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Irrigated vegetable production dominates the landscape of the Central Sands region of Wisconsin, where sandy soil limits nutrient and water retention. Sweet corn (Zea mays L. var. rugosa) was managed organically in 2011 and 2012 growing seasons to evaluate effects of organic N input and weed management with respect to sweet corn yield and soil N content. The first treatment factor was early season manure, including spring-seeded field pea (Pisum sativum L.) incorporated as a green manure cover crop, pelletized poultry manure, and no manure. The second treatment factor was weed management intensity. The last factor was varying N application rate, split applied as feather meal during the growing season. There was a positive yield response to feather meal in both years with yields reaching 18.6 and 21.5 Mg ha–¹ in 2011 and 2012, respectively, with 224 and 112 kg N ha–¹ feather meal application, respectively. Early season manure treatments did not clearly affect yields despite 90 kg N ha–¹ applied as both manure types in 2012, and lower rates of 33 and 75 kg N ha–¹ applied in 2011 as field pea and poultry manure, respectively. These results underscore the well-known potential for rapid nutrient loss on coarse soil and management challenges associated with asynchrony between organic N release and crop uptake. Weed management contributed to an interaction effect on yield, with early tillage potentially controlling weeds in both treatments. This study demonstrated benefits of in-season organic amendment use, though limited potential for early season application on loamy sand.

Documentation of on-farm sustainability in agricultural sectors is becoming an essential element to ensure market access. An assessment process was developed to help soybean farmers document practices and verifiable advances in community, environmental and economic sustainability. Technical difficulties in analyzing and summarizing such assessment data include a large number of practices, correlation in variables, and use of discrete measures. By combining non-negative principal components analysis and common-weight data envelopment analysis, we overcame these difficulties to calculate a composite sustainability index for each individual farm and for the farm group as a whole. Applying this method to assessment data from 410 US Midwestern soybean farmers gave average sustainability scores of 0.846 and 0.842 for the soybean-specific and whole-farm assessments, respectively. Scenario analysis examined the impact if the bottom 10% of growers adopted the top ten sustainability drivers identified by the analysis. The average sustainability score only increased by 2%, but the minimum score increased from 0.515 to 0.647 for the soybean-specific assessment, and from 0.624 to 0.685 for the whole-farm assessment, while the lowest 10th percentile increased from 0.635 to 0.819 for the soybean-specific assessment, and from 0.634 to 0.920 for the whole-farm assessment. These results suggest that significant advancements could be made through focused efforts to improve adoption of sustainable practices by soybean farmers at the lower end of the spectrum.

Irrigated processing snap bean (Phaseolus vulgaris L.) production in Wisconsin, mostly in the central sands region, ranks first in both yield and harvested hectarage in the U.S. However, there is little information assessing N need across processing snap bean varieties under different irrigation strategies on sandy soils. The objective of this study was to determine the effects of N rate and irrigation on yield, pod quality, and other agronomic traits across different varieties with known differences in nodulation. Results indicated that nodulating varieties such as DMC04-95 consistently produced higher yields than the non-nodulating variety Huntington by 3.5 to 4.3 Mg ha–¹. Yield and pod quality responses to in-season supplemental N fertilizer at the rates of 0 to 135 kg ha–¹ varied across varieties. In each year, Huntington responded the most to N fertilizer, and had the lowest harvest index and the poorest pod quality. Reduced irrigation on sandy soils did not significantly reduce yield and pod quality when applied in minimal quantities sufficient to avoid permanent drought stress during blossom and pod set. Across years, the optimal in-season N rate was 90 kg N ha–¹. This, together with the 22 kg N ha–¹ applied as starter fertilizer, suggests 112 kg N ha–¹ is the optimal N rate for irrigated snap beans on sandy soils in the central sands region of Wisconsin. This rate is greater than recommended from previous studies conducted in other soil types, and may be warranted only when high yielding varieties are grown.

