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Issue No. 583

The Vegetarian Newsletter 

A Horticultural Sciences Department Extension Publication on 
Vegetable and Fruit Crops 

Eat your Veggies and Fruits!!!!!

Publish Date: 
April 2013

Overcoming Salinity Barriers to Crop Production in Florida IST Summary

G. David Liu

Horticultural Sciences Department, IFAS, University of Florida

In 2012, vegetable and fruit growers suffered from economic loss caused by salinity problems. Vegetable yields were reduced by 50% due to salinity in some production fields in the Hastings area. The average potato tuber yield loss was approximately $900 per acre of farm gate value. Additionally, reports of losses in broccoli, cucumber, and blueberries ranged from some yield loss in annual crops to loss of not only yield, but in the case of blueberry, entire shrubs were lost due to salinity stress. To minimize any further economic loss, we invited a salinity specialist, Dr. Stephen Grattan from the University of California at Davis and four UF-IFAS extension specialists to share their expertise in alleviating salinity problems in an In-service Training (IST#: 30688). The training was conducted in Hastings. After that, a dinner meeting with growers was held on the IFAS Research Farm and a Horticultural Sciences seminar was welcomed by the gators in Fifield Hall in March 2013. The trainings are available online at the links below.

The instructors and topics in the IST training--Strategies for Minimizing Salinity Problems and Optimizing Crop Production included:

·         Dr. Jeff Ullman – Soil Salinity in Agricultural Systems: The Basics

·         Dr. Mark Clark – Sources of Salinity in Irrigation Water and Strategies to Minimize

·         Dr. Lincoln Zotarelli – Fertilizer as a Source of Salinity on Potato Production

·         Dr. Stephan Grattan (UC-Davis) –Strategies to Minimize Crop Loss under Saline Conditions

·         Dr. Brian Boman – Managing Salinity in Florida Citrus

The new techniques presented by the specialists are helpful for growers to optimize vegetable and fruit production under saline stresses. Crops vary in their tolerance to salinity. Generally, crops are more sensitive to salinity during early vegetative growth and crop’s tolerance progressively increases as the crop matures. It is imperative to monitor irrigation water salinity and soil moisture status during irrigation season. Yield loss increases with salinity level. Yield loss is approximately 10% for an increase of every 1000 parts per million (ppm) in total dissolved solids (TDS). Irrigation well depth and pumping volume can influence the degree of saltwater entrainment. Backfilling to wells and reduced pumping volumes can mitigate salinity stress. Nutrient balancing is critical to minimize salinity problems. Calcium (gypsum) can increase calcium uptake and reduce salinity issues to some extent but gypsum itself can also increase electrical conductivity (EC) and probably exacerbate saline stress if too much gypsum is applied. Growers need careful irrigation, fertilization and cropping management to deal with salinity issues.

This IST training was video recorded and is available online. A table of contents with a complete listing of the topics and hyperlinks to those topics are available at:

 http://hos.ufl.edu/faculty/gdliu/service-training#IST30688

583.1.1.jpg

Dr. Grattan is presenting in the IST training meeting in Hastings on March 26, 2013.

Dr. Stephan Grattan’s seminar in the Horticultural Sciences department was titled:

Crop Salt Tolerance: How to Balance Science and Policy.

This seminar was also video recorded and is available online at:

http://hos.ufl.edu/faculty/gdliu/dr-guodong-david-liu

Vegetarian article

SmartIrrigation Apps for Citrus and Strawberry

K.W. Migliaccio, G. Vellidis, C. Fraisse, K.T. Morgan, J.H. Andreis

                A team of researchers and extension specialists at the University of Florida and the University of Georgia have been developing new irrigation apps for smartphones and tablets. The new apps will be part of a suite of irrigation apps we hope to expand to other commodities within the southeastern United States. Detailed information on the project can be found at:  http://www.nespal.org/smartirrigation/.

