Use of alternative row covers and pollinators to manage insect pests and improve cucurbit production and profitability

Each participating farm has a slightly different crop mix and production method. However each participating farm did use the same alternative row cover called Proteknet, sourced from Dubois Agrinovation in Quebec, Canada (at the time of these trials, the material was not available in the U.S.). This nylon, netted material is said to have a lifespan of 5 years, while allowing plenty of light penetration and airflow. One farm also used a more traditional spun-bonded row cover, Agribon-15.

Each farm trial site used the row cover material in a different way. Details for each farm are below:

Farm #1 – Beech Grove Farm
Producers Anne and Eric Nordell elected to utilize a tunnel design that is included in the SARE-sponsored High Tunnels manual and accompanying DVD by Ted Blomgren and Tracy Frish.

Project set-up in 2008
Their caterpillar tunnel measured approximately 102 ft x 10.5 ft wide. Using materials on hand at the farm, the tunnel was erected and the Proteknet was placed over the hoops, which was secured to the soil with plastic row cover pegs. Greenhouse plastic (6-mil) was then layered over the Proteknet and hoops for protection until risk of frost had passed. The poly cover was held in place with clothesline over the tunnel and tied to 36 inch rebar stakes set halfway between each hoop. The ropes created the segmented “caterpillar” look and allowed for side ventilation by propping up the plastic with boards or forked branches.

In the tunnel the outer beds were planted with three rows of early lettuce (Apr. 23 – May 2) to maximize space in the tunnel. Lettuce sales were approximately $1200, which equaled the total estimated cost of the caterpillar tunnel materials (rebar, poly, clothesline, anti-insect barrier) at 2008 prices.

On May 8 cucumbers (variety Olympian) were transplanted 12 in. apart on bare soil in the middle bed of the tunnel. For comparison, a field planting of cucumbers (same variety) was planted 12-15 in. apart on bare soil on May 7. These rows were covered with Agribon-19 until removed for pollination on June 15.

Cucumber yields were determined by marking three, 10 ft. sections in each row (in the hoophouse and the field trial) and collecting the total number of cucumbers harvested. Harvest from the standard (bare soil, Agribon row cover removed for pollination) 72 ft. of cucumbers, July 8-August 2 yielded 463 marketable fruit and 97 culls (21%).

Harvest yields from the new practice in the caterpillar tunnel yielded, from 102 ft. of cucumbers June 30-August 4, 1246 marketable fruit and 166 culls (16%). The growers consistently harvested 40 or more cucumbers per day beginning July 3.

Bumblebee colonies purchased from Koppert Biology Systems were used to pollinate the cucumbers in the caterpillar tunnel was placed on June 19. All farm trial sites used bumblebee colonies as their pollination source.

Advantages to this system included low labor and inputs, as well as frost protection plus increased soil warming and air temperature. This method resulted in 100% cucumber beetle control during crop establishment and minimal bacterial wilt (two plants).

Caterpillar construction was low cost and labor. Compared to floating row cover, the caterpillar increased air and soil temperature before and after pollination resulting in significantly earlier and larger harvest. The insect mesh is the key to providing side ventilation without bumblebees escaping or cucumber beetles invading.

Disadvantages included the caterpillar tunnel requiring more labor and materials for construction and management than floating row cover. Headroom is somewhat limited (6.5 ft at peak), access is awkward under the sides, and soil preparation is not possible with field equipment.

Although cucumber beetle damage to leaves and fruit was minimal, a fair number of these determined insects managed to get in the tunnel, by the third week of July, possibly under the sides where the anti-insect screen was not secured tightly to the ground and definitely at the ends of the caterpillar where the mesh did not reach the soil (due to miscalculation when ordering the material). Regardless, the earlier, higher quality harvest of cucumbers added diversity and income to their stand at their farmers’ market.

They intended to use the caterpillar tunnel for cucumbers again in 2009, with modifications to improve the seal of the Proteknet.

Project set-up in 2009
The experiment was repeated in 2009, reducing the length of the caterpillar tunnel to match the size of the anti-insect barrier. They also added a third treatment to see if we could realize the advantages of the caterpillar for cucumber beetle exclusion and earlier harvest using one of their existing portable hoophouses. They simply lathed the anti-insect barrier to the inside of the doorframes at both ends of the 12 x 48’ portahoopy. A zipper sown into the mesh by Keystone Tarps provided access.

In 2009, they placed oversized “washers”, made out of 1 x 4 x 6” scrap lumber, with a ¾” hole drilled in the center, over the rebar posts to prevent the ends of the PVC hoops from sinking in the soil.

