Browsing by Author "Morse, Ronald D."

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    Developing methods of strip cropping cucumbers with rye/vetch
    Ogutu, Maurice Okendo (Virginia Tech, 2000-11-20)
    The purpose of this research carried out in 1998 and 1999 was to develop methods for strip cropping of cucumbers with rye/vetch and black plastic mulch. Effects of planting methods, weed control measures, and cover crop management techniques on pest and beneficial insects, petiole sap nitrate-nitrogen, soil moisture, yields and economic viability were assessed. Four treatments, namely cucumber direct seeded in black plastic mulch on tilled bare ground (conventional); cucumber direct seeded in black plastic mulch laid over incorporated rye/vetch residue; cucumber direct seeded into no-till rolled rye/vetch; and seedlings transplanted into no- till rolled rye/vetch, were evaluated in a randomized complete block design. Weeds were controlled in half the plot by critical manual weeding and pre-emergence herbicides applied in the other half in all treatments except the conventional system. Three-week interval staggered plantings of buckwheat to provide flowers for adult beneficial insects were also evaluated. Results obtained indicate that rye/vetch habitat is more attractive to beneficial insects than cucumber beetles before rolling or flail mowing. There were higher densities of adult Diptera (an indicator for Tachinid parasitoids) in both years and of Pennsylvania leatherwings in 1999 in plots with rye/vetch than in plots with rye only before planting. Preferential attraction to adult Diptera was not found after planting with no differences in cumulative densities between no-till and black plastic mulch plots after rolling or flail mowing. However, adult Diptera densities were positively correlated with cucumber yield, higher densities of cucumber beetles occurred in black plastic mulch than in no-till plots in both years, and bacterial wilt, transmitted by cucumber beetles, was reduced in no-till in 1999. Similarly, rye/vetch habitat plots had a higher diversity of Carabidae species (in both habitat areas and crop rows) before rolling or flail mowing, and higher densities of Carabidae (in habitat areas), Staphylinidae (in both habitat areas and crop rows) and spiders (in crop rows) after rolling or flail mowing. Black plastic mulch plots with flail mowed, incorporated rye/vetch residues had higher petiole sap nitrate-nitrogen and higher early season cucumber plant dry weights than in conventional plots; later in the season, the highest petiole sap nitrate-nitrogen occurred in no-till plots. No-till had higher marketable cucumber yield than plastic systems. The profitability of these production systems depended more on differences in marketable yield than on cost differences. The plastic with incorporated rye/vetch and no-till transplant systems were more profitable during early harvests in late July, while no- till direct seeded and transplant systems were more profitable from early August onwards. The three-week interval staggered planting of buckwheat led to conservation of beneficial insects, and the second and third seeded buckwheat flowering periods coincided with the period vetch had lost flowers.
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    The effect of maleic hydrazide in controlling plant populations in the strawberry in southwest Virginia
    Gingras, Rene Joseph (Virginia Tech, 1977-08-15)
    The effects of Maleic Hydrazide (MH) in controlling strawberry plant populations were studied. Foliar applications of MH at 1000 ppm resulted in reduced runner length. The effect of MH sprays appeared to be directly related to the stage of rooting at the time of spray applications. Rooted plants were affected less than non-rooted plants. By the end of the growing season (Oct. 31) plant populations were significantly less than the control (matted row) and equaled that of a hand thinned treatment. Sprayed and hand-pruned plots were significantly lower in yield and fruit number. Berry size was the same for all treatments.
