Late blight update – August 11

Late blight has been confirmed in numerous tomato fields in Chatham-Kent in recent days. Disease pressure is very high and weather conditions are good for disease development and spread.

Growers in the Chatham-Kent region or near other late blight outbreaks should consider shortening their fungicide schedule to five days while weather conditions remain favourable for late blight (moisture from rain, fog, dew and moderate temperatures). In areas of high disease pressure, such as Chatham-Kent, targetted late blight fungicides that have some level of systemic activity, should be added to the program. It is critical to rotate chemical families when using these products.

[Ratings are shown for late blight activity based on information from Dr. Tom Zitter, Dept. of Plant Pathology and Plant-Microbe Biology, Cornell University, Ithaca, NY. 0 = no effect or not labelled; + = poor; ++ = OK to good; +++ = very good. P, p = protectant; C, c = curative; A, a = antisporulant (capitalized indicating stronger activity)]

Fungicide registrations for tomato:

  • chlorothalonil (Bravo, Echo, group M5) – contact fungicides – have been very effective protectants in tomato [++, P]
  • mancozeb (Penncozeb, Manzate, Dithane, group M3), metiram (Polyram, group M3) – contact fungicides – have been very effective protectants in tomato [++, P]
  • Acrobat 50 WP (group 40)– translaminar – has some ability to move into the plant – must be tank-mixed with another late blight fungicide from a different chemical family – can add to the fungicide program, but rotate chemistries [++, P, c, A – use as preventative]
  • Cabrio EG (group 11) – translaminar – has some ability to move into the plant – strobilurins generally rated lower than the other targetted late blight materials by researchers – preventative only – tank mix with stronger late blight product [+, P, a]
  • Presidio – translaminar, some “kickback” activity – registered (in tank mix with Bravo) [+++, P, C, A]
  • Torrent 400SC (group 21) – protectant, contact (limited locally systemic) – should be tank-mixed with a non-ionic or organosilicone surfactant [++, P]
  • Reason 500 SC (group 11) – locally systemic and translaminar – has some ability to move into the plant – must be tank-mixed with mancozeb or Bravo 500 [not rated]
  • Revus (group 40)– translaminar, some “kickback” activity – have some ability to move into the plant – can add to the fungicide program, but rotate chemistries and use in combination with protectants for resistance management [++, P, c, a]
  • Tanos 50 DF (group 11/27)– translaminar, some “kickback” activity – has some ability to move into the plant – can add to the fungicide program, but rotate chemistries and use in combination with protectants for resistance management [++, P, C, a – use as preventative]
  • Tattoo C (group 28/M5)– systemic + protectant, some “kickback” activity – has some ability to move into the plant – includes a systemic ingredient plus a protectant ingredient from a different chemical family [rating for propamocarb 720 g/L: ++, P, C, A (Tattoo C is propamocarb 375 g/L + chlorothalonil 375 g/L)]
  • Zampro (group 45/40)– two active ingredients – protectant and systemic, translaminar – can move into the plant [not rated]

Previous 2015 late blight posts: July 30, July 24, July 21, July 14, July 13, June 24

Identifications of late blight genotypes for Ontario are provided by L. Kawchuk, AAFC Lethbridge, Alberta, Canada.

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