CULTIVATING QUESTIONS
Concerning the Bio-Extensive Market Garden
by Anne and Eric Nordell of Trout Run, PA

Caterpillar vs Cucumber Beetle

The Winter 2009 CQ on portable hoophouse construction featured an article by Ted Blomgren and Tracy Frisch about caterpillar tunnels. At the end of the column, we promised to report on our own experience growing cucumbers in one of these inexpensive walk-in tunnels after we had completed the second year of the SARE-sponsored curcubit pest experiment coordinated by Penn State Cooperative Extension and The Pennsylvania Association for Sustainable Agriculture.^[1]

We got the idea for the project when attending a twilight meeting at Tewksbury Grace Farm in August, 2007. Leah and Johnny Tewksbury led a tour of their intensively-planted one acre garden and then related their first year’s experience using full season row cover to prevent cucumber beetles and squash bugs from attacking their winter squash. They harvested over 560 lbs of heirloom squash from a 4 by 75’ bed for their 35 share CSA. This was a huge improvement over previous years when winter squash had been a complete crop failure due to intense insect pressure.

The Tewksburys noted a few reservations they had about using the Agribon 15 floating row cover, suspended over low hoops, as a full season insect barrier: Heat stress may have limited yields. Likewise, the super dense foliage under the cover may have prevented the quad of bumblebees placed inside the Agribon 15 from pollinating all of the flowers. The row cover also blew off several times over the course of the summer and was completely shredded during a late season hail storm.

Driving home from the meeting, we couldn’t help wondering if there was a durable but lightweight material on the market comparable to window screen, something with a fine enough mesh to exclude cucumber beetles and squash bugs but porous enough to prevent overheating and sailing away in a stiff wind. Discussing the idea with Ted Blomgren at the NOFA-NY Conference that winter, he suggested that we check out the Dubois Agrinovation exhibit.^[2] Sure enough, they had samples of a lightweight poly mesh designed specifically for excluding insects and other pests from vegetable crops. Although much more expensive than floating row cover, the new Proteknet anti-insect barrier came with a guaranteed life expectancy of 8-10 years and a high UV and mechanical resistance rating.

We chose to use the full season insect mesh on early cucumbers because we thought this high value crop would give a better return on the expensive Proteknet and imported bumblebees than the moderate income winter squash. Besides, using floating row cover until early blossom had always provided enough protection from the first wave of cucumber beetles for the winter squash, as well as our second planting of cucumbers, both direct seeded the end of May or the beginning of June. Not so for our early cucumbers transplanted out in the field the first part of May. Removing the row cover to allow native pollination of the first planting of cucumbers Caterpillar vs Cucumber Beetle almost always coincided with the first wave of beetles, reducing the yield by stressing the vines and resulting in a high cull rate due to the cucumber beetles scarring the fruit.

We also decided to use the Proteknet suspended over a poly covered tunnel, thinking this might be an improvement over laying the mesh directly on the cucumbers for several reasons. First, we hoped that the warmer conditions in the hoophouse would enhance earliness, quality and yield. Second, we did not want to fool with repeatedly moving and recovering the full season insect barrier for the daily harvest of cucumbers. Finally, we thought the experiment was the perfect excuse for trying out a caterpillar tunnel. Using materials we already had on hand, we erected a 10 ½’ by 102’ caterpillar one morning during a January thaw, and then covered it with insect barrier and greenhouse plastic before planting a single row of cucumbers and two beds of early lettuce in May of 2008.

The results exceeded our expectations. Transplanted 12” apart on May 8, the 102’ row of Olympian cucumbers yielded more than 40 fruit per day beginning on July 3. The total harvest, starting June 30 and ending August 4, was 1246 marketable cukes and 166 culls (13%).

By contrast, our early field cucumbers, transplanted on May 7 and row covered until June 15, did not come into full production until ten days later and yielded half as much as the caterpillar with a total of 463 marketable fruit from the 72’ row plus 97 culls (21%). The higher cull rate in the field was almost entirely due to cucumber beetle scarring while the cukes that did not make the grade in the caterpillar were misshapen, presumably due to incomplete pollination or uneven soil moisture.