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    Effect of Poultry Litter-Yard Waste Compost Application on Phosphorus Availability in Diverse Soils
    Mankolo, Regine Ndole (Virginia Tech, 1997-10-08)
    Land application of poultry litter has been successfully practiced for centuries to maintain and improve soil fertility, although over application may promote loss of nutrients through runoff or leaching. To decrease the potential for adverse environmental impacts of N and P in groundwater, a new approach developed in this research was to use a composted mixture of poultry litter (PL) and yard waste (YW) as a soil amendment for corn (Zea mays L.) production. Objectives of this research were to evaluate effects of pre-compost C:N substrate ratios for poultry litter-yard waste compost (PYC) on the availability of soil P, to determine the P response of corn plants to inorganic P, PL and PYC application, and to study relationships between P availability and both inorganic P and PYC application. Langmuir isotherms were used in this research to select soils with relatively high P fixation capacities. Phosphorus sorption maximum for soils evaluated were as follows: 304 and 449 micrograms of P per gram for A horizon Coastal Plain soils (Series: Kempsville and Myatt, respectively); 487 micrograms of P per gram for an A horizon Ridge and Valley soil (Series: Frederick); 918 and 603 micrograms of P per gram for A horizon Piedmont soils (Series: Elioak and Vance, respectively); 1099 microgram of P per gram for mine tailings (Series: Emporia located in the Coastal Plain); and 1524 microgram of P per gram for A and upper mixed horizon soil (Series: Starr from Piedmont region). Based on intermediate to high P sorption maxima, soil from the Vance and Starr series and mine tailing from Emporia series were selected for greenhouse research to evaluate P availability of PYC . Treatments applied to the soil in the greenhouse and field studies consisted of various levels of P as Ca(H₂PO₄)₂.H₂O, PL and PYC from 15:1, 20:1, and 25:1 C:N ratio substrates. Each P source increased dry weight of corn plants grown in the greenhouse by alleviation of P deficiency. Phosphorus uptake from PYC and PL application was either equal to or higher than P uptake from an equal level of P application as Ca(H₂PO₄)₂.H₂O. Application of 87.2 kg of P per ha increased corn grain yields in a field experiment on Vance sandy loam from 6340 kg per ha on the control to a range of 10,170 to 11,350 kg ha for PYC digested from the three C:N ratio substrates. The yields on PYC treatments were attributed to a combination of factors including slow mineralization of P with less fixation during the growing season. The low P fixing capacity results from the blockage of H₂PO₄⁻ sorption by competition of negative charge from organic material and from the displacement of H₂PO₄⁻ in soil solution by OH⁻ from application of the alkaline composts. It would be desirable from the standpoint of more PL utilization to prepare composts from low substrate ratio substrates. Hence, in this research composts were prepared from 15:1, 20:1, and 25:1 C:N substrates, which consisted of PL and YW. The composting process was complete after only four months for the PYC from the 20:1 and 25:1 C:N ratio substrates. Yard waste compost without PL may require somewhere between two to three years for complete composting as opposed to four months with PL addition. The composting was incomplete in four months (presence of undigested leaves and NH₃) for the PYC from the 15:1 C:N ratio substrate. The latter compost resembled poultry manure rather than a high quality compost after the 4-month composting period.
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    Effect of tillage system and nitrogen rate on tomato yield
    Tessore, Carlos (Virginia Polytechnic Institute and State University, 1982)
    Experiments to evaluate the effects of tillage systems and nitrogen fertilizer rates on fresh market 'Pik Red' tomato (Lycopersicon esculentum Mill.) production were carried out at Blacksburg, Virginia (1981 and 1982) and at Carrasco and Jackson, Uruguay (1981-2). Two tillage systems were used: (a) conventional tillage (CT) - plowed, disced and rototilled, and (b) no-tillage (NT) using paraquat at 0.5 kg/ha. Four different nitrogen (N) rates were used: 40, 80 and 120 kg N/ha broadcast at transplanting and a 40/40 kg N/ha split applications - 40 kg N at transplanting and another 40 kg N after the flowers of the first cluster had set. During 1982, at Blacksburg a 0 kg N/ha rate was added. For all locations and years, water availability was equal or higher in NT plots than with CT after transplanting. The largest differences were found at the beginning of the growing season. Soil under NT tended to be cooler than under CT; these differences in soil temperature are attributed to higher moisture content with NT than CT and the shading effect of the mulch in the NT plots. Soil Nitrate (NO3) content was equal or lower with NT than with CT at Carrasco and Jackson. Absorption of NO3 by the rye cover crop in NT plots probably was a major cause of NO3 differences between tillage systems. Nitrogen, P and K content in leaf tissue were equal or higher while Ca and Mg were equal or lower in NT plants than in CT plants. Nitrogen tissue content was increased by the N rate only at Carrasco; no effect of N rate was found on absorption of other nutrients at Carrasco or Jackson. Total yield was not affected by the tillage systems except for Blacksburg in 1982 when the NT plots outyielded CT plots. Marketable yield was consistently increased by the NT system at all locations and years. Unmarketable yield was equal or higher with CT than with NT. No effect of the N rate was found for any yield or yield components except for Blacksburg in 1981 where the total average weight was affected by the N rate. Water availability rather than N supply is believed to be the limiting factor to yield production at all locations and years. Blossom-end rot was consistently reduced by the NT system at all locations and years. Improved water availability with NT than with CT was probably responsible for a more steady Ca supply to growing fruit with NT than with CT, thus reducing the incidence of the disorder.
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    Effects of maturity and seed size on seed vigor and plant growth in snap bean (Phaseolus vulgaris L.)
