Threats From Beyond Our Borders: Exotic Diseases and Pests in Citrus MaryLou Polek, Plant Pathologist Vice President Science & Technology Citrus Research Board
Disease: The Malfunctioning of Cells & Tissues Expressed as Symptoms Biotic: Infectious pathogens include fungi, nematodes, bacteria, viruses, viroids Abiotic: Air pollution, nutrient deficiencies, too much water/improper soil moisture Insect Pests: Inject salivary toxins while feeding, larvae feed on plant/fruit, eat leaf tissue, girdle tree trunk
Disease: The Malfunctioning of Cells & Tissues Expressed as Symptoms Biotic: Infectious pathogens include fungi, nematodes, bacteria, viruses, viroids Abiotic: Air pollution, nutrient deficiencies, too much water/improper soil moisture Insect Pests: Inject salivary toxins while feeding, larvae feed on plant/fruit, eat leaf tissue, girdle tree trunk
Transmission occurs naturally by: insect vectors Mites Sharpshooters Asian citrus psyllid Aphids
Transmission occurs naturally by: Weather:
Transmission occurs artificially by: humans grafting
Clausena lansium (Lour.) Skeels: wampi, wampee ACP and maybe HLB
Disease Triangle Host Disease Pathogen Vector
Pathogens Discussed Today HLB CVC Leprosis Black Spot Sweet Orange Scab
Huanglongbing - HLB Yellow Shoot Disease Leaves point up Yellow sectoring
Causal Agent.. Candidatus Liberibacter a bacteria - asiaticus - africanus - americanus Photo by Mike Irey Lives in phloemassociated cells
Symptoms Premature fruit drop Asymmetrical yellowing (green islands) Blotchy mottle Similarity to mineral deficiencies, toxicities and other diseases Photo by Mike Irey
HLB: Fruit Symptoms Asymmetry Reduced size Aborted seeds Greening Normal
HLB - Fruit Symptoms Photo by M. Garnier Excessive & premature fruit drop Decreased fruit size Poor color - often remains green at bottom of fruit Extreme bitter taste - not fit for juice!
Adult psyllids usually feed on the underside of leaves (2-4 mm) When feeding, they tip their body at a 45 o angle Asian citrus psyllid Eggs are bright yellow-orange, almond-shaped and are laid on the tips of growing shoots or in the crevices of unfolded feather flush leaves
What To Look For Notched leaves Lots of wax Nymphs & eggs on new flush Adults more in center of tree 45 o feeding angle of adults Use a hand lens Study tree for 10 min+
Potential Pathways Into California Photos by David Kellum Murraya and other Rutaceous plants used as green filler
ACP on a Sticky Trap
Disease Triangle Host It is CRUCIAL to control the psyllid Disease Pathogen Vector
Citrus Variegated Chlorosis (CVC) A xylem- associated bacterium
CVC: Xylella fastidiosa Vector = Sharpshooters
Citrus Variegated Chlorosis (CVC) healthy Only occurs in South America, especially Brazil
Disease Triangle Citrus Variegated Chlorosis (CVC) host Glassy-winged sharpshooter disease pathogen vector
Leprosis Causal agent is a Rhabdovirus Transmitted by Brevipalpus mites
Vectored by Citrus Flat Mites: Brevipalpus spp. Infectious Pathogen: Citrus leprosis virus
symptoms Leprosis
Leprosis Bark symptoms Note: no staining
Stem lesions Leprosis
Disease Triangle Leprosis: Citrus leprosis virus host disease pathogen Vector??
Citrus Black Spot Caused by the fungus: Guignardia citrocarpa
Citrus Black Spot: G. citrocarpa Requires: humid sub-tropical climates Distribution: South America, Australia, Africa, China, SE Asia United States: Limited area in Florida Symptoms: Blemished fruit Unmarketable as fresh fruit Reduced yield Premature fruit drop Control by fungicide application and irrigation practices Trade issues
Sweet Orange Scab Fungal disease: Elsinoe australis Widespread in Texas 15 parishes in Louisiana, Mississippi Recently detected in Arizona Trade ramifications
Elsinoe australis Sweet Orange Scab Sweet orange, lemon, lime, mandarins, grapefruit Spread mainly by human-mediated spore dispersal, infected fruit & nursery stock Control by pruning, fungicide application, removal of infected trees and unharvested fruit Reduces fruit quality and therefore marketability Overwinters on fruit Distribution: Argentina, Bolivia, Brazil (Minas Gerais, Rio de Janeiro, Rio Grande do Sul, São Paulo), Ecuador, Paraguay, Uruguay
********* New detection in Arizona
Take Your Pick! Thank you!!!