                The SmartIrrigation Apps will provide information on irrigation scheduling using real-time weather data (from Florida Automated Weather Network (FAWN) and the Georgia Automated Environmental Monitoring Network (GAEMN)) and forecast data (from National Weather Service). Specifically, rainfall, temperature, wind speed, relative humidity, and solar radiation data will be used from these sources. The data will be used to estimate a simple irrigation schedule specific to the user’s location. The field locations will be associated with the nearest FAWN or GAEMN weather station. The simple irrigation schedule will include evapotranspiration (ET) estimations using the Penman-Monteith equation. In addition to ET, growing degree days may also be used to estimate plant water needs depending on the crop. Each app is developed considering the specific crop characteristics and how the user would best benefit from the app.

                Two operation systems, iOS and Android, will be developed providing apps for iphone, ipad, and Android device users. Apps will be designed with the user in mind and be adapted as needed. Currently, the citrus and strawberry apps are available in beta format and are being tested by growers. For more information on the citrus app, contact Dr. Kelly Morgan (conserv@ufl.edu). For more information on the strawberry app, contact Dr. Clyde Fraisse (cfraisse@ufl.edu). We anticipate release of apps for cotton and urban turf in 2013.

EXAMPLE PROTYPE

Step 1: Define location

The user can access information or input a new field by selecting a location using a list or map. Only locations with weather stations (FAWN or GAEMN) are selectable options. Weather data from the respective location will be used in the irrigation calculations. In addition, information from the National Weather Service will be used to provide forecasting information for improving irrigation.

Step 2: Tool selection

Depending on the app, different tools will be listed. The app also includes user preferences and documents to assist the user. The navigation menu can be used to learn more about irrigation as related to the particular production system.

Step 3: Data entry

Some information is input to the app by the user. The app uses this information to perform calculations. The information requested is crop specific and is limited to what the user can reasonably answer.

While this prototype is for an iPhone, each app will be developed for iPad and Android devices as well. Changes will be made to the different apps based on stakeholder evaluation and feedback.

Step 4: App output

App output will provide information on how to schedule irrigation based on real-time weather data and forecast weather data. The outcome is expected to reduce irrigation water that is not used by the crop or increase water use efficiency of the crop. App output will change daily to reflect daily data and predictions. The apps will be accessible through our project web site for the project life. Post-project, they will be housed with FAWN and AGROCLIMATE.

Step 1Step 2
Step 3Step 4

NEW RECOMMENDATIONS FOR MANAGING TARGET SPOT ON TOMATOES: REFRAIN FROM USING QoI FUNGICIDES.

Gary Vallad, Department of Plant Pathology, GCREC, Wimauma, FL

and

Mathews Paret, Department of Plant Pathology, NFREC, Quincy, FL.

Target spot, caused by Corynespora cassiicola, is one of the most important foliar fungal diseases of tomato in Florida. The disease can result in severe yield losses as a result of blighting of foliar tissues and direct fruit infections. Initial foliar symptoms of target spot consists of small, pinpoint, water-soaked lesions that appear on the upper leaf surface that eventually turn tan to dark brown. These small lesions can be easily be mistaken for bacterial spot or speck. However, as the lesions increase in size they become quite distinct (Figure 1). Target spot lesions have tan centers surrounded with circular bands and often a chlorotic halo and may eventually lead to extensive chlorosis of the rest of the leaf. Expanding lesions of each pathogen can coalesce leading to the rapid collapse of leaflets (Figure 1). Similarly, these expanding lesions can girdle petioles and stems leading to a rapid blight of affected foliar tissues. Tomato fruit are also quite susceptible to target spot. On ripe fruit, large brown circular lesions develop with pale brown centers that often crack (Figure 3). Lesions on green immature fruit begin as small, dark brown, sunken lesions that can quickly develop into craters as they expand, especially when exposed to ethylene to stimulate ripening (Volin et al. 1989).  Fruit lesions on shipped green fruit are especially problematic, as these lesions are often colonized by secondary organisms that lead to post-harvest decay during shipping.  Shipments of tomatoes containing excessive numbers of fruit with symptoms of target spot or post-harvest issues can be rejected at the final destination or require the packinghouse to cover the repacking costs associated with sorting out defective fruit.

