Richard A. Ashley

Interference of large crabgrass (Digitaria sanguinalis), redroot pigweed (Amaranthus retroflexus ), and hairy galinsoga (Galinsoga ciliata) with bell pepper

Abstract Large crabgrass, redroot pigweed, and hairy galinsoga are three important weed species in bell pepper and other crops in the northeastern United States. Field experiments were conducted in 1998 and 1999 to determine the influence of density and relative emergence time of the three weed species on bell pepper fruit yield. Densities of 0, 1, 2, 4, 8, 16, and 32 plants m−1 row were established for each weed species from naturally occurring weed populations. The effects of relative emergence time were studied by investigating the different yield responses to weeds emerging at two different times: 3 d or 2 wk after transplanting of pepper. Both weed density and relative emergence time affected pepper yield loss. The relative competitive ability of weed species varied between years. Large crabgrass was the most competitive species in 1998 and the measure of yield loss at low weed densities, I, was estimated to be 34% on the basis of the nonlinear hyperbolic equation. Redroot pigweed was most competitiv...

Effect of Trap Position, Habitat, and Height on the Capture of Pepper Maggot Flies (Diptera: Tephritidae)

Abstract Trapping results indicate that pepper maggot, Zonosemata electa (Say), flies occupy tree canopies adjacent to fields when not on host plants. Several in- and near-field trap positions were used to find a reliable monitoring system for adult pepper maggots. Traps baited with liquid ammonium hydroxide (Stills-style trap), hung in the canopy of trees on the edges of pepper fields, caught significantly more Z. electa flies than when positioned lower along the treeline or in the field. In a second experiment, significantly more pepper maggot flies were captured in sugar maples compared with choke cherry trees, which indicates a pest preference for certain nonhost habitats. The lowest trap height tested (2.1 m) failed to capture Z. electa flies in either tree species when the pest population level was low. These studies demonstrated that pepper maggot flies can be reliably detected with Stills-style traps positioned at ≈6.4 m height within the canopy of sugar maple trees adjacent to pepper fields. Fruit oviposition scars also are useful site-specific indicators of pepper maggot presence/absence and may aid in determining if insecticide applications are necessary and in timing sprays.

The potential use of plant physiological responses to water stress as an indication of varietal sensitivity to drought in four potato (Solanum tuberosum L.) varieties

Four potato varieties were subjected to water stress under controlled conditions. Leaf relative water content, leaf diffusive resistance, and photosynthesis were measured on stressed and unstressed plants during a stress period and during the recovery period following stress relief. Subsequent to the stress, plants were grown to maturity with optimal water supply. Mature plants were harvested and tuber yield and haulm production measured. Stressed plants of all varieties exhibited an increase in leaf diffusive resistance and a decrease in relative water content, transpiration, and photosynthesis as soil moisture decreased. Significant varietal differences in leaf diffusive resistance of stressed plants are apparent and offer promise for development of a screening technique for varietal sensitivity to drought based on stomatal response to water deficits.ResumenCuatro variedades de papa fueron sometidas a estrés de agua bajo condiciones controladas. El contenido relativo de agua en hoja, la resistencia a difusión en la hoja, y la fotosíntesis fueron medidas en plantas bajo estrés y sin ella durante el periodo de recuperation. Posterior a la estrés, las plantas fueron mentenidas hasta su madurez en condiciones de óptima suplementación e agua. Las plantas maduras fueron cosechadas midiéndose el rendimiento en tubérculos y parte aérea. Las plantas sometidas a estrés de todas las variedades exhibieron aumento en resistencia a difusión en la hoja y disminución en contenido relativo de agua, transpiración y fotosintesis al dismunuir la humedad del suelo. Diferencias varietales significativas en resistencia a difusión en la hoja de plantas bajo estrés son promisorias para utilizarlas como técnica de selectión en sensibilidad varietal a sequia basándose en la respuesta de los estomas a deficiencia de agua.