    Herat, Lakshman Gamini (Virginia Tech, 1992-04-15)
    Stage of maturity at harvest and relative seed size can affect seed vigor. Greenhouse and field studies were conducted to determine the effect of seed maturity on seed vigor, storability, and subsequent plant growth of four cultivars of snap bean (Topcrop, Provider Black, Provider White, and Cherokee Wax). Seeds harvested between physiological maturity (PM) and harvest maturity (HM) showed the highest seed vigor and storability. At PM, seed moisture content was about 55%. A drop in seed fresh weight and a pod color change from green to yellow appear to signal the stage of PM. Delaying harvest past HM reduced seed vigor. The three cultivars with colored seed coats showed higher seed vigor than Provider White. Climatic and weathering effects on maturity, vigor, and yield of Topcrop and Cherokee Wax seed were evaluated at three locations (L-I, L-2, and L-3) in Sri Lanka having different agro-climatic conditions. Seeds that developed and matured under cooler conditions (L-l) produced higher yields and had larger size, better color, and higher vigor. Seeds developed and matured faster under warmer conditions (L-3); however, seed vigor and yields were lower and seed vigor dropped prior to HM. Cherokee Wax was the most tolerant to field weathering. Seeds of Topcrop and Cherokee Wax were separated by weight into three seed sizes (small, medium, and large) and evaluated for crop performance in two plantings (12/90 and 3/91). Field emergence was higher from larger seeds in the second planting, where the soil conditions were more stressful. Seedlings and plants at the flowering stage were larger and pod yields higher from larger seeds. The cultivar x seed size interaction was significant for pod yield per plant. Topcrop showed no differences, while with Cherokee Wax, pod yield per plant increased with increase in seed size during both plantings. Seeds produced from small seeds were similar or higher in vigor, indicating that small seeds could be used for seed production purposes. The data from these experiments indicate that vigor in snap bean seeds can be optimized by harvesting at an early stage after PM and by grading to remove small seeds.
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    Effects of nitrogen source and level on the growth and composition of Sinningia speciosa Lodd
    Nolan, Sharon Lee (Virginia Polytechnic Institute and State University, 1982)
    Gloxinia (Sinningia speciosa Lodd.) seedlings were grown in 2 media to determine the maximum percentage N that can be supplied as NH₄ and the minimum concentration of a soluble complete fertilizer that can be applied without reducing plant quality under different light and temperature conditions. In one group of experiments, plants were supplied modified Hoagland's solutions in which the N source and level were varied. Shoot dry weight of gloxinias grown in an organic medium in the winter was lower with 100% NH₄ than with 100% NO₃ but was unaffected by N level, while in the fall shoot dry weight was lower with 100% NH₄ than with 0 or 50% NH₄, and was reduced at 16 rather than 8 meq N liter⁻¹. In the summer, shoot dry weight did not vary with N source or concentration when treatment solutions were collected and reused for 1 week. Flower bud count at harvest did not vary with N source in the winter but was reduced at 100% NH₄ in the fall and summer. Time to flower bud set was unaffected by N source, but was increased by applying 16 rather than 8 meq N liter⁻¹. In the winter, leaves of plants receiving 75-100% NH₄ were dark green early in the studies, but became chlorotic, twisted and quilted before plants matured; in the summer and fall these symptoms of NH₄ toxicity were absent. Leaf chlorophyll content was greater for plants grown in quartz sand when given 100% NH₄ rather than 100% NO₃. In related studies, gloxinias were treated at every watering with a soluble 20N-8.7P-16.7K fertilizer. Shoot dry weight was greater and time until flower bud set shorter at 200 than at 0, 400 or 600 ppm N in the summer; shoot dry weight and flower bud count were greater at 100 than at 200-400 ppm N in the winter. Days until flowering in the summer and days until bud set in the winter were unaffected by fertilizer levels. Tissue composition varied with N source and level and Ca(OH)₂ treatment although lime application did not affect any external plant characteristics.
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    Effects of priming and stage of development on vigor and longevity of muskmelon (Cucumis melo L.) seeds
    Oluoch, Melkizedek O. (Virginia Tech, 1996)
    Muskmelon seeds were harvested at eight stages of development to determine the optimal harvest time for best seed quality and long-term storage. Several types of osmotic and matric priming treatments were investigated to determine the optimal treatment for maximal seed vigor and to test the effects of priming on seed storage life. The most effective priming treatments for improved germination of muskmelon seeds occurred at water potentials (Ψ) between -1.5 and -1.8 MPa and at priming durations of 4 to 7 days. Osmotic priming in KNO₃ and PEG 8000 solutions was more effective than matric priming with calcium silicate, vermiculite, and Hayter loam soil. Priming increased the storage life of newly matured 40 and 45-days after anthesis (DAA) stored seeds but decreased the storage life of 55 DAA seeds. Fifty, 55, and 60-DAA seeds showed the greatest tolerance to adverse storage conditions and water stress and had the greatest seedling vigor. The highest quality seeds were attained 50 to 60 DAA from fruit harvested after edible maturity but before the onset of severe decomposition. After 6 years of storage, seeds washed in water at harvest were more vigorous and resistant to accelerated aging than unwashed seeds at most stages of development. Primed seeds retained some beneficial effects after 9 years of storage at optimal conditions but lost viability, vigor, and uniformity of germination more rapidly than non primed seeds following controlled deterioration. Instron analysis showed that priming weakened the perisperm envelope tissue prior to radicle emergence. Less force was required to puncture primed seed pieces than non primed. The penetration force and energy required to puncture the perisperm envelope tissue decreased gradually during imbibition, increased steadily during seed development and dry storage, and was negatively correlated with seed vigor. Priming accelerates enzymatic breakdown of perisperm envelope during germination. Endo-β-mannanase-like activity declined steadily during imbibition and was higher in non primed seeds than primed seeds, indicating that enzymatic activity in the perisperm peaked during priming. Flow cytometry revealed that the beneficial effects of priming and seed maturity do not correlate with DNA replication activity in muskmelon seeds. This study has shown that seed maturation inside the fruit until just after edible maturity is necessary for highest muskmelon seed vigor. Priming treatments should be performed as close to the planting date as possible, because primed seeds exhibit reduced storage life compared to non primed seeds.
