Vegetable and Fruit Disease Update

Steve Bost Extension Plant Pathologist

University of Tennessee scbost@utk.edu

PowerPoint available at https://tiny.utk.edu/ag/VegandFruit

Hot Topics from 2013

• Botrytis – strawberry

• Spray program – tomato

• Downy mildew – pumpkin

• Bitter rot – apple

• Orange rust - blackberry

Botrytis Gray Mold in Strawberries Fungicide resistance

• Surveys of Botrytis in the Carolinas have indicated resistance to Topsin M (MOA Group 1) in all isolates.

• Resistance to the other MOA groups varied.

What to do?

Fungicide resistance testing for Botrytis Clemson University – Dr. Guido Schnabel

Free service for Southeastern states

Instructions for submitting samples:

Collecting and Mailing Guidelines for Fungicide Resistance Testing_gs-2

20 to 40 dead blossoms or 150 healthy blossoms.

Collected randomly.

Or dead leaves, if can’t find dead blossoms

OR wait until harvest and submit cotton swabs with spores (too late to help you, but still good info)

Mailing

Put the flowers or the 10 swabs in plastic bag. Package with information about the origin of the sample (farm name, state), your name, phone number, and e-mail address. Mail to:

Guido Schnabel

Clemson University

105 Collings St/220 BRC

Clemson, SC 29634

phone (864) 643 7131

When to expect your report: The day they receive the sample you will get an email notification. After notification, results sent to you by email in 7 days (for flowers and leaves if get sufficient spores) or 4 days for swabs.

What to do if you don’t get your Botrytis tested? (I.e., I don’t know what fungicides will work in my field)

Fungicide

Mode of Action Group

Captan M

Thiram M

Topsin M 1

Scala 9

Inspire Super 3+9

Fontelis 7

Pristine 7+11

Elevate 17

Switch 9+12

Resistance a threat to all mode of action (MOA) groups other than “M”. Spread out risks by rotating three MOA groups. An “M” product should be included, alone or as a tank mix with one of the other groups. Avoid Topsin M. Switch has fared well in surveys but resistances to all other than “M” have been found.

Early blight of tomato… …very common & very damaging

A spray program must be built around controlling it. Programs that rely on the Group 11’s (Quadris, Cabrio, Tanos)

have not.

Cultural methods of control are helpful but inadequate. A new spray program was needed. In a trial conducted at Nashville, TN, all labeled fungicides considered candidates for a tomato spray program were compared.

Early blight damage on a resistant variety.

Early Blight of Tomato 2013 Field Trial, Nashville

This trial was a search for replacements for the Group 11 fungicides – Quadris, Cabrio, and Tanos. Plants were sprayed 3 times at weekly intervals and evaluated 1 week after the 3rd spray.

c

c

c

c

b

b

b

a

a

0 5 10 15 20 25 30

Untreated check

Quadris 6.2 fl oz

Tanos 8 oz

Cabrio 12 oz

Bravo 2.75 pt

Manzate 3 lb

Switch 14 oz

Inspire Super 20 fl…

Fontelis 20 fl oz

Leaf area affected (%)

Pro

du

ct &

rat

e/7

5 g

al

The results were used to guide the development of non-strobilurin-based spray programs.

Early Blight of Tomato 2013 Trial, Highland Rim REC

Four spray programs were evaluated on trellised, ‘Mountain Glory’ tomatoes sprayed every 7-10 days, beginning 3 wks after planting.

Pro-gram

Product and rate per acre at application number Early blight % leaf area

affected (final)

1

2

3

4

5

6

7

8

9

10

Check none none none none none none none none none none 88.0 a*

1 Quadris 6 fl oz

Manzate Quadris 6 fl oz

Manzate Quadris 6 fl oz

Manzate Quadris 6 fl oz

Manzate Quadris 6 fl oz

Manzate 57.5 b

2 Manzate Manzate Manzate Manzate Manzate Manzate Manzate Manzate Manzate Manzate 23.3 c

3 Fontelis 10 fl oz** + Manzate + Kocide

Manzate Fontelis 10 fl oz

+ Manzate + Kocide

Manzate Fontelis 10 fl oz

+ Manzate + Kocide

Manzate Fontelis 10 fl oz

+ Manzate + Kocide

Manzate Fontelis 10 fl oz

+ Manzate + Kocide

Manzate 0.3 d

4 Inspire Super 1 pt

Manzate Fontelis 1 pt

Manzate Inspire Super 1 pt

Manzate Fontelis 1 pt

Manzate Inspire Super 1 pt

Manzate 0.1 d

* Column means followed by the same letter are not significantly different (LSD, P=0.05). ** The minimum labeled rate of Fontelis is 1 pt/acre.

Excellent control of early blight was provided by spray programs containing Inspire Super or Fontelis.

Unsprayed check Program 4

Early blight resistant tomato varieties 2013 trials

Variety

Early blight (% leaf area affected)

Fruit type

Vine habit Davidson Wilson

Mountain Magic1 25 25 salad indeterminate

Matt’s Wild Cherry2 40 45 cherry indeterminate

Plum Regal1 40 45 plum determinate

Juliet2 45 - salad indeterminate

Mountain Fresh Plus2 53 55 large determinate

Defiant1 60 67 medium determinate

Iron Lady1 63 - medium determinate

Amelia2 63 60 large determinate

Florida 912 65 55 large determinate

Plum Crimson1 65 65 plum determinate

Mountain Glory3 70 - large determinate

Brand Names

chlorothalonil Bravo

Chloronil

Echo

Equus

Initiate

mancozeb Dithane

Manzate

Penncozeb

Koverall

Roper

Example Spray Program Where bacterial diseases are expected

Applica-tion no.

