Introduction

Demand for fresh, local, and high-quality produce is increasing in the Northeast (Bloom et al., 2018). With climate change exacerbating many abiotic stresses, including heat, drought, flooding, and the increase in the frequency of extreme weather events, it is imperative to investigate adaptation tactics for successful vegetable production. 

A general warming trend is predicted by climate models in a high CO2 scenario, punctuated by drought, heat waves, flooding and rainfall intensity, and fewer frost days. In North America, New England is losing its snow cover at the fastest rate (Young, 2023). Heat stress is of particular concern in the Northeast, with heat waves projected to increase in frequency in Connecticut by up to eight per year by 2050. Interestingly, frost and freeze events are also of concern in this region, as we witnessed this past spring. Immense crop loss can result from unexpected or unseasonable drops in temperature (Anyah et al., 2019). Such stresses amplify concerns regarding crop growth, pollination, pest and disease pressure, and yield and quality of marketed produce. There are tactics for adaptation that show promise and warrant further investigation and discussion. The use of tools such as tunnels, row covers, insect netting, shade cloth, synthetic mulches, landscape fabrics, and tarps create controllable microclimates, mitigating some negative effects of the aforementioned abiotic stresses and putting the power back into the grower's hands. In this article, we will explore each tactic in detail and their potential benefits and drawbacks. 

High, caterpillar, and low tunnels

High tunnels, also known as hoop houses or polytunnels, are typically covered with a translucent polyethylene film and have a frame made of metal or PVC pipes. They trap heat from the sun which allows early planting in the spring and late harvests in the fall, and frequently result in an increase in crop yields. High tunnels also shield plants from adverse weather conditions like heavy rain, hail, or strong winds, reducing the risk of crop damage. These structures can also deter certain pests and diseases, reducing the need for chemical interventions (Janke et al., 2017).

Caterpillar tunnels, also known as low-cost tunnels or mini-tunnels, are smaller and more affordable versions of high tunnels. They consist of metal hoops covered with plastic sheeting. Caterpillar tunnels are easy to assemble, making them accessible to small-scale growers. These tunnels can be moved to different locations to allow for crop rotation. 

Low tunnels are the most basic form of tunnel structure. They consist of hoops or arches made of wire or plastic, covered with plastic sheets. Low tunnels provide localized protection, creating a unique microclimate for individual rows or plants. This is especially useful for frost-sensitive

crops. They effectively shield crops from insects and birds without the need for chemical pesticides. Low tunnels can extend the growing season in smaller, targeted areas.

Row cover and insect netting

Row covers are synthetic, spun-bonded fabrics that are placed over crops to create a microclimate, typically to retain heat, increase humidity, exclude pests, and protect sensitive crops from frost or freeze. They can be used as "floating" row covers that are placed directly over crops such as brassica, lettuce, greens, onions, and sweet corn, or draped and secured over wood, metal, or PVC supports for crops that have tender and exposed growing points such as tomatoes, peppers, and vining crops. Insect netting, such as Proteknet or other similar materials, can be used in the same fashion as row cover. However, insect netting is specifically for excluding insect and bird pests and does not provide the same temperature control as row cover (McDermott et al., 2020). Insect netting is a great alternative to ensure pest exclusion when the use of row cover would cause excessive heating. 

Row cover comes in heavy, medium, and light weights. Heavier weights are thicker, more durable, and can be used to increase temperatures by up to 8°F (Traunfeld, 2023). Such temperature increase can push plant growth along significantly during cooler periods of the growing season, or when fast, vigorous plant growth is preferred. Protection to about 25°F is possible with a heavy-weight material (Hochmuth, 2022). Medium and lightweight row covers can be used during warmer periods when coverage is needed for pest control and lightweight covers can be kept on from transplant to harvest, dependent on ambient temperatures (Mahr, n.d.).  Row covers must be removed at bloom for fruiting crops to encourage bee or wind pollination.

Row covers have been found to enhance the yield of a crop, primarily through temperature and humidity moderation (Hochmuth, 2022). Such moderations can result in earlier production of cooler season crops and increases in yield by up to 25% in some covered cucurbits (Helbacka, 2002). 

The efficacy and durability of row cover or insect netting are contingent upon its proper use (Bernitz, 2020). Some drawbacks of row cover or insect netting are the ease of use, excessive heating compared to ambient temperatures, and the quality of the material. Many who have implemented row cover will know well the struggles of using it. It can tear or rip easily, it gets picked up by the wind when attempting to install it, is an additional cost, and it lasts anywhere from one to three years but can be difficult to extend its life past a few growing seasons. Additionally, pests can become trapped beneath cover or netting, or pests that overwinter in the soil may emerge under the cover. Weed pests similarly will benefit from the use of row cover. Removal and replacement of the cover to cultivate or hand weed will be necessary for sufficient control. However, yield enhancements under row cover, in most cases, outweigh the negatives or drawbacks associated with its use.