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    The effects of priming on vigor and viability of broccoli (Brassica oleracea var. italica Plenck) seeds
    Jett, Lewis W. (Virginia Tech, 1994-12-15)
    Seed priming is a controlled hydration process, followed by dehydration, that allows pregerminative metabolic activity to proceed without germination. The objective of this research was to investigate the effects of priming on intrinsic characteristics of seed germination including temperature, water, and development, in order to understand how priming affects the germination of broccoli (Brassica oleracea var. italica Plenck) seeds. Priming of broccoli seeds consistently improved germination and emergence rate in the laboratory and field and was related to the accumulation of a specific level of hydropriming units expressed in MPa*h. Priming reduced the sensitivity of seed germination to temperature and increased the temperature range of germination but did not lower the minimum temperature for germination. Primed seeds leaked less electrolytes at supraoptimal temperatures (≥ 35°C) compared to nonprimed seeds. In the field, primed seeds produced a greater plant stand and yield under stressful emergence conditions. Under optimal conditions in the field for stand establishment, the advancement in emergence of primed seeds did not carry over to earlier, greater yields. Matric priming, using calcium silicate as the carrier in the ratio 1.0:0.8:1.8 (seed:carrier:water; by weight) for 7 d at 20°C, was superior to osmotic priming using polyethylene glycol (pEG 8000) at -1.2 :MPa in nearly all variables examined. This may be attributed to reduced respiration during priming of seeds in PEG or nutrient uptake by seeds in calcium silicate. The testa was observed to be a barrier to broccoli seed germination. Priming-induced changes to the physical characteristics of broccoli seeds included increased volume (32%) and an irreversibly expanded, and weakened testa with some minute cracking near the area where the radicle emerges. Primed seeds germinated faster, in part by maintaining a lower hydrotime constant, and thus exhibited a greater progression towards germination per unit water potential at a constant temperature compared with nonprimed seeds. It was hypothesized that, since the testa threshold was reduced after priming by expansion and formation of free spaces, the reversibly expanded embryo of primed seeds does not become immediately appressed to the testa upon rehydration. Thus the yield threshold component controlling the rate of germination of primed seeds is lower by the amount of the testa threshold. The priming effect is more than just reducing the yield threshold as indicated by a significant invigoration of seeds with split testae. Despite the increased volume as a result of the formation of free spaces, primed broccoli seeds did not imbibe more water or have a greater turgor at full hydration. Priming did not lower the minimum water potential allowing germination, and primed seeds did not plateau in water uptake but, instead, moved immediately from imbibition to expansive growth. Priming improved the germination rate of broccoli seeds at all stages of maturity with the most significant effects at stages before attainment of maximum dry weight. Dry storage of broccoli seeds at harvest able maturity (≥ 56 days after pollination) did not improve germination, indicating a lack of post harvest dormancy.
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    Effects of topping, stem density, and stage of vine cutting on canopy growth and tuber yield yield of potato (Solanum tuberosum L.)
