MSU’s Research results for bacterial canker in tomatoes

Research indicates it is best to manage canker before field planting tomatoes.

Midwestern growers and processors have tried to manage bacterial disease as it occurred in the field. Researchers at MSU formed a team to test fungicide applications to greenhouse transplants prior to planting in the field. The greenhouse was targeted because the spread and increase of bacteria is favored by the wet, humid conditions and the close spacing of the tomato transplants. Multiplication and spread of the bacterium is less likely in the field because of the lowered relative humidity, air movement, and increased plant spacing. Also, it is more economical and efficient to spray transplants while in the greenhouse than to spray plants once they are placed in the field. If application of copper could suppress the bacteria on the very susceptible transplants, healthier plants would be moved to the field, and widespread devastation and yield losses avoided.

Trials were conducted in a commercial greenhouse using 288-plug sheets of tomato transplants. Fungicide treatments were applied to transplants as soon as the first true leaves were visible. Subsequent sprays were applied every five days until the transplants were removed from the greenhouse and planted in the field. Prior to moving plants out to the field, samples were taken within each block to see how far the bacterium had spread. Applications of copper hydroxide, copper hydroxide + mancozeb, Agrimycin, and Agrimycin + copper hydroxide to transplants in the greenhouse effectively suppressed the bacterium. The diseased plants produced a 38% smaller yield than the healthy plants (Table 1). Fruit produced by the diseased plants were smaller than those produced by the healthy plants. Plants treated with copper hydroxide, copper hydroxide + mancozeb, Agrimycin, and Agrimycin + copper hydroxide and exposed to bacterial canker yielded similarly to the healthy plants and produced full-sized fruits. Results suggest early and frequent applications of these fungicides can limit the spread and increase of bacterial canker among tomato transplants in the greenhouse. Further, it appears that these fungicide applications in the greenhouse can increase the yield in the field compared to untreated diseased plants.

Table 1. Field results and yield when tomato transplants were sprayed with
bactericides in the greenhouse, exposed to bacterial canker, and then established
in the field.

Treatments, applied at 5-day intervals Yield (lb/5 plants)
Trial 1 Trial 2
Untreated healthy….................... 40.2 a 42.2 a
Untreated diseased….................. 25.1  b 21.6  bc
Mancozeb…................................. 19.9  b 19.3  c
Copper hydroxide….................... 37.1 a 35.8 ab
Copper hydroxide + mancozeb… 34.4 a 35.1 ab
Agri-mycin…............................... 36.9 a 35.3 ab
Copper hydroxide + Agri-mycin. 43.0 a 48.0 a

*Column means with a letter in common are not significantly different
(Fisher’s LSD; P≤0.05).

The results of our study clearly show that even under severe disease pressure, applying copper hydroxide alone or in a combination with mancozeb at 5-day intervals to transplants in the greenhouse once true leaves have emerged results in transplants that produce yields comparable to that of healthy plants. Agri-mycin was also effective. We believe that these results offer the tomato industry a reliable and easily implemented means of avoiding significant yield losses resulting from bacterial canker. Continued sprays in the field are warranted, especially in fresh market tomatoes where blemishes on fruits are unacceptable.

Manage canker while in the field.

Tomato ‘Mountain Spring’ plants were hand-transplanted following a fresh market planting design and drip irrigation was provided. The beds were 2 ft wide, 6 in. high and 50 ft long with rows spaced at 5.5 ft apart. Each row comprised of two treatments, 22.5 ft long with a 5-ft section in the middle that was reserved for inoculated plants. Treatments consisted of Kocide 2000 (copper hydroxide) at 2 lb/A, OxiDate (hydrogen dioxide) at 4 pt/A, Tanos (famoxadone and cymoxanil) at 0.5 lb/A alternated with Kocide 2000 (copper hydroxide) at 1.5 lb/A, Actigard (acibenzolar-S-methyl) at rates of 0.02, 0.03, and 0.05 lb/A with remaining applications at 0.05 lb/A alternated with Kocide 2000 at 1.5 lb/A; untreated control. Treatments were applied preventively and then reapplied every 5 days through the growing season. All treatments received alternating Bravo WeatherStik (chlorothalonil) at 1.5 pt/A and Manzate (mancozeb) at 2 lb/A applications to prevent fungal infections and were applied at the same time as the bactericidal treatments. All treatments were sprayed from the center of the row outward to encourage natural spread of disease from the inoculum source.

In our study, bacterial canker spread 18 feet in 3 weeks. Bacterial canker was lower for the Actigard-, Kocide 2000- and Tanos-treated plants compared to plants treated with OxiDate or the untreated diseased plants, but numbers may not be statistically different (Table 2). Foliar disease symptoms of OxiDate-treated plants were statistically similar to the untreated diseased plants. Actigard and Kocide 2000 offered superior control of bacterial canker foliar symptoms compared with either OxiDate or the untreated diseased plants. Tanos alternated with Kocide 2000 effectively suppressed disease symptoms and was shown to be helpful in managing bacterial canker.

Table 2. Field evaluation of bactericides for bacterial canker symptoms.

Treatments Leaf blight (%)z Wilting leavesy Plant vigorx
Untreated control….................. 30.0 aw 69.8 a 5.0 a
OxiDate…................................. 40.0 a 72.8 a 4.0 a
Kocide 2000….......................... 10.0  bc 40.3  b 7.3  bc
Tanos alternate Kocide 2000… 21.3  b 18.3 ab 6.0  b
Actigard alternate Kocide 2000…...................................... 7.5  c 18.3  b 8.0  c

zPercent of leaf exhibiting marginal leaf necrosis.
The number of strikes exhibiting unilateral wilting over a 22.5 ft treatment row.
Overall plant vigor was rated on a 1 to 10 scale with 10=a completely disease free plant, 8=showing <10% marginal necrosis and/or minor unilateral wilting; 6=increased marginal leaf necrosis but <30% and/ or moderate unilateral wilting; 4=increasedmarginal leaf necrosis but less than <50% and/or severe unilateral wilting; 2=increased marginal leaf necrosis but less than <70% and/or entire plant showing unilateral wilting symptoms; and 1=dead plant.
Different lower case letters within the same column denote statistical difference (P<0.05).

Also see: Bacterial canker ravages processing tomatoes

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Dr. Hausbeck’s work is funded in part by MSU‘s AgBioResearch.

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