One of the most serious tuber quality concerns of US chip potato growers is stem-end chip defect, which is defined as a localized post-fry discoloration in and adjacent to the vasculature on the stem end portion of potato chips. The severity and incidence of stem-end chip defect vary with growing location and variety, but quantitative data describing this are not available. A multi-year and location study was conducted to evaluate chipping potato varieties for tolerance to stem-end chip defect formation and to quantify defect severity and incidence regionally and temporally. It was observed that higher night temperature in July and August compared to the regional 30-year history was consistently associated with higher SECD severity. Average SECD severity was linearly correlated with incidence of chips having severe SECD. Chip color and tuber stem-end glucose content were significantly correlated with average SECD score across all treatments. Multiple tuber samplings from early growing season to mid post-harvest storage demonstrated that some varieties, such as Nicolet and Pike, had fewer stem-end chip defects than other varieties across years and locations. Stem-end chip defect was rarely observed prior to harvest, but was apparent at the time of harvest on multiple varieties depending on the year and location. Tuber stem-end sucrose and glucose prior to harvest were not indicators of defect development at harvest and out of storage, but pre-harvest chip color was significantly correlated with defect severity 10 weeks after preconditioning was finished.

Trace amounts of acrylamide are present in many foods cooked at high temperatures. Acrylamide in processed potato products is formed from reducing sugars and asparagine and is a product of the Maillard reaction; this reaction typically occurs during frying and baking of food products. Processed potato products, including fries and chips, are relatively high in acrylamide compared with other foods and contribute substantially to dietary acrylamide. Acrylamide content in potato products is strongly affected by processing conditions, potato variety, field management, environmental conditions during tuber growth, and tuber storage conditions. Numerous approaches have been described that could potentially reduce the acrylamide content of potato products, but many influence finished product sensory attributes and may be difficult to implement. Health concerns related to acrylamide in food center on its role as a potential carcinogen. Research using feeding studies with rodent models and epidemiological studies with humans are ongoing and are likely to provide future guidance for acceptable amounts of acrylamide in food.

Skin-set is a necessary prerequisite for potato storability, but there is little published information on the effect of cultural conditions on the development of skin-set. The phellogen layer acts as a lateral meristem for the peri- derm and while active, fracture of its thin radial walls leads directly to skinning injury during harvest and handling into storage. During maturation of the periderm, these radial walls thicken. Red-skinned cultivars are often grown in muck soils in Wisconsin to improve skin condition and color. We tested skin-set and phellogen radial wall thickness for 'Red Norland' tubers grown on either loamy sand or muck soils in central Wisconsin. Skin-set varied between years and soil types, but there was no consistent effect of soil type on skin-set. Phellogen radial walls in Red Norland tubers doubled in thickness between bulking and vine-kill, but did not change in the three week period following vine- kill even when skin-set improved. Physiological processes other than cell wall thickening must be responsible skin-set during the three weeks following vine death.

Global consumption of potato (Solanum tuberosum L.) continues to shift from fresh potatoes to value-added processed food products such as potato chips. One serious tuber quality defect of chipping potatoes is stem-end chip defect, which results in chips with dark-colored vasculature and adjacent tissues at the tuber stem end after frying. In this study, treatments of moderate water deficit for 14 days, alone or in combination with moderate daytime heat stress at 30 °C, as well as varied chemical maturity of tubers at harvest were imposed in controlled-environment greenhouses. Only temperature stress for 14 days in 1 of 2 years significantly changed the occurrence of stem-end chip defects. Water deficit for 14 days and chemical maturity of tubers harvested at four time points from early tuber bulking to after vine senescence did not have significant impacts on defect incidence or severity. Biochemical analyses showed that more severe defects with larger areas of dark color on the stem end of chips were associated with increased amounts of tuber stem-end glucose and increased stem-end acid invertase activity. We conclude that moderate environmental stresses and maturity of tubers at harvest are not sufficient to consistently cause stem-end chip defect.

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.

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.

There is significant interest from processors in producing organic sweet corn and snap bean. However, large-scale production is necessary for this to be a practical and economical venture for processors. This study focused on the feasibility of managing weeds in organic sweet corn and snap bean, utilizing methods that are practical in large hectarage. Tactics such as rotary hoe, interrow cultivation, and a stale seedbed were evaluated alone or in combination. Hand-weeded and herbicide-based treatments were included for each crop for comparison. Percentage weed control, weed biomass, and crop yield were quantified, and net profit was calculated for each treatment. Organic weed management was feasible in snap bean, with yields similar among several of the organic treatments and the herbicide treatment in all 3 yr of the study. Interrow cultivation was the most effective means of organic weed control in snap bean. Organic weed management was possible in snap bean because it is a short-season crop and an effective competitor with weeds in the crop row. Organic weed management was more difficult in sweet corn because of the longer crop season and poor competition with weeds in the crop row. In sweet corn, the organic treatment involving three interrow cultivations was the only one consistently similar in yield to the herbicide treatments. Higher net profits were attained for most of the organic treatments in both crops because of the organic premium. Market saturation and organic premium adjustments are factors for grower consideration in this potential industry, particularly for sweet corn production.

