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Carl E. Niedziela Jr. and Paul V. Nelson

A new tube method for determining physical properties in container substrates was compared to an existing system. While both offer the advantages of undisturbed substrate and measurement of properties without altering the geometry of the substrate in the container, the tube method is easier to conduct. Both methods proved equally effective for determining air-tilled porosity, container capacity, total porosity, bulk density, and particle density.

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Susan C. Miyasaka, Charles E. McCulloch, and Scot C. Nelson

Taro leaf blight (TLB), caused by the oomycete pathogen Phytophthora colocasiae, is a worldwide disease that threatens the sustainable cultivation of the tropical root crop taro (Colocasia esculenta). To evaluate taro germplasm from Asia, Hawai‘i, and several South Pacific Islands for resistance to TLB, 119 cultivars were planted along the Hamakua Coast of Hawai‘i (mean annual rainfall of 130 inches) in plots containing five or 10 plants that were replicated over time from 1993 through 2005. Fresh and dry weights of corms were measured after about nine months, with rotten portions removed and weighed. When epidemics of TLB occurred (in nine out of 12 years), visual estimates of disease severity on leaves were assessed using a modified Horsfall–Barratt scale. The correlations between mean dry weight yields for each cultivar and mean severity of TLB, and, respectively, between mean yields and mean severity of corm rots were calculated. As severity of TLB or severity of corm rots increased (suggesting increased susceptibility of particular cultivars to TLB or corm rots), mean dry weight yields decreased significantly (r 2 = 0.37 and 0.22, respectively). “Multiple comparisons with the best” (MCB) were conducted on fresh and dry weight yields, severity of TLB, severity of corm rots, percentage dry matter of corm, and consumer acceptance. Five cultivars were found to be “among the best” with: 1) fresh or dry weight yields that did not differ from the highest level; 2) severity ratings for TLB that were significantly lower than the highest level, suggesting TLB resistance; and 3) percentage of corm rots that were lower than the highest level, suggesting disease resistance. These cultivars, four of which originated from Palau, were Dirratengadik, Merii, Ngesuas, Ochelochel, and Sawa Bastora. Two commercial cultivars from Hawai‘i, Bun Long and Maui Lehua, had fresh and dry weight yields that were significantly lower than the maximum and severity of TLB injury that did not differ from the highest level, indicating that conventional breeding of taro to improve TLB resistance could improve yields of commercial taro cultivars, particularly in areas where epidemics of TLB occur.

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Randy S. Nelson, Esther E. McGinnis, and Aaron L.M. Daigh

Although sedges (Carex L. spp.) are commonly recommended for planting in rain gardens, little work has been carried out in evaluating the ability of sedge species to tolerate the challenging moisture fluctuations in this environment. Seven sedge species native to the north central United States, yellow fox sedge [Carex annectens (E.P. Bicknell) E.P. Bicknell], plains oval sedge [Carex brevior (Dewey) Mack. ex Lunell], gray’s sedge (Carex grayi J. Carey), porcupine sedge (Carex hystericina Muhl. ex Willd.), palm sedge (Carex muskingumensis Schwein.), pennsylvania sedge (Carex pensylvanica Lam.), and sprengel’s sedge (Carex sprengelii Dewey ex Spreng.), were evaluated in a greenhouse trial to determine their ability to tolerate repeated flooding and drought cycles. Treatments consisted of two flood periods (2 or 7 days), followed by one of three drought set points measured by volumetric water content (VWC) thresholds of 0.05 (severe drought), 0.10 (moderate drought), or 0.15 m3·m−3 (drought onset). Each plant was subjected to a minimum of four flooding and drought cycles. For sprengel’s sedge, plains oval sedge, gray’s sedge, and yellow fox sedge, there was no significant difference in shoot counts between severe drought, moderate drought, and drought onset treatments. Shoot mass and root mass for all sedge species were significantly reduced under the severe drought set point. Plants subjected to the 7-day flood treatment exhibited significantly increased shoot mass compared with those in the 2-day flood treatment. Plains oval sedge showed a significantly higher shoot mass than all other species under all treatments. Visible damage ratings suggest that sprengel’s sedge, plains oval sedge, gray’s sedge, and yellow fox sedge could be suitable for the rain garden environment under all but the most extreme drought conditions. Results show that plains oval sedge, yellow fox sedge, and gray’s sedge may be able to tolerate harsh flooding and drought cycles that can occur in rain gardens. For the remaining species, supplemental irrigation of rain gardens should be considered during drought.

