What are the challenges to scab management? Fusicladium effusum is - PowerPoint PPT Presentation

What are the challenges to scab management? • Fusicladium effusum is a variable pathogen (a record of host resistance breaking down) • Current fungicides – and fungicide resistance • Weather – can preclude timely spray application (for example, 2013) • Pecan trees eventually grow tall (>15 m, >50 ft)

Hedging and scab • Hedging is done for several reasons. But how might it influence scab and scab management in the southeast? • We explored this for the first time in 2013 – Results of experiments at three locations in GA (Weston, Marshallville and Valdosta) – Experiments in Weston and Marshallville trees 14 m (~45 ft) – At Valdosta site, trees 18 m (60+ ft) – Allows a contrast of hedging effects on scab in trees of different heights • 2013 was a year conducive to the disease (it was wet, with regular rainfall) • Susceptible cultivars developed severe scab despite frequent fungicide application

Hedging – the process

Hedging and scab - concerns • Fresh growth produced throughout the season on hedged trees is susceptible to scab (susceptible cultivars) • This could be more difficult to control in the southeast • Consequently, fruit on hedged trees may have more severe scab • However, an advantage may be hedged orchards are more open (more air movement, therefore conditions less conducive to scab) New growth produced Not hedged Hedged throughout season What if this is the outcome……?

So what effect does hedging have on pecan scab? • Three experiments on commercial orchards in 2013 • Weston, Marshallville and Valdosta, • All experiment treatments replicated (3 to 5 times). Standard experiment designs • Assessed for scab at 3 to 4 heights on 1 to 4 occasions • Only sampled row-sides • Analyzed using general linear modeling with means comparison by t- grouping

Tree management and fungicide treatments – Weston, GA • Pawnee trees ~45 ft tall and hedged to 40-45 ft (planted 2000, 14 y old) • All received the same fungicide treatments • But different tree hedging/removal management practice • Sampled at 5, 8 and 11 m (15, 26 and 37 ft) Treatment East hedged West North South Tops Tops Jan-Feb hedged Jan- hedged 8 hedged 8 hedged 16 rehedged 2012 Feb 2012 Mar 2013 Mar 2013 May 2013 16 Jul 13 1. No thinning or hedging (check) No No No No No No 2. Pattern thinned on diagonal No No No No No No 3. Selectively tree thinned (Dr. Bill Goff‟s method). Replanted with No No No No No No spaded trees of high scores 4. Dormant hedged on 2 sides, following year hedged on opposite 2 Yes Yes Yes Yes No No sides. Cuts 12 feet from trunk on each side. Cut tops on hedged sides when height exceeds row width (started cutting tops in 2013). Repeat the pattern over 2-year periods 5. Hedge one side of the tree each year. Also cut tops on hedged sides Yes No Yes No No No when height exceeds row width (started cutting tops in 2013) 6. Repeat 4, except only on expected “on year” No No Yes Yes No No 7. Hedge tops mid May. Repeat July every year. Hedge 2 sides July No No No No Yes Yes during “on year”. Opposite 2 sides next “on year” Fungicide treatments (12 applied) – all ground applications Date Fungicide and rate (100 gal/acre) 04-03-13 Sovran- 3 oz (every other middle) 04-08-13 Sovran- 3 oz (every other middle) 04-17-13 Sovran- 3 oz + Fungiphite- 32 oz + Nickel CBM- 16 oz 04-30-13 Topsin- 19.2 oz 05-15-13 AgriTin- 9.6 oz 06-02-13 Agri Tin- 12 oz + Fungiphite- 32 oz 06-13-13 Quadristop- 12.8 oz 06-27-13 AgriTin- 12 oz + Fungiphite- 32 oz 07-12-13 AgriTin- 12 oz + Elast- 25.6 oz 07-22-13 AgriTin- 12 oz + Fungiphite-32 oz 08-03-13 AgriTin- 12 oz + Elast- 25.6 oz 08-16-13 AgriTin- 12 oz

Hedging experiment - Weston, GA Treatment effects on scab on leaflets and fruit 9 September 2013 Treatments Incidence on leaves • On foliage incidence ranged Pawnee (40-45 ft tall) from 1 to 6% leaflets infected 12 Seven treatments % leaflets with scab • On foliage scab was least on the 9 A 1. Not hedged (control) AB check, and treatments 2, 5 and B 6 2. Pattern thinned on diagonal C 6 C C C 3. Selectively tree thinned 3 (using Dr. Bill Goff‟s method). • It was most on leaves of Replanted with spaded trees 0 treatments 4 and 7 1 2 3 4 5 6 7 of high scores 4. Dormant hedged on 2 sides. • On fruit all treatments had Treatment F=7.9, P<0.0001 Following year hedged on severity ≥40% opposite 2 sides. Cuts 12 feet Severity on fruit from trunk on each side. Repeat the pattern over 2- • Treatment 3 had least severe 80 A year periods scab (40%) % fruit area scabbed B B BC 60 BC C 5. Hedge one side of the tree D each year • Treatments 2,4 and 5 had 40 6. Repeat 4, except only on severity similar to the control 20 expected “on year” (1) 7. Hedge tops mid May. 0 1 2 3 4 5 6 7 Repeat July every year. • Treatment 7 had most severely Hedge 2 sides July during “on scabbed fruit (>63%) Treatment = F=21.3, P<0.0001 year ”. Opposite 2 sides next “on year”. Data analyzed using general linear modeling. Letters indicate significant differences based on t-grouping ( α =0.05). 95% Confidence Intervals are indicated.