Sold two-for-a-dollar, the gross return from the 20” by 102’ bed of caterpillar cucumbers was a little over $600. That was virtually the same gross return from each bed of early lettuce, transplanted on April 23 and May 2, and priced at $2/head. The following crops of fall lettuce and salad mix doubled the gross income to approximately $3600. Assuming a net income of 33% – which we think is conservative – the caterpillar paid for itself the first year. That’s based on 2008 prices for the materials (PVC pipe, rebar, 6 mil greenhouse plastic, clothesline, and Proteknet anti-insect barrier), totaling almost $1200. This accounting of the caterpillar expenses did not include the cost of labor for construction or the hefty annual outlay for the bumblebees, $65 for the quad plus $42 shipping from Koppert Biological Systems.^[3]

To offset the high cost of the imported pollinators, we limited the 2009 cucumber planting in the caterpillar to 48’ and put the rest of the middle bed into trellised Brandywine tomatoes. Not only did the heirloom tomatoes, sold at $3/piece, give a much higher return on the investment in the bumblebees, but they remained productive until the end of the summer, compensating, to a large degree, for the complete loss of our small planting of field tomatoes which we cut down at the first signs of the dreaded late blight plaguing the Northeast unusually early in 2009.

To see if we could minimize the investment in the pricey Proteknet, we tried using the anti-insect barrier on the door openings of one of our existing portahoopies. As it turned out, the savings from using a small fraction of the insect mesh was cancelled out by the cost of having the Proteknet custom cut and hemmed to match the end frames of the portahoopy and sewing in a zipper door for access. In retrospect, the least cost option would have been to build our own cucumber beetle impervious doors for this portahoopy using readily available and less expensive window screen.

As for convenience and management, we thought the screened-in portahoopy offered a couple of advantages over the caterpillar. With the PVC hoops resting on top of the 4” sill beams, the portahoopy provided more head room and a wider interior than the walk-in tunnel even though both use the same 20’ long Schedule 40 pipes for bows. Although entering the portahoopy through the zipper door for cucumber harvest was not a whole lot easier than propping up, or ducking under, the sides of the caterpillar, we did not need to attach the Proteknet to the door frames for cucumber beetle protection until after we had finished soil preparation, transplanting, and most of the lettuce harvest, making access for these tasks much more convenient.

The big disadvantage of the portahoopy design is the length must be limited to insure adequate end-to-end ventilation, requiring a lot more time and materials for framing, doors, and customized screening. The walk-in caterpillar tunnels, on the other hand, can be made as long as the available greenhouse plastic (300’) with a much lower investment in materials and labor, and the potential to reap a significantly higher return on a hive of bumblebees. The least cost and most convenient option might be to follow the example of Windflower Farm, described in the High Tunnels manual,^[4] which uses steel bows with a 16’ wide span to maximize the planting area and head room inside their quarter-acre of caterpillar tunnels.

From an environmental perspective, we are not all that comfortable with using the Proteknet on either type of tunnel. The poly mesh plus PVC hoops and greenhouse cover add up to a lot of polluting, fossil fuel inputs and goes against our farm goal of relying on the internal resources of the farm as much as possible. Shelby Fleischer, the Penn State entomologist supporting this SARE project, also warns that the population of native squash pollinators could crash if the majority of growers began using full season insect barrier with imported bumblebees. He is now collaborating on a multi-state experiment to improve the habitat for native pollinators and to test the simple practice of leaving row covers on curcubits for 10 days past early blossom for reducing cucumber beetle damage, and the bacterial wilt they transmit, without significantly impacting fruit set.

Given these ecological concerns, we intend to limit tunnel production of curcubits to small plantings of high value crops, like the early cucumbers. For field-scale production, we are sticking to low input management and the pre-blossom use of floating row cover. A case in point: we have continued the experiment of growing-our-own mulch for winter squash described in the Summer ’08 CQ on “Market Farming After Peak Water.” We round out this column on curcubit and hoophouse concerns with a grow-your-own mulch photo update and a Penn State Extension article on nutrient management for high tunnel production.

