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Alan McKeown and Cathy Bakker

Soil and crop management practices suggest the possibility of sulfur deficiency for cole crops in Southern Ontario. A 3-year study was conducted to evaluate rates of calcium and sulfur on yield of `Huron' late-storage cabbage. Treatments were based on CaSO4 applied at 0, 1000, 2000, and 3000 kg·ha–1 `Novacal' (Ca 27%, S 19%, Mg 2.5%, Dolomex Inc., Portage-du-Fort, Quebec, Canada), a granulated gypsum product. Potassium sulfate and calcium nitrate were used as elemental controls. Potassium and nitrogen levels were balanced with potassium chloride and ammonium nitrate. Phosphorous applications were based on soil analysis. All treatments were applied pre-plant incorporated. This trial was repeated on sand and loam soils typical of soil used for cabbage production in southern Ontario. Applications of sulfur increased yield of cabbage on sand and clay, although the optimum rate varied from year to year. Medium and high rates produced the highest yield in the first year, while low rates were more effective in the second and third seasons. Response of cabbage to calcium varied from year to year. Medium and high rates of calcium increased yield on sand, but had no effect on clay in the first year. Calcium had no effect on yield on either soil type in the second year. However, in the third year, low rates of calcium produced the highest yield on both sand and clay. Although there were no visual symptoms of deficiency, applications of sulfur, and to a lesser extent calcium, increased yield indicating that a `hidden hunger' for these elements may exist on some soils in southern Ontario.

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Alan McKeown and Cathy Bakker

Fertigation is a promising strategy to improve nitrogen use efficiency, yield, and quality of cabbage (Brassica oleracea var. capitata), but there is a lack of data relevant to growers in Ontario. Field trials were conducted in 2003 and 2004 to determine the optimum rate of water and nitrogen application in terms of yield and quality of `Huron' cabbage. Treatments consisted of combinations of target soil moisture levels (25% to 100% field capacity) and nitrogen fertilizer (0–400 kg·ha-1 N) as dictated by a central rotatable composite design. Nitrogen applications were split with 50% broadcast and incorporated before planting and the remaining split into weekly applications via a trickle irrigation system. Water was applied two to three times per week to bring soil moisture up to the target levels. Maximum marketable yield was reached at a combination of 400 kg·ha-1 N and a soil moisture target of 100% field capacity. Many heads were undersized or undeveloped at low rates of nitrogen. Applications of nitrogen required for high yield and quality can pose a risk of leaching; however, use of fertigation minimizes potential in-season leaching. Estimated total residual nitrogen at harvest ranged from 83–211 kg·ha-1 N, which could have a negative impact on the environment. Thus, there is a considerable challenge to reduce environmental impact without economic losses. Improved knowledge of in-season nitrogen requirements might further reduce the levels of nitrogen applied without reducing yield and quality.

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Sean Westerveld, Alan McKeown, and Mary Ruth McDonald

In previous work with carrots (Daucus carota L.), little effect of nitrogen could be found on yield, but low nitrogen increased foliar disease. To determine if residual soil nitrate supplies sufficient nitrogen for carrots, plots were located on the same site for 3 years. Two sites were selected, one sand (pH 8.1, 2.6% OM), one organic (pH 6.0, 75% OM). Treatments consisted of 0%, 50%, 100%, 150%, and 200% of recommended levels (kg·ha-1) for organic (60) and mineral soils (110), plots were spilt in half with one fertilized every year, one in 2002 and were arranged in a split plot design with four replications. Foliar and soil samples were taken for nitrate analysis plus levels of Alternariadauci and Cercospora carotae foliar blight were recorded each year. Applied nitrogen had no effect on yield on muck soils. Over 3 years on mineral soils, total yield ranged from 36 to 48 t·ha-1 with no applied N. On mineral soils, yield was maximized at (kg·ha-1) 110, over 165, and 55-165 in 2002, 2003, and 2004, respectively. Stands on mineral soils were reduced at or above recommended rates in 2004. It is possible that carrots obtained considerable nitrogen perhaps deep in the soil profile. As in previous studies, applied nitrogen reduced foliar blights. Thus, nitrogen application is required for pest management purposes even if there is almost sufficient residual nitrogen for yield.

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Sean M. Westerveld, Mary Ruth McDonald, and Alan W. McKeown