No varieties with resistance to target spot are commercially available; therefore, growers rely on cultural practices and the judicious application of fungicides for disease management (Pernezny et al. 1996 & 2003; Schlub et al. 2009).  Fungicide resistance has already been documented for C. cassiicola on cucumber in Japan (Ishii et al. 2007 and 2010; Miyamoto et al. 2007 and 2010).  No efforts have been made to assess fungal isolates for resistance in Florida.  Pernezny and colleagues (2002 and 2005) demonstrated in field trials that fungicide programs that included the Quinone outside inhibitors (QoI) azoxystrobin (Quadris) and pyraclostrobin (Cabrio), or the succinate dehydrogenase inhibitor (SDHI) boscalid were more effective than foliar applications of chlorothalonil.  However, as early as 2008, field trials at the Gulf Coast Research and Education Center in Balm showed that the effectiveness of QoI fungicides for managing target spot was limited.

Recent field trials were performed at the Gulf Coast Research and Education Center in Balm and at the North Florida Research and Education Center in Quincy to assess the relative effectiveness of various contact fungicides like mancozeb and chlorothalonil, and specific QoI, SDHI, demethylase inhibitor (DMI), and methionine biosynthesis inhibitor (MBI) fungicides for the management of target spot on tomato (Table 1 and Table 2).  Both trials showed the QoI fungicides were relatively ineffective for managing target spot.  In general, fungicide treatments that contained either the MBIs, pyrimethanil (Scala and Luna Tranquility) or cyprodinil (Inspire Super); the SDHIs, boscalid (Endura), fluopyram (Luna Privilege and Luna Tranquility), fluxapyroxad (Priaxor), or penthiopyrad (Fontelis); or the DMIs, difenoconazole (Bravo Top, Quadris Top, Revus Top, and Inspire Super) or flutriafol (Topguard) performed better than those treatments that contained the QoIs azoxystrobin (Quadris) or pyraclostrobin (Cabrio) alone or alternated with chlorothalonil (Bravo).  Interestingly, treatments utilizing a QoI fungicide formulated with either an SDHI (Priaxor), or DMI (QuadrisTop) were still effective for managing target spot.

A small collection of 18 isolates of C. cassiicola isolated from tomato throughout Florida were tested for growth on media amended with various concentration of the QoIs azoxystrobin and pyraclostrobin, or the SDHIs boscalid, penthiopyrad, or fluopyram.  Based on these plate assays, all isolates were insensitive to the QoI fungicides with most isolates displaying EC50 (effective concentration to limit fungal growth by 50%) of over 50 ppm (Figure 4).  Two isolates were insensitive to boscalid and penthiopyrad, although two other isolates also displayed low sensitivity to boscalid.  All isolates were found to be sensitive to fluopyram, including the two isolates that were characterized as insensitive to boscalid and penthiopyrad.  Subsequent greenhouse tests with seedlings treated with several fungicides, including azoxystrobin (Quadris), fluopyram (Luna Privilege), boscalid (Endura), penthiopyrad (Fontelis), chlorothalonil (Bravo), and mancozeb (Pencozeb) prior to inoculation with two isolates C. cassiicola insensitive to SDHI and QoI fungicides.  Not only do the results demonstrate the complete failure of azoxystrobin to reduce target spot severity, but show that the QoI application in the presence of a QoI insensitive strain actually increased disease severity relative to the non-treated control (Figure 5).  In addition, SDHI insensitive nature of the isolates compromised target spot control with Endura and Fontelis, but not to Luna Privilege as determined by the plate assays. 

