Search Results

You are looking at 41 - 50 of 910 items for :

  • All content x
Clear All
Free access

Alfonso Hernández-Barajas, José Luis Vera-Medina, and Dr. Benito Alvarado-Rodriguez

During a two-year-period, a study was made in the field in order to know the ocurrence of aphids in the broccoli crop. It was possible to know that the total aphid population is higher in winter plantings where more than 240 aphids/plant were found Spring and fall plantings, in comparison, less than 20 aphids/plant were encountered. The species more common were the cabbage aphid (Brevicoryne brassicae L.), the most prevalent species in the crop, getting more than 80% of the population, and the green peach aphid (Myzus persicae Sulzer) with a little bit more than 17% of the total. The natural parasitism in all plantings was around 17%. By species, parasitism in B. brassicae was higher in springs (70% of the total) and fall plantings where the parasitic wasp Diaretiella rapa e (MacIntosh) was probably more active. The sane pattern was obtained for M. persicae, in which the parasitism was again higher in spring and fall plantings (20% of the total) and very low during the winter. Regarding leaf preference, a very defined pattern was found in the M. persicae than for B. brassicae.

Free access

F. Todd Lasseigne, Timothy J. Smalley, Harry A. Mills, and William P. Miller

Ilex crenata `Helleri' (Helleri holly) can experience landscape establishment problems in the Southeast. Since aluminum toxicity is a major problem in acid soils of the Southeast, this experiment studied the effects of aluminum on Helleri holly grown in solution culture. A modified Hoagland's solution contained low phosphorus concentrations (32 μM), a 1:1 NH4+:NO3 - nitrogen ratio, and aluminum treatments consisting of 0, 222, 444, 889, and 1332 μM Al supplied at equal ratios from AlCl3·6H2O and Al2(SO4)3·18H2O. The MINTEQA2 (version 3.11) chemical speciation model was used to predict activity of ions in solution. Shoot growth and root length were not affected by aluminum after 12 weeks in solution culture. Total plant nutrient uptake was monitored weekly. Results indicate that Helleri holly does not take up aluminum ions even though NH4 + is the preferred nitrogen source. Other studies have shown increased aluminum toxicity effects when NH4 + is the preferred nitrogen source.

Free access

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

Free access

D.I. Leskovar, L.A. Stein, and F.J. Dainello

This study was conducted to determine the effect of within-row plant spacing and mulching on growth, quality, and yield of an experimental semi-savoy spinach (Spinacia oleracea L.) genotype `Ark-310' to produce a high-quality fresh-market product. Spinach transplants were established in the field on 13 Nov. 1995 and 3 Dec. 1997. Within-row spacings were 15 and 25 cm, and mulching treatments were bare-soil and black polyethylene mulch. Plants were destructively sampled weekly (1996) or bi-weekly (1998) for leaf area (LA), leaf number, leaf dry weight (LDW); and root dry weight (RDW) measurements. Plants grown on plastic mulch at 25-cm spacing had the greater LA, LDW, and RDW than when grown at 15-cm spacing on mulch or bare-soil. Leaf number and specific leaf area (LA/LDW) were less affected by either spacing or mulching. The amount of soil on harvested leaves was lowest on plants grown on plastic mulch in both years. In one year, total yields (MT/ha) were 42% higher when plant spacing decreased from 25 cm to 15 cm, while mulch increased yields by 20 %, a response that was independent of plant spacing. These effects were not evident in the year with higher rainfall. It appears that for a root-cut or loose leaf spinach, yield efficiency and product cleanliness of `Ark 310' spinach may be further improved by combining high plant density with efficient irrigation and fertilization programs under mulch and drip.

Free access

Daniel I. Leskovar, Larry A. Stein, and Frank J. Dainello

The objective of this work was to determine the effect of within-row plant spacing and mulching on growth, quality, and yield of an experimental semi-savoy spinach (Spinacea oleracea L.) genotype `Ark-310' to produce a high quality fresh market product. Within-row spacings were 15 and 25 cm, and mulching treatments were bare-soil and black polyethylene mulch. Plants were destructively sampled weekly (1995-96) or bi-weekly (1997-98) for leaf area (LA), leaf number, leaf dry weight (LDW) and root dry weight (RDW) measurements. Plants grown on plastic mulch at 25-cm spacing had greater LA, LDW, and RDW than when grown at 15-cm spacing on mulch or bare-soil. Leaf number and specific leaf area (LA/LDW) were less affected by either spacing or mulching. The amount of soil on harvested leaves was lower on plants grown on plastic mulch in both years. In one year, total yields (MT/ha-1) were 42% higher at 15-cm than at 25-cm plant spacing, while mulch increased yields by 20%, independently of plant spacing. These effects were not evident in the year with higher rainfall (1997-98).

