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Hector R. Valenzuela and Randall Hamasaki

Experiments were conducted to evaluate the effect of two different compost materials and several compost: synthetic N fertilizer ratios on the growth, yields, and nematode infestations in head and semi-head lettuce, and basil. Treatments were homemade compost at 25 MT/ha, Amend compost at 25 MT/ha, N alone at 150 kg·ha–1, and Amend compost at 25 MT/ha plus 0, 100, 200 or 300 kg N/ha. The basil trial followed the lettuce experiment on the same treatment beds to evaluate the long-term effects of compost applications. Compost plus 100 kg N/ha resulted in the greatest yields of 12 to 24 MT/ha for the semi-head and head lettuce trials, respectively. Basil was harvested for 6 months during a 10-month growth cycle. Highest basil yields of 64 MT/ha and canopy growth were obtained with a combination of compost plus synthetic N fertilizer, with 300 kg N/ha required for maximum yields during the 6-month harvesting period. By the last sampling date nematode counts were lowest for plots that received compost treatment alone and highest for the controls and for plants receiving synthetic N fertilizer alone.

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Hector R. Valenzuela and Joseph DeFrank

Living mulches offer a low-input alternative to achieve weed control while minimizing herbicide applications, decreased fertilizer leaching, insect and nematode management. and improved soil texture. A study was conducted to evaluate the effect of a Rhodes Grass (Chloris gayana cv. Katambora) living mulch on the growth and productivity of ten eggplant. Solanum melongena, cultivars grown under fertigation. The living sod was established at the Univ. Hawaii Waimanalo Experiment Station in June 1992. Soil analysis was taken before experiment initiation. Ten eggplant cultivars were transplanted on both living-mulch and control (woven-polyethelene mulch) plots on 4 March 1993. Weekly or bi-weekly harvests were conducted for six months. beginning on 19 May 1993. In addition plant height and canopy dimensions were determined on 16 April. and 10 Nov. Plant growth was monitored throughout the experiment. Soil samples were taken from the eggplant rhizosphere, hare-ground and in Rhodes grass monoculture, for nematode count determinations. Soil samples were also taken for nutrient determination after completion of the experiment. Overall yields were greater in the polyethelene mulch than in the living mulch plots. A differential response was observed on the response of cultivars to cropping system. However the most vigorous cultivars performed well in both systems. The living mulch system showed potential for nematode management in eggplant agroecosystems.

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Hector R. Valenzuela, Joseph DeFrank, and Greg Luther

The diamondback moth (DBM). Plutella xylostella, is the number one pest of cabbage in the the world. The pest is resistant to most pesticides registered for its use, and resistance has also been detected in several areas for registered biopesticides. Four experiments were conducted to: 1) Determine the tolerance to DBM feeding among 20 commercial head cabbage cultivars, 2) Evaluate the effect of three nitrogen fertility levels on DBM numbers. and 3) Evaluate the effect of Indian mustard. Brassica juncea trap crops as a tool to manage DBM populations in head cabbage agroecosystems. Experiments were conducted at University of Hawaii experiment stations located in Kamuela. Hawaii, and in Kula, Maui. The trap crop treatments consisted of planting two border rows of Indian mustard in cabbage field borders. Three or 4 biweekly insect counts were conducted for each trial. Insect counts consumed of destructive sampling of 3-6 plants per plot and determination of larvae and pupae number and parasitation levels. The nitrogen studies found more DBM in monoculture cabbage receiving 300 kg Ha-1 N than in controls even though cabbage yields did not vary among treatments. A range of tolerance to DBM feeding was found among the cultivars tested. The trap crop system was shown to be more effective during the summer than in the winter months. Data indicates that the trap crop also acted as attractant for beneficial insects, which may aid in the biological control of DBM in cabbage

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Hector R. Valenzuela, Osamu Kawabata, and Harry Yamamoto

