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Lisa Wasko DeVetter, Rebecca Harbut, and Jed Colquhoun

Recent cultivar releases of cranberry (Vaccinium macrocarpon) have been reported to differ in terminal bud development, biennial bearing tendencies, and external bud appearance. However, verification of these claims and cultivar comparisons with respect to these characteristics are lacking. The objectives of this project were to 1) evaluate flower initiation, bud development, and potential return bloom across several cultivars of cranberry, including recent introductions; and 2) determine the relationship between external appearance of buds and the presence/absence of flower initials. Samples of upright shoots representing the cultivars Searles, Stevens, HyRed, and Crimson Queen were collected from a commercial cranberry marsh located in central Wisconsin during the 2011 and 2012 growing seasons. Collected uprights were separated based on reproductive status (i.e., reproductive or vegetative). Buds were then dissected and analyzed for presence/absence of flower initials using light and scanning electron microscopy. Growing degree days (GDD) were calculated and related to the progression of bud development. Flower initials were first observed on 29 July 2011 and 10 July 2012, or 290 and 322 GDD, respectively. Excluding ‘Searles’, dates of initiation were the same across all cultivars and did not differ based on reproductive status. Descriptive bud data demonstrated that wider buds are more likely to contain flower initials and overall bud width tended to be greater among recent cultivar releases. Biennial bearing tendencies were also lower among recently released cultivars, as exhibited by greater occurrences of potential return bloom. Results from the study provide evidence that recently released cultivars differ in bud development, have an increased potential for return bloom, and overall wider buds. These findings suggest newer cultivars may have different mechanisms regulating mixed bud development and other yield-contributing factors.

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Heidi J. Johnson, Jed B. Colquhoun, and Alvin J. Bussan

There is significant interest from vegetable processors, growers, and consumers in organic sweet corn (Zea mays) production. Organic nitrogen (N) management is particularly challenging in high N consuming crops such as sweet corn because of the low N content and low N to phosphorus (P) ratios of organic soil amendments. Various management programs were compared to determine the optimal combination of soil amendments and green manure crops for organic sweet corn production. Alfalfa (Medicago sativa), rye (Secale cereale), and field pea (Pisum sativum) were used as green manure crops. Composted poultry manure and a high N content organic fertilizer were used as organic amendments. Ammonium nitrate was used in a conventional management program for comparison. Treatments were designed to deliver a full rate of N (150 lb/acre), a half rate of N (75 lb/acre), and to limit the amount of P applied. Phosphorus can become a source of pollution when applied to erodible soils, particularly when soils already contain excessive P. Sweet corn yield in many of the organic programs was highly variable among years while the yield was more consistent in the conventional program. This was attributed to differences in organic N mineralization in both the green manure crops and the amendments. The most stable yield from an organic treatment, among years, was achieved using the commercially available organic N fertilizer. Commercially available amendments were costly, and although organic sweet corn received a premium price in years when organic yields were lower, profit was reduced by the high cost of N management.

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Renata L. Solan, Jed B. Colquhoun, Richard A. Rittmeyer, and Daniel J. Heider

Field trials were conducted at Hancock, WI, in 2008 and 2009 to determine reduced-herbicide weed management programs for ‘Russet Burbank’ and ‘Bannock Russet’ potato (Solanum tuberosum) based on cultivars’ developmental characteristics. Six treatments applied to each cultivar included: preemergence (PRE) broadcast s-metolachlor and metribuzin (the industry standard); PRE in-row banded s-metolachlor and metribuzin with cultivation at 15% canopy development; postemergence (POST) broadcast rimsulfuron and metribuzin; POST between-row banded glyphosate; POST in-row banded rimsulfuron and metribuzin with cultivation at 15% canopy development; and cultivation alone at 15% canopy development. In 2008 and 2009, for both cultivars, visual assessments indicated weed suppression was reduced when glyphosate was POST between-row banded, compared with other treatments, and weed suppression was consistently high when rimsulfuron and metribuzin were POST broadcast. As expected, in-row weed control was consistently poor when glyphosate was between-row POST banded, providing no in-row weed control. Regardless of cultivar or year, in-row weed control was comparable to or better than the industry standard when herbicides were broadcast or in-row banded with cultivation at 15% canopy development. Potato yield was poor when glyphosate was POST between-row banded and when cultivation was used without herbicide application. Yield was consistently high when herbicides were POST broadcast, which provided no reduction in treated area from the industry standard of PRE broadcast. In both years, ‘Russet Burbank’ yield was greatest when herbicides were POST in-row banded with cultivation at 15% canopy development; ‘Bannock Russet’ yield was greatest when herbicides were PRE in-row banded with cultivation at 15% canopy development. Cultivar-appropriate weed management systems that band herbicides over the crop row in combination with cultivation would provide a two-thirds decrease in herbicide application from the industry standard without risk of yield loss.

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Heidi J. Johnson, Jed B. Colquhoun, Alvin J. Bussan, and Carrie A.M. Laboski

Organic sweet corn (Zea mays) production is challenging for growers because of the high nitrogen (N) requirements of sweet corn and the relatively low N content of organic soil amendments. Total N supplied and rate of mineralization throughout the growing season are two important aspects in determining the optimal N management program. Green manure (GrM) crops, composted manures, and commercially available organic fertilizers are used to manage N in organic production systems. Using a combination of these tactics can optimize N while minimizing cost. In this study, we used combinations of composted poultry manure (CPM) and two organic fertilizers (one high N and one with a balance of nutrients) with three GrM crops [rye (Secale cereale), alfalfa (Medicago sativa), and pea (Pisum sativum)] in a loamy sand soil for a 112-day laboratory incubation study. Total plant available N (PAN) was quantified at six times throughout the 16 weeks to determine total N mineralized and rate of N release from each of the management programs. The CPM and the high N organic fertilizer mineralized completely within the first 6 weeks of the study, while only 65% of the other organic fertilizer mineralized by the end of the study. Total N mineralized from pea grown as a GrM for 48 days was comparable to the amount of N mineralized from rye suggesting that pea as a GrM crop should not receive an N credit in field production on a sandy soil. Significant quantities of PAN were mineralized from alfalfa residue, the equivalent of 80 lb/acre, although this is not sufficient for sweet corn production. The combination of alfalfa and the high N organic fertilizer provided sufficient N for sweet corn production and the mineralization rate closely matched sweet corn need. The release of N from CPM, even in combination with GrM crops, was asynchronous with sweet corn crop need.