Date of Award:

1-1-2010

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Plants, Soils, and Climate

Advisor/Chair:

Daniel T. Drost

Abstract

Producing red bell peppers in high temperature and light environments can be challenging because many new semi-indeterminate varieties produce small plant canopies that leave fruit exposed to damage (sunscald) caused by solar radiation. Pepper production in Utah coincides with high air temperatures and solar radiation levels during July, August, and September. Increasing plant canopy size is one way to protect fruit from solar radiation. Low tunnels optimize plant growth by increasing air and soil temperatures. Growing plants under low tunnels early in the season could increase fruit shading later in the season. Another way to protect fruit is by using mechanical shade. Hanging shade cloth over a crop has been shown to decrease air temperatures and solar radiation levels reaching fruit. While the common production practice is to horizontally orient shade cloth, vertically orienting shade cloth may also be effective by providing shade to the crop in the morning and evening.

These protection methods were evaluated in Layton, Utah for effectiveness of increasing yield by decreasing sunscald occurrence. While plants grown under low tunnels for two weeks after transplanting had larger canopies, they did not increase yield or decrease sunscald compared to plants not grown under low tunnels. Vertical shade increased yield and decreased sunscald most effectively when combined with plants grown under low tunnels. Vertical shade protected exposed fruit when the sun was at lower elevations while increased canopy shade protected fruit when the sun was at high solar elevations. Horizontal shade completely eliminated sunscald and produced the largest yields of high quality fruit. The additional costs associated with using supplemental shade were offset by increased yields and higher value of larger fruit.

Separate studies were carried out to determine how sunlight and wind influence the temperature of pepper fruit. Sunlight exceeding 550 W·m-2 increased pepper fruit surface temperature (FST) to damaging levels. Wind decreased pepper FST but moderate wind speeds (3.0 m·s-1) did not decrease it below damaging levels. To insure protection, growers should apply supplemental shade when solar radiation levels exceed 550 W·m-2. These results provide improved guidelines for growers interested in using supplemental shade to provide pepper fruit for local and national consumption. Additionally, pepper growers in high air temperature and light environments can increase productivity and profitability with the use of supplemental shade.

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