Bill Shoemaker wshoemak at inil.com
Thu Dec 6 09:22:05 EST 2001

>About a month ago I posted about my first experience growing tomatoes in
>a small hoophouse which I had just finished building in the spring.
>Now for the questions for the experts:
>I plan to go back in there with tomatoes in early April at the latest.
>How soon can I expect to get in trouble growing tomatoes in the same spot
>year after year?  How much will trying to get all the old residue out
>(including the roots) help?  What kind of rotation plan would I need
>(using additional hoophouses) if I wish to continue growing hoophouse

>Marlin Burkholder, Virginia

I hope I don't wake you up with this response Marlin.

You raise several good issues about hoophouses, or as I like to call them,
Hi-Tunnels. Raising tomatoes as a Fall crop almost always runs into the
problem of fluctuating low temps. You can temps in the low 20's one night
and go for eight weeks following with nothing lower than 28 degrees. Tunnels
can protect well down to about 25 but then as it gets colder damage starts
to occur. I believe there is a role for supplemental heat in these things,
not to heat to optimum temperatures through the Winter, but to provide heat
to keep temperatures from falling below a floor temperature. There needs to
be some work done to determine the most economical system for doing it. I'm
hoping to do some work on it if I can get it funded.

I'll share one question I have. Could a grower install a hydronic heating
system in the floor of a tunnel? A hydronic system forces heated water
through a tubing system buried in the floor, heating the floor. The heat
rises from the floor, heating the whole tunnel but focusing it on the root
system first. The system could be heated with a hotwater heater, driven by a
small pump. It could even be prewarmed with passive solar heat. Anyone tried
this idea?

Second, you raised the issue of tomato hornworm. I have experienced the same
thing. Things look beautiful about the end of May, you go back in two days
later and the tops of the plants are scalped and you can practically hear
the munching. It's no joke to find 3-5 hornworms in each plant feasting
away. The tunnel provides artificial protection for the hornworms and their
parents (actually sphinx moths) can't get out so they keep laying eggs.
That's why you end up with super populations. You might consider releases a
natural predator/parasitoid of hornworm larvae. There is a wasp parasatoid
you can release that loves hornworm larvae. You would probably see some loss
of foliage with this strategy but tomatoes can lose some foliage and keep on
pumping out fruit. Or you can just use a DiPel spray as the plants get to
the flowering stage, repeating it once every 10 days or so.

You mentioned rotation. I think this is a very important issue. You could
probably get away with repeating a tomato planting 2 or 3 times. But at some
point you will build up a population of pathogens in the soil that could
potentially stay high for a long time, and could represent a risk to the
genetic resistance in most of today's tomato varieties. If you grow
heirlooms it could happen very quickly. While you could rotate crop families
within a tunnel, that strategy is suspect as the pathogens can move
laterally in the soil with soil moisture. If you can do it, you're better
off using profits from one season to plow into a couple more tunnels so you
can rotate crops across tunnels. Be sure to make sure you rotate crop
families, not just species. In other words rotating peppers and tomatoes is
no rotation at all. Rotate tomatoes, melons, cole crops, salad greens,
corn?, and throw in some cover crops of different plant families. Consider a
soil solarization in mid-summer. These could make a big difference in soil
pathogen build-up.

Lastly, I thought I'd comment on soil quality. Because it doesn't rain in
tunnels the soil needs to be irrigated. Most people use tillers to prepare
for the planting. I work with a soil that has about 5.5% organic matter, a
real nice prairie loam. I've found if you don't activly promote soil
microbiological health your soil will become very tough. Adding aged manure
fertilizers or good compost will make a big difference in how well your soil
will respond to the tunnel. These techniques will also play an important
role in suppressing soil pathogen levels (as long as the compost is made

I've said enough. Hope your experience with tunnels goes well.

Bill Shoemaker
Sr Research Specialist, Food Crops
Univ of Illinois - St Charles Hort Research Center

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