In conclusion, the QoI fungicides azoxystrobin and pyraclostrobin have been found to be ineffective for the management of target spot on tomato, as demonstrated in field and greenhouse experiments, and with assessment of individual isolates on amended media.  Additional research is needed to determine whether QoI insensitivity extends to the non-strobilurin QoI fungicides such as fenamidone (Reason) and famoxidone (Tanos).  Until results of such assessments are complete, growers are advised to avoid the QoI fungicides for target spot management altogether and utilize fungicides with active ingredients from the SDHI, DMI, and MBI classes of fungicides (Table 3).  While all isolates were determined to be insensitive to QoI fungicides, only two isolates were found to be insensitive to the SDHI fungicides boscalid and penthiopyrad.  No evidence of cross resistance with the fluopyram was observed, similar to other characterized boscalid-insensitive isolates of C. cassiicola identified on cucumber in Japan (Ishii et al. 2010; Miyamoto et al. 2010).  These findings suggest that the frequency of SDHI insensitivity in Florida exists, but is relatively low.  Further studies are underway to better characterize the levels of sensitivity among C. cassiicola isolates to various fungicide classes throughout the Southeast.  Such studies are relevant for making resistance management recommendations to growers, as is demonstrated by the recent finding of QoI insensitivity among the isolates in this limited collection.  Growers should follow resistance management guidelines and rotate among products with different modes of action based on their FRAC classification.  Further information pertaining to FRAC classification can be found at the website for the Fungicide Resistance Action Committee, http://www.frac.info/

Literature Cited:

Ishii, H. Miyamoto, T., Ushio, S., and Kakishima, M. 2010. Lack of cross-resistance to a novel succinate dehydrogenase inhibitor, fluopyram, in highly boscalid-resistant isolates of Corynespora cassiicola and Podosphaera xanthii. Pest Management Science 67:474-482.

Ishii, H., Yano, K., Date, H., Furuta, A., Sagehashi, Y., Yamaguchi, T., Sugiyama, T., Nishimura, K., and Hasama, W. 2007. Molecular characterization and diagnosis of QoI resistance in cucumber and eggplant fungal pathogens. Phytopathology 97:1458-1466.

Miyamoto, T., Ishii, H., Stammler, G., Koch, A., Ogawara, T., Tomita, Y., Fountaine, J.M., Ushio, S., Seko, T., and Kobori, S. 2010. Distribution and molecular characterization of Corynespora cassiicola isolates resistant to boscalid. Plant Pathology 59:873-881.

Pernezny, K., Stoffella, P., Havranek, N., Sanchez, J., and Beany, A. 2005. BAM! Kicking control of target spot up a notch. Acta Horticulturae 695:175-179.

Pernezny, K., Stoffella, P., Collins, J., Carroll, A. and Beany, A. 2003. Control of target spot of tomato with fungicides, systemic acquired resistance activators, and a biocontrol agent. Plant Protect. Sci. 38:81-88.

Pernezny, K., Datnoff, L.E., Mueller, T. and Collins, J. 1996. Losses in fresh-market tomato production in Florida due to target spot and bacterial spot and the benefits of protectant fungicides. Plant Dis. 80:559-563.

Schlub, R.L., Smith, L.J., Datnoff, L.E., and Pernezny, K. 2009. An overview of target spot of tomato caused by Corynespora cassiicola. Acta Horticulturae 808:25-28.

Pernezny, K., Datnoff, L.E., Rutherford, B. and Carroll, A. 2000. Relationship of temperature to growth, sporulation, and infection of tomato by the target spot fungus Corynespora cassiicola. 1999-2000 Report of Tomato Research (Florida Tomato Committee).

Volin, R.B., Pohronezny, K. and Simone, G.W. 1989. Severe spotting of fresh-market tomato fruit incited by Corynespora cassiicola after storm-related injury. Plant Dis. 73:1018-1019.


Table 1.  Results of tomato target spot trial at GCREC in Wimauma, FL, Spring 2011.

Disease Severity (%):

Bacterial

Treatment, rate/Acre (application timing)

24-May

31-May

AUDPC

Spot (%)

Actigard, 0.5 oz/100 gal (1-3)…………………………………….

16.1

c

37.5

cde

1021

c

90.8

e

Actinovate, 6 oz (1-3)…………………………………………….

43.7

a

67.0

a

2520

a

97.0

ab

Bravo WeatherStik, 1 pt (1,3)…………………………………….

32.7

b

56.2

ab

1924

b

95.5

a-d

BravoTop, 1.5 pt (1,3)……………………………........................

