A Georgia Perspective of Pecan Scab Management. Lenny Wells UGA Horticulture

Transcription

1 A Georgia Perspective of Pecan Scab Management Lenny Wells UGA Horticulture

2 Disease Cycle Epidemics build up on fruit (conidia) Summer Epidemics build up on young Leaves (conidia) Spring Winter Autumn Fungus becomes dormant as stroma Overwinters as conidia and stroma

3 Pecan Scab Rain frequency is more important than total rainfall. Heavy rain at any time of day favors scab. Light evening rain that keeps trees wet all night lead to more scab than rainfall ending early enough to allow trees to dry.

4 Pecan Scab Symptoms Leaves are most susceptible 7 21 days after bud-break New leaves & shoot elongation for ~ 90 days March April May Reduced photosynthesis Leaf retention in the fall Source of inoculum

5 Severity (%) Effect of Delayed Spray Programs on Nut Scab (Desirable, 2003) (17 rainy days in April and May) thru 9 2 thru 9 3 thru 9 4 thru 9 Nontrt 19-Jun 26-Jun 3-Jul 10-Jul 17-Jul 24-Jul 31-Jul 7-Aug Tim Brenneman, UGA Plant Pathology

6 Pecan Scab Timing of infection is important. 1st 2-3 weeks = moderately susceptible Mid-Jun to Mid Jul = most susceptible

7 Nut Growth & Damage Potential D A M A G E P O T E-MAY M-MAY E-JUNE M-JUNE E-JULY M-JULY E-AUG M-AUG E-SEPT N U T G R O W T H

8 Pecan Disease Management Cultivar selection Chemical control Selection Timing Coverage Tree health Environment Sunlight & air movement

9 FUNGICIDE COVERAGE Tree Size Tree Spacing Sprayer Operation Wind Speed (~1.5 mph) Misdirected or weak air blasts

10 AIR BLAST SPRAYING AIR

11 UNIFORM COVERAGE Top to Bottom & Side to Side

12 Without Volute With Volute

13 Aerial Application Not a substitute for ground application Useful when ground application is difficult or impossible

14 Dormant Spray Conclusions Of the dormant sprays evaluated, Elast provided the most disease reductions, but the benefits were relatively small and not consistent across all trials ----Tim Brenneman, UGA Plant Pathology

15 Hedge Pruning and Scab Not hedged Hedged After hedge pruning, fresh growth is produced and grows throughout the season These leaves are susceptible to scab (susceptible cultivars) Consequently, fruit on hedged trees may have more scab pressure Clive Bock, USDA

16 Clive Bock: Summary ~12-14 m (40-45 ft) Under the same fungicide regime hedge pruning cannot be said to increase or decrease scab severity in the canopy up to 40 ft (12.5 m) There is an increasing advantage to hedging as more of the fruit are within reach of effective fungicide coverage & inoculum removed Clive Bock, USDA

17 Fungicide class FRAC group Common name Trade name(s) Resistance risk MBCs (benzimidazoles) 1 thiophanatemethyl Topsin M; T-methyl high QoIs (strobilurins) 11 azoxystrobin pyraclostrobin kresoxim-methyl trifloxystrobin Abound, Quadris Top*, Quilt* Headline; Pristine*** Sovran Absolute*, Adamant* medium DMIs (sterol inhibitors, triazoles) 3 propiconazole fenbuconazole metconazole difenoconazole tebuconazole Orbit, Propimax, Bumper, Tilt Quilt* Enable Quash Quadris Top* Folicur, Tebuzol, Absolute*, Adamant*, Topsin XTR** medium Organotins 30 fentin hydroxide SuperTin, Agri Tin low to medium Guanidines U12 dodine Elast (Syllit) low to medium Phosphonates (phosphites) 33 phosphorous acid and salts Phostrol, ProPhyt, FungiPhite, Reliant, Fosphite, Kphite, Phiticide, Rampart, Topaz, Viathon**** low * Formulated mixture of a DMI and a QoI *** Formulated mixture of an SDHI and a QoI ** Formulated mixture of a DMI and an MBC **** Formulated mixture of a DMI and phosphite

18 Pecan Disease Management Fungicide Resistance Management Use formulated mixtures or tank mixes Alternate different MOA Maintain effective rates Use low-risk fungicides when possible Use when most effective

19 Systemic Fungicide Movement in Pecans Strobilurins, DMIs, and phosphites show some movement up into existing foliage, and excellent movement into new leaves not present when sprayed Phosphites also move down (at least 2 leaves) into existing foliage

20 Phosphites (ProPhyt, Phostrol, Kphite, Rampart, Reliant, Fungi-phite, etc.) Phosphorous acid salts; NOT phosphate (fertilizer) Have very good activity on pecan scab, anthracnose, and other diseases; stronger on leaves than nuts Highly systemic in the tree, up and down Cheap and have a different mode of action (both direct on pathogen and increased plant defenses) Have been used A LOT in Georgia the last couple years, especially to combat fungicide resistance

21 DMI/Strobilurins and Resistance DMI--MOA Group 3: Managemnet Moderate Risk Stand-alone use is not recommended where reduced sensitivity is known or suspected. Best used as a tank mix Strobilurin---MOA Group 11: Moderate risk Do not make more than 2 sequential applications. If only using solo products, group 11 fungicides should not be used in more than 1/3 of the total number of fungicide applications. If using group 3 tank-mixed with other modes of action, they should not be used in more than 1/2 of the total number of fungicide applications.

22 Three Part Season Pre-pollination Bud break through nut set day intervals Post-pollination Nut set to shell hardening day intervals After shell hardening

23 Pre-Pollination Best options are DMI/Strobilurin mixes (Absolute, Quilt, Custodia, TopGuard) Alternate with Phosphite alone (2 qt/acre rate) or tank mixed with DMI or Strobilurin

24 Post-Pollination Best options are Elast alone or tank mixed with Tin or Phosphite Alternate DMI/Strobilurin Mixes (Absolute, Quilt, Custodia, TopGuard, Quadris Top*)

25 DMIs Strobilurins TPTH Elast Phosphite leaf scab nut scab Apr May Jun Jul Aug Sep downy spot powdery mildew zonate leaf spot Phytophthora Any scab program Topsin-M DMIs strobilurins TPTH phosphite strobilurins

26 Managing Scab Spray Based on Weather and Location Air Flow and Sunlight Spray on time Do not go more than 14 days from mid June-mid August on Desirable no matter what Get Good Coverage Rotate Fungicides If its not broke don t fix it Nuts don t have to be 100% clean