Row Cover Use Methods for Cucurbit Pest and Pollinator Management

Final report for OS14-091

Project Type: On-Farm Research
Funds awarded in 2014: $14,995.00
Projected End Date: 12/15/2017
Grant Recipient: Oklahoma State University
Region: Southern
State: Oklahoma
Principal Investigator:
Dr. Jim Shrefler
Oklahoma State University
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Project Information

Abstract:

Evaluation and comparison of management methods for using row covers to exclude insect pests from cucurbit crops showed that daily cover removal during morning hours resulted in squash yields comparable to those obtained without row covers where insecticides were employed. Yields appeared to be lower with the current practice of using row covers up until the initiation of flowering, at which time covers are removed completely.  The original plan was to evaluate these practices as an approach for use with early season plantings.  Due to an unusually wet spring field activities and planting were accomplished about one month later than intended.  The results obtained for crop yield and insect pest incidence were comparable for two of the three study sites.  The third study site had a very low insect pest incidence. 

Project Objectives:

Objectives

Field trials are being used to evaluate row cover use and management for the exclusion of insect pests in cucurbit vegetable crops. The practices that are being evaluated are designed to address the exclusion of insect pests from the crop as well as the need for pollinator access to the crop.

Project objectives are:

  1. Evaluate possible row cover management practices to determine their efficacy and practicality of implementation.
  2. Increase grower awareness of alternative insect pest management practices for cucurbit crops.
  3. Communicate to growers the concepts being employed in the practices used in this research, including both the insect pest management and pollinator aspects.

Cooperators

Click linked name(s) to expand
  • Dr. George Driever
  • Dr. Eric Rebek
  • Harold Stephens
  • Kenda Woodburn
  • Merritt Taylor
  • Alan Pruit
  • Jim Vaughn
  • Rodney Farris
  • Robert Havener

Research

Materials and methods:

Trials were conducted in Oklahoma at three locations during each of 2015 and 2016.  The locations and descriptions are as follows.

  1. A commercial farm in Atoka County with a sandy loam soil. The field was fallow for several years prior to the project.
  2. The grounds of Shawnee Feed Center and Farmers Market (which has a vegetable production demonstration site) in Shawnee in Pottawatomie County. The soil is silt loam that was brought in to make a raised area for vegetable trialing.
  3. The Oklahoma State University Mingo Valley Research Station (Oklahoma Vegetable Research Station) at Bixby. The soil is a very fine sandy loam and well suited to vegetable production.

At all locations soil was prepared and plastic mulch and drip irrigation were installed.  Three planting beds, each about 3 feet wide, were constructed and were spaced 10 to 12 feet center to center.   Raised beds were used in Atoka and Shawnee.  The yellow summer squash cultivar Enterprise was used for all trials.  Plots were 15 feet long and separated end to end by about 8 feet.  Six plants were planted in the center of the row and spaced evenly for a distance between plants of about 2 feet.  Plants were established by either direct seeding or using transplants.  Transplants were also started at the time of direct seeding to serve as a supply of plants to fill in where plant establishment was not successful.   As soon as possible after planting, row covers were installed over the squash plots. Covers were supported by hoops made of 10 foot lengths of electrical conduit and were 52 inches wide and 45 inches tall.  Hoops were positioned by placing them over 3 foot long sections of ½ inch rebar that was driven into the soil.  Row cover material (DeWitt Row Cover Plus) was placed over the hoops and held in place with large metal office supply binder clips.  Row cover material edges were covered with soil to eliminate possible entry points for insects. 

The specific treatments are as follows.

  1. No row cover and apply insecticide when insect pest presence is observed.
  2. Cover rows until plants have a female flower and then remove covers.
  3. Cover rows until plants have a female flower, wait 2 more weeks, and then remove covers. This treatment will be referred to as “delayed cover removal” or (DCR).
  4. Cover rows until plants have female flowers, and then begin a daily procedure of uncovering in the morning for 1.5 to 2 hours, then recovering. This treatment will be referred to as “short brief removal” or (SBR).
  5. Cover rows until plants have female flowers, and then begin a daily procedure of uncovering in the morning for 3 to 4 hours, then recovering. This treatment will be referred to as “long brief removal” or (LBR).

The target timing for initiation of row cover removal treatments was when half of the plants had a first female flower. 