Free access

José A. Franco, Víctor Cros, Sebastián Bañón, Alberto González, and José M. Abrisqueta

The influence of two irrigation treatments during nursery production on the post-transplant development of Lotus creticus subsp. cytisoides was studied. The treatments lasted 96 days and consisted of irrigating 2 days/week with a total of 2.3 L of water per plant over the whole nursery period (T-2) or irrigating six days per week with a total of 7 L of water per plant (T-6). T-2 plants had greater root length: shoot length ratio and higher percentage of brown roots, an indicator of more resistance to post-transplant stress. Minirhizotrons revealed more active root growth in the surface soil of the T-2 plants, although the plants of both treatments rapidly colonized the whole soil depth studied (0-160 cm deep). T-2 plants had greater stem length growth per unit of soil area covered.

Free access

Shann Tanner, Christina Wells, and Gregory Reighard

The effectiveness of soil solarization as an alternative to methyl bromide (MBr) fumigation in replanted peach orchards was investigated at the Musser Fruit Research Farm near Clemson, S.C. A split plot experimental design was used, with soil treatment as the whole-plot factor and rootstock as the sub-plot factor. In Spring 2002, preexisting trees were removed from the study site, and six orchard rows were cultivated and subsoiled. In June, two rows were covered with clear polyethylene sheeting and solarized for the remainder of the summer. In November, two additional rows were treated with MBr (474.3 kg·ha-1), while the two remaining control rows received no soil sterilization treatment. In Jan. 2003, 36 `Redglobe' peach trees budded on Guardian™ or Lovell rootstock were transplanted to the site, and one minirhizotron was installed beneath each tree. Minirhizotron observations were made every 14–21 days from Feb. through Oct. 2003, and stem caliper measurements were taken on four dates during this interval. Trees grew significantly larger in the MBr and solarized rows than in the control rows (P< 0.1; Tukey's hsd), but there were no differences in stem caliper growth between MBr and solarization-treated trees. Reduced aboveground growth in control trees may have been related to greater carbon expenditure belowground: in the absence of soil sterilization, fine root median life spans were reduced by 27–28 days (P< 0.0001; proportional hazards regression) and rates of root production and mortality were significantly higher (P< 0.1; repeated measures ANOVA). Solarization and MBr fumigation appeared to provide similar benefits in reducing root turnover and improving aboveground growth at this site.

Free access

Timothy K. Broschat

All leaves from 10 replicate Cocos nucifera L. `Malayan Dwarf' (COC) and Phoenix canariensis Chabaud (CID) trees were sampled for leaf nutrient analysis. In addition, the leaflets of the youngest fully expanded leaves and the third oldest leaves were divided into five groups along the primary leaf axis and these leaflets were then cut into thirds to determine nutrient distribution patterns within leaves and leaflets. Nutrient remobilization rates were calculated for N, P, K, Mg, and Mn. Results showed that N, P, and K were highly mobile within and between leaves of both species of palms. Up to 31% of the N, 66% of the K, and 37% of the total P in the oldest leaves were ultimately remobilized to newer leaves within the palm. Magnesium remobilization rates averaged ≈71% for CID but only ≈10% for COC. The middle-aged leaves appeared to be the primary sink for Mg in COC, rather than the youngest leaves as in CID. Manganese was also quite mobile in both species, with up to 44% of the total Mn remobilized in CID. Samples consisting of recently matured leaves were determined to be the most appropriate for Ca, Fe, Mg (COC only), and Zn, but oldest leaves are more suitable for N, P, K, and Mn analysis.

Free access

Nicole E. Burkhard, Derek H. Lynch, and David C. Percival

Within-row weed management of highbush blueberry (Vaccinium corymbosum L.) is reliant upon herbicide applications. However, in organic production, herbicides are typically not permitted and alternative methods must be used. The impact of thick (25-cm) mulch applications on weed pressure in an organic production system was initiated at a commercial operation in Nova Scotia, Canada, during 2005. A split-plot experimental design was used with five blocks (replications), six treatments, and five plants per split plot (cv. Duke). The whole-plot factor consisted of mulch/fertility treatments and included: i) control (no amendment); ii) ammonium sulphate fertilizer (30 kg·ha-1 N); iii) pelletized poultry manure (60 kg·ha-1 N); iv) pine needles (80 t·ha-1); v) horse manure and sawdust compost (550 t·ha-1); and vi) seafood waste compost (360 t·ha-1). The split-plot factor consisted of level of hand weeding (–/+). Weed control was assessed by sampling percent ground cover and weed shoot biomass in three 0.25-m2 quadrats in nonweeded subplots. Blueberry leaf N content, plant canopy volume, and berry yield (fresh weight and number) were recorded. The manure/sawdust compost and pine needle treatments had the lowest weed biomass and percent ground cover values, thereby providing the best weed control. Weed shoot biomass, blueberry leaf N, plant canopy volume, and berry yield were greatest in the seafood waste compost treatment. Results from this preliminary study indicate the potential of using these groundcover treatments to improve organic cultural management practices.