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Thomas A. Bewick, Larry K. Binning, and Nelson E. Balke

Absorption of “C-labeled glyphosate by whole carrot (Daucus carota L.) plants infected or not infected by swamp dodder (Cuscuta gronovii Willd ex R & S) increased from 14% 1 day after treatment to 56% 14 days after treatment. Absorption of 14C-labeled glyphosate did not increase from 14 to 45 days after treatment. 14Carbon-labeled glyphosate appeared in the carrot root 1 day after application and its concentration increased with time in both infected and noninfected plants until 14 days after treatment. From 14 to 45 days after treatment, the concentration of 14C-labeled glyphosate in the roots decreased. At 1 day after treatment, dodder tissue contained as much 14C-labeled glyphosate as any physiological sink in the carrot. At 45 days after treatment, dodder tissue contained more 14C-labeled glyphosate than all other physiological sinks, except the petiole of the treated leaf. Swamp dodder stems had absorbed 14C-labeled glyphosate directly from a solution within 1 day after treatment. Chemical name used: N-(phosphonomethyl)glycine (glyphosphate).

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G.S. Miner, E.B. Poling, D.E. Carroll, L.A. Nelson, and C.R. Campbell

Annual-hill strawberry (Fragaria ×ananassa Duch.) production with black plastic mulch and drip irrigation is gaining popularity in North Carolina. Two experiments (E1 and E2) were conducted on a Wagram loamy sand (Arenic Kandiudult) in 1992 and on a Norfolk sandy loam (Typic Kandiudult) in 1993 to investigate the effects of fall-applied N and spring-applied N and K on `Chandler' strawberry yield and fruit quality. E1 treatments included factorial combinations of banded fall-applied N (0, 34, and 67 kg·ha-1) and drip spring-applied N (0, 0.19, 0.37, 0.56, and 0.75 kg·ha-1·d-1 and 0, 0.37, 0.75, and 1.12 kg·ha-1·d-1 in 1992 and 1993, respectively). E2 treatments included combinations of drip spring-applied N (0.56, 1.12, 1.68, and 2.24 kg·ha-1·d-1) and K (0.46, 1.39, and 2.32 kg·ha-1·d-1 and 0, 0.75, 1.49, and 2.24 kg·ha-1·d-1 in 1992 and 1993, respectively). There were no significant interactions among main effects for any of the measured variables. Market yield maximized with total N at ≈120 kg·ha-1 with one-half banded in the fall and the remainder drip-applied in the spring. Fruit firmness decreased with increasing N rate. Fruit pH and concentrations of total acids and soluble solids were not affected by N treatments, but soluble solids increased as the harvest season progressed. Plant crown number was not affected by N treatment but crown yield increased with N rate similar to market yield. There was no response to drip-applied K for any variable in either year. Based on soil test, fall-applied K (broadcast-soil incorporated) met the K requirements both years.

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C. A. Clark, R. A. Valverde, J. A. Wilder-Ayers, and P. E. Nelson

Symptoms of chlorotic leaf distortion (CLD) develop on vigorously growing sweetpotato (Ipomoea batatas) plants during sunny weather. They include chlorosis and twisting of young, expanding leaves and the appearance of white material on the adaxial leaf surfaces. The white material consisted of extramatrical fungal mycelia and Fusarium macroconidia. Fusarium lateritium Nees was isolated from surface-sterilized vine segments, leaf primordia, apical meristems, flower parts and true seeds of plants with CLD. Meristem-tip-culture-derived plants (mericlones) did not develop symptoms when grown for extended periods under disease-conducive conditions in the greenhouse. The fungus was not isolated from mericlones or other plants which had remained symptomless in the greenhouse but was isolated from lower nodes of symptomless plants from growers' fields. Symptoms developed on 84% of 185 mericlones of nine sweetpotato genotypes inoculated with F. lateritium isolated from CLD-affected plants. The pathogen was reisolated only from inoculated mericlones.

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James L. Gibson, Brian E. Whipker, Dharmalingam S. Pitchay, Paul V. Nelson, and C. Ray Campbell

Elemental deficiencies of N, P, K, Ca, Mg, S, Fe, Mn, Cu, Zn, and B were induced in `Osaka White' ornamental cabbage (Brassica oleracea var. acephala L.) plants. Seedlings were planted in 4.7-L plastic containers and fertilized with a complete modified Hoagland's solution or this solution minus the element that was to be investigated. Plants were harvested for tissue analysis as well as dry weight when initial foliar symptoms were expressed and later under advanced deficiency symptoms. Root architecture was also recorded for the plants treated with the solutions. The containers were replicated three times for each of the two harvests and were randomized in a complete-block design. Deficiency symptoms for all treatments were observed within five weeks. The most dramatic expression of foliar symptoms occurred with N (a purplish tinge on underside of lower foliage leading to necrotic margins on the mature leaves), P (elongated internodes and a purplish tinge on underside of mature leaves), K (compact internodes with chlorotic lower foliage leading to necrotic patches on the leaf margins and blade), Fe (bright yellow upper foliage leading to a bleach white appearance), Ca (complete meristem necrosis with lower foliage becoming chlorotic then necrotic), and B (deformed young leaves and fully expanded leaves becoming thick, leathery, and brittle). The dry weight of plants treated with solutions not containing N, P, Ca, Fe, or B was significantly lower when compared to the control. Foliar tissue concentration data will assist plant tissue analysis laboratories in establishing foliar symptom standards for grower samples.

