Evaluation of Alternative Coverings for Year Long Utilization of Caterpillar Tunnels
The purpose of this project is to make use of a structure typically used for late and early season extension, known as caterpillar tunnels, during the hot summer months. Caterpillar tunnels are temporary or semi-permanent hoop structures. The ground support for ours are 1-3/8″ galvanized pipe, used as top rail for chain link fence. Each 126″ piece of pipe is cut into four sections and driven into the ground on five foot centers in rows 13 feet apart. A 20 foot piece of 1-1/2″ pvc pipe is slipped over each galvanized pipe and bent to the corresponding pipe to form a hoop 13 feet wide and approximately seven feet tall. This structure resembles a small high tunnel without any base boards or solid end walls. A post is driven in at the end of each tunnel. For structural rigidity, a ridge rope is tied to one end post, wrapped around the top center of each hoop and tied to the post at the other end. The covering is also terminated at each end by tying to the same posts. Between each hoop, a stake, in our case a piece of rebar, is driven into the ground. These are used as anchors for overhead ropes to keep the cover in place. A sandbag is placed between the rebar and cover to keep the cover on the ground and to protect the cover from the cut end of the rebar. Peaks of the hoops and the valleys of the anchor ropes give the tunnel a segmented caterpillar-like appearance.
Making use of these structures during the summer will make them even more affordable to own by amortizing their use over a longer period. It is hoped that full utilization of these will increase farm profits. We are testing the suitability of shade cloth to cover these structures and comparing the results of the four fabrics. The shade cloths are all 50% shading and are black, white, red, and a reflective aluminized material. Kale and cucumbers were planted in each tunnel and an outdoor control crop through woven black ground cover. The ground cover is used to suppress weeds as cultivation within the confines of a caterpillar tunnel is difficult.
I evaluated each tunnel for its ability to exclude pests, improve working conditions, and increase yields. Random samples of plants were to be selected and monitored for pest pressure. Yields and internal air temperatures were recorded. Soil temperatures were also recorded as they could have an impact on plant performance.
The fabrics were left on the tunnels for the longest period possible in order to evaluate any shortcomings in durability.
All of the ground supports were driven in on May 1, 2016
Construction of the tunnels was completed on June 7, 2016
All plants were transplanted on June 9 and 10, 2016.
The first cucumbers were harvested on July 1, 2016. The control crop yielded more in the first week but the others then caught up.
Harvesting concluded on August 28, 2016.
On October 6, 2016, I spoke at a SARE grant writing workshop. It was hosted by Lincoln University and was held at MU Southwest Extension Center in Mt. Vernon. I spoke about my experience writing my grant and performing the experiment.
On January 12, 2017, I removed the covers from the structures.
Impacts and Contributions/Outcomes
Within the first 48 hours of planting, 80% of the kale transplants were destroyed by cutworms. The pests must have been present in the soil prior to planting. Organic insecticide, spinosad, was used immediately but with no effect. The rest of the kale was lost over the following week. Cucumbers were unaffected.
The only significant pest pressure on the control crop was from blister beetles on the cucumbers. Pyganic was used to control blister beetles. Two applications were made at a five day interval and were successful. The damage was minimal. The tunnels did seem effective at excluding blister beetles. A large number of moths (primarily imported cabbage moths), however, became trapped in all tunnels. If it had been a species which feeds on cucumbers, or the tunnel contained a crop which they fed on, it would have been devastating. In addition, after the harvest period ended, squash bugs took up residence within the tunnels.
Cabbage loopers did breed in the black tunnel, and their caterpillars fed on cucumber fruits and leaves. I have never observed that in field production and believe the situation was created by the entrapment of the moths and the absence of their typical feeds. Caterpillars were controlled with an application of BT. Yields were affected because of this.
As for worker comfort, we found a wide variance in each tunnel. With the exception of the red cover, all the shade cloths were manufactured by Dewitt but each have a different weave. The red and white were identical in structure and had thicker threads and a tight weave. The black cover had much finer threads, looked more like window screen, and was the only structure you could see through. The reflective cover had a thread thicker than the black, finer than the red and white, and a more open weave. The material construction was really the largest factor in worker comfort. While the air temperatures in each tunnel were the same as the outdoor temperatures, air circulation in the red and white tunnels was severely limited. This made working in them unbearable. It was generally more comfortable in the black or silver tunnels than working outside.
Due to the massive loss of Kale seedlings within days of transplant, only cucumber yields were recorded. Two tunnels yielded less than the control crop. The black tunnel yielded 18% less pounds of cucumbers and the silver tunnel yielded 6% less than the control crop. The white tunnel yielded 16% more pounds of cucumbers and the red tunnel yielded 18% more. Yields in the black tunnel were affected by pest pressure. More testing will need to be done to determine if the type of color has a direct relation to yields. The project will be repeated in 2017 on a different field.
Soil temperature variances were negligible with the average soil temperature being: reflective silver, 77 degrees Fahrenheit; black, 77.4 degrees; red, 77.6 degrees; white, 77.9 degrees; outdoor control crop, 82.4 degrees. The control crop was found to be 5.4 degrees warmer than the coolest tunnel (reflective silver).
Beyond the measures of the experiment, I believe the best attribute of these tunnels was the appearance of the fruits. While sunscald was rare in the outdoor crop, it was completely absent from the tunnels. Wind damage was also absent from the covered plots. Wind damage will vary by location and season but is of concern in our area, and this method of production eliminated it. Because of the lack of pollinators, parthnocarpic greenhouse varieties were chosen. These varieties were Socrates, Picolino, and Tyria, all of which are thin skinned varieties. While many factors affect the quality of field grown cucumbers, the quality of the cucumbers grown within the tunnels was consistently very high. The protection offered by these structures shows promising results for high value crops, such as cucumbers. In addition, while soil temperatures did not appear to show a correlation in yield of our cucumbers, a 5.4 degree temperature difference over an unshaded plot could be significant for other crops.