Archives for posts with tag: fungicides

I didn’t think that tomato plants were susceptible to powdery mildew. At least, I have never seen the fuzzy white spores on any of our vines.

But one of the Country Taste Beefsteak tomato plants has developed the affliction and it is rapidly spreading. Fortunately, the vine had all but stopped producing so there will be very little loss as a result.

I guess this is the downside to this year’s late growing season (and next year, the tomatoes will get the baking soda spray).

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Since mid-summer, I’ve been spraying the cucurbit leaves with a baking soda and peroxide solution on a more or less weekly basis (see July 12, 2014). Why? To ward off powdery mildew.

I’ve tried other approaches such as pruning the affected leaves and spraying with diluted milk. The first method was futile (too little too late). The efficacy of the second method was difficult to assess (I was using pasteurized milk, not raw). Perhaps the progress was slowed but, in the end, the plants were overcome.

The baking soda solution, on the other hand, seems to be working very well. The first signs of powdery mildew did not appear until very late (the end of August) and the spread has been slow. The mildew has been limited to a small fraction of the leaves.

Unfortunately, the spray is not completely effective. Powdery mildew is still present and, eventually, it can still have a detrimental effect. The cucumbers are more susceptible but the summer squash have suffered a bit, too.

Also unfortunate is the fact that the spray does nothing to prevent bacterial wilt. We have had fewer cucumber beetles this year (who knows why?) but clearly they’ve given our cukes the kiss (well, bite) of death.

This year, I am determined not to lose the battle against powdery mildew.

It’s probably a futile goal—quixotic, really—because we have suffered it every year that we’ve kept the vegetable garden, starting in 2011. Spores of Erysiphe cichoracearum, the fungus responsible for powdery mildew in cucurbits, are present, brought here from elsewhere by the wind (most likely) or by spontaneous manifestation (not likely but it is easy to understand why people once believed in it).

Sadly, the fungus is well-suited to survival and produces resting spores called chasmothecia (all of this is according to the folks at UC Davis; see “UC IPM Online”) that can—and do—resist the freezing weather that kills off weaker organism over winter. The only way to eradicate it is with fungicide, the most effective of which I have no interest in using.

No, eradication is not the answer; management is. And the key to management of powdery mildew is anticipation and early detection. It will appear—that’s inevitable—so I must be ready for it. And that means starting to spray the leaves of the cucurbits, which in our garden are the cucumbers and squash, with a preventative solution and starting to spray them now.

Last year, I found a good recipe on Late Bloomer’s website (see “Late Bloomer – National Heirloom Expo 2013 – Episode 36”; there is other interesting stuff there) and I mixed up a batch today. It’s a simple concoction of water, baking soda, hydrogen peroxide, and dish detergent (which I suspect is there to help the solution adhere to the plant).

I made a loop through the garden this afternoon, spraying each cucumber and squash leaf as I passed. My intuition tells me that spraying while the garden is in direct sunlight is preferable because the sun will evaporate the water, leaving the NaHCO3 and H2O2 (I have no idea what is the chemical formula for dish detergent but it’s probably too long to fit) behind to coat the leaves and inhibit fungal growth.

For the remainder of the season, especially in the fall when the humidity of summer remains but the nights are cooler, I will have to re-spray on a weekly (or so) basis.

Maybe I can’t win the battle but perhaps if I am diligent, I (and the cucurbits) won’t be routed.

The string beans weren’t the only plants that got pulled out this weekend.

The tomatoes, about which I have been obsessing lately, have not been improving despite my pruning of several days ago (see September 27, 2013).  Once infected with late blight (the suspected culprit), the plants have little hope of recovery without the use of fungicides.  Late blight is caused by oomycetes, non-photosynthetic fungi (perhaps that’s redundant?) that spread through the production of millions of oospores.  Oomycete is a cool word but it is a very uncool organism.

I have read about using a baking soda spray in several publications and websites (see, for instance, Late Bloomer’s Episode 2.16) and will probably try that next year, starting early in the season to prevent onset.  We’ll plant the tomatoes in the west planter—the best we can do, in terms of crop rotation—and keep everything as clean as possible.  However, given the ease with which the oospores spread and their ability to survive, underground, through severe weather, we are at a disadvantage (and greatly outnumbered).

It’s much too late for any kind of spray this year so I pulled out the spindly vines of the Sungold, Black Cherry, Brandywine (red and yellow) and Aunt Ruby’s German Green tomatoes that remained.  There were plenty of green (i.e., unripe) tomatoes but none that were fit to eat.  On all of the plants suffering from blight, the disease had spread to the fruit.  I don’t mind a rotten spot or two or even the occasional wormhole or bird peck, but the brown lesions, with their white spore sites, make even the best looking tomato unappetizing.

I’m happy to say that the plants were otherwise healthy and had produced extensive root systems (which required a fair amount of effort to pull out).  I was also pleased (and surprised) to see that the Country Taste Beefsteak tomato vines continue to resist the late blight; there were no signs of the lesions or brown spots on the leaves or stems.  This makes them a very good candidate for next year’s garden.

Of course, they are suffering from something else, possibly Septoria leaf spot (my hypothesis is based on review of photos of afflicted plants online) or maybe early blight.  Unfortunately, all of these conditions are spread by spores, the production of which is favored by the cool, humid weather that occurs in the fall.  I left the beefsteaks alone (well, I may have trimmed a few branches) in the hope that we will be able to harvest the dozen or so ripening tomatoes that are still on the vine.