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Dharmalingam S. Pitchay, James L. Gibson, C. Ray Campbell, Paul V. Nelson, and Brian E. Whipker

The margin of error in pinpointing the difference in deficiency symptoms between calcium and boron is high. Several experiments were conducted in the greenhouse to induce as well as to differentiate the exact foliar and root symptoms of Ca and B. The experiments were conducted with modified Hoagland nutrient solutions. The treatments were with or without Ca or B salts for inducing total deficiency symptoms. Symptoms were expressed on the upper part including the growing point of the plant. In absence of Ca, marigold and zinnia plant heights were reduced by 58% and 37%, respectively, from the control. However, the reduction in height was only in the 27% and 25% range for B deficiency. Ca deficiency was noted as a blackened region on the leaf blade (early stage symptoms) which progressed into necrotic spots on the newly formed leaves. Severe necrosis, was observed on the growing point with advanced Ca deficiency. B deficiency results in a leathery and gray color in zinnia, needle like and narrow leaflets in marigold. The leaf blades were brittle in all B deficient species. B deficient plants roots were stiff and leathery and lateral roots possessed black nodule like endings at the tips. The Ca deficient roots expressed less side branching and at the advanced stage the roots were shorter and fewer with severe necrotic symptoms. The above initial and advanced deficiency symptoms appeared earlier in treatments without Ca than B. Images of Ca and B deficiency symptoms, as well as tissue concentration values will be presented.

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Ka Yeon Jeong, Paul V. Nelson, Carl E. Niedziela Jr., and David A. Dickey

The objective of this study was to determine how plant species, fertilizer potential acidity/basicity rating (PABR), and fertilizer concentration affect root substrate pH. Three experiments were conducted. In the first experiment, 13 herbaceous species were grown in a root substrate of three sphagnum peatmoss: one perlite (v/v) with deionized water and a neutral fertilizer (NF) with a PABR of 0 for 78 days to determine species relationships to substrate pH. The decrease in substrate pH ranged from 0.14 to 2.45 units, depending on species. In the second experiment, four of the 13 species from the previous trial representing the range of pH suppression were grown under similar growth conditions as the first experiment for 70 days. Substrate pH was lowered in the range of 0.47 to 2.72 units. In the third experiment, three fertilizers with PABRs of 150 kg·t−1 CaCO3 equivalent alkalinity, 0 neutral, and 193 kg·t−1 CaCO3 equivalent acidity were applied in a factorial design at 100 and 200 mg·L−1 N at each irrigation to kalanchoe (the species with the greatest pH suppression from the previous experiments) for 56 days. When applied at the lower fertilizer rate (100 mg·L−1 N), the PABRs resulted in the final substrate pH levels of 4.68, 5.60, and 6.11 for the acidic fertilizer (AF), NF, and basic fertilizer (BF), respectively. At the high fertilizer rate (200 mg·L−1 N), substrate pH declined continuously to 3.97, 4.03, and 4.92 for the AF, NF, and BF, respectively. Expression of PABR depended on the balance between the abiotic (chemical) effect of the fertilizers vs. the biotic (physiological) effects of the fertilizers on microbes and plants. The PABR was best expressed when the fertilizer supply was just adequate or lower indicating a closer connection to the biotic effect.

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Paul V. Nelson, Cheon-Young Song, Jinsheng Huang, Carl E. Niedziela Jr., and William H. Swallow

Fertilizers with a high proportion of nitrogen (N) in the nitrate (NO3 ) form are used in the ornamental industry to promote compactness in plants. Although the common belief is that it is the high proportion of NO3 that causes compactness, these formulations also contain no or a low level of phosphate, which can also cause compactness. This study was conducted to assess the relative effects of NO3 to ammonium (NH4 +) ratio and phosphate supply, as found in high NO3 fertilizers, on seedling shoot growth. A series of fertilizers was formulated in which the level of phosphate and proportion of N in the NO3 form were varied factorially. Additionally, commercial fertilizers varying in these same two nutrient components were tested to verify the results obtained using the formulated fertilizers. Test plants included gomphrena (Gomphrena globosa L.), impatiens (Impatiens wallerana Hook. F.), petunia (Petunia ×hybrida Juss.), marigold (Tagetes erecta L.), and tomato (Solanum esculentum Mill.) grown as plug seedling crops. A strong inverse relationship occurred between the supply of phosphate and extent of compactness. The relationship between proportion of N in the NO3 form and compactness was comparatively small. In most comparisons within the study, shoot size increased with increasing proportion of NO3 , contrary to common belief. These data indicate that it is the limited phosphate level in high NO3 fertilizers that accounts for compactness rather than the high proportion of N in the NO3 form.