The Nutrient Management Act (NMA) established in the province of Ontario in 2002 has prompted a re-evaluation of nitrogen (N) management practices. However, N management research in Ontario is currently outdated. The experiment in this 3-year study was designed to establish the yield response of carrot (Daucus carota) to N fertilization on mineral and organic soils and identify the relative yield effects of preplant and residual soil N. In 2002, N was applied at 0%, 50%, 100%, 150%, and 200% of recommended N application rates in Ontario as ammonium nitrate (organic soil: 60 kg·ha-1 preplant; mineral soil: 110 kg·ha-1 split 66% preplant/33% sidedress). Experimental units were split in half in 2003 and 2004, and N was applied to one half in 2003 and both halves in 2004 to identify the effects of residual N from the previous season on yield. Crop stand, yield, and quality were assessed at harvest, and storability was assessed by placing carrots into cold storage for 6 months. Nitrogen application rate had no effect on the yield, quality, or storability of carrots grown on organic soil. On mineral soil there were no effects of applied N in the first year of the 3-year study. In the second and third year on mineral soil, yield increased in response to increasing N, up to 200% and 91% of the recommended application rate, respectively, based on the regression equations. Yield declined above 91% of the recommended application rate in the third year due to a decrease in stand at higher N application rates. There were no effects of N on carrot quality or storability on mineral soil. On mineral soil, residual N from the 2002 season had more effect on yield at harvest in 2003 than N applied in 2003. This major effect of residual soil N on yield provides an explanation for the lack of yield response to preplant N application in previous studies conducted in temperate regions. These results indicate that there is no single N recommendation that is appropriate for all years on mineral soil. Assessing the availability of N from the soil at different depths at seeding is recommended to determine the need for N application.

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Sean M. Westerveld, Alan W. McKeown, and Mary Ruth McDonald

An understanding of nitrogen (N) uptake and the partitioning of N during the season by the carrot crop (Daucus carota subsp. sativus [Hoffm.] Arkang.) is required to develop more efficient N fertilization practices. Experiments were conducted on both organic and mineral soils to track the accumulation of dry matter (DM) and N over the growing season and to develop an N budget of the crop. Treatments included two carrot cultivars (`Idaho' and `Fontana') and 5 N rates ranging from 0% to 200% of the provincial recommendations in Ontario. Foliage and root samples were collected biweekly from selected treatments during the growing season and assessed for total N concentration. Harvest samples were used to calculate N uptake, N in debris, and net N removal values. Accumulation of DM and N in the roots was low until 50 to 60 days after seeding (DAS) and then increased linearly until harvest for all 3 years regardless of the soil type, cultivar, and N rate. Foliage dry weight and N accumulation were more significant by 50 to 60 DAS, increased linearly between 50 and 100 DAS, and reached a maximum or declined slightly beyond 100 DAS in most cases. The N application rates required to maximize yield on mineral soil resulted in a net loss of N from the system, except when sufficient N was available from the soil to produce optimal yield. On organic soil, a net removal of N occurred at all N application rates in all years. Carrots could be used as an N catch crop to reduce N losses in a vegetable rotation in conditions of high soil residual N, thereby improving the N use efficiency (NUE) of the crop rotation.

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Sean M. Westerveld, Alan W. McKeown, and Mary Ruth McDonald*

Residual nitrogen (N) in agricultural soils is an environmental concern. Nitrogen requirements for carrots were examined over a two-year period in Ontario, Canada. Carrots, cvs. `Idaho' and `Fontana' were seeded into organic and mineral soil in 2002 and 2003 in the same plots. In 2002, N was applied at 0%, 50%, 100%, 150%, and 200% of current Ontario recommendations. Each experimental unit was split in half in 2003 with one half getting the same N rate as in 2002, and the second half getting no applied N. At harvest, total and marketable yield, weight per root, and quality were assessed. Yield and quality were unaffected by N rate in both mineral soil in 2002 and organic soil in both years. On mineral soil in 2003 there was a linear increase in total and marketable yield and weight per root with increasing N rate, with total yield ranging between 36 and 55 t/ha. However, in the treatments given no N in 2003, yield also increased from 36 to 47 t/ha between the 2002 no N and high N treatments. Consequently, a large portion of the increase in yield in 2003 on mineral soil was due to residual N from the previous season. Carrots are capable of taking up very high amounts of N from the soil over a growing season, but may only require additional N for maximum total yield if soil N content is low due to low mineralization rates or depletion by a previous crop. However, low N rates can reduce the ability to harvest the crop due to increased carrot leaf blight severity even when yield is unaffected.

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Mary Ruth McDonald*, Kevin Vander Kooi, Cathy Bakker, and Alan McKeown

Globe artichoke (Cynara scolymus L.) is a high value cool season crop which requires vernalization to induce flower formation. The climate in Ontario does not allow for survival of perennial cultivars or for consistent natural vernalization of annuals. Three methods of vernalization were tested: a controlled environment chamber, a lighted cold storage, or GA3 application in the field. Plants, cv. Green Globe Improved, were grown in a greenhouse set at 25 °C day temperature in 72-cell Styro-foam trays in a peat mix. At 4 weeks, plants receiving vernalization were transferred to growth chambers, or lighted coolers (four standard 8 foot cool white fluorescent lamps) at 10 °C for two weeks. The others stayed in the greenhouse. GA3 treatments (PROGIB, 15 g ai/ha) were applied at 2, 4 and 6 weeks after transplanting. Cultivars Green Globe Improved, Imperial Star, Emerald, and Large Green Globe were evaluated in separate trials. Trials were conducted at Simcoe, on coarse sand in a high heat area, and Kettleby, on organic soils in a cooler area of Ontario. Shortly after planting at Simcoe several 30 °C days occurred which devernalized and injured the crop. Artichokes grew well at the Kettleby site. Vernalization in the growth chamber was most effective and resulted in the earliest bud formation and highest total yield (1503 cases/ha). Large Green Globe was not well adapted to Ontario conditions. Imperial Star and Emerald produced the highest yields, 2180 and 1779 cases/ha, respectively. Globe artichokes can be grown successfully as an annual crop in cool production areas of Ontario.

