Wednesday, August 01, 2012

trying to prevent late blight

On Saturday, I found what looked like late blight in tomatoes in our community garden. I have been watching for it since it was confirmed a week ago in a field a mile away. I sent a sample for analysis (to UMass plant lab) and late blight was confirmed on Monday. Since then, its amazing how fast the infection has spread. Five plots now have nearly dead tomatoes and gardeners are in the process of removing the plants and debris. Adjacent plots have early infections.

My plot is on the far side of the garden from the start of the infection. Today, was another dreary wet afternoon. Perfect for spread of the fungus. I read that covering with plastic can protect the plants. I have been spraying with copper fungicide for two weeks, but thought it would be good to experiment with another method too. I haven't had such nice looking tomato plants in a long time and would love to have them produce into September.

So, today Skippy and I went to my plot and I put up a bit of a frame with some old wood poles lashed together with string. I spread a sheet of plastic over this and secured it with string. It covers the top and about 2-3 feet down on the side, but leaves plenty of room for airflow from below. I'm thinking the idea is to reduce the number of spores that can fall on the top of the plants. Also, keep the plants dry in all this rain we are having. While traveling in Switzerland, I saw that many home gardens had plastic coverings over their tomato plants. tomatoes under plastic 038

Its an experiment for me, just to see what happens. It will make it harder to get good coverage with the spray, but I am planning to spray again tomorrow.

It rained yet again just as I finished putting up the plastic. Underneath the tomatoes are dry. This seems to be good. I am really curious to hear if anyone has experience with tomatoes under plastic.

tomatoes under plastic 041 tomatoes under plastic 120 tomatoes under plastic 138 tomatoes under plastic 140


vishnu said...

In Germany and Switzerland, growing tomatoes under plastic is the only feasible way to get ripe tomatoes. Our neighbor told us that 15 years ago he never had a problem with it, but now late blight shows up every year without fail and I think gardeners have accepted it as normal. As the summers here are cool and wet, keeping the plants dry is key. Many people just build a plastic roof over the plants. I have even seen some crazy constructions involving old umbrellas. It is very common to see garden centers selling 'tomato houses' which are in essence high tunnels or small greenhouses.

kathy said...

Thanks so much for commenting! I couldn't find much information about this online, but on a train ride through the countryside in Switzerland near Basel and into the Alps, most gardens had tomatoes covered with plastic. I remember hearing gardeners from Holland and UK saying late blight is an every year thing for them.

Interesting that this also sounds like it is new for you - as it wasn't there 15 years ago but is now every year. Ours started 4 years ago - 2009 - and seems regular here now too. Our summers in New England have becen quite soggy recently, while much of the rest of the US has been hot and dry.

My tunnel is a poor version of a high tunnel. No one here will know what is going on.

Auntie Beak said...

thanks for the update, kathy. i'll be fascinated to see if your measures work.

kathy said...

I had to make some adjustments to my plastic cover this morning following last night's rain. Water had collected on the top in a giant puddle and also humidity was collecting inside the tent. Thought the photo doesn't look like it, the structure I used is actually a square flat surface.

I rolled up the sides a bit to give better air circulation. I also added some cross poles to support the top better and get rid of the pockets where the water collected.

I realize now that a hoop or a tepee structure would work better. I will see if I can adjust it sometime.

vishnu said...

If you google images for "tomatenhäuser" in German, you will get a good idea of what people here are doing. As you mention, humidity is a problem, which is why most people just build a roof, to allow air circulation. My mother in law hates plastic in her garden so she uses wooden boards for her roof. The plants get a bit less sun, but stay blight free until late in the season. I have only been in Germany/Switzerland for 5 years, and it has always been a problem in that time span, especially at community gardens where disease spreads quickly and probably finds plenty of places to overwinter. As to why it just started 15 years ago, my guess is more people became interested in growing 'exotic' (for here anyways) plants and weren't informed/diligent about controlling disease.

kathy said...


Interesting thoughts on "why".

Here it started 4 years ago, maybe paralleling an upsurge here in new gardeners, community and home gardening, and organic methods? Blighted material gets composted or left to rot in plots. Then again, we have also had an increase in damp cool summers it seems.

Anonymous said...

Located in Middlesex County, MA. I just finished sprayed with liqui-cop on Monday morning of this week since it just finished raining on Sunday night. Will probably re-spray early next week with rain due tomorrow and on Saturday.

kathy said...

I pulled the cover off yesterday and stored the plastic. We are having another hot dry week. With the plants showing drought stress, I don't think I need to have a rain shield.