Sunday, November 14, 2010

Decision Time

This is not a post I wanted to write.

I've been growing tomatoes for a long time, but this year seems to be the year when Bad Things Will Happen. Despite treating with copper fungicide, the septoria leaf spot I wrote about last week has continued to spread through the tomatoes—even tomatoes that are more than 50 feet apart are all suffering from it.

At first, I couldn't figure out why this year would be so much worse than any other. I've had leaf spot every year and been able to control it with copper fungicide spray (organic), good tomato hygiene and leaf removal. For a while, I thought it might be the mix of heirloom and heritage tomatoes I'm growing, but that argument never really made sense. I've grown heirlooms and heritage tomatoes before with no problem.

The best explanation I can come up with is construction. ("Huh?" you say. "Construction?") Yeah, construction. My neighborhood is the midst of a pretty massive infrastructure project. The roads are all torn up and our cars are continually covered with dust. The pool filter has to be backflushed almost every week. So obviously, there's a lot of particulate matter in the air this year—and fungal diseases live in the ground. My best theory now is that my plants are being coated with airborne fungal spores stirred up from road construction.

Anyway, it doesn't really matter why, because I have to figure out what to do. The copper spray is not working—the disease has continued to spread relentlessly. Here is the breakdown:
  • Brandywine: Lightly affected
  • Victoria Supreme paste tomatoes: Unaffected (this one, btw, is VFFNA)
  • Yellow pear: Severely affected
  • Heinz tomatoes: Severely affected
  • Cherokee Purple: Moderately affected
So ... my decision basically is this: do I switch to a stronger, commercial fungicide? The two best fungicides to control septoria leaf spot are chlorothalonil (sold as Daconil) and mancozeb (sold as Bonide Mancozeb). Of these, Daconil is easier to get—I believe they stock it at most large garden centers. As for efficacy, I looked for studies and didn't really see a consensus. According to North Carolina State University, mancozeb provides superior control for septoria, while some state ag departments I looked at recommended chlorothalonil.

Unfortunately, with the way this is spreading, I think my choice is pretty clear: treat with Daconil (primarily for convenience) or dramatically lower my expectations for this season's crop.


No comments:

Post a Comment