Methanol sprays reportedly increased yields of several crops in Arizona by 50 to 100 percent (Nonomura and Benson PNAS 89:9794(1992). Reports from other parts of the country have shown conflicting results with regards to the effect of methanol sprays on yields of horticultural crops. Several greenhouse and growth chamber (controlled temperature. day length, and photosynthetic photon flux) experiments were conducted to evaluate the effect of methanol sprays on the growth and productivity of several vegetable crops in Hawaii. Treatment spray solutions consisted of 20-25% methanol, 0.5% low biuret urea. 0.001% chelated iron, and 0.02% surfactant. Control sprays only contained urea, chelated iron, and surfactant. Each experiment consisted of at least 5 weekly methanol sprays. Flowering cabbage, Brassica campestris var. parachinensis, had greater biomass production when sprayed with methanol in the late summer months. Similar results were obtained with choi sum in a 2 by 2 factorial experiment with methanol and water stress treatments. However, choi sum did not respond to methanol treatments in follow-up greenhouse trials. perhaps attributable to the shorter and Overcast days experienced in the fall and winter. Okra, chili pepper, and eggplant showed no response to methanol sprays. Okra showed a trend toward increase yields in response to methanol sprays, but differences were not significant. Follow-up studies in the greenhouse and in the field, which include evaluation of photosynthetic efficiency through chlorophyll fluorescence determinations will be presented.

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Hector R. Valenzuela, Bruce Schaffer, and Stephen K. O'Hair

Net gas exchange and growth were determined for cocoyam [Xanthosoma sagittifolium (L.) Schott] growing in 30%, 50%, and 100% sunlight and fertilized with 0 or 475 mg N/kg nutrient solution. Interactions between N and shade were observed for lamina area per plant, top : corm ratio, corm weight, transpiration (E), stomatal conductance (g,), and lamina N and chlorophyll concentrations. When N treatments were pooled, shade-grown plants (30% and 50% sunlight) had greater lamina areas, lamina and petiole biomass, top: corm (fresh weight) ratios, and corm fresh weights than plants grown in full sunlight. All of these criteria also had higher values for plants that received the N-fertilizer solution (+ N) than for plants that received the N-free solution (- N), when shade treatments were pooled. When N treatments were pooled, 100%-sunlight plants had greater net CO2assimilation (A) rates than shade plants. Water-use efficiency (WUE), A, g., and E for 100%-sunlight-grown plants were higher for + N than for - N plants. For shade plants, however, A and E were similar between N treatments. When N treatments were pooled, shade plants had a greater lamina chlorophyll concentration on a dry-weight basis than 100%-sunlight plants, whereas content on an area basis was similar among shade treatments. Among shade treatments, chlorophyll contents on an area and dry-weight basis were higher for + N than for - N plants. Plants grown in 100% sunlight had higher lamina N concentrations (area and dry-weight bases) than shade plants. The interactions between N and shade showed that cocoyam response to N depends on incident photosynthetic photon fluxes during growth.

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Hector R. Valenzuela, Stephen K. O'Hair, and Bruce Schaffer

Cocoyam was grown in 100%, 50%, or 30% daylight to determine the effect of light intensity on growth characteristics at various stages of plant development. Beginning ≈ 2 months after planting, growth was monitored at three or four monthly intervals. Plants grown in shade had more petiole and leaf lamina growth and extension, as well as increased top: corm plus cormel ratio (dry-weight basis), than plants grown in 100% daylight. Shade-grown plants had a higher leaf area index and specific leaf area than sun-grown plants. Sun-grown plants had a higher net assimilation rate and specific leaf density than shade-grown plants. Linear equations were developed to predict lamina area through measurements of leaf lamina width and length, petiole length, and lamina dry weight.

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Hector R. Valenzuela, Stephen K. O'Hair, and Bruce Schaffer

The effects of shade during leaf development on photosynthetic activity of cocoyam [Xanthosoma sagittifolium (L.) Schott] were investigated. Net gas exchange and N and chlorophyll concentrations were determined for cocoyam leaves growing in 30%, 50%, or 100% sunlight. Net CO2 assimilation (A) and water use efficiency (WUE) were greater for plants grown in 100% sunlight than for plants grown in less sunlight. Substomatal CO2 concentration increased with increased shading. Stomatal conductance (gs) and transpiration (E) did not vary significantly among treatments. Diurnal paterns for A were positively correlated with gs, lamina temperature, relative humidity, and photosynthetic photon flux (PPF). Lamina N concentrations, determined on lamina dry weight and lamina area bases, increased with increased PPF. Shade plants (30% and 50% sunlight) had greater chlorophyll: N ratios (dry-weight basis) and greater lamina area: lamina dry weight ratios than 100% sunlight-grown plants, which indicates increased photosynthate and N allocation to leaves of shade plants and maximization of light interception.