Environmental stress during the growing season can reduce the quality of stored Solanum tuberosum (potato) tubers. Changes in greenhouse grown Russet Burbank tuber water potential and tuber composition following periods of moderate drought, heat, or drought and heat stress were characterized. Decreased leaf and tuber water potentials were observed at the end of stress treatments. Decreased tuber water potential caused dramatic declines in tuber pressure potential. Tuber sucrose content increased with the severity of stress. Changes in tuber glucose and malic acid contents were also observed. Stress during early tuber bulking had a larger effect on tuber sugars at the end of the stress period than stress during late bulking. Stem-end glucose concentration of tubers at harvest after vine senescence was greater in tubers from plants stressed at early tuber bulking compared to late bulking.

Maleic hydrazide has been reported to increase the proportion of US #1 (> 113 g) potatoes and lower the concentration of reducing sugars of potato tubers in storage, thus improving fry color. We tested the effect of three different application timings of maleic hydrazide on total and US #1 yields, average tuber weight, “b” and cull yields, and tuber glucose and sucrose concentrations at harvest and after storage. The cultivars evaluated included two round white potatoes, Atlantic and White Pearl, and one russeted cultivar, Freedom Russet. Maleic hydrazide had no effect on total yield or US #1 yield for either round white cultivar, but increased both total and US #1 yield for Freedom Russet. In addition, maleic hydrazide reduced average tuber weight for Atlantic. These yield effects were dependent on application timing. Maleic hydrazide had no effect on yield of cull tubers. Maleic hydrazide did not lower glucose or sucrose concentrations at harvest or during storage for any of the cultivars tested, and increased Atlantic tuber glucose concentration at harvest. In summary, the effect of maleic hydrazide on yield was cultivar-dependent and maleic hydrazide did not reduce tuber glucose concentrations for any cultivar tested.

Compacted soils have been found in intensively cultivated vegetable crop regions of Central Wisconsin, resulting in the wide scale use of subsoil tillage by growers. The goal of this project was to assess potato (Solanum tuberosum L.) yield and quality response to soil compaction and subsoil tillage. Potato quality factors evaluated were marketable yield, tuber size distribution, internal quality, and sugar concentration. A controlled small plot experiment and several field scale experiments located in collaborating grower fields were conducted to assess potato and soil responses to subsoil tillage. Cone index profiles showed the potential for limited root growth below the compacted soil layer with values >2.0 MPa. Subsoil tillage reduced cone index values to

Pink eye (PE) is a tuber disorder that leads to processing complications and bud-end rot in storage. Despite the significance of PE for the potato processing industry, limited progress has been made in understanding the physiological basis of this disorder. Although the internal autofluorescence that characterizes PE has been described, the external symptoms of PE have not been well characterized or correlated with internal cellular symptoms. It is of vital importance to determine the physiological and cytological effects of PE in order to understand how it is caused and to develop effective management strategies to prevent the disorder. External symptoms progressed from pinkish discoloration around tuber eyes to water-soaked and corky patch lesions. Internal symptoms progressed from erratic browning around cortical cell walls to necrotic zones and cells with dark, circular inclusions. These areas often became surrounded by an internal PE-related periderm, while the native periderm often became compromised or lost. Vital staining with fluorescein diacetate showed that cortical and periderm cells underneath the native phellem became non-viable in PE tissue. Immunolocalization of homogalacturonan and extensin epitopes indicated that these cell wall polymers were not altered in pink eye afflicted tissues. These results conclusively show that the PE disorder results in or is caused by cell death in tissue underneath the native phellem, but does not lead to either cell wall breakdown or extensin deposition which is often characteristic of pathogen activity.

A densely compacted soil layer has been a prevalent feature of the vegetable crop production region of Central Wisconsin, resulting in poor water drainage, increased susceptibility to tuber disease, and reduced yield and quality in potatoes. Subsoil tillage has been implemented on a wide-scale for management of problems associated with compacted soil layers. Pink eye is a tuber disorder that causes storage and processing losses. Periods of moisture stress and increased hill temperatures have been linked to pink eye incidence, but the cause of this disorder is unknown and few specific management recommendations exist. The goals of this work were to quantify the impact of compacted soils and subsoil tillage on development of potato pink eye. Small plot experiments were conducted to quantify response of soil conditions and potato pink eye to soil compaction and subsoil tillage. Compacted soils resulted in higher volumetric soil water content and extended periods of free water, especially after substantial precipitation events. Subsoil tillage allowed for more rapid movement of water following large precipitation events decreasing periods of free water. More compacted soils also had higher soil temperatures. Subsoil tillage delayed the development and progression of pink eye symptoms, but did not influence overall incidence. Increased soil moisture and temperature corresponded with more rapid development of pink eye in compacted and conventionally tilled soils. This research suggests subsoil tillage may be useful in reducing the severity of pink eye symptoms by alleviating compacted subsoil layers that limit water drainage. In addition, prevention of compaction reduced soil temperatures which limited pink eye development.