Shade cloth

Another promising tactic is the implementation of shade cloth, either installed above field crops or over high tunnels/greenhouses. While shade cloth is manufactured in 10-90% densities, 30% density is typically used in our climate to assess the impacts of shade on crop productivity, soil moisture and temperature, and air temperature, and has shown promise in lowering ambient temperatures and reducing light intensity (Johnson, G. & Ernest, E., 2020). Continuous exposure of tomato truss to high temperatures (day/night temperatures of 90/79°F) significantly reduces the number of pollen grains per flower and decreases their viability (Pressman et al., 2002). Shade cloth can mitigate heat extremes and manage large fluctuations in ambient temperatures, especially affecting pollen viability and fruit surface temperature, the latter being an important factor in sunburn potential (Maughan et al., 2017). 

There are slight concerns regarding yield reduction, however, using the proper density shade at critical time periods can alleviate such concerns. Research suggests that timing the application of shade cloth during sensitive periods of fruit development can help reduce physiological damage and increase both yield and quality in certain crops (Maughan et al., 2017). While there typically is not a marked increase in the number of fruit, the quality and size of fruit is significantly improved compared to unshaded plants (Ernest, 2022). 

There is not an abundance of research testing the impacts of shade cloth on yield, marketability, and soil or air temperatures. This warrants further experimentation and is a developing area of interest. 

Synthetic mulches

Conventional polyethylene and biodegradable plastic mulches can be used in production to control weeds, soil moisture, soil temperature, and to increase crop yield. Additionally, these mulches generally provide erosion protection, and a reduction in nutrient/fertilizer leaching as well as evapotranspiration, leading to increased soil moisture (Gheshm, 2020). Different types of mulches have different results. Overall, mulches have been shown to manage fluctuations in temperature, while black plastic mulch raises soil temperatures, and white (or white-on-black) and silver mulches lower soil temperatures (Snyder et al., 2015). Plastic mulches (both polyethylene and biodegradable) have been shown to dramatically increase yield and nitrogen mineralization while having no negative effects on the marketability of the product (Samphire et al., 2023). 

Soil moisture regulation is a crucial element of using plastic mulches. This is achieved through the reduction of evapotranspiration from the soil surface through covering planted areas, which can be particularly advantageous in drier environments (Ma et al., 2018). 

While there are many advantages to implementing plastic or biodegradable mulch, there are still some disadvantages. For instance, mulches don't allow for natural soil cooling from precipitation, which can result in higher overall soil temperatures when compared to bare ground (Ghimire et al., 2020). The cost of mulch, both the material and time and labor necessary to install it, can be substantial to take on year after year, especially since mulches can't be reused. Thisleads us to the last downside-the environmental cost of using polyethylene mulches. Non-biodegradable mulches create extra waste on the farm and must be removed and disposed of properly. Removal of mulch can be frustrating since it requires specialized equipment plus a fair amount of hand labor. 

Biodegradable mulches, unlike polyethylene mulch, are tilled after use and will biodegrade in the soil. While they cost slightly more than conventional mulches, the savings would be substantial at the end of the season as the mulch removal and disposal costs are avoided. Before purchasing, users should verify that the biodegradable mulch product meets biodegradable mulch standards. Some relevant standards include EN 17033, ASTM D6400, ASTM D5338, and TUV-Austria OK Biodegradable Soil.

Current biodegradable mulch products do not meet National Organic Program (NOP) standards for use in certified organic systems.

Landscape fabrics

Landscape fabric has features similar to plastic film, but its durability permits multi-year (5-7 years) use, which would reduce excessive waste produced from the typical single-season use of polyethylene film. It conducts water and air and conserves them in the soil. It can be used in beds as well as in row middles. Controlling weeds in the row middles leads to a reduction of insect pests and diseases surviving in non-crop hosts. Seeing as they are bulky and generally require manual installation, they are primarily used in small areas such as high tunnels and garden-size plots. 

Tarps, solarization, and soil steaming

A black plastic tarp, commonly obtained as a silage cover, is applied to the soil surface for a duration of 3-6 weeks for multiple purposes. It can serve to establish a stale seed bed, terminate cover crops, regulate soil moisture, and elevate soil temperature. It smothers the weeds by obstructing sunlight and creates a warm and moist environment beneath it. Consequently, it fosters a vibrant soil ecosystem, promoting the presence of earthworms and beneficial bacteria, but can also attract small rodents and slugs. There are logistic challenges in using black plastic tarping, including applying and securing the tarps, moving them across fields, and potential water ponding.

Soil solarization can be achieved by using transparent plastic sheets and sealing their edges. By covering the prepared soil with transparent plastic during the hot summer months, from as short as one day to a few weeks depending on solar radiation levels, soil temperatures are elevated to levels lethal to numerous soilborne pests, pathogens, and weed seeds. Growers are also exploring other innovative tools such as soil steaming to combat soilborne pests, pathogens, and weed seeds, especially in high-value spaces such as high tunnels. These tools reduce reliance on chemical pesticides, making them environmentally conscious options.

Conclusion

The adaptation tactics discussed above demonstrate significant promise by offering effective solutions. The utilization of tools such as tunnels, row covers, insect netting, shade cloth, synthetic mulches, landscape fabrics, and tarps empowers growers to establish more controlled microclimates, effectively mitigating adverse effects and restoring control to the hands of the grower. While these methods do involve additional expenses, they consistently result in improved crop yields and enhanced quality. Growers should exercise their own discretion when incorporating these techniques into their farming plans. In closing, these strategies provide a practical means of addressing climate-related challenges in agriculture, enabling growers to optimize their yields and achieve higher-quality produce.

References

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