9.0

d

27.9

efg

627

de

92.1

de

BravoTop, 1.5 pt (1,3); Kinetic, 0.125 % v/v (1,3)........................

9.0

d

33.8

def

670

d

95.1

a-d

BravoTop, 2 pt (1,3); Kinetic, 0.125 % v/v (1,3)………………...

6.7

d

20.6

gh

465

fg

97.0

ab

Cabrio, 8 oz (1,3); Herbimax, 0.5 %  v/v (1,3); Bravo WeatherStik, 1 pt (2)………………………..................................

18.5

c

37.5

cde

1144

c

97.0

ab

Endura, 3.5 oz (1,3); Bravo WeatherStik, 1 pt (2)………………..

16.1

c

32.7

def

985

c

95.1

a-d

HeadsUp, 1 g/L (Prior to transplant,1,3)…………........................

37.8

ab

45.4

a-d

2107

ab

93.9

b-e

Inspire Super, 20 fl oz (1,3); Bravo WeatherStik, 1 pt (2)…….....

5.6

d

13.7

h

360

h

94.4

b-e

Fontelis, 24 oz (1,3); Bravo WeatherStik, 1 pt (2)…………….....

5.6

d

33.0

def

507

efg

94.0

b-e

Luna Privilege (drip), 6.84 oz (1,3); Bravo WeatherStik, 1 pt (2)..

9.0

d

32.7

def

666

d

92.8

cde

Luna Privilege (foliar), 6.84 oz (1,3); Bravo WeatherStik, 1 pt (2)

5.6

d

33.0

def

507

efg

95.1

a-d

Luna Tranquility, 11.2 oz (1,3); Bravo WeatherStik, 1 pt (2)…....

6.7

d

32.6

def

561

def

94.0

b-e

Priaxor, 4fl oz (1,3); Induce, 0.25 % v/v (1,3); Bravo WeatherStik, 1 pt (2)………………………..................................

5.6

d

23.3

fg

435

gh

98.5

a

Priaxor, 6 fl oz (1,3); Induce, 0.25 % v/v (1,3); Bravo WeatherStik, 1 pt (2)………………………..................................

7.9

d

23.3

fg

535

d-g

97.7

ab

Quadris Flowable, 6.2 fl oz (1,3); Bravo WeatherStik, 1 pt (2)….

18.5

c

37.5

cde

1144

c

95.5

a-d

Quadris, 6oz (1,3); Herbimax, 0.5 % v/v (1,3); Bravo WeatherStik, 1 pt (2)………………………..................................

18.5

c

37.5

cde

1144

c

97.0

ab

QuadrisTop (8fl oz)……………………………………………….

9.0

d

33.0

def

669

d

96.3

abc

Revus Top, 7 oz (1,3); Bravo WeatherStik, 1 pt (2)……………...

9.0

d

27.9

efg

627

de

96.3

abc

Scala, 7 fl oz (1,3); Bravo WeatherStik, 1 pt (2)…………………

9.0

d

32.6

def

662

d

96.3

abc

Non-treated Control………………………………………………

32.7

b

56.2

ab

1953

b

94.4

b-e

P =

< 0.0001

< 0.0001

< 0.0001

0.0030

The treatments were applied on 12 May, 20 May, and 27 May (corresponding with applications 1 to 3 above) on a per acre basis, unless specified.  Target spot and bacterial spot severity was assessed as the percentage of total leaf area affected by disease using the Horsfall-Barratt scale; values were converted to mid-percentages and fit to a lognormal distribution for final statistical analysis.  Area under the disease progress curves (AUDPC) was calculated using the formula: Σ([(xi+xi-1)/2](ti-ti-1)) where xi is the rating at each evaluation time and (ti-ti-1) is the time between evaluations.  Means followed by the same letter are not significantly different at α=0.05.


Table 2.  Results of tomato target spot trial at NFREC in Quincy, FL, Spring 2011.

Treatment, rate/A (application timing)

Yield (kg/ha)

AUDPC

Medium

Large

X’Large

Total

Topguard, 3.5 oz (weekly)……...

