Search

The ability to use the protoporphyrinogen oxidase (PPO)-inhibiting herbicides fomesafen, flumioxazin, and sulfentrazone in potato is limited regionally or by soil texture, largely because of crop injury noted in research in the 1990s. With that in mind, we evaluated whether reducing the herbicide rates could maintain weed control while providing more consistent crop safety. Studies were conducted on a silt loam and a coarse-textured loamy sand soil. Soil texture played a greater than anticipated role in PPO-inhibitor herbicide injury risk as it relates to high-precipitation events. For example, in 2020 at the silt loam location, there were five precipitation events across the season that exceeded 2.5 cm, including one 6 d after treatment (DAT), and a seasonal total precipitation that was over 10 cm greater than the previous year. Despite excessive moisture and initial potato injury as high as 27% where flumioxazin was applied at the high rate with S-metolachlor, by 29 DAT injury was less than 10% in all treatments, and marketable tuber yield was similar among treatments. In contrast, in 2020 at the loamy sand location, there were four precipitation events across the season that exceeded 2.5 cm, and potato injury was as much as 60%. In 2020 the high amount of injury from flumioxazin was hypothesized to be caused by precipitation before herbicide application and not after, suggesting a need for more research in this area. This work documents the fine line between yield reduction presumably caused by reduced weed control and yield reduction assumed to be related to herbicide injury. This delineation between adequate weed control and consistent crop safety may differ by soil texture and environmental conditions, supporting the notion that custom-tailored weed management may become more necessary as high-precipitation events become more common in upper midwestern U.S. agricultural systems.

Weed management in carrot is challenging, given slow and inconsistent crop emergence and early-season growth and the lack of practical season-long management tools such as herbicides. We investigated holistic carrot production systems with a focus on minimizing inputs while optimizing resource use. In an overall sense, results of this work were consistent between years, and stark. The choice of carrot variety had a moderate influence on carrot foliar canopy development and, subsequently, weed density. For example, ‘Cupar’ carrot formed a complete crop canopy sooner than the other dicer-type ‘Canada’ variety. Likely as a result, density of weed species such as spotted ladysthumb and common lambsquarters was less where ‘Cupar’ was grown compared with where ‘Canada’ was grown. Gibberellic acid as a foliar application was not successful in these studies and, in a few cases, may have even increased weed-seed germination and establishment. Adding two carrot rows to the current regional industry-standard three-row bed system not only enhanced competitiveness with weeds but also improved carrot yield without additional fertilizer, water, or pest management inputs. By far, though, the most successful strategy to reduce weed density while maintaining or improving carrot yield was to delay seeding by 17 to 19 d. We anticipate more holistic production system research that integrates low-input alternatives in other crops as herbicide-resistant weeds proliferate while few new herbicides are developed. As was demonstrated in this research, such novel approaches can be successful without adding significant economic burden to the farmer or increasing risk of crop failure.

Linuron herbicide has been a mainstay of carrot weed management for years, but uncertainty around regulatory registration review and an increased prevalence of herbicide-resistant weeds have spurred interest in identifying alternatives that can be readily adopted in production. With this context in mind, herbicide programs were evaluated on a coarse-textured, low organic matter soil in 2015 and 2016. Season-long weed control without compromising yield was possible with weed management programs that included prometryn POST instead of linuron. With that said, a PRE herbicide such as pendimethalin was critical to establish an early-season competitive advantage for carrot plants over weeds, and careful attention should be paid to the prometryn rate, as selectivity is marginal. Carrot is often interseeded with a grain nurse crop to mitigate risk of wind erosion. Nurse crop injury was minimal where S-metolachlor, pendimethalin, or prometryn was applied at rates labeled for PRE use in carrot, with the exception of where prometryn was applied at rates above 1.1 kg ai ha−1.