Potato (Solanum tuberosum) yield has been optimized for in-row spacings ranging from 15 to 40 cm depending on region, targeted market, variety, and other factors. Production goals require optimizing tuber size to maximize crop value. Our goal was to evaluate the effect of plant, stem, and tuber density on stem and tuber set, potato yield, tuber size distribution, and other quality factors. Research plots were established within a 20-ha commercial production fi eld, and analysis was done with linear and nonlinear regression. Plant density decreased with increasing in-row plant spacing. Stem density increased linearly with increasing plant density, but response differed across years. Tuber density increased to a maximum of 190 tubers m –2 in response to plant and stem density, with stem density more accurately predicting tuber set. Yield was related to plant, stem, and tuber density using nonlinear regression, more accurately predicted by stem and tuber density than by plant density. A hyperbolic model was used to predict yield with estimated maximum yield of 86 Mg ha –1 when related to stem density. Average tuber size was related to stem and tuber density using the inverse yield law and estimated maximum average tuber size of >200 g. The distribution for tuber sizes was estimated as a Weibull probability density function that predicted changes in tuber size in response to stem and tuber density. The hyperbolic model accurately predicted tuber density and yield with the added benefi t that estimated parameters have biological importance, unlike polynomial or other regression models used to predict crop yield. Modeling tuber size distribution over different stem densities provides a mechanism for future economic analysis to optimize management and conduct sensitivity analysis to determine the most important factors infl uencing crop value.

‘MegaChip’ is a medium-late variety for chipping, with round-oval tubers of white tan skin and white flesh. MegaChip has consistently shown good to high yield potential. The tubers bulk early and produce a good size distribution for chipping. The specific gravity is consistently high and is close to the solid content of ‘Atlantic’. MegaChip has longer dormancy than ‘Snowden’ and Atlantic and stores well. It produces high quality chips that have an excellent color both from the field and after storage at 7.2 to 10 C. MegaChip showed a high level of resistance to common scab at most locations in North Central Regional trials and is moderately resistant to foliar early blight, powdery scab, pink rot, dry rot and soft rot. MegaChip is also fairly resistant to shatter bruise.

Brown centre (also referred to as incipient hollow heart, brown heart, or sugar centre) and hollow heart are common physiological disorders of potato. Brown centre and hollow heart are caused by similar conditions, but can occur concurrently or separately in potato tubers. No plant pathogens have been associated with brown centre or hollow heart development and seed tubers afflicted with brown centre or hollow heart commonly produce daughter tubers with no symptoms. Furthermore, tubers afflicted with brown centre or hollow heart show no external signs or symptoms on the tuber and are rarely affected by secondary pathogens. Brown centre can be described by accumulation of brown discolouration of pith tissue which is unique relative to other disorders that cause internal browning. The brown discolouration occurs as a result of cell necrosis caused by cell membrane and organelle damage. Brown centre commonly leads to development of hollow heart under conditions suitable for its development. Conversely, brown centre may not develop into hollow heart or can disappear as the potato plant recovers from conditions and stress that led to its development. Hollow heart is best described by the development of cavities in the pith of the tuber. Hollow heart can occur anywhere along the length of the tuber but always occurs in the central pith. Hollow heart does not occur at the tuber surface. Hollow heart is best described by single or multiple cavities that are traverse or run longitudinal to the pith. Cavities can be a few mm up to 2 or more cm in diameter and can run nearly the entire length of the tuber depending on the severity of the disorder. Cavities are irregularly shaped and can be in the shape of narrow slits or in the form of stars. Potato Research (2007) 50:395–398 DOI 10.1007/s11540-008-9087-0