The crop was monitored for fruit production and harvested as needed.  Harvest data for each location was pooled across harvest dates and is presented as yields obtained over 2-week harvest intervals. The 2-week intervals begin with the initial fruit harvest that occurred at the location.

The experimental design in each trial was a randomized complete block with three replications.  Squash yield data is presented in terms of fruit numbers per plot.  Data was analyzed using analysis of variance and means were separated using Duncan’s Multiple Range Test.

Insect pest and pollinator incidence was observed periodically to ascertain the specific insects present in the trials. 

Research results and discussion:

2015 Trials

Squash yield data for the 2015 trials is shown in Table 1.  Fruit production during the first 2-week harvest period was primarily in the plots that were not covered or those with covers removed at first flowering.  At the Shawnee and Bixby locations the first harvest period yields were significantly greater in these treatments as compared to the DCR treatment and the treatments with brief cover removal and replacement (Table 1). 

During the second 2-week harvest period yields did not differ significantly across treatments for the Atoka and Shawnee locations.  However, there was a numerical trend at each location of greater yields in the BCR treatment compared to LCR treatment.  Similarly, for the Bixby location yields were substantially and significantly lower with the LCR treatment as compared other treatments. 

During the final 2-week harvest period the responses across treatments differed for the 3 locations.  At the Atoka location only the untreated plots had appreciable fruit yields.  At Shawnee yields were comparable across treatments and were numerically comparable to the yields obtained in the second harvest period.  For the Bixby location yields were comparable for all treatments except the untreated plots where fruit numbers were significantly lower.  This is explained by the fact that many of these plants had died. 

2016 trials

Yield data for the 2016 trials is presented in Table 2.  For the Atoka and Shawnee locations fruit production during the first 2-week harvest periods was primarily in the plots that were not covered or those with covers removed at first flowering (Table 2). At Bixby there were comparable yields across all treatments except for the untreated plots. The untreated plots had significantly lower yields than where the cover was removed completely at first flowering.  An explanation for the fruit production in plots with delayed cover removal and brief uncovering is that covers were removed or damaged by high winds and plots remained uncovered for several days until replacement cover material could be obtained. The low yields in the untreated plots are explained by the fact that plants in some of these plots were weak from the start for undetermined reasons. 

At the Atoka location the second 2-week harvest period yields were comparable across all treatments except for the delayed cover removal treatment.  Here, yields were numerically about one half of the others.  At Shawnee yields were also comparable across the same treatments except for the DCR.  In this case, however, yields were substantially and significantly greater where cover removal was delayed 2 weeks after first flowering.  At Bixby yields were comparable across the untreated, the delayed cover removal, and the BCR treatments.  Compared to these, yields were greater for the treatment uncovered at 50% flowering and the LBR treatment.  Because of the previously discussed cover removal by the wind the explanation of these differences would be rather speculative.  It is of interest that for the treatments with brief cover removal yields were numerically double for the 3-hour cover removal period compared to the 1.5-hour removal. 

For the final harvest period in 2016 all treatments at Atoka were still producing fruit and yields were similar across treatments. At Shawnee appreciable yields were still being obtained during this period.  Substantially greater numerical differences were found in the delayed cover removal treatment and the treatments with brief cover removal compared to the untreated and where covers were removed completely at 50% flowering. At Bixby there were no significant differences among treatments at the final harvest period but the numerical trend of yield values followed a pattern very similar to that of the second 2-week harvest period.

Looking at the results of squash yields across locations and trials it can be seen that covering squash with row covers is an effective means of preventing the pollination that is needed for fruit set. Squash will not set fruit if pollinators are not present (Layton, 2015). This was exemplified in the first harvest period at each location in at least one year of the trials.  There were exceptions for Atoka in 2015 and at Bixby in 2016.  In Atoka, a yield of 4.3 fruits per plot was obtained in the SBR treatment. Looking at the data for individual harvests was pooled to produce the 2-week harvest period values (data not shown), this fruit production came in at the final days of the 2-week period.  At Bixby, as previously mentioned, a wind storm removed or damaged the covers and exposed the plants to pollinator access, which explains the appreciable early yields in all treatments. 

Looking at the squash fruit yields of the second 2-week harvest interval, there was appreciable fruit production in all treatments at all locations and for both years.  For the Atoka location in both years, and Shawnee in 2015, there were no significant differences across treatments. The delayed uncovering treatment produced significantly greater yields that were double those of the other treatments at Shawnee in 2016 but showed no advantage at Bixby in either year. The two treatments with brief uncovering and recovering did not differ significantly from each other in any individual trial and there were not any consistent trends of the duration of uncovering having any advantage over the other. 

