Document Type

Thesis - University Access Only

Award Date

2000

Degree Name

Master of Science (MS)

Department / School

Plant Science

Abstract

Along with wheat (Triticum spp.) and rice (Oryza sativa L.), com is one of the most important food crops produced in the world. As with any crop, many variables (climate, soil, moisture, etc.) can influence crop growth and final yield. Pests such as weeds and insects are examples of these variables. Yellow foxtail and western corn rootworm (WCR) are two major pests found in com production. Managing these pests, as well as many others, is necessary for successful production of corn. Foxtails (Setaria spp.) are a cosmopolitan weed species found throughout the temperate zones of the world. They are economically important weeds found in many corn fields. Today, 43 different species of foxtail can be found in the United States. The most common species found in the com belt region include green, giant, and yellow foxtail. In recent years, yellow foxtail has proven increasingly difficult to control. Corn rootworms (Diabrotica spp.) are among the most destructive insects attacking U.S. corn fields. Each year, large percentages of U.S. com acreage are treated for this pest. The larval stage is the most damaging stage in the insects life cycle. Larvae cause damage by physically feeding upon corn roots. This damage disrupts the normal flow of water and nutrients into the plant, and weakens the plant root system. In the com belt region, the western com rootworm causes the majority of the damage. Field studies were conducted to determine the effect that yellow foxtail competition has on com growth and yield and how nitrogen fertilizer may influence that competition. Plots were established near Morris, MN and Brookings, SD in 1995 and 1996. Treatment combinations consisted of four densities of yellow foxtail and two levels of nitrogen fertility. Several plant growth parameters were measured from both the corn and yellow foxtail at the V-6 and silking com stages, as well as at harvest. Final grain yield was also measured. Field studies also were conducted to determine how yellow foxtail and soil types influence western com rootworm populations. Plots were established near Brookings and Aurora, SD in 1995 and 1996. Treatments consisted of WCR eggs deposited in the soil at various distances from the com plant with yellow foxtail occupying the area between the WCR eggs and the com plants. WCR beetle emergence, head capsule widths, and several plant growth parameters, along with yield, were measured from July through October. As yellow foxtail densities increased, foxtail biomass also increased, however, individual plant weights and tillers/plant decreased as a result of the intraspecific competition. As a result of interspecific competition, com biomass, com plant height, corn plant greenness, and grain yield also decreased as yellow foxtail densities increased. Additional nitrogen helped to offset some of the competition between corn and yellow foxtail. Extra nitrogen resulted in com plants that were taller and greener, and these plants produced more biomass and yield. Competition from yellow foxtail coupled with climate stresses such as temperature and moisture, have more of a negative impact on corn compared to yellow foxtail pressure alone, when climate conditions are normal. Total WCR beetle emergence was greater from a soil with higher percentages of silt and clay than from a soil with more sand. Sandy soils have soil particles that are angularly shaped and are more abrasive and damaging to larvae as they migrate through the soil. Furthermore, sandy soils dry more easily than clays, resulting in larval dessication. On the other hand, WCR beetle emergence began sooner in the sandy soil than the silt-clay soil. Increased soil pore space and less water retention allows a sandy soil to warm faster than a heavier soil. A warm soil that is moist, but not saturated, will result in earlier egg hatch, faster development, and earlier emergence. More WCR beetles emerged from the corn only plots compared to the corn/foxtail plots. Furthermore, beetles began emerging sooner from the corn only plots. This suggests that yellow foxtail is an alternate host plant for WCR larvae, however it is a poor substitute for corn, the preferred host plant. Extended presence of yellow foxtail near the corn row seems to delay and/or suppress WCR beetle emergence, and results in beetles that are developmentally inferior (smaller head capsule widths).

Library of Congress Subject Headings

Corn -- Diseases and pests

Foxtail

Western corn rootworm

Corn -- Growth

Format

application/pdf

Number of Pages

143

Publisher

South Dakota State University

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