Potato tuber pink eye (PE) is a disorder of unknown origin that results in significant postharvest quality deterioration and rot. Little is known about the physiology of PE, including the characteristic tissue autofluorescence that defines the PE syndrome. The objective of this research was to identify the source of PE-induced autofluorescence and PE-related susceptibility to infection. The suberized barrier of the native periderm and cellular characteristics of neighboring parenchyma tissues were investigated to determine their involvement in the PE disorder. The results create a new physiological model describing the disorder and addressing the enigma of PE. Characteristics of the PE model emerge from the following results: (1) the integrity of the suberized barrier of the native periderm was compromised or absent in some surface areas of PE tubers thereby implicating the breakdown of the native periderm and its associated suberin barrier with PE and the susceptibility of PE tubers to pathogen infection; (2) the PE complex was characterized by unusual suberin poly(phenolic) (SPP) accumulations in the cortical parenchyma followed by latent suberin poly(aliphatic) (SPA) accumulations that were generally insufficient to form a complete barrier that was competent to block infections by pathogenic bacteria and fungi; (3) the aberrant absence or compromised integrity of the suberin barrier, including associated waxes, resulted in erratic increased susceptibility to water vapor loss known to cause tuber shrinkage and flaccidity; (4) widespread accumulations of SPP on parenchyma cell walls were the durable source of autofluorescence commonly used to determine the presence of the disorder; (5) the erratic development of unusual internal phellogen and periderm layers that, if complete with SPA, blocked hyphal advancement; (6) combined, the data provide a plausible explanation for PE infection court and rot anomalies as they occur without ingress of a wound opening. Results also demonstrated that neutral red may be used as a sensitive fluorochrome to detect intact hydrophobic areas in hyphae. Collectively, the results provide compelling evidence that the PE disorder includes a physiological basis.

Persian darnel control options are limited and unmanaged populations can cause substantial crop yield loss. Integrating crop diversification and higher crop seeding rates into a cropping system might improve Persian darnel management. Field experiments were conducted to determine the effect of different crops and increased crop seeding rates on Persian darnel fecundity. Persian darnel produced up to 2,800 seeds per plant and 53,000 seeds/m2when grown without competition. Increasing crop density reduced Persian darnel tillers per plant, seed weight, and fecundity. Increasing crop density reduced Persian darnel fecundity 0.4 to 0.2% per spring wheat plant, 0.6 to 0.1% per canola plant, and 16 to 8% per sunflower plant. Persian darnel fecundity was impacted the greatest by reduced weed seedling establishment, which was caused by crop competition and seeding sunflower late in the spring preceded by a nonselective herbicide application. Results indicated delaying the seeding of spring crops or including a late-seeded warm season crop, like sunflower or safflower, in the cropping system is an effective weed management tool for reducing Persian darnel fecundity.

Millennium Russet is a medium-late variety with long tubers having light russet skin and white flesh. It has potential as a fresh market and processing (french fries) variety. The tuber type of Millennium Russet is similar to Russet Burbank, but with better external and internal quality. The marketable yield, tuber set, and specific gravity are higher than Russet Burbank. Tubers show good fry color when processed from cold storage (7.2 C). Millennium Russet has a bland flavor and is less mealy and discolored than Russet Burbank. Chemical maturity of Millennium Russet occurs at approximately the same time as Russet Burbank, but it has lower sucrose levels in the bud and stem end. The glucose levels of Millennium Russet were 50% less than Russet Burbank throughout the first 4 months of storage at 10 C. Low glucose levels in the stem end of Millennium Russet when processed out of storage suggest tolerance to stress and low vulnerability to sugar end. Millennium Russet is resistant to common scab and corky ring spot, moderately resistant to dry rot, pink rot, and black scurf, and moderately susceptible to Verticillium wilt, bacterial wilt and brown rot. Millennium Russet is more sensitive to blackspot bruise than Russet Burbank, but more resistant to shatter bruise. Tuber yield of Millennium Russet was less responsive to nitrogen rates when compared with Russet Burbank, but tuber size distribution was more responsive to increases in in-row spacing.

Integrated weed management practices, such as crop rotation and increased seeding rates, potentially improve weed management. Yet, few studies compare competitive interactions of weeds with different crops. This research quantified the impact of Persian darnel on spring wheat, canola, and sunflower yield across different seeding rates. Increasing crop density increased yield when Persian darnel affected crop yield early in physiological development. Crop yield loss was estimated to reach 83, 70, and 57% for spring wheat, canola, and sunflower, respectively, at high Persian darnel densities. Persian darnel reduced spring wheat yield by limiting the number of tillers per plant and seed per tiller; reduced canola yield by limiting the number of branches per plant, pods per branch, and seed per pod; and reduced sunflower yield by limiting the number of seed per plant. Persian darnel affected crop growth early in physiological development, indicating that interspecific interference occurred early in the growing season. Cultural and resource management aimed at reducing Persian darnel impact on resource availability and crop yield components will reduce Persian darnel impact on crop yield.