For the final harvest period the only significant differences that were detected were found between the insecticide treated control and other treatments. At Atoka in 2015 the yields were greatest in this treatment but lowest at Bixby. At Atoka insecticide application was given substantial attention as squash bugs were abundant in the trial. At Bixby, however, insect pest populations were relatively low and less attention was given to application of insecticides to this treatment. Apparently the plants were attacked by squash bugs which resulted on their decline. Looking across the various treatments that employed covers there is no indication that any of the treatments had a consistent effect on the squash yields obtained in the latter part of the production period. 

The results of these two years of trials suggest that the squash yield responses to the treatments that we evaluated are rather erratic. In certain situations, certain treatments were advantageous as compared to others, an example being at Shawnee in 2016 for the second harvest period of the DCR treatment where yields were at least two times greater as compared to the other treatments.  Based on observations made over the course of this study there are several factors that may have an influence on the effectiveness of a given treatment.  One is that row covers have an influence on plant growth.  Plants that were under the covers were clearly larger than those not covered.  Another observation was that the pollinator complexes varied across the trial locations and years.  Each of metallic bees (a sweat bee), squash bees, bumble bees and honey bees were prevalent pollinators in at least one trial.  It is conceivable that differences in the flower visitation habits of these could have influenced the yields obtained in certain treatments.  For example, the SBR and LBR treatments would likely have been visited more when honeybees, which move rapidly from flower to flower, were the primary pollinator, than when the pollinators were squash bees, which tended to spend much more time in a given flower. 

Over the two years of the trials the primary insect pest that was observed was the squash bug Anasa tristis (De Geer).  This insect is a major pest of squash in the region and due to its activity infested plants are weakened and fruit production and quality are reduced (McLeod).  The attractiveness of squash to this insect was observed repeatedly during these trials when the insect was found walking and ovipositing egg masses on the external surface of the covers that prevented the insect from accessing squash plants. 

Participation Summary
1 Farmer participating in research

Educational & Outreach Activities

3 Journal articles
2 Webinars / talks / presentations
2 Workshop field days

Participation Summary:

200 Farmers
Education/outreach description:

Publications/Outreach

Conference Presentations

Driever, G, J. Shrefler, M. Taylor, E Rebek and K. Woodburn.  2016. Row cover use for insect management on summer squash, Year 1. Proceedings of the 36th Annual Horticulture Industries Show.  Page 136 – 138.  https://docs.wixstatic.com/ugd/d47e26_6d21be088a2448a5b28a9b3fe75a8a89.pdf  Oral presentation and proceedings summary.

Shrefler, J., E. Rebek, K. Woodburn, G. Driever, and H. Stephens. 2016. Row cover for Squash Integrated Pest Management (IPM).  Organic Oklahoma 2016 Fall Conference.  October 6 and 7, 2016.  Oklahoma City.  Oral Presentation.  

Shrefler, J., G. Driever, K. Woodburn, E. Rebek and M. Taylor.  2017.  Row covers: An alternative means to pest control in cucurbits.  1st annual Texas Hispanic Farmer and Rancher Conference: Growing together, Creciendo Juntos. September 14-15, 2017, McAllen Texas. Oral Presentation.

Field Meetings

September 2015 – Field meeting at the Bixby location.  Handout provided.

September 2016 – Field meeting at the Bixby location.  

August 2016 - Field meeting at the Atoka location.  Handout provided.

August 2016 – Field meeting at the Shawnee location.  Handout provided.

Records of dates are not available but at Shawnee Master Gardeners visited the Shawnee trial location to learn about insect pest IPM.

Learning Outcomes

80 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation
Key changes:
  • As mentioned in the “Impact of the Results/Outcomes” section, the project has heightened the awareness among growers and gardeners of the possibility of using row covers to exclude insect pests from cucurbit crops. In addition, as a result of working with row covers, we have learned of additional benefits to using this cultural practice in vegetable crop production that are being further evaluated.

Project Outcomes

Project outcomes:

Impacts

Promising results were obtained in the first year of this two year project.  This was so even though the original intention was to address pest management with earlier planting.  It will be important to compare results over years to determine responses to the treatments are consistent. 

Outreach events were held at two of the trial locations in 2015.  At the other location only individual visits with growers and Extension Educators were held. 

