Evaluation of Screened High Tunnels for Organic Vegetable Production in Colorado

Summary:

During the summers of 2006 and 2007, we evaluated four different high tunnel coverings to see if we could reduce the incidence of insect vectored diseases by excluding the vectors from the crops. We were also interested in seeing how these different coverings would hold-up under our weather conditions, and if there would be differences in the micro climate within the tunnels that would impact three different commonly grown vegetable crops.

In Colorado, the most common and problematic disease vectors on organic crops include western flower thrips ( Frankliniella occident alis) , which vectors tomato spotted wilt on tomatoes (as well as a number of other diseases to other crops), potato psyllid ( Bactericerca (=Paratrioza) cockerelli ) which is responsible for psyllid yellows on solanaceous crops, beet leaf hopper (Circulifer tennelus ) which vectors curly top virus, and striped cucumber beetle ( Ac alymma trivittatum ) which causes direct damage and also vectors bacteri al wilt to cucurbit crops. Colorado summer conditions are characterized by high light conditions, low relative humidity, and about 120 frost free days; an increase in the use of high tunnels attests to growers’ attempts to extend the production season and improve the climatic conditions for high v alue crops.

The project was originally intended to be completed in one year, however, the chance migrations of psyllids failed to materialize in 2006, and beet leaf hopper numbers were also very low, so we were unable to compare severity of insect vectored disease of unprotected crops with those in the screened tunnels. However, the lack of insect pressure allowed us to make crop growth comparisons under the different treatments without having to factor-in possible insect impact, which was an unexpected benefit. Another unexpected but very useful event was the occurrence of a microburst of very high wind, which put the different covering materi als to the test of extreme weather conditions.

Overall, the crops performed very well under all of the covers, in spite of high temperatures in the tunnels. Melon yields were similar to field production; however tomato and spinach yields and qu ality were superior in the tunnels.

Two of the materials evaluated failed under high winds; the 1.5 oz spun bond polyester (SBP) shredded, and the polyvinyl alcohol (PVA) came apart at the sewn seams. The polyethylene (PE) covers held up to all weather events.

In 2007 the SBP and PVA were replaced with more durable greenhouse insect screening material(LS Econet), which survived very high winds, small hail, and excluded disease vectoring insects.

During 2007 we experienced infestations of western flower thrips, potato psyllid, and cucumber beetle, but relatively few beet leaf hoppers; allowing us to evaluate the effectiveness of a stronger insect screening material which also provided some climate attributes.

For complete report in Microsoft Word click here.