Vegetable production is an important component of various types of farms in Oklahoma and surrounding states and farm sustainability depends on achieving consistent production of a marketable crop to have continuity in the market. The long, warm growing season in the region makes cucurbits a well-adapted enterprise. However, cucurbit crops are not free of production risks, and a general hazard is that posed by insect pests. For some, effective control measure are available and typically involve the use of synthetic insecticide applications. For others, control measure can be either difficult to employ, of limited efficacy, or non-existent.
Recent research (Driever et al., 2016) showed that row covers can be used to exclude pests, and at the same time, provide crop assess to insect pollinators, thereby enabling production without using insecticides. Although effective, the material has several drawbacks, including high temperatures under cover that could interfere with fruit set, insect pest entry through open covers, and a high incidence of disease, such as powdery mildew. Thus, while the development of this pest management technique for cucurbit crops would add to the sustainability of farms in the region by improving the predictability of being able to product marketable cucurbits, we need to find a suitable row cover material that will not only exclude insect pests, but one that will be convenient to use, not be conducive to diseases, and be cost-effective.
We propose to compare several products for use as row cover for the explicit purpose of excluding insect pests from cucurbit crops, specifically squash.
We will determine the effectiveness for excluding insect pests, effects of cover materials on the incidence of diseases, and the influence of the row cover materials on crop microenvironment and light transmission.
We will conduct field trials over two years at two locations using the treatments: no row cover as an untreated control; a frost blanket type material; a woven mesh netting that is used for insect exclusion in the tree fruit industry; and a formed mesh material used for insect exclusion purposes.
Squash plants will be examined weekly for insect pest pressure, fruit set, disease incidence and other possible treatment effects.
We established the row cover trial at two locations in Oklahoma, Langston and Stillwater. The Langston site was a field planted previously in sweet potato and a cover crop of radish and clover. The Stillwater site was a vegetable garden that had been planted with tomatoes and other vegetable crops in previous years. Due to lack of space and poor weather in spring 2019, we had to modify Objective 3 and only plant squash once at both sites. Squash (‘Lioness’ summer squash) was planted in the center of each row, placing 12 seeds on 1-foot centers. Squash plants were later culled so that six healthy plants remained in each plot. Due to saturated field conditions, squash planting was delayed until late May at both research locations. Treatments consisted of the following: 1) heavy fabric – DeWitt row cover deluxe plus 1 oz material; 2) woven mesh fabric; and 3) light fabric – DeWitt row cover 0.5 oz material. Treatments were compared against control plots that remained uncovered. All treatments and the control were replicated three times for a total of 12 plots, each measuring 15 feet long by 4 feet wide. Each plot was covered with one of the three row cover fabrics corresponding to treatment, except for control plots which were left uncovered. Assail 30SG (acetamiprid) was applied at a rate of 5.3 oz/acre to plants in control plots for early season control of squash bugs and squash vine borer. These were protected with insecticide as a precaution against losing young plants under heavy insect pressure. A pre-emergent herbicide was applied at each site to reduce pressure from annual grasses and annual broad-leaf weeds.
Aluminum tubes measuring 1-inch diameter were bent to form a U-shaped frame. Three frames were erected in each treatment plot, one in the center and two at each end of the plot. Metal frames were secured to the ground by inserting each end into rebar, which was driven into the ground at a depth of 12 inches. Each type of row cover fabric was cut to sufficient length for full coverage of treatment plots and stretched over the metal frames, allowing enough slack to prevent tears. Row cover fabric was secured to the metal frames using 2-inch binder clips and covered on all sides with enough soil to prevent insects from crawling under the fabric.
At two weeks after flowering began (50% of squash plants with female flowers), row covers were opened on the long sides of each plot for a period of 2 hours every weekday morning (approximately 0700 to 0900 h) for a total of 3 weeks, allowing pollinators to access the flowers. Insect sampling occurred twice weekly after plants were just beyond seedling stage. Counts of squash bug eggs, nymphs, and adults were made for each plant within a plot, then summed across plants for each life stage. Other insects were recorded as they were encountered, including aphids, cucumber beetles, and squash vine borers. These insects were eliminated by hand removal to minimize interference with squash bug activity within each plot. Pollinators (e.g., squash bees) were also recorded as they were encountered. Insect counts were recorded in all plots throughout the summer, terminating in mid-August as squash plants began to senesce and not yield fruit. During fruit production, fruits that had reached marketable size were harvested from each plot approximately every 5 days. Marketable fruits were separated from culls (misshapen, damaged, etc.), and the total weight of marketable fruit was recorded for each plot. Harvested squash were donated to a local food bank.
We are in the process of refining our data analyses for the 2019 season. Preliminary results were different between the two study sites. At the Langston site, we did not find any significant differences among treatments and the control for season totals of squash bug eggs, nymphs, and adults. However, significant differences were found at the Stillwater site. For all life stages of squash bug, a greater abundance of insects was found in uncovered control plots compared to plots covered with the woven, heavy, and light fabrics. In the data table below, means within a column followed by the same letter are not significantly different (Tukey’s HSD, P ≤ 0.05, PROC ANOVA, SAS 9.4).
|Mean No. Squash Bugs (± S.E.)|
|Control||10.3 (1.2) a||184.3 (80.1) a||1439 (408) a|
|Heavy||3.3 (2.3) ab||91.3 (20.8) ab||180 (44) b|
|Woven||1.0 (1.0) b||11.3 (3.7) bc||275 (156) b|
|Light||0.7 (0.7) b||0.7 (0.7) c||67 (50) b|
Squash bug eggs were significantly reduced in all plots covered by row cover fabric compared to the control. For nymphs and adults, abundance was lower in plots covered by the woven and light row cover fabric compared to the control. Therefore, we observed a reduction of all squash bug life stages in plots covered by any type of row cover fabric tested at the Stillwater site. We are uncertain why no significant results were obtained at the Langston site. However, squash bug pressure was much higher at that site, and row covers were damaged several times (and subsequently repaired) when strong storm systems moved through Langston in early spring. These factors may explain the lack of statistical significance at the Langston site.
No significant differences were observed in the total weight of marketable fruit throughout the season, although marketable weight tended to be higher in plots covered by row cover fabric. This is one indication that the physiology of squash plants (e.g., photosynthesis) was not hindered under any of the row cover fabrics. On the other hand, these results indicate that even though row covers reduced pressure from squash bugs, overall yield of squash did not increase.
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