Results of the first year were presented at a regional grower oriented horticulture conference and at an Oklahoma vegetable grower outreach meeting.  HIS Proceedings article

Educating growers and gardeners on the management of cucurbit insect pests has been a long-term effort among entomologists and horticulturists in Oklahoma.  Extensive research has been conducted in the state over many years to address this issue.  The interest in conducting this project arose in part from the project director’s interaction with many growers who were in search of more effective control options for these insects, and in particular the squash bug. During the course of the study the project has enabled more interaction and discussion among growers and agriculturists on management of squash bugs.  Previously published recommendations for using row covers to exclude this insect pest from cucurbit crops leaves growers with questions regarding when to remove the covers.  The results of the trial do not provide a concise recommendation that provides an answer to this question.  However, we now have a better understanding of the factors that should be considered in future studies, such as providing a specific pollinator insect at the location of the trial.  Several growers, after hearing about this work, say that they are trying covers as a means of excluding squash insect pests.  This interest in the concept will help generate a knowledge base among growers.  This is a good time for this to happen because row cover materials have recently become more readily available in retail outlets to small scale growers and gardeners.

Accomplishments

Three trials were conducted in 2015 and each was located within an important production region in the state. Of the five treatments that were evaluated, one that employed daily cover removal during morning hours resulted in squash yields comparable to those of a treatment that used only insecticides and no row covers.  Yields appeared to be lower with the current practice of using row covers up until initiation of flowering, at which time covers are removed completely. 

This research hinges greatly on pollinator biology and behavior. Results were comparable for two trial locations that had similar pest incidence.  For these same locations there were differences in pollinator species presence.  This is important in that it emphasizes the importance of pollinator diversity in the development of pest management practices that may also influence pollinators which are critically important for cucurbit crops.

Recommendations:

Farmer Adoption

As mentioned in the “Impact of the Results/Outcomes” section, the project has heightened the awareness among growers and gardeners of the possibility of using row covers to exclude insect pests from cucurbit crops.  In addition, as a result of working with row covers, we have learned of additional benefits to using this cultural practice in vegetable crop production that are being further evaluated. 

Areas Needing Additional Study   

Additional research is planned to compare row cover materials for use in insect exclusion.  One drawback to the material chosen for this study is that it did not enable viewing crop condition and insect pests without opening or removing the cover.  Comparisons of the treatments we studied should be made for specific planting seasons.  Due to the complexity of the current study we establish trials as field conditions, weather and investigator schedules permitted.  For treatments that involved daily opening and closing of covers more research is needed to determine whether the effectiveness of this approach may be dependent on specific pollinators.

Economic Analysis

We have not conducted an economic analysis.  In general, the use of row covers has associated costs including the cost of materials (cover supports and fabrics) and the added labor. However, if the use of insecticides is not an option, the use of row covers is a viable alternative to be considered.

References

Bolin, P. and L. Brandenberger (eds.).  2001.  Cucurbit integrated crop management.  Oklahoma Cooperative Extension Service E-853.  Oklahoma State Univ., Stillwater, Okla.

Cartwright, B., J.C. Palumbo and W.S. Fargo.  1990.  Influence of crop mulches and row covers on the population dynamics of the squash bug (Heteroptera: Coreidae) on summer squash.  J. of Econ. Entomol. 83(5) 1988-1993.

Hardesty, Shermain. 2008. The growing role of local food markets.  Amer. J. Agr. Econ. 90(5) 1289-1295.

Layton, Blake. 2015. Unpollinated squash.  Bugs Eye View Number 13. http://extension.msstate.edu/newsletters/bugs-eye-view/2015/unpollinated-squash-no-13

McLeod, Paul. Identification, Biology and Management of Insects Attacking Commercially Produced Vegetables in Arkansas. http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.616.241&rep=rep1&type=pdf

Riley, D., J.V. Edelson, M. Miller, G. Cuperus, R. Roberts, N. Roe, and J. Anciso.  1997.  Integrated pest management in cucurbit crops in the south central U.S.:  Pest status, attitudes toward IPM and a plan for implementation.  USDA / CSREES, IPM Implementation Special Program report.

Shrefler J. and L. Brandenberger. 2014. Use of plastic mulch and row covers in vegetable production. Oklahoma Cooperative Extension Service.  Fact Sheet HLA-6034.  http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-1099/HLA-6034web2014.pdf

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Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.