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Plant Pathology


2011 Foliar Fungicide Spray Guide for Tomatoes in North Carolina

Kelly Ivors and Frank Louws, Extension Plant Pathologists
Department of Plant Pathology, North Carolina State University

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Tomato foliar diseases.There are several diseases that attack tomato leaves and fruit in North Carolina. Some diseases are caused by bacteria, such as bacterial canker (Clavibacter michiganensis subsp. michiganensis), bacterial spot (Xanthomonas perforans), and bacterial speck (Pseudomonas syringae pv. tomato). Other important foliar diseases are caused by fungi, such as early blight (Alternaria solani), late blight (Phytophthora infestans), and Septoria leaf spot (Septoria lycopersici) (Fig. 1).

late blight on top of leaf
late blight on fruit
early blight
Botrytis
       
Septoria leaf spot
bacterial speck
bacterial spot

Fig 1. Tomato diseases (from top left to bottom right): late blight on top side of leaf, late blight on fruit, early blight, Botrytis gray mold on fruit, Septoria leaf spot, bacterial speck, and bacterial spot.

Effective chemicals. There is no SINGLE product that is effective against all important foliar diseases. For example, mancozeb gives good control but chlorothalonil gives only fair control of early blight; however chlorothalonil, mandipropamid (one of the active ingredients in Revus Top), and fluopicolide (Presidio) are presently the best products for managing late blight. In addition, copper-based products are effective against bacterial canker, but some strains of the speck and spot bacteria are resistant to copper; the use of Actigard has been shown to be effective in reducing all 3 bacterial diseases. And Boscalid (Endura) has excellent activity against Botrytis gray mold and early blight. Therefore, it is necessary to use a combination of products in a spray program to optimize disease management. One important consideration is that products have different preharvest intervals (PHI). A product with a PHI greater than 1 day such as mancozeb (PHI = 5 days) cannot be used when growers harvest 2 or more times per week. Another important consideration is fungicide resistance management. For example, early blight resistance to the QoI fungicides (most strobilurins- i.e. Cabrio, Quadris or Evito) was detected in western North Carolina during the 2007-2009 growing seasons because it has been used extensively for early blight control.

Volume-based spray schedule. The following suggested weekly spray schedule (Table 1) takes into account the above considerations and label restrictions of different products and is based on many years of field research in North Carolina. Labeled rates of products are usually listed on a per acre basis, but for staked tomatoes, these should be applied on a per volume basis. The reason for spraying on a per volume basis is that early in the season when plants are small, less volume (and thus, less product) is needed to obtain full coverage than later in the season when plants are larger and more spray volume is needed to obtain full coverage. To determine your mixing rate, first determine the maximum spray volume per acre for your sprayer for fully-grown plants. Then mix the acre rate for a given product in the maximum spray volume that it takes to cover an acre. For example, mancozeb products are labeled at 3 lbs per acre. If the maximum spray volume is 100 gallons per acre for your sprayer when plants are full grown, then mix the mancozeb product at the rate of 3 lbs per 100 gallons of spray. At the start of the season, it may take only 25 to 30 gallons per acre to obtain full coverage. The volume of spray per acre is then increased as plants grow and spray nozzles are added until the maximum 100-gallon volume per acre is reached at full plant growth.

The purpose of this schedule is to provide a general spray program, which can be altered depending on disease pressure and weather conditions.

Table 1. Suggested weekly spray schedule and productsx For foliar tomato disease control in NC.
Week Products
Week 1 before harvest mancozeb (1)y + copper + Actigard (1)y
Week 2 mancozeb (2) + copper
Week 3 mancozeb (3) + strobilurin (1)y + Actigard (2)
Week 4 mancozeb (4) + copper
Week 5 Endura LOW RATEz (1) + Actigard (3)
Week 6 mancozeb (6) + copper
Week 7 mancozeb (7) + strobilurin (2) + Actigard (4)
Week 8 mancozeb (8) + copper
Week 9 during harvest Endura LOW or HIGH ratez (2) + chlorothalonil (1)
Week 10 Revus Top (1)y OR Presidio (1)y OR Ranman (1)
Week 11 chlorothalonil (2) + strobilurin (3)
Week 12 Revus Top (2) OR Presidio (2) OR Ranman (2)
Week 13 Endura LOW or HIGH ratez (3) + chlorothalonil (3)
Week 14 Revus Top (3) OR Presidio (3) OR Ranman (3)y
Week 15 chlorothalonil (4) + strobilurin (4)
End of season Finish season with chlorothalonil

x Mancozeb, copper, chlorothalonil, and strobilurin are common names for products sold under various trade names (see Table 2). Actigard, Endura, Ranman, Revus Top, and Presidio are trade names of products from Syngenta, BASF, FMC, Syngenta, and Valent respectively. Refer to labels, table 2 and the text above for rates to use in volume-based spraying.
y Total number of applications per season is restricted by the label.
z Low rate of Endura controls early blight; high rate controls early blight & Botrytis gray mold. High rate is only necessary if conditions are conducive for gray mold (cool / wet right before & during harvest). Total max rate allowed per season is 25 oz.

Strobilurin products must be rotated as per label restrictions, and to limit development of fungicide resistance in the early blight pathogen. Actigard applications should be limited to reduce the risk of phytotoxicity and plant stunting.

Growers also have the option of incorporating Regalia OR Serenade Max into their spray program; Field trials have found these products to have some efficacy against bacterial spot.

Table 2. Amount of product / 100 gallons, assuming a max. of 100 gallons / acre at full plant growth
Common name FRAC PHI (days) Product name Amount/100 gal
Acibenzolar S-methyl P

14

Actigard 50WG

0.33 to 0.5 oz

Bacillus subtilis 44

0

Serenade Max

1.0 to 3.0 lb

Boscalid 7

0

Endura

LOW RATE 3.0 oz
HIGH RATE 9.0 oz

Chlorothalonil M

1

Bravo Ultrex, Equus DF
Bravo Weather Stik

2.6 lb
2.75 pt

Cyazofamid 21

0

Ranman

2.1 to 2.75 fl oz

Fixed copper M

0

Kocide 3000
Cuprofix Ultra 40 Disperss

0.75 to 1.75 lb
1.25 to 3.0 lb

Fluopicolide 43

2

Presidio

3.0 to 4.0 fl oz
with 20-50 GPA

Mancozeb M

5

Manzate Pro-stick, Penncozeb 75DF, Dithane DF-45

1.5 to 3.0 lb

Mandipropamid + Difenoconazole 40 + 3

1

Revus Top

5.5 to 7.0 oz

Reynoutria sachalinensis N/A

0

Regalia

0.5 to 1.0 gallon

Strobilurin 11

0
1
3
3

Cabrio EG
Quadris 2.08F
Tanos
Evito

8.0 to 12.0 oz
5.0 to 6.2 fl oz
6.0 to 8.0 oz
3.8 to 5.7 fl oz

Note: Recommendations for the use of agricultural chemicals are included here as a convenience to the reader. The use of brand names and mention or listing of commercial products does not imply endorsement by North Carolina State University nor discrimination against similar products or services not mentioned. Individuals who use agricultural chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Examine a current product label before applying any chemical. For assistance, contact your county North Carolina Cooperative Extension Agent.

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Updated March 8, 2011