8,049 b

14,655 b

28,584  abc

51,288 bc

1,747 ab

Topguard, 7.0 oz (weekly)……...

9,149 ab

19,030 a

35,281 ab

63,460 a

1,053 de

Topguard, 14.0 oz (weekly)……

9,253 ab

17,843 ab

35,861 a

62,956 a

1,202 cd

Topguard, 28.0 oz (weekly)……

8,688 ab

17,337 ab

33,273 abc

59,298 ab

1,068 de

Topguard, 10 oz (weekly) + Koverall, 1.5 lb (weekly)………

11,010 a

17,857 ab

29,908 abc

58,775 ab

715 e

Koverall, 1.5 lb (weekly)………

8,570 ab

18,248 ab

25,848 bc

52,666 abc

732 e

Quadris, 6.0 oz (weekly)……….

8,596 ab

15,009 b

24,087 c

47,691 c

2,108 a

Scala, 7.0 oz (weekly)………….

10,659 ab

15,578 ab

30,064 abc

56,301 abc

844 de

Bravo Weatherstik, 2.0 pt (weekly)…………………………

9,715 ab

17,339 ab

27,914 abc

54,968 abc

1,580 bc

Control – water…………………

9,642 ab

16,354 ab

27,651 abc

53,646 abc

1,913 ab

P =

0.4965

0.3266

0.2584

0.1192

<0.0001

The treatments were applied weekly on a per acre basis, unless specified.  Target spot severity was assessed as the percentage of total leaf area affected by disease using the Horsfall-Barratt scale; values were converted to mid-percentages prior to final statistical analysis.  Area under the disease progress curves (AUDPC) was calculated using the formula: Σ([(xi+xi-1)/2](ti-ti-1)) where xi is the rating at each evaluation time and (ti-ti-1) is the time between evaluations.  Means followed by the same letter are not significantly different at α=0.05.


Table 3.  List of recommended products labeled on tomato for managing target spot*.

Mode of Action (FRAC)

Fungicide

Commercial Name

Multi-site, contact fungicide (M3)

mancozeb

Dithane, Penncozeb

Multi-site, contact fungicide (M5)

chlorothalonil

Bravo, Equus

SDHI; Succinate Dehydrogenase Inhibitors (7)

boscalid

penthiopyrad

fluxapyroxad

Endura

Fontelis

Priaxor (with pyraclostrobin)

DMI; Demethylase Inhibitors (3)

difenoconazole

RevusTop (with mandipropamid)

Inspire Super (with cyprodinil)

MBI; Methionine biosynthesis inhibitors (9)

pyrimethanil

cyprodinil

Scala

Switch** (with fludioxonil, FRAC 12)

Inspire Super (with difenoconazole)

*  Information provided in this table applies only to Florida. Be sure to read a current product label before applying any product.

**  Labeled for tomato, but not specifically labeled for target spot.

Figure 1.  Foliar symptoms of target spot caused by Corynespora cassiicola consist of brown-black lesions with subtle concentric rings giving them a target-like appearance; severe outbreaks can cause massive blighting and loss of leaves. 


Figure 2.  Through a handlens or low power microscope, long stalk structures called conidiophores baring single or chains of conidia that are long, hyline with 4 – 20 cross walls (pseudosepta).


Figure 3. Fruit symptoms of target spot often consist of small sunken lesions that can develop larger zonate lesions as the fuit ripens.


Figure 4.  Plate assay showing showing the differential sensitivity of several Corynespora cassiicola isolates to the succinate dehydrogenase inhibitor, boscalid in the fungicide Endura.  Plate to the left is the non-amended control and the plate to the right is amended with Endura at a rate equivalent to 5 ppm of boscalid.  Notice the boscalid insensitive isolate on the lower right side of each plate.


Figure 5.  Results of a tomato seedling test with plants treated with several fungicides 5 days prior to inoculation with two strains of Corynespora cassiicola insensitive to SDHI and QoI fungicides.  Each bar represents the mean of 10 plants per a treatment with 95% confidence interval.