Economically solvent fresh-market potato production is predominantly dependent on the ability to efficiently produce consistent tuber quality and high yield, and the ability to meet first-to-market demand with early-season potatoes. Unfortunately, these two qualifiers often work against each other in terms of production management. In response, we studied integrated potato vine management programs that support timely early-season potato harvest. Vine management with a flail chopper, roller, and flame burner used alone or followed by diquat was evaluated when initiated 21 or 14 d prior to harvest in 2015 and 2016. Potato varieties included ‘Yukon Gold' and ‘Dark Red Norland'. Potato leaf and stem management, as well as tuber skinning, stolon separation, grade, and yield were quantified. Among mechanical methods, potato leaf and stem management were poor when vines were rolled or mowed but better when flail chopped. In general, vine management and tuber skin set was better when treatments were initiated 21 d prior to harvest as opposed to 14 d. Vine management, tuber skin set, and yield were comparable when potato vines were flail chopped followed by flame burning and where diquat was applied twice, offering a viable program for smaller scale or organic production.Nomenclature: Diquat; potato, Solanum tuberosum L.

Slow carrot emergence and canopy development render the crop a poor competitor with weeds. In this study, the ability to suppress weeds and maintain yield in the presence of weeds was compared among nine carrot varieties that included those selected by plant breeders for rapid vegetative canopy development compared to traditional varieties. Two weed management treatments were compared: handweeding for 21 d after carrot seeding versus handweeding for the entire carrot season. In years and locations with low to moderate weed pressure, such as in the 2014 study, differences among carrot varieties in weed competitiveness or tolerance were less apparent and therefore less relevant. Maximum carrot yield loss to weed competition among varieties was 28% in 2014. Yield loss in the presence of weeds was 15% or less with six of the nine carrot varieties. However, when weed pressure was intense in the 2015 study, both carrot plant density and carrot canopy development were inversely related to weed biomass. Carrot yield loss in the presence of weeds ranged from 38 to 87%. Despite correcting seeding populations for differences in germination among carrot varieties, carrot stand establishment varied greatly and would likely affect subsequent weed control measures such as timely cultivation or herbicide application. Future research efforts are warranted that consider carrot stand establishment factors and their relationship with integrated weed management programs.

In a repeated multi-year study, mother potato plants were exposed to herbicides at rates that simulated off-target application, such as through tank contamination. Following exposure of mother plants to herbicides, seed from mother plants was planted in the following growing season and crop growth, yield and tuber quality were quantified. Visual injury from herbicides was observed both in the mother plant and daughter tuber growing seasons and occasional impacts on tuber yield were noted. However, an inconsistent relationship was observed for herbicide related injury and tuber yield reductions of mother potato plants with daughter tuber growth and yield. The lack of consistency in the relationship between visual potato injury in the mother plant production and adverse daughter tuber growth and yield in the following year challenges traditional crop scouting as a tool to predict off-target herbicide risk near seed potato production. Nomenclature: 2,4-D; aminopyralid; cloransulam-methyl; dicamba; flumiclora...

Red beet growers have expressed interest in adopting the microrate herbicide approach originally implemented in sugarbeet to achieve season-long weed management. Several red beet herbicides were first labeled for use in sugarbeet and lack substantial residual weed control. In response, red beet herbicide programs were evaluated that included a PRE application followed by up to three POST applications of various herbicide combinations. This research, however, indicated that herbicide programs that included PRE herbicides followed by as few as one or two POST applications that involve multiple active ingredients can provide season-long weed control. This observation was consistent across a broad spectrum of weeds, between two study locations that varied in soil type, and during two growing seasons. Herbicide programs that included only a PRE and six-leaf red beet growth stage application were successful at two locations in maintaining weed control and crop yield relative to hand-weeded red beet. Furthermore, these herbicide programs reduced the number of applications by 50% compared with the full programs, reducing crop injury risk and grower cost.