Hedging experiment - Weston, GA Tree height effects on scab, 9 September 2013 Severity on fruit Incidence on leaves 100 10 A % fruit area scabbed A 80 8 % leaflets scabbed B 60 6 B 40 4 C C 2 20 0 0 5 8 11 5 8 11 15 ft 26 ft 37 ft 15 ft 26 ft 37 ft Sample height (m) Sample height (m) F=31.4, P<0.0001 F=637.4, P<0.0001 • Disease control measures are less efficacious at greater heights (even in hedged systems in years of severe epidemics) • Despite a rigorous fungicide program (12 fungicide applications) Data analyzed using general linear modeling. Letters indicate significant differences based on t-grouping ( α =0.05). 95% Confidence Intervals are indicated.

Hedging experiment – Marshallville, GA • Desirable trees 14 m (~45 ft) and hedged to 12-14 m (40-45 ft) Marshallville, GA • Planted 1996, 18 y old Desirable (14 m, 45 ft tall) • Hedged one side 2 March 2013 Two treatments 1. Not hedged (control) • All received the same fungicide treatments 2. One side hedged • Sampled at 6, 6-9 and >9 m (<20, 20-30 and >30 ft) Fungicide treatments (14 applied) Dates Type Fungicide and Rate (100 gal/acre) 4-9-2013 Ground AgTin 12 oz 4-22-2013 Ground AgTin 6 oz + Bumper (propiconazole) 6 oz 5-6-2013 Ground Absolute 500SC 6 oz 5-20-2013 Ground Absolute 500SC 6 oz 6-4-2013 Ground AgTin 12 oz 6-12-2013 Ground AgTin 12 oz 6-26-2013 Ground AgTin 12 oz 7-8-2013 Aerial AgTin 12 oz 7-15-2013 Ground AgTin 12 oz 7-29-2013 Ground AgTin 12 oz 8-6-2013 Aerial AgTin 12 oz 8-12-2013 Ground Absolute 500SC 6 oz 8-21-2013 Aerial Absolute 500SC 6 oz 8-26-2013 Ground SuperTin 12 oz

Hedging experiment – Marshallville, GA Treatment and height effects on scab on leaflets 8 Aug 2013 10 Oct 2013 Marshallville, GA 30 40 A A % leaflets with scab Desirable (14m, 45 ft tall) A % leaflets with scab A 30 20 Two treatments 20 10 1. Not hedged (control) 10 0 2. One side hedged 0 One side Not hedged Hedged Not hedged hedged Treatment F=0.4, P=0.6 Treatment F=0.01, P=0.9 60 40 A % leaflets with scab A 50 B % leaflets with scab A B 30 CB CB 40 C B 20 30 10 20 0 10 <6 m 6 to 9 m >9 m 0 <20 ft 20-30 ft >30 ft <6 m 6 to 9 m >9 m <6 m 6 to 9 m >9 m <20 ft 20-30 ft >30 ft <20 ft 20-30 ft >30 ft Height F=7.6, P=0.0005 Treatment × Height F=3.9, P=0.02 • No effect of hedging on the incidence of infected leaflets • A pronounced effect of height on incidence of infected leaflets (Treatment × Height interaction in October)

Hedging experiment – Marshallville, GA Treatment effects on scab on fruit Marshallville, GA • Hedged treatment no different to non-hedged in August Desirable (14 m, 45 ft tall) Two treatments • By October, the fruit on the hedged trees has 1. Not hedged (control) slightly more disease compared to the non-hedged 2. One side hedged 10 October 2013 8 August 2013 60 12 A A Severity (% area) Severity (% area) B 45 A 9 30 6 15 3 0 0 Hedged Not hedged Hedged Not hedged Treatment F=1.7, P=0.2 Treatment F=5.01, P=0.03 Data analyzed using general linear modeling. Letters indicate significant differences based on t-grouping ( α =0.05). 95% Confidence Intervals are indicated.

Hedging experiment – Marshallville, GA Marshallville Tree height effects on scab severity on fruit Desirable (14 m, 45 ft tall) • August – hedged trees have more disease only at heights >9 m (30 ft) Two treatments 1. Not hedged (control) • By October there was no Treatment × Height 2. One side hedged interaction (only height effect) 8 August 2013 10 October 2013 20 90 Hedged Not hedged A A 75 Severityy (% area) Severity (% area) 15 B 60 BC B 10 BC BC 45 C C 30 5 15 0 0 <6 m 6 to 9 m >9 m <6 m 6 to 9 m >9 m <6 m 6 to 9 m >9 m <20 ft 20-30 ft >30 ft <20 ft 20-30 ft >30 ft <20 ft 20-30 ft >30 ft Height effect F=104.8, P=<0.0001 Treatment x Height effect, F=3.8, P=0.02 Data analyzed using general linear modeling. Letters indicate significant differences based on t-grouping ( α =0.05). 95% Confidence Intervals are indicated.