A comparatively small amount of the expensive Proteknet was required to keep cucumber beetles, as well as rabbits and birds, out of the portahoopy. Since the poly cover was lathed to the sill beams, the cucumber beetles could not enter the structure at ground level. Access was easier than the caterpillar, at least initially, as the anti-insect barrier did not need to be attached to the door frames until soil preparation, planting and most of the early lettuce harvest has been completed. The portable hoophouse provided a lot more headroom than the caterpillar even though both were built with 20’ PVC bows. The 12’ width of the portahoopy also allowed for three 3’ wide beds, increasing early lettuce production by one third (two extra rows on either side of the cucumbers) plus the opportunity to replant the outside edge of the lettuce beds to a heat loving summer crop, like basil.

The customized zipper door (including hemming the edges of the Proteknet) cost $120.00. They were not entirely successful at creating a tight seal between the mesh and the inside of the irregular doorframes. (The framing of the portahoopy end walls was not designed with this in mind.) A few beetles managed to get into the structure by the second week of June. The construction of the portable hoophouses required more materials and labor, and moving them was more involved and time consuming than the caterpillar. Because the portahoopies rely on end-to-end rather than side ventilation, their length was limited to prevent overheating. By contrast, the caterpillars were made as long as the available poly cover, up to 300’.

On May 13, they transplanted 46 Olympian cucumber plants 12” apart in a single row at all three sites. They removed the floating row cover from the field planting and installed the bumblebee quads in the caterpillar and portahoopy on June 16. Cucumbers were slower to come into production than in 2008, presumably due to the consistently cooler weather. As of July 12, they had only harvested 117 marketable fruit from the cucumbers in the caterpillar, 121 from the portable hoophouse and 7 from the field. Cucumber beetles arrived earlier in 2009 and beetle pressure was much more intense than in 2008. All of the culls from the field planting were a result of beetle scarring while the culls from the screened structures were due to misshapen fruit.

In 2008, bumblebee activity seemed very low in the caterpillar. They only saw 1-2 bees flying at any one time. Adding tomatoes in 2009 to the caterpillar, and basil, intentionally allowed to flower, to the portahoopy, noticeably increased the number of bees we observed flying around and actively pollinating. The increased bumblebee activity did not translate into higher cucumber yield or quality. However, since tomatoes are a higher return crop than cucumbers, adding tomatoes to the caterpillar structure provided a better return on the investment in bumblebees, especially in 2009 year when the caterpillar delayed late blight until the end of August.

Farm #2 – White Frost Farm
Project set-up in 2008
Producers Kit and Cathy Kelley elected to use the Proteknet material to cover two hoophouse structures approximately 60 ft x 12 ft. Plantings included one hoophouse where direct seeded winter squash (variety Waltham) was planted under black plastic, and the second with transplanted winter squash under black plastic (same variety). T-tape was used for irrigation. In 2008 they did not use a bed former to lay the black plastic and t-tape, instead it was covered with old hay to hold it in place. The plastic should then come up easily and the hay will be put into the ground as mulch.

For comparison field plantings of winter squash (same variety) in two beds, under black plastic measuring 130 ft x 3 ft were created. One bed was direct seeded and the other transplanted. Yields were determined by collecting weights and counts of all marketable squash.

The first hoophouse was transplanted with butternut squash on June 27. The hoophouse with the direct seeded butternut squash was planted with zucchini squash on the north side and cucumbers on the south side. They thought there would be a several week delay between the direct seeded hoophouse and the transplanted hoophouse, as well as providing an earlier crop of zucchini so the introduced bumblebee pollinators would have a natural pollen source and they would have an early crop for market. Same varieties of zucchini and cucumbers were planted uncovered outside the hoophouse, as well as direct seed butternut squash.

In August the producers realized the foliage had grown so large on the zucchini that they decided to harvest the zucchini as a one-time picking and pulled the plants to provide more space for the butternut squash. In retrospect, the extensive growth habit of the butternuts the 12 ft. of width in the high tunnel is not enough for the vines to fully extend.

On August 9, 65 pounds of zucchini was harvested from the direct seeded hoophouse and 86 pounds were harvested from the direct seeded, uncovered plot in two pickings. Butternut squash harvests resulted in the following; for direct seeded uncovered, 107 marketable fruit and for direct seeded hoophouse, 112 saleable fruit. For transplants the results were for uncovered, 137 saleable fruit and hoophouse transplants yielded 164 saleable fruit.