Uncontrolled kochia plants that regrow after small-grain harvest can produce substantial numbers of seeds. An average of 4,100 seeds per plant were produced between harvest (late July to mid August) and the first killing frost (late September) at three locations in Montana. Field experiments were conducted to determine the optimal timing of postharvest herbicide applications to prevent kochia from producing viable seeds. Herbicide treatments were applied at three timings from late August to mid September. The most effective treatments were glyphosate (631 g/ha) and paraquat (701 g/ha) applied at the second application timing (late August to early September). These treatments reduced kochia seed production by 92% or greater at each site. Kochia regrowth by this time had sufficient leaf area for herbicide absorption, but few viable seed had been produced. Herbicide treatments at the first and third application timings were generally less effective and more variable in reducing kochia seed production. Sulfentrazone (157 g/ha) and 2,4-D (561 g/ha) were not as effective at reducing seed production as other herbicide treatments.

The advent of site-specific weed management has generated research aimed at predicting weed spatial distributions from existing weed maps or correlations with soil properties and edaphic factors. Forecasting the spatial distribution of annual weeds requires knowledge of fecundity, dispersal, management, and suitable habitat distribution. We hypothesized that wild oat habitat was limited by field-scale heterogeneity in plant-available water. We eliminated seed number and dispersal limitations by seeding wild oat in areas with and without historical wild oat patches in three similarly managed spring wheat fields that differed in soil properties and wild oat infestations and were situated within a 160-km radius of Great Falls, MT. Wild oat habitat was quantified by wild oat leaf area growth rate, mature shoot biomass, seeds produced per plant, biomass water use efficiency, and competitive ratio with spring wheat. Soil texture and plot elevation correlated with existing wild oat patch areas in indivi...

Glyphosate-resistant crop species have increased in number over the past decade as growers eagerly adopt this simple and effective weed management technology. Glyphosate-resistant wheat cultivars are being developed and may soon be available to growers. The objective of this paper is to discuss the pest management implications of glyphosate-resistant wheat in the western United States, a region stretching from the Great Plains to the Pacific Ocean that produces more than 80% of the nation's wheat crop. The benefits of glyphosate-resistant wheat include: (1) improved weed control, particularly of difficult-to-control weeds, such as winter annual grasses belonging to the Aegilops, Avena, Bromus, Lolium, Poa, Secale, and Setaria genera; (2) an ability to control weeds resistant to currently available wheat herbicides; (3) an extended application window for control of late-emerging weeds; and (4) improved crop safety. Although these benefits are not to be minimized, they need to be considered in the light of ...

Managing weed infestations in a spatially precise manner requires accurate and cost-effective weed identification techniques. The goal of our research was to quantify the accuracy of continuous weed presence–absence maps and assess how management based on those maps may affect producer net returns. Each continuous sampled map covered the entire field and contained vector polygons labeled as either wild oat presence or wild oat absence. The accuracy of the continuous wild oat maps at each sampling time was determined from georeferenced quadrats of wild oat densities. The accuracy of the continuous wild oat seedling maps ranged from 48.3 to 87.1% among the six site-years. The accuracy of the wild oat seedling maps improved by at least 8% when a 10-m buffer was included around areas mapped as wild oat presence. The accuracy of continuous wild oat panicle maps from the combine at harvest ranged from 65.8 to 90.9% among the six site-years. The variation in accuracy for the wild oat seedling maps among...

The objectives of this study were to use a computer simulation model to predict the influence of herbicides and mechanical treatments on giant foxtail population dynamics, annualized net return (ANR), and the giant foxtail economic optimum threshold (EOT) in a corn–soybean rotation over 20 yr. Mechanical treatments were interrow cultivation in corn and rotary hoe in soybean. Herbicides at full (1 ×) and half (½ ×) rates applied alone reduced giant foxtail seedbank 95% within 4 and 8 yr, respectively. Predicted seedbank dynamics had more variability when managed with herbicides at ½ × than at 1 × rates applied alone. Mechanical treatments integrated with herbicide at ½ × rates resulted in giant foxtail seedbank and variability similar to herbicides at 1 × rates applied alone. ANR was maximized when herbicides were applied between ⅜ × and 9/16 × rates applied alone. As initial giant foxtail density increased from 100 to 10,000 seeds m−2, the herbicide rate that maximized ANR increased. Economic opt...

