the subtropics so full sun was not a problem. Syvertsen & Albrigo, 1980. Photosynthesis is maximum At 330C. Hence the beneficial effect of 0.2 particle films is due to increased production of carbohydrate. Particle films also interfere with 0.1 Photosynthesis parasitoids and result in conductance Stomatal major disruption of natural control of scales which become severe secondary pests. Rainfastness of particle films needs (Syvertsen and Lloyd, 1994) improvement. Chemical management of aboveground weevil stages Monitoring peak abundance is important for timing pesticide application Adulticide combined with ovicide is most effective Egg laying begins 7-10 days post emergence of adult from soil Choice of adulticide should be integrated with rotation schedule for psyllid resistence management Chemical management of aboveground weevil stages 90 Chemical Treatment NoTreatment 80 d 25 Yield 2007 70 c c 60 32 31 50 b b b b 40 21 24 b 21 (Mean + + (Mean SE) 34 30 24 Yield Per Tree (Kg) Per Tree Yield a a 20 19 20 10 0 C22 C32 C35 Cleo Swingle Remember, rootstock is also critical and choice is based on Phytophthora species present at site. Search for enemies in center of origin of pest – Classical biological control Quadrastichus hatiensis Aprostocetus vaquitarum Parasitoids of D. abbreviatus introduced into Florida from Caribbean countries. Some establishment has occurred, particularly in south Florida, but effective control has not. Currently searching in highland areas to Ceratogramma etiennei find wasps that are more cold tolerant. Egg parasitoids, Ceratogramma etiennei, Quadrastichus haitiensi, from Puerto Rico/Guadeloupe (putative center of origin). No Larval, pupal or adult parasitoids known. Past failures attributed to widespread use of carbaryl, lack of correlation of life cycles of pest and prey and winter temperatures. Strains of Bacillus thurengiensis recently discovered / GMO possiblities for exotoxin. Ants prey on larvae (particularly fire ants; see handout showing >98% mortality from ants, nematodes and other natural enemies). Mortality Rate for Diaprepes Larvae from Neonate Drop to Adult Emergence Mean No. Mean No. Mortality Neonates/m2 Adults/m2 Rate Year 2000 376.25 6.05 98.39% Year 2001 945.51 6.73 99.29% Neonates Cone Trap Funnel Trap Adults Predation on Diaprepes Neonates: Field Assay - Assay dish (4 mm x 48 mm dia) - 20 neonates per dish - 20 minute observation periods - 3 groves - 199 replicates, 3980 neonates Predators of Neonates on the Soil Surface % Predation Red Imported Fire Ant 10 20 30 40 Ants: Solenopsis invicta Buren Solenopsis invicta 140 (Hymenoptera; Formicidae) Pheidole moerens 132 Dorymyrmex reginicula 46 Brachymyrmex obscurior 42 Dorymyrmex bureni 41 Cardiocondyla emeryi 38 Paratrechina bourbonica 23 Pheidole morrisi 12 Hemipteran: 1 Geocoris floridanus N = 475 Termites Identification of the pest Order Isoptera Family Rhinotermitidae • Small to medium size, white to yellow • Social groups and have a highly developed caste system • Most common Reticulitermes flavipes Termites Biology and ecology • Pine-palmetto woodlands are their natural habitat • When planted with citrus, termites were maintained in the buried wood • Feed on living bark of young trees above and belowground areas, girdling the tree • P. nicotinae often infects trees attacked by termites McCoy (1999) Citrus Health Management Termites IPM • Removal of wood residues, especially before planting • Shallow planting to expose upper scaffold roots • Avoid tree wraps for cold protection • Monitoring regularly with wood bait blocks or wooden stakes McCoy (1999) Citrus Health Management Ants Identification of the pest Order Hymenoptera Family Formicidae • Ubiquitous social insects • Ants may play an important roll in the dynamics of citrus production and successful pest management Predator Omnivorous Foliar damage Humans • Solenopsis invicta, fire ant Ants Biology and ecology • S.