    Okeyo, James Ajuoga (Virginia Tech, 1995)
    Seed tubers of ‘Yukon Gold’ potato (Solanum tuberosum L.) exhibit strong apical dominance, resulting in low stem density after planting. After emergence, the terminal buds reimpose apical dominance on the rest of the canopy leading to production of few secondary branches. Therefore, several experiments were conducted at the Virginia Polytechnic Institute and State University Kentland Research Farm, Blacksburg in 1992, 1993, and 1994 to evaluate the effects of topping [(excising 2-3 cm from the terminal buds at 1 to 2 weeks after the date of plant emergence (WAE)], stage of vine cutting at ground level, and main stem density on canopy growth, tuber bulking rate, and tuber yields of potato. Topping (3 years) and vine cutting (2 years) at 1 WAE resulted in more uniform plant stands and increased average yield of US No. 1 tubers of ‘Yukon Gold’ by 16 and 14%, compared to untopped and uncut plants, respectively. When plants of ‘Kennebec’, ’Superior’, and ’Yukon Gold’ were topped in 1994, yield of US No. 1 tubers increased by an average of 10%, indicating that topping could be used to improve tuber yield of potato cultivars exhibiting different growth habits. The increased tuber yields following topping resulted from a combination of increased leaf area duration and increased period of tuber bulking. Cutting vines of ‘Yukon Gold’ at 2, 4, and 6 WAE in 1992 and 1993, decreased yield of US No. 1 tubers by 11, 69, and 38% and by 19, 56, and 48%, respectively. Yield of US No. 1 tubers increased with increased stem density and increased in-row spacing. Interaction effects between in row spacing and topping were significant. Control plants of ’Yukon Gold’ produced higher tuber bulking rates and yield of US No. 1 tubers than topped plants at 15 cm in-row spacing, while topped plants had higher tuber bulking rates and yield of US No. 1 tubers than control plants at 20, 25, and 30 cm in-row spacings. Neither topping nor in-row spacing increased the incidence of hollow heart of tubers in 1994. The results showed that the difference in tuber yield between topped and control plants was greater during long growing season and topped plants should be spaced at 25 cm in-row in order to obtain maximum tuber yield.
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    Efficacy and selectivity of the herbicide rimsulfuron in potatoes [Solanum tuberosum], transplanted tomatoes [Lycopersicum esculentum], and transplanted peppers [Capsicum annum]
    Ackley, John A. (Virginia Tech, 1994-04-06)
    Rimsulfuron {N-[[ 4,6-dimethoxy-2-pyrimidinal)amino ]carbonyl]-3-( ethylsulfonyl)-2-pyridinesulfonamide} is a new sulfonylurea herbicide under development by E.I. Dupont de· Nemours & Company Inc. for preemergence and postemergence grass and broadleaf weed control in Solanaceous vegetable crops. The efficacy and selectivity of rimsulfuron were determined in potatoes, transplanted tomatoes, and transplanted peppers in field studies in 1991, 1992, and 1993. Treatments included rimsulfuron and metribuzin alone and in combination in potatoes and tomatoes, rimsulfuron alone in peppers, and sequential applications of rimsulfuron in tomatoes and peppers. Application timings included preemergence and postemergence in potatoes, while only post-transplant applications were evaluated in tomatoes and peppers. Preemergence applications of rimsulfuron controlled weeds if rainfall was received within a few days following application. Control was often greater in potatoes and tomatoes than in peppers. These differences likely relate to more frequent rainfall events in potatoes and tomatoes than in the later-planted peppers.
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    Evaluation of yield and quality of five potato cultivars grown in Southwest Virginia
    Ajuoga, Okeyo James (Virginia Tech, 1992-10-07)
    Potato (Solanum tuberosum L.) cultivars Atlantic, BelRus, Kennebec, Superior, and Yukon Gold, grown at six locations in Southwest Virginia, were analyzed for yield, percent dry weight, specific gravity, soluble protein, and ascorbic acid. Thereafter. tubers were cold stored at 3 C for six weeks, reconditioned at 25 C for two weeks, and analyzed for percent dry weight, specific gravity, soluble protein, and ascorbic acid. Potato grown in one location was analyzed for glucose, fructose, sucrose, and total sugars. Another experiment was conducted to evaluate the effect of seed type and in-row spacing on yield and quality of Yukon Gold. Cultivar and location influenced yield and quality of potato at harvest, after cold storage, and following reconditioning. Kennebec, Atlantic, and Yukon Gold produced higher yield of US No. 1 tubers than Superior and BelRus. Atlantic and BelRus had higher percent dry weight and specific gravity than the other cultivars. Specific gravity increased during cold storage and following reconditioning. Percent dry weight increased during reconditioning but did not change during cold storage.
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    Fall and spring broccoli yields and weed control under no-till and conventional tillage with overseeded legume living mulches
    Infante, Michelle Louise (Virginia Tech, 1994-11-21)
    Experiments were conducted with 'BigSur' broccoli (Brassica oleracea var. italica Plenck) at two sites in fall of 1993 and at two sites in the spring of 1994 on a Hayter loam in southwestern Virginia. Objectives were to determine the tillage main-plot (CT = conventional tillage, and NT = no-tillage) and weed-control subplot (C = no overseeding or preemergent herbicide; HB = oxyfluorfen; RC = red clover (Trifolium pratense L.); WC = Dutch white clover (Trifolium repens L.); and HV = hairy vetch (Vicia villosa Roth) effects on broccoli yield and weed suppression. At all sites, marketable broccoli yield was equal or higher in NT than CT and was unaffected by overseeded legume living mulches. Overseeded legumes suppressed weeds as well as the HB in three of the four sites. These data show that the NT systems used in these experiments can suppress weeds and produce high broccoli yields and that overseeded legume living mulches can be effectively established after transplanting to suppress weeds without reducing broccoli yield.