The adoption of precision technologies that spatially register measurements using global positioning systems (GPS) greatly facilitates conducting large-scale on-farm research by farmers. On-farm experiments that utilize producer equipment include variations in agronomic practices that occur in situations where we want to predict the effect of inputs on yield. The domain of inference for such on-farm studies therefore more closely matches that desired by researchers. To investigate the feasibility of on-farm research using GPS, a study was conducted to evaluate the potential benefit of site-specific weed management. The study utilized producer-maintained field-scale equipment on four Montana farms in dryland spring wheat production. Paired site-specific and whole-field herbicide treatment areas were established in 0.9 to 1.9-ha blocks using consultant weed maps and a geographic information system (GIS). Yield was unaffected by herbicide treatment strategy (site-specific or broadcast). Minimal dete...

Field studies were conducted in 1995 and 1996 to determine the rate response of velvetleaf seedling survival, seed production, and shoot biomass to postemergence herbicides in corn and soybean. Dicamba and imazethapyr were applied to corn and soybean, respectively, at 1, ½, ¼, ⅛, 1/16, 1/32, and 0× labeled rates. Velvetleaf mature plant density was linearly related to seedling density, thus indicating that seedling survival was not density dependent, even after seedling densities exceeded 150 plants m−2. Seedling survival as influenced by herbicide was described by a dose–response curve in corn and soybean. In corn, seedling survival ranged from 0 to 48% across herbicide treatments and years. Seedling survival was greater at the ½× or lower herbicide rates than at the 1× rate. In soybean, maximum seedling survival was 61 and 14% in 1995 and 1996, respectively, and minimum seedling survival was less than 2% in each year. Seedling survival was less in 1996 than in 1995 because velvetleaf was infect...

The objectives of this study were to model the influence of herbicides, wilt disease, and mechanical treatments on velvetleaf population dynamics, annualized net return (ANR), and economic optimum threshold (EOT) in a 20-yr rotation involving alternate years of corn and soybean. Mechanical treatments were interrow cultivation in corn and rotary hoeing in soybean. Herbicides at a quarter (¼×) rate or lower did not reduce velvetleaf seed banks without mechanical treatments in the absence of wilt. Herbicides at full (1×) and half (½×) rates decreased velvetleaf seed banks 95% within 6 and 20 yr, respectively, when there was no wilt. Herbicides at ½× rates with mechanical treatments reduced the seed bank 95% in only 10 yr, but mechanical treatments did not increase the rate of seed bank decline with 1× rates. Wilt infection had to occur annually to reduce velvetleaf seed banks as effectively as herbicides at 1× rates alone. ANR was maximized with herbicides at reduced rates, even though they were not...

Traditionally, herbicide efficacy has been evaluated by visual ratings, but these data provide little insight to the biological response of weeds to herbicides. Field studies were conducted in 1995 and 1996 to determine the rate response of Setaria faberi seedling survival, seed production, and biomass to postemergence herbicides in Zea mays and Glycine max. Nicosulfuron and sethoxydim were applied to Z. mays and G. max, respectively, at 1×, 12×, 14×, 18×, 116×, 132×, and 0× the label rate. Mature plant density of S. faberi was linearly related to seedling density, indicating that seedling survival was not density dependent. Based on a nonlinear dose–response analysis, maximum S. faberi survival was 55% in Z. mays across years and 60 and 45% in G. max in 1995 and 1996, respectively. Minimum survival was 0% except for Z. mays in 1996 when it was 13%. The minimum survival was greater in Z. mays in 1996 due to greater survival of late cohorts than in 1995. Setaria faberi seedling survival was greate...