The material performed as hoped. The Proteknet held up to high winds, was maintenance free and maintained a captive bumblebee population for pollination.

Bumblebee colonies purchased from Koppert Biology Systems were used to pollinate the winter squash in both hoophouse structures.

Project set-up in 2009
In 2009 the project set-up at White Frost Farm was modified to plant only one hoophouse with Waltham butternut squash, since the farm’s yield in 2008 exceeded market demand (7 hills with saved seed and 7 hills with seeds from High Mowing Seed).

A second hoophouse included late plantings in a single row of 2 hills of Blenheim Melon, 5 hills of Triple Crown watermelon, 2 hills of Picolino cucumbers and 12 hills of Suyo Long cucumbers. The same seed and hill configuration was planted parallel to the hoop house.
The late planting was mulched and irrigated the same as 2008.

The season’s excessively wet spring and summer adversely affected the germination of the melons, cucumbers and butternut squash. The hoophouse sites were located on clay-based soils, and remained wet to some extent the entire season. The melons and cucumbers planted outside the hoophouse that germinated to the cotyledon stage were subjected to a wave of striped cucumber beetle. It became apparent the site choice was poor given the continuous wet weather pattern, so they abandoned this phase of the project.

The mesh covered portable hoophouse was durable, isolated the crop from outside pests, and coupled with the domestic bees as pollinators, the system attributes are transferable to higher value crops beyond the cucurbits.

White Frost Farm is considering adapting this system to raspberries, a crop under pressure from Japanese beetles. Also the Brassica crops they grow come under tremendous flea beetle pressure and a finer mesh is another route of exploration they are considering.

Farm #3 – Tewksbury Grace Farm
Project set-up in 2008 & 2009
In 2007 & 2008 Leah and John Tewksbury conducted seasons’ trials of organic control of cucurbit pests in field cucumbers and winter squash. Methods of control were fairly simple, basically using hoops and barrier cloths (Agribon 19 or Proteknet) to keep out unwanted pests, namely squash bugs, striped and spotted cucumber beetles, and squash borers. A hive of purchased bumblebees was placed under each crop “tunnel” to pollinate flowers. They also conducted an ancillary field trial on the organic control of flea beetles on eggplants, using essentially the same techniques as mentioned above.

Some background: during the second trial season (2008), they sought a new material to replace the Agribon because they found it trapped excessive heat in the low tunnels, and during the height of summer, these very hot conditions caused chronic stress on the plants. Tunnel ends had been screened to provide venting, but did little to alleviate trapped heat. They also found that Agribon was easily subject to wind damage and disturbance. Though adequately bricked down, the material acted like a kite, and several times came completely undone, thus potentially exposing plants to pests as well as creating tedious labor to reinstall. Finally, the Agribon was significantly tattered after two hailstorms in the ’07 season, thus allowing the possibility for unwanted pests to access the plants and also bumblebee pollinators to exit. After some research, our group decided on a promising material, Proteknet, (available at www.Duboisag.com) which was supposed to be durable and non-ripping, and not trap heat, since it is a screen-like material

Cucumbers

In each trial season, they planted 3 succession crops of cukes in a 4’ wide x 75’ long raised bed, the first transplants planted in late May, the second round in mid-June, and the final round in late June/early July. They planted 1/3 of the bed at each time, with 24” spacing, 2 transplants offset down the row. Roughly 10 varieties of cukes were interplanted, including white, Asian, and traditional (e.g., Martketmore) style fruits.

After transplants were planted, a heavy layer of straw mulch was applied to the bed. Then, the bed was hooped with 9-gauge wire, covered in Proteknet (2008 and 2009), and bricked down on all edges. A bumblebee hive was placed under the low tunnel during the last week or two of June (as flowering began). During harvest time, the hive was closed, which allows bees in, but prevents exiting, so that when they removed the cover to harvest, bees did not escape. The hive is re-opened after every harvest.

They have had great success with this method, and found the Proteknet to perform well, though we noticed that plant tendrils would latch on to the mesh and create small openings. However, no striped or spotted cucumber beetles were seen inside the material. And they saw yields of first-rate, unscarred fruits during each season. They definitely plan to use these control methods in the future.

Winter Squash

During the first year of these on-farm trials (2007 – not funded by SARE), they used Agribon 15 floating row cover as a barrier cloth. They planted over a dozen varieties of winter squash in a 4’ x 75’ raised bed, using 24-inch spacing, with 2 plants offset down the row. Heavy straw mulch was applied after planting. Using 9-gauge wire hoops and flexible 10’ pieces of 1/2" PVC piping inserted over rebar, they covered a 16’ w x 75’ l section with Agribon 15. A hive of bumblebees was placed under the tunnel in late June. Despite an excessively hot, droughty 2007 season, this bed yielded 561 lbs of unblemished winter squash, as no squash bugs or cucumber beetles penetrated under the cloth to damage plants.