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    Flowering Control and Production of Strobilanthes dyerianus Mast. (Persian Shield)
    Gamrod, Erin Elizabeth (Virginia Tech, 2003-04-08)
    Grown for its distinctive foliage, Strobilanthes dyerianus is a popular bedding and container plant. A problem in production is that over-wintered stock plants often flower. Once the plant becomes reproductive, stem elongation slows and floral buds arise from every node, rendering the plants useless for propagation. The objectives of this research were to examine the effectiveness of manipulating environmental factors and the application of ethephon on preventing floral bud initiation, as well as determine optimal nitrogen rate for stock plant culture. The first experiment was performed in a glass greenhouse and ran 11 weeks, utilizing 8 h, 10 h, 12 h and a 4 h night interruption photoperiod treatments to determine critical photoperiod. None of the photoperiod treatments were significant for inhibiting flowering and there was a positive correlation between plant size and flowering. A second experiment was performed in growth chambers to create three photoperiods (8 h, 12 h and 16 h) with two temperature regimes (24C day/ 21C night and 17C day/ 14C night) for a total of six treatments. Neither photoperiod nor temperature inhibited bud initiation, and there was no correlation between plant size and flowering. The third experiment examined potential use of ethephon to maintain vegetative plants. Six rates of ethephon (0, 150, 300, 450, 600 or 750 mg·Lˉ¹) were applied at three frequencies (weekly, biweekly and monthly) over an eleven week period. Floral initiation was not totally inhibited, but flowering was highly correlated to plant size. Additionally, plant growth response to nitrogen was examined to determine the optimal rate for stock plant production. Plants were treated with 0, 100, 200, 300 or 400 mg·Lˉ¹ N from a 15 N – 2.2 P – 12.4 K fertilizer at each irrigation for eight weeks. There were no differences among plant quality ratings for plants receiving 100, 200, 300 or 400 mg·Lˉ¹ N, and plants grown with 200 mg·Lˉ¹ N had the largest leaf area and shoot dry weight.
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    Food webs and phenology models: evaluating the efficacy of ecologically based insect pest management in different agroecosystems
    Philips, Christopher Robin (Virginia Tech, 2013-09-02)
    Integrated pest management (IPM) is defined as an effective and environmentally sensitive approach to pest management that relies on a combination of common-sense practices. Integrated pest management programs use current, comprehensive information on the life cycles of pests and their interactions with host plants and the environment. This information, in combination with available pest control methods, is used to manage pest populations by the most economical means, and with the least possible hazard to people, property, and the environment. True IPM takes advantage of all appropriate pest management options including, as appropriate, the judicious use of pesticides. It is currently estimated the IPM in its full capacity is being practiced on less than ten percent of the agricultural land in the U.S. The primary objective of this research was to evaluate land management decisions and create new tools to promote a true IPM approach and encourage growers to reevaluate their method of insect control. To accomplish this I developed new predictive tools to reduce or eliminate unnecessary insecticide application intended to target cereal leaf beetle in wheat, and assessed a conservation biological control technique, farmscaping, to determine its true impact on lepidopteran pest suppression in collards.
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    Impact of Conservation Tillage on Soil Erosion and the Agronomic Performance of Flue-Cured Tobacco
    Jones, Bruce (Virginia Tech, 1998-12-08)
    Conservation tillage tobacco production has gained little producer acceptance since introduction in the late 1960's. Yield reductions, tobacco quality issues, unacceptable weed control, and inadequate planting equipment limited practice adoption and substantiated the need for continued research. The recent developments of a Subsurface Tiller-TransplanterTM and the herbicide SpartanTM renewed producer interest in conservation tillage and led to an investigation with both flue-cured and Virginia dark-fired tobacco. Flue-cured tobacco was transplanted into rye mulch on bedded rows and subsequently cultivated at various timings. Conservation tillage significantly reduced soil erosion approximately 92 percent and tobacco yield approximately 23 percent when row cultivation was not applied. Row cultivation significantly increased tobacco yield without increasing soil erosion. The yield of conservation tillage tobacco receiving a minimum of two cultivations was similar to conventional tobacco. The second study evaluated wheat, rye, crimson clover, and mixtures of crimson clover with either wheat or rye as cover crop mulches for conservation tillage production of Virginia dark-fired tobacco. Conservation tillage, regardless of cover crop, reduced dark-fired tobacco yields approximately 779 and 488 pounds per acre in 1996 and 1997, respectively. The removal of cover crop residue for hay did not lower tobacco yield compared to leaving residue on the soil surface. Row cultivation increased conservation tillage tobacco yield approximately 247 pounds in 1997 regardless of cover crop. The nitrogen contribution of crimson clover was minimal in both years of the study and did not affect tobacco performance.