In the first of 2 field studies, weed biomass and soybean seed yield were used to evaluate 16 soybean genotypes for competitive ability against 12 weed species at Rosemount, MN, in 1992 and 1993. The yield and ranking of soybean genotypes often varied with the weed species. Grass weed species reduced yields the most, and small-seeded broadleaf weeds reduced yields the least across years. ‘Parker’ was highly competitive, as it suppressed weed biomass and produced high soybean yield. ‘Kato,’ ‘Kasota,’ ‘Dawson,’ and ‘Glenwood’ minimized weed biomass and maintained soybean yield while in competition with grass weeds but yielded poorly relative to other soybean genotypes in weed-free conditions. ‘Lambert’ produced high soybean yield in weed-free conditions, but yield dropped markedly when in competition with grass weeds. ‘Grande,’ ‘Heifeng 25,’ and ‘Norman’ soybeans were poor competitive genotypes in weedy situations and low yielding in weed-free conditions. A 2nd field study conducted at Rosemount and St. Paul, MN, during 1993 evaluated 16 soybean genotypes under 4 levels and durations of weed pressure for weed competitiveness. Parker, ‘Sturdy,’ and M89-794 were most competitive in suppressing weed biomass and producing high yields. Lambert yielded fairly well but allowed high weed biomass. M89-1743, M89-1006, ‘Archer,’ and ‘Ozzie’ yielded poorly and did not sup press weed biomass production. No relationship was found between weed competitiveness and soybean canopy area, height, and volume measured 30–45 d after planting (DAP).

Quality and storability of potato tubers harvested for storage are affected by their chemical, physiological and physical maturity. The sucrose concentration in potato tubers is indicative of the chemical maturity of the crop and of the potential processing quality of the crop after storage. High reducing sugar concentrations result in undesirable discoloration of Med potato products. Sucrose does not directly contribute to the discoloration of tuber tissue upon frying, but it influences reducing sugar concentrations during storage. Physiologically mature tubers have maximized their dry matter content, resulting in high specific gravities that are desirable for most aspects of potato processing. We examined the effect of different planting and vine-kill dates on the sucrose and glucose concentrations and specific gravity of five processing potato cultivars grown at Hancock, WI, during 2002 and 2003. Although planting date usually had no effect on sugar content at harvest, sucrose and glucose content decreased with earlier planting date at vine-kill in one of two years. Greater sucrose and glucose concentrations and specific gravities were found at harvest with later vine-kill dates. Of particular concern for processing, stem-end glucose concentrations consistently exceeded bud-end glucose concentrations for all cultivars, regardless of the cultural parameters implemented. Physically immature tubers have poor skin set and are prone to skinning and mechanical damage during harvest, which renders them more vulnerable to dehydration and infection by rotting pathogens in storage. Skin set of ‘Russet Burbank’ tubers in 2003 improved with late vine-kill timing. Our data indicate that chemical maturity does not necessarily correlate with either physiological or physical maturity in processing cultivars, thus rendering the use of cultural practices to improve tuber maturity at harvest problematic.

Sugar-end defect is a tuber quality disorder and persistent problem for the French fry processing industry that causes unacceptable darkening of one end of French fries. This defect appears when environmental stress during tuber growth increases post-harvest vacuolar acid invertase activity at one end of the tuber. Reducing sugars produced by invertase form dark-colored Maillard reaction products during frying. Acrylamide is another Maillard reaction product formed from reducing sugars and acrylamide consumption has raised health concerns worldwide. Vacuolar invertase gene (VInv) expression was suppressed in cultivars Russet Burbank and Ranger Russet using RNA interference to determine if this approach could control sugar-end defect formation. Acid invertase activity and reducing sugar content decreased at both ends of tubers. Sugar-end defects and acrylamide in fried potato strips were strongly reduced in multiple transgenic potato lines. Thus vacuolar invertase silencing can minimize a long-standing French fry quality problem while providing consumers with attractive products that reduce health concerns related to dietary acrylamide.

Freedom Russet was developed from a cross between ND14-1, a parent with scab resistance, and W1005rus, a parent with good processing quality. It is a mid-season cultivar and can be used for dual purposes for both fresh market and processing. The tubers of Freedom Russet are oblong-long with medium-dark russet skin, and have an attractive appearance. Freedom Russet tubers have better external and internal qualities than Russet Burbank tubers. The total and US No. 1 yield of Freedom Russet is equal to or higher than Russet Burbank in most environments. The specific gravity of Freedom Russet is similar or 1–3 unit less than Russet Burbank. Freedom Russet produced better fry color than Russet Burbank when processed after storage at 10, 8.9, and 7.2°C. It showed similar susceptibility to both early blight and late blight compared to Russet Burbank. Freedom Russet is resistant to common scab and moderately resistant to powdery scab. It is similarly susceptible to soft rot and pink rot as Russet Burbank, and clearly expresses bacterial ring rot symptoms. Freedom Russet is tolerant to Verticillium wilt and showed better yield potential than Russet Burbank under early dying pressure.