However, they had trouble with excessive heat, wind ripping the row cover off, and significant hail damage to the Agribon cloth, so in 2008, they switched to the aforementioned Proteknet material, which seemed promising. Instead of a single 4’ x 75’ raised bed, they planted two “sister” 4’ x 75’ beds (side by side), so they could use one large piece of Proteknet over both, and hope to double their yields. Plant growth was robust with lots of vining and formed fruit. They noticed squash bugs on the exterior of the Proteknet material by late June.

As the squash plants grew, leaves pressed against the material, and they observed squash bugs feeding and laying eggs on the leaves through the material (note: squash bugs were unable to do this through Agribon, which is a spun material, rather than woven screen). Also, squash tendrils aggressively attached to the Proteknet and created many small openings; this issue appears much more problematic with low tunnels rather than high tunnels or hoophouses. This material is not knit, so if it is snagged in any way, it tends to open and unravel. Also, after installation they noticed about a 4-inch opening along a center seam, apparently missed during the custom sewing.

Despite seeing some squash bugs on the exterior, all was well until they pulled the cloth off to inspect plants in late July when they found widespread squash bug infestation (eggs and nymphs) throughout the patch. They hand groomed plants as best as possible. In early August, they inspected again, and found continued infestation, also observing a few striped and spotted cuke beetles under the material. Unfortunately, the 2008 crop crashed due to heavy squash bug pressure, and our harvest suffered a significant impact from the pest damage. Two 4’ x 75’ beds covered in Proteknet yielded 393 lbs of moderately to severely blemished fruits, compared to 2007’s one 4’ x 75’ Agribon 15-covered bed’s yield of 561 lbs of unblemished fruits.

They could not determine how such a severe infestation occurred – it is as if there was no barrier cover on at all. The few scattered holes did not seem sufficiently large and accessible enough to allow such a severe infestation. Also, there were no cucurbits on these beds prior to 2008.

So, in 2009, they decided to use the floating row cover (Agribon 19, instead of 15, due to size availability) again as the barrier cloth, since the Proteknet was unable to prevent pest damage on winter squash. They planted only one 4’ x 75’ raised bed (with a barrier cloth spanning 16’ across to cover vine sprawl) this year, again planting a dozen winter squash varieties. One hive of bumblebees was placed under the low tunnel in early July.

They resolved the problems with wind pick-up by placing tie-downs over the floating row cover to keep it in place; this simple method worked, though they did not experience any significant wind or rainstorms during the 2009 growing season. Excessive heat is still a potential issue (not in 2009’s cool season, however), as is hail damage.

The Agribon initially appeared to keep squash bugs off of plants. By late June, however, they began spotting squash bugs on the screen exteriors that cover each end of the bed. By mid-July, they removed the row cover to find, to our dismay, complete squash bug infestation in one half of the bed (that contained the earliest transplants). The squash fruits were too immature to harvest at this time, so they were left for a couple more weeks before the plants began completely crashing from the pest pressure. In early August, they harvested what they could from this infested part, removed all damaged plants and debris, and removed the remaining row cover entirely off the bed in the hopes of allowing some beneficial predators to reduce the impact of the infestation on the remaining plants.

Despite heavy pest damage, they had surprisingly good 2009 yields (727 lbs from a 4’ x 75’ bed), perhaps due to the abundant rainfall that helped produce vigorous transplants. Their winter squash experiments have been inconsistent and bewildering! We have learned that only a handful of females are necessary to lay thousands of eggs, so if they are able to penetrate barriers, they can still flourish.

• Farm #1 – Nordells – Caterpillar Design, 2008
• Farm #1 – Nordells – Portable Hoophouse
• Farm #2 – Kelleys – Hoophouse construction, 2008
• Farm #2 – Kelleys – Butternut squash harvest, 2008
• Farm #3 – Tewksbury – Winter squash covered with Proteknet
• Farm #1 – Nordells – Portable Hoophouse door access, 2009
• Farm #3 – Tewksbury – Cucumbers covered by Proteknet, 2008 & 2009
• Farm #3 – Tewksbury – Winter squash covered with Agribon
• Farm #2 – Kelleys – Hoophouse in wet 2009 location
• Farm #3 – Tewksbury – Winter squash yields