Observations on Sunflower Rust in Nebraska and Management Efforts with Fungicide Application Timings

Transcription

1 Observations on Sunflower Rust in Nebraska and Management Efforts with Fungicide Application Timings Robert M. Harveson Extension Plant Pathologist University of Nebraska Panhandle REC, Scottsbluff

2 Rust in Nebraska Sunflower rust, caused by the obligate fungal pathogen Puccinia helianthi Rust is present to some extent each year in Nebraska - both cultivated and wild sunflowers In commercial production it often occurs late enough in the season that yields are not affected and treatment is not considered to be necessary - can cause significant losses on susceptible hybrids under conducive conditions

3 Spore Stages Pathogen has a complex life cycle consisting of 5 distinct spore stages all of which occur on sunflower: Uredial reddish-brown (rust) colored and the most commonly observed stage Also the most damaging can have multiple cycles during the season Telial overwintering stage

4 Spore Stages In early spring, teliospores germinate to produce basidiospores which can re-infect sunflowers Flask-shaped pycnia are formed on the upper leaf surface Aecia develop from the pycnia - usually on the lower leaf surface directly below the pycnia Aeciospores, formed in developing aecia, then re-infect sunflowers to create new uredia completing the life cycle

5 Uredia change to telia with cooler temperatures Pathogen Life Cycle Overwinters as teliospores Basidiospores infect sunflowers and form pycnia Aeciospores re-infect sunflowers creating new uredia Aecia develop from the pycnia

6 Uredia change to telia with cooler temperatures Pathogen Life Cycle Overwinters as teliospores Basidiospores infect sunflowers and form pycnia Early Spore Stages Aeciospores re-infect sunflowers creating new uredia Aecia develop from the pycnia

7 Rust Survey in 2009 Temperatures during April, May, and early June were 6 F cooler with 5.5 inches higher rainfall than the 30 year average First pycnia and aecia observed in late May A survey of western Nebraska conducted over the next four weeks on volunteers from 2008 production fields (>50 fields/locations) Early spore stages found in 44 (85%) of surveyed sites

8 Pycnia Early Spore Stages Aecia

9 Early Spore Stages

10 Uredia

11 Telia

12 Fungicide Evaluations - Methods Two distinct studies conducted: Fungicide evaluations (testing 5 products) Control, Proline (5.7 oz), Prosaro (6.5 oz), Tebuzol (4.0 oz), Headline (9.0 oz), and Quadris (9.0 0z) Fungicide application timings Control Headline (R1, R4, and R6) Tebuzol (R1)/Headline (R4)/Tebuzol (R6) Tebuzol (R1, R4, and R6) Tebuzol (R1)/Headline (R4) Headline (R4)/Tebuzol (R6)

13 Methodology Planted - 6/21 and 6/22 Plots - four 22 inch rows, 30 ft long with sprinkler irrigation Plots inoculated - 7/26 Sprays made at R1 (8/02), R4 (8/20), and R6 (9/03) growth stages Ratings made 9/1-9/2 and 9/16-9/17 on upper two leaves from each of ten plants per plot Harvested 9/23

14 Fungicide Evaluations Field Map

15 Sunflower Rust Fungicide Evaluations a Disease Ratings (2009) ab bc Severity Ratings (0-9) bc Control Proline Prosaro Tebuzol Headline Quadris c bc

16 Sunflower Rust Fungicide Evaluations 2009 Seed Yield (lbs/acre) a a ab b b b Control Proline Prosaro Tebuzol Headline Quadris

17 Sunflower Rust Fungicide Timing Evaluations Disease Ratings (2009) ab a cde bcd de bc Severity Ratings (0-9) ab bcd ed e Control HL1 HL2 HL3 THT TB1 TB2 TB3 TB-HL HL-TB

18 Sunflower Rust Fungicide Timing Evaluations Seed Yield (lbs/acre) a ab ab ab ab ab ab ab ab b Control HL1 HL2 HL3 THT TB1 TB2 TB3 TB-HL HL-TB

19 Rust Effects on Yield lbs per acre Planting 1 Planting 2 Sprayed Control

20 June 8, 2009

21 July 28, 2009

22 Rust Effects on Sunflower Yield lbs per acre Planting 1 - June 22 Planting 2 - June 30 Sprayed Control

23 Future Studies Early stages have rarely been observed Survey for early spore stages again in 2010 Forecasting mechanism for estimating fungicide application timings? Further investigate infection and yield loss in relation to time of infection (age of plants) Uredial pustule Aecial clusters

24 Thank you! Questions?

25 Thank You Questions?