Introduction to Pecan Diseases and General Management Original Presentation by Damon Smith/Jen Olson Modified and Presented by Jackie Lee Horticulture IPM Extension Specialist Little Rock, AR
Contact Information Jackie Lee University of Arkansas Cooperative Extension Service 2301 S. University Little Rock, AR 72204 501-671-2191 jalee@uaex.edu
Infectious Disease Agents (Pathogens) FUNGI: cause the great majority of plant diseases; thousands have been reported BACTERIA: six genera are known to cause plant diseases VIRUSES: Submicroscopic obligate parasites NEMATODES: small nonsegmented worms PHYTOPLASMAS and SPIROPLASMAS: submicroscopic obligate parasites PROTOZOANS: motile microscopic animals PARASITIC PLANTS: use feeding structures to feed on plants
Fungi Most common of plant pathogens Attack all plant parts About 16,000 fungal plant pathogens Unit of infection = spore or mycelium Multi-celled Visible, microscopically E.g. Pecan scab, Powdery mildew Spread by wind, splash, insects, water, tools
Mycelium on leaf surface
SPREAD OF FUNGAL SPORES Air currents of 1 MPH or more can carry fungal spores long distances Spores often form during the night hours when humidity is high Become detached with dropping humidity in the morning hours as temperatures rise and air movement increases, and are borne aloft by convection currents created by warming of soil
Spore germination and infection Spores require high humidity for development (>90%) Spores require water film on the host tissue to germinate Many germinated fungal spores penetrate plant tissue directly, or enter through the leaf pores (stomates) or wounds. Most conidia can survive from several hours to several days if conditions necessary for germination are not met.
Fungi Powdery mildew Pecan scab
Plant Disease Triangle Example Host Pecan Pathogen Pecan Scab Environment Fungus: Cladosporium caryigenum Periods of extended leaf wetness; cool to moderate temperatures
Manipulate the Host Component Genetic resistance most powerful disease management tool Native trees (fewer disease problems) Plant stress management Stress predisposes plants to disease Host Pathogen Environment
Manipulate the Environment Do not over fertilize many diseases are more severe when there is an excess of nitrogen available Reduce competition for water, light, nutrients Provide adequate air movement and light penetration Host Pathogen Environment
Reduce Amount of Pathogen Exclusion Preventing the introduction of a pathogen (verify clean planting stock) Eradication Constant observation and early diagnosis is critical Sanitation Removing pathogen infested plant material from the area Host Pesticide Use Pathogen Environment
Pecan Scab Jackie Lee, Horticulture IPM Extension Specialist
Overwinters as stroma on shucks, petioles, and stems Pecan Scab Cycle Spores produced in spring with warmer temps and rainfall Fusicladium effusum Fusicladium effusum
Plant Disease Triangle Example Host Pecan Pathogen Pecan Scab Environment Fungus: Cladosporium caryigenum Periods of extended leaf wetness; cool to moderate temperatures
Native vs. Cultivars
Scab Management for Native Pecans Open up groves to air and light; remove heavily scabbing trees; promote drainage Assess crop load while scouting for casebearer & make spray decision Make fungicide applications
Fungicide applications for Native Pecans 1. First casebearer (pollination complete) 2. 1st Cover (2-3 weeks after first casebearer)* 3. 2nd Cover (2-3 weeks later)* 4. Subsequent cover sprays as needed*
Cultivars: More Intensive
Scab Management For Cultivars Plant resistant cultivars Open up orchards to air and light; promote drainage Implement a fungicide spray program 1. Phenological Scheduling Method (based on plant growth stage) 2. Pecan Scab Model???? (weather-based, Internet accessed)
Resistance Highly susceptible Moderately susceptible Low susceptibility (resistant) Burkett Caddo Barton Squirrel s Delight Colby Choctaw Western Creek Graking Wichita Giles Kanza Kiowa Lakota Maramec Mount Mohawk Nacono Oconee Osage Shawnee Pawnee Peruque Stuart Native Trees
Phenological/Plant Growth Method of Fungicide Application 1. Pre-pollination ( ~ parachute stage of development) 2. First casebearer (pollination complete) 3. 1st Cover (2-3 weeks after first casebearer)* 4. 2nd Cover (2-3 weeks later)* 5. Subsequent Cover sprays as needed*
Scab influence on yield (Bill Reed)
Pecan Scab Advisory Needed 1. Weather-based disease advisory, Internet accessed, location specific 2. Uses weather data from 115 weather stations in the Mesonet system 3. Calculates # scab hours (hours during which temp > 70 F and RH > 90 %) accumulated in last 14 unprotected days towards fungicide application thresholds 4. Also has information on using the advisory, cultivar susceptibilities, fungicide application thresholds, fungicides and rates
Scab Advisory Spray Thresholds Highly susceptible cultivars Moderately susceptible Natives, low susceptibility 10 scab hours 20 scab hours 30 scab hours
***Labels change, Refer to label before application. Restrictions on numbers of applications and timing (shuck split) Products Product Active FRAC Rate/Acre Tilt propiconazole 3 4-8 fl oz Stratego Propiconazole + trifloxystrobin Orbit 45WP AGPAK/SuperTin Propiconazole+tri phenyltin 3,11 10oz 3,30 Refer to label Headline SC pyraclostrobin 11 6-7oz Merivon Fluapyroxad+pyra clostrobin 7,11 5-6.5oz Adament 50WG Topsin M 70WDG Topsin M 70WP Super Tin 80WP Tebuconazole+trifl oxystrobin Thiophanatemethyl Triphenylin hydroxide 3,11 3-8oz 1 1lb 30 5-7.5oz
Products http://www.uaex.edu/publications/pdf/mp1 54year2016/mp154completebook2016.pdf MP154 Arkansas Plant Disease Control Products
In the future. Produce decision aides and educational materials What is needed????? Farm visits: jalee@uaex.edu 479-530-8163
Questions?