Product

1 mancozeb + Actigard

2 mancozeb + copper

3 Fontelis + Actigard

4 mancozeb + copper

5 Inspire Super + Actigard

6 mancozeb + copper

7 Fontelis + Actigard

8 mancozeb + copper

Applica-tion no.

Product

9 Inspire Super + Actigard

10 mancozeb/chlorothalonil* + copper

11 Fontelis + copper

12 chlorothalonil + copper

13 Inspire Super + copper

14 chlorothalonil + copper

15 Fontelis + copper

*The 5-day PHI for mancozeb interferes with harvest. Switch to chlorothalonil when harvest begins. When not using mancozeb, discontinue use of copper if possible. NOTE: If late blight occurs, appropriate fungicides must be added. Fontelis and Inspire Super do not have any late blight activity.

Notable restrictions: Actigard: 14-day PHI Fontelis: 72 fl oz/A/season Inspire Super: 47 fl oz/A/season See labels for other restrictions.

Relative Effectiveness of Fungicides against Early Blight

Product MOAa group

PHIb

(days) Max. use/acre/seasonc Max. no.

consecutive apps. Early blight

control ratingd

chlorothalonil M 0 15 lb a.i. (7-14 apps.) no limit 3

mancozeb M 5 22.4 lb (7-30 apps.) no limit 3

Cabrio 11 0 96 oz (8 apps.) 1 0e

Quadris 11 0 37 fl oz (6 apps.) 1 0e

Tanos 11,27 3 72 oz (9 apps.) 1 0e

Priaxor 7,11 0 24 fl oz (3 apps.) 2 5

Endura 7 0 21 fl oz (6 apps.) 2 4

Fontelis 7 0 72 fl oz (3-4 apps.) 2 5

Inspire Super 3,9 0 47 fl oz (2-3 apps.) 2 5

Revus Top 3,40 1 28 fl oz (4-5 apps.) 2 3

Scala 9 1 35 fl oz (5 apps.) 2 2

Switch 9,12 0 56 fl oz (4-5 apps.) 2 3

a MOA=mode of action. Do not rotate products containing ingredients belonging to the same MOA group, with the exception of Group M. Rotation is not required of members of this group. b PHI=pre-harvest interval. c Where presented as a range of applications, the appropriate number depends on the rate(s) used. d Scale of 0-5, 0=no control and 5=excellent control. e Not recommended due to the widespread occurrence of resistant strains.

Spray Program Design

• Always rotate fungicides with nonrelated fungicides. The “always rotate” rule does not apply to the multi-site fungicides mancozeb and chlorothalonil. The risk of resistance developing to them is extremely low.

• Spray to protect, not to rescue.

– Disease control is better if the spray program is begun before diseases are observed.

– Pathogen resistance is much less likely to occur if the product is applied to a small population of the fungus than to a large one. DO NOT APPLY FONTELIS OR INSPIRE SUPER TO SEVERELY DISEASED CROPS. It is important that we retain their effectiveness.

PowerPoint available at https://tiny.utk.edu/ag/VegandFruit

Cucurbit Downy Mildew

Downy Mildew

Applying sprays before infection provides best

control for any disease, but is

particularly important for downy mildew.

Bravo

Fungicide efficacies (0=no control, 5=excellent control)

MOA Group Powdery Downy White blight

Chlorothalonil * 2 2 3

Mancozeb * 0 2 3

Sulfur * 4 0 0

Quintec 13 5 0 0

Rally 3 2 0 0

Pristine 7+11 3 0R 3

Quadris 11 0R 0R 2

Cabrio 11 0R 0R 4

Fontelis 7 4 0 0

Presidio 43 0 3 0

Ranman 21 0 4 0

Zampro 45+40 0 3 0

* These three products do not need to be rotated – no resistance problem. R Indicates widespread resistance. THIS IS NOT A COMPLETE LIST OF REGISTERED FUNGICIDES.

Pumpkin Spray Strategies

Diseases present Strategy

None Chlorothalonil or mancozeb every 7 to 14 days; scout field.

Powdery mildew Choose two powdery mildew products and alternate them. Tank mix with chlorothalonil or mancozeb.

Downy mildew

Choose two downy mildew products and alternate them. Tank mix with chlorothalonil or mancozeb.

White blight

Choose two non-related white blight products and alternate them.

http://cdm.ipmpipe.org/ Downy mildew tracking and forecasts:

A pumpkin variety with resistance to downy mildew discovered at

Highland Rim REC in 2013.

Was by chance. Two fungicide trials, each involving a different variety. Great difference in downy mildew severity between unsprayed Hybrid Pam and Camaro.

Hybrid Pam Camaro

Downy mildew on 28 Aug (13 days after initial infection) HRREC Trial, 2013

Hybrid Pam Camaro

Downy mildew on 23 Sep HRREC Trial, 2013

Camaro A 25-lb pumpkin with resistance to downy mildew and powdery mildew, but its light

orange color may not be acceptable.

Bitter Rot Lesions tend to be sunken, with concentric rings of fruiting bodies.

Results of tests on detached fruit At Soil, Plant and Pest Center

Best activity

• Inspire Super

• Ziram

• Captan

• Merivon

USE A SURFACTANT

Black Pox Helminthosporium papulosum

Captan, Ziram, Topsin M

Orange Rust

Rally, Tilt, Orbit, Abound, Cabrio, Pristine