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    Influence of Lime and Micronutrient Amendments on Growth of Containerized Landscape Trees Grown in Pine Bark
    Wright, Amy Noelle (Virginia Tech, 1998-07-31)
    Growing landscape trees in containers is a common practice in the nursery industry. In the southeastern United States, pine bark is often used as a container substrate, and two common amendments to pine bark are lime and micronutrients. In this study, three experiments were conducted to determine the effect of these amendments on the growth of a wide range of landscape tree species grown in pine bark. In the first experiment, nine species of landscape trees [Acer palmatum (Japanese maple), Acer saccharum (sugar maple), Cercis canadensis (redbud), Cornus florida (flowering dogwood), Cornus kousa (kousa dogwood), Koelreuteria paniculata (golden-rain tree), Magnolia x soulangiana (magnolia), Nyssa sylvatica (blackgum), and Quercus palustris (pin oak)] were grown from seed in two pine barks: pH 4.7 (low) and 5.1 (high). Preplant amendment treatments to each pine bark (Pinus taeda) were: with or without dolomitic limestone (3.57 kg.m-3) and with or without micronutrients (0.9 kg.m-3, Micromax™). The same experiment was repeated using Koelreuteria paniculata and Quercus palustris, the same lime and micronutrient treatments, and two pine barks: pH 5.1 (low) and 5.8 (high). In both experiments, micronutrients increased shoot dry mass and height for all species, while lime decreased shoot dry mass and height for all species. Effect of bark type in the first experiment was variable, while shoot dry mass and height were highest in the low pH bark when the experiment was repeated. Substrate solution element concentrations increased when micronutrients were added, decreased when lime was added, and in general, concentrations were higher in low pH bark than in high pH bark. In the third experiment, Koelreuteria paniculata was grown from seed in pine bark amended with 0, 1.2, 2.4, or 3.6 kg.m-3 dolomitic limestone and 0 or 0.9 kg.m-3 micronutrients (Micromax™). Initial pH for each lime rate was 4.0, 4.5, 5.0, and 5.5, respectively. Adding micronutrients increased shoot dry mass and height. Lime increased growth only at the 1.2 kg.m-3 rate. In general, substrate solution element concentrations increased when micronutrients were added and decreased when lime was added. In all three experiments, adding micronutrients was necessary regardless of pine bark pH, while adding lime was not necessary.
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    Influence of temperature, soil moisture, and planting depth on germination and emergence of 'Packman' broccoli
    Elson, Marshall Kent (Virginia Tech, 1989-06-05)
    Broccoli growers in Southside Virginia have had difficulty with stand establishment. This research was undertaken to identify potential causes of poor stand establishment. Temperature and soil moisture conditions in Southside Virginia during July and August are often less than favorable for seedling growth. Experiments were designed to test the temperature and moisture stress limits for germination and emergence of 'Packman' broccoli, under the controlled conditions of growth chambers.
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    Integration of High Residue/No-till and Farmscaping Systems in Organic Production of Broccoli
    Benson, Gordon Brinkley (Virginia Tech, 2006-05-01)
    High-biomass cover cropping enhances marketable yields in organic production of vegetables, linked to the improvement of soil quality and weed control. Although, during transition from chemical to organic cover-cropping production, especially with no-till systems, reduction of nitrogen availability to the main crop and increase in weed and pest pressure may occur. In 2004-2005, summer and fall broccoli (Brassica oleraceae L. Botrytis Group) crops were grown in twin rows on permanent (controlled traffic) raised beds (185-cm wide). Before broccoli transplanting, high-biomass cover crops were grown in specific bed areas. Legumes (Vicia villosa, Glycine max L., and Crotolaria juncea L.) on bed tops (grow zones) and grass species (Secale Cereale L., Setaria italica L., and Sorghum bicolor X S. bicolor var. Sudanese) in the alleyways (bed shoulders and bottoms). Experimental treatments were tillage (conventional, CT; and no-tillage, NT), farmscaping (with and without), and nitrogen sidedressing (with and without, applied 3 weeks after transplanting as a mixture of sodium nitrate - 22 kg N ha-1 - and feathermeal - 44 kg N ha-1). Weeds were managed by mechanical cultivation in CT and a spot weeding by hand in NT treatments. High numbers of beneficial insects (Cotesia glomerata, Cotesia orobenae and Diadegma insulare) kept the primary insect pest population (Pieris rapae, Evergestis rimosalis (Guenee), and Plutella xylostella) at a pest to predator ratio below 4:1. Although the excellent insect pest control was attributed to the farmscape plantings, pest level and crop yields were not significantly affected by farmscaping (likely due to the close proximity of the farmscaped plots (10-50m from non-farmscaped)). Broccoli yield averaged 62% higher in fall than summer (12.1 vs. 7.5 t ha-1) likely due to cool weather conditions during broccoli head development (October), increasing head size, uniformity, and marketability. In 2004, broccoli yield in CT plots was either equal or slightly higher than NT (9.5 vs. 9.0 t ha-1). However, in 2005, broccoli yield in CT plots was significantly higher in both spring (8.8 vs. 6.8 t ha-1; p = 0.0258) and fall crops (13.5 vs. 12.3 t ha-1 with p = 0.0484). Nitrogen sidedressing improved yield in all plots (9.8. vs. 12.7 t ha-1) and particularly in NT (8.6 vs. 12.1 t ha-1), indicating that availability and/or synchrony of nitrogen was a limiting factor. Incorporating high-N legume residues in the grow zones resulted in a lesser N response in CT.