Caterpillar Construction at Beech Grove Farm

1. Mark two rows 10’ 8” apart the length of the tunnel site.
2. Set 30” pieces of rebar 5’ apart in each row. Drive them 20” deep, leaving 10” of the 5/8” rebar sticking out of the ground.
3. Slide the 20’ long 1” Schedule 40 PVC pipe over the rebar posts to form flexible hoops at least 7’2” high at the peak.
4. Make a flexible ridge purlin from rope by looping clothesline around the top of each hoop from one end of the tunnel to the other. Tie the ridge purlin rope to 36” long rebar anchors set in the ground approximately 8’ past the ends of the hoophouse.
5. Set 3’ long rebar stakes halfway between each hoop and angled away from the tunnel to serve as anchors for the Proteknet and greenhouse cover.
6. Pull the insect barrier over the tunnel.
7. Pull the poly cover over the insect barrier.
8. Tie ropes to the rebar anchors on one side of the tunnel and throw them over the top of the caterpillar. Tie securely to the anchors on the other side. Start in the middle of the caterpillar to hold the poly cover in place, then proceed to step 9 before securing the rest of the ropes.
9. Bunch the plastic at the ends of the tunnel and tie to the ridge purlin anchors. The 24’ wide poly cover and insect mesh should be at least 40’ longer than the tunnel to insure plenty of material for bunching and making a good seal with the soil at the ends of the caterpillar.
10. Improvise heavy-duty 4’ tall props for side venting the tunnel using forked branches or scrap lumber with a V cut out of the top. A couple of 6’ props come in handy when a temporary doorway is needed.

Pros and Cons of Caterpillar Construction

Without a doubt, the caterpillar is faster and simpler to build, and to move, than the portahoopies described in the Winter 2008 and 2009 CQs. The reason: these walk-in tunnels dispense entirely with end frames and doors, usually the most expensive and time consuming aspect of hoophouse construction.

Using the anti-insect barrier on the caterpillar provided several unexpected benefits: It added much more stability to this super flexible structure. The mesh material also noticeably slowed the wind flow through the tunnel when ventilated. We did not have to drop the sides in windy weather as strongly recommended in Ted Blomgren and Tracy Frisch’s High Tunnels manual.^[4] The insect barrier also stopped birds, rabbits and other wildlife from entering this moveable hoophouse.

The only challenging part of caterpillar construction was bunching the ends of the greenhouse plastic and tying it securely to the ridge purlin anchors. Not only is this awkward to do, but high winds tend to lift the plastic and loosen the ropes. We ended up adding a second rope from the ridge purlin anchor to the top of the first hoop to stabilize the end of the tunnel. We also placed heavy stones on the edges of the plastic to maintain a better seal with the soil at the ends of the caterpillar. For similar reasons, it was necessary to reposition the poly cover and retighten the ridge purlin and tie-down ropes at least once each growing season.

The tie-down ropes give the caterpillar its characteristic look, but they also depress the greenhouse cover, reducing head room between each hoop. In addition, we had the strange sensation that the tunnel was shrinking over the course of the first season. Sure enough, when we removed the poly and insect mesh in preparation for winter, we noticed that the hoops had sunk 8-10” into the soft soil! To remedy the situation, we slipped extra large “washers,” made out of 4 by 8” pieces of scrap lumber with a ¾” hole drilled in the center, over the 5/8” rebar posts to support the 1” PVC pipe at ground level.

Hoofnotes:

1. For a final report on this SARE project by the three cooperating farm families – Johnny and Leah Tewksbury, Kit and Cathy Kelley, and ourselves – contact Michele Gauger at the PASA office: PO Box 419, Millheim, PA 16854-0419. 1-814-349- 9856, michele@pasafarming.org.
2. Dubois Agrinovation, Quebec, Canada. 1-800-667-6279, www.duboisag.com. The Proteknet is manufactured and cut-to-size in England. Allow at least 8-10 weeks for delivery.
3. Koppert Biological Systems, Inc. in Romulus, Michigan. 1-800-928-8827, www.koppertonline.com.
4. The High Tunnels manual, edited by Ted Blomgren and Tracy Frisch, can be ordered from the UVM Center for Sustainable Agriculture, 63 Carrigan Drive, Burlington, VT 05405, 1-802-656-5459 for $15. It is available on-line for free: www.uvm.edu/sustainableagriculture/hightunnels.html. The accompanying High Tunnels DVD was also funded by SARE and costs $15.
5. Growing For Market is published ten times a year by Fairplain Publications, Inc., PO Box 3747, Lawrence, KS 66046, 1-800-307-8949, www.growingformarket.com. One year print subscription is $33, $60 for two years. Electronic edition: $30; $89 includes full access to GFM archives.
6. “Henpecked Compost and U-Mix Potting Soil” can now be found in the SFJ online archives. We hope to update this Spring 1992 article in a future CQ with details of the homemade tumbler we now use to meet the NOP composting requirements.