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Sean M. Westerveld, Alan W. McKeown, and Mary Ruth McDonald

Alternaria leaf blight (ALB) and Cercospora leaf spot (CLS) are economically important diseases of carrot in Ontario. Field experiments were conducted in the Holland Marsh, Ontario, to determine the effect of nitrogen (N) application rates on both diseases. Five rates of N were applied to organic and mineral soils in which two carrot cultivars, Idaho and Fontana, were grown in each of 2002, 2003, and 2004. Both diseases were rated every 2 weeks on a scale of 0 (healthy) to 10 (tops destroyed), and the number of live (green) leaves per plant was assessed at harvest. In addition, three N rates were applied to carrot plants grown in the greenhouse, and the plants were inoculated with Alternaria dauci (Kühn) Groves and Skolko. Disease severity, senescence, and sap nitrate-N concentration were assessed. In the field trials, the response of ALB and CLS to N application rate was relatively consistent across cultivar, soil type, and year. Area-under-the-disease-progress curves typically increased with decreasing N rate for both diseases. In lower N treatments, this resulted in fewer live leaves per plant at harvest. In the greenhouse, ALB severity increased with increasing amount of leaf senescence at final assessment. The results suggest that N application rate could be used to reduce the need for fungicide applications to control these diseases in the field.

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Catarina Saude, Alan McKeown, Bruce D. Gossen, and Mary Ruth McDonald

Field trials were conducted to evaluate resistance to clubroot (Plasmodiophora brassicae, pathotype 6) in green cabbage (Brassica oleracea var. capitata) and napa cabbage (Brassica rapa ssp. pekinensis) at sites in southern Ontario in 2009 and 2010. The reaction of green cabbage cultivars Kilaton, Tekila, Kilaxy, and Kilaherb and the commercial standard cultivars, Bronco or Atlantis, were evaluated on organic (two site-years) and mineral soils (two site-years) that were naturally infested with the clubroot pathogen. In addition, fluazinam fungicide was drench applied to one treatment of the commercial standard cultivar immediately after transplanting. The napa cabbage cultivars Yuki, Deneko, Bilko, and Mirako (in 2009) and Emiko, Mirako, Yuki, and China Gold (in 2010) were evaluated only on organic soils (two site-years). At harvest, the roots of each plant were assessed for clubroot incidence and severity. Also, plant and head characteristics of the resistant green cabbage cultivars were evaluated at one site in 2010. The green cabbage cultivars Kilaton, Tekila, Kilaxy, and Kilaherb were resistant to pathotype 6 (0% to 3.8% incidence), but ‘Bronco’ was susceptible (64% to 100% incidence). Application of fluazinam reduced clubroot severity on ‘Bronco’ by 6% at one of three sites. Resistance was more effective in reducing clubroot than application of fluazinam. Plant and head characteristics of the resistant cultivars were similar to those of ‘Bronco’ treated with fluazinam. Napa cabbage cultivars Yuki, Deneko, Bilko, Emiko, and China Gold were resistant to clubroot (0% to 13% incidence), and ‘Mirako’ was highly susceptible (87% to 92% incidence). We conclude that the clubroot resistance available in several cultivars of green and napa cabbage was effective against P. brassicae pathotype 6.

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Alan W. McKeown, John W. Potter, Mary Gartshore, and Peter Carson

Root lesion nematodes (Pratylenchus penetrans Cobb) are well-adapted to sandy soils and have a host range including most agronomic, horticultural, and wild species grown in Ontario. As native climax sand-prairie species have coexisted with the nematode for millennia, resistance or tolerance may have developed. We have screened using the Baermann pan technique, soil samples taken from a private collection of sand-prairie species collected from local prairie remnants. Several species [Liatris cylindracea Michx., Monarda punctata L., Pycnanthemum virginianum L., Echinacea purpurea (L.) Moench] proved to be excellent hosts (>500/kg of soil) of root lesion nematode, confirming the presence of this nematode in the soil. Over two seasons, we determined that 10 plant species belonging to the families Asclepiadaceae, Compositae, Graminae, and Leguminosae to support very low numbers of P. penetrans. Brown-eyed susan (Rudbeckia hirta L.) had no root lesion nematodes throughout both seasons, Butterfly weed (Asclepias tuberosa L.) very low counts, while Switch grass (Panicum virgatum L.) and Indian grass [Sorghastrum nutans (L.) Nash] had detectable root lesion nematodes on only one sampling date each year. Big Bluestem (Andropogon gerardii Vitman), Little Bluestem [Schizachyrium scoparium (Michx) Nash], Sand Dropseed [Sporobolus cryptandrus (Torr.) Gray], Side-oats Grama [Bouteloua curtipendula (Michx.)) Torr], Broomsedge (Andropogon virginicus L.), Bush clover [Lespedeza capitata (Michx] also are poor hosts. These species have potential as cover or rotation crops useful for nematode management.