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    Long-term copper availability and adsorption in a sludge-amended Davidson clay loam
    Anderson, Martha Ann (Virginia Tech, 1997-04-04)
    A single application of aerobically digested sewage sludge was applied by Rappaport et al. (1988) in 1984 at rates up to 210 dry Mt ha⁻¹ on a Davidson clay loam (clayey, kaolinitic, thermic, Rhodic KandiuduIts). The heavily contaminated sludge supplied up to 760 kg Cu and 620 kg Zn ha⁻¹, which are below current cumulative limits, but above annual loading limits for these metals (USEPA, 1993). Rappaport et al. (1988) reported an increase in DTPA extractable Cu and Zn with increasing sludge rate. They observed a linear increase in com yields with an increase in sludge rate, which was attributed to high levels of available N supplied by the sludge. In the present residual study, conducted at the same research site, DTPA extractable Cu and Zn followed the trend observed by Rappaport et at. (1988). However, a linear decrease in corn and sorghum yields was observed with increasing sludge rate. The sludge-related decrease in yields was attributed to phytotoxicity (probably a combination of Al, Cu, Mn, and Zn) induced by low soil pH levels. Whole plant tissue concentrations of eu and Zn at the high sludge rates were above the normal range, however grain concentrations were within the normal range. An adsorption study was conducted, in which soils were amended with Ca(OH)₂ and Al₂(S0₄)₃, to ascertain the effect of decreased pH on Cu adsorption on the soil. Copper adsorption maxima decreased with a reduction in soil pH in all treatments. The effect of ionic strength on Cu adsorption was also investigated. Regardless of pH or ionic strength, Cu adsorption increased with an increase in sludge rate. This adsorption increase was attributed to the higher organic matter content of the sludge treatments. The organic matter at the highest sludge rate was approximately double that of the control after 11 years. The adsorption study shows that sludge amendment has long-term effects on metal retention in soils and the field study reveals that careful management of sludge-amended soils is necessary to prevent phytotoxicity.
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    Mechanization of the selective harvest of broccoli
    Wilhoit, John Hiram (Virginia Polytechnic Institute and State University, 1989)
    An investigation was made of concepts for mechanizing the selective harvest of broccoli. Selective harvesting has advantages over once-over harvesting because of greater yield and reduced handling requirements. Results of a preliminary experiment measuring broccoli stalk cutting forces indicated that the blade speed for a broccoli cutting mechanism should be as fast as possible to minimize the required cutting force. A manually-directed, powered cutting device was designed to fit readily into existing broccoli harvest systems. In tests the first year with the device, the harvest rate was substantially faster than hand harvest rates measured at commercial farms, but the level of leaf-stripping achieved with the device was unacceptably low. A new cutting device included an added leaf-stripping mechanism and had a mounting arrangement that allowed the harvesting of two double rows at once. In tests the second year, leaf-stripping was much improved, but the overall harvest rate was only marginally better because of extra manipulation required to activate the leaf-stripping mechanism. Measurements related to mechanical harvesting were made on broccoli plants both years. Head height, stalk diameter, and head weight were strongly affected by harvest time and in-row plant spacing. Height and stalk diameter were moderately correlated to head diameter. A regression model for predicting head diameter from height and stalk diameter indicated that potential exists for using a combination of the two parameters for sizing broccoli heads. Head weight was highly correlated to height and stalk diameter. Two concepts for automatic mature head selection were evaluated. The results of an experiment measuring the force required to uproot broccoli plants indicated that physically sizing broccoli heads using spaced fingers would only be feasible if late season irrigations could be incorporated in a harvest system. Digital image processing for head selection appears more promising. An image processing algorithm based on the gray level run length method of textural analysis was developed for predicting broccoli head area. Accurate head classification was obtained with the model. For an automatic selective harvester, an image processing system can be coupled with a cutting device with the major advantage that leaf~stripping can be accomplished automatically during the harvesting action.