Agronomic crops with resistance to the herbicides dicamba and 2,4-D are currently in the regulatory approval process. The potential increased use of these herbicides has raised concern among vegetable producers about potential off-target movement and implications to crop yield. The overall goal of this research was to describe the relationship between visually estimated crop injury and snap bean and potato yield and quality. In snap bean in 2011, injury from dicamba 7 d after treatment (DAT) ranged from 19% at the 1.2 g ae ha−1application rate to 45% at the 7.0 g ae ha−1application rate. By 28 DAT in 2011, injury from 2,4-D was similar to the nontreated control. However, early-season injury in 2011 delayed snap bean flowering and reduced crop yield compared to the nontreated control for all treatments except where the 1.4 g ae ha−1rate of 2,4-D and glyphosate at 7.0 g ae ha−1were applied. Snap bean injury from dicamba was greater than that from 2,4-D at all rating timings in 2011 and two of three rating timings in 2012, and crop yield was reduced compared to where 2,4-D was applied and the nontreated control in both years. Potato tuber size distribution was variable and total yield did not differ among treatments and the nontreated control in 2011. In 2012, tuber size distribution was again variable, but more nonmarketable cull potatoes were harvested when dicamba was applied to 25-cm potato plants at the 7.0 g ae ha−1rate compared to any other treatment. Snap bean injury observations about 3 wk prior to harvest were strongly correlated with crop yield (r= −0.84 and −0.88 in 2011 and 2012, respectively), allowing time to make informed harvest decisions relative to crop quality. In contrast, the relationship between potato injury and tuber yield was poor and highly variable in both years.

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.

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.

Field research was conducted to evaluate the effectiveness of herbicides and carrot mowing for swamp dodder control. Herbicide evaluation indicated the highest carrot yield and lowest crop injury with pendimethalin compared to the industry standard linuron. Swamp dodder control with pendimethalin was greater than 80% at 56 and 70 d after planting (DAP). Other herbicides controlled swamp dodder, but crop injury was unacceptable. Carrot yield was greater where pendimethalin or s-metolachlor was applied compared to all other herbicides. Carrot mowing once 72, 86, or 100 DAP and mowing twice (72 plus 100 DAP) reduced the percentage of carrots infected with swamp dodder. Carrot infection level was least when mowed 100 DAP, and mowing did not increase yield compared to the non-treated check. These results suggest that the integration of pendimethalin for early-season swamp dodder control, followed by mowing 100 DAP, could reduce the impact of swamp dodder on carrots. Nomenclature: Linuron; s-metolachlo...

Potato producers rely heavily on herbicides for the majority of weed control. However, recent occurrences of herbicide-resistant weed populations and the lack of new herbicide registrations have stimulated interest in alternative strategies. The choice of potato cultivars that can suppress or tolerate weed competition could be a component of an integrated weed management system to reduce reliance on herbicides. The competitive ability of 10 potato cultivars—‘Atlantic’, ‘Bannock Russet’, ‘Dark Red Norland’, ‘Goldrush’, ‘Rodeo’, ‘Russet Burbank’, ‘Russet Norkotah’, ‘Snowden’, ‘Superior’, and ‘Villetta Rose’—was evaluated in 2006 and 2007 in Hancock, WI. Weed competition treatments included (1) weedy throughout the season, (2) weed-free from emergence to 4 wk after emergence (WAE) by hand-weeding, and (3) weed-free by hand-weeding for the entire season. Potato cultivars did not differ in ability to reduce weed biomass. Early-season time of potato emergence and canopy closure, as well as weed competition treatments, were strongly related to potato tuber yield. In general, Bannock Russet yield relative to weed-free controls of the same cultivar was less than that of most other cultivars. Overall, Atlantic, Russet Burbank, Snowden, and Superior yields (relative to weed-free control yields) usually were greater than the yields of other cultivars under weedy conditions. Although the ability to suppress weeds was similar among cultivars, differences in yield among cultivars grown in the presence of weeds suggest differential tolerances of weed competition.

Swamp dodder continues to spread through Wisconsin carrots, reducing crop yield and quality. Greenhouse research was conducted to evaluate the effect of swamp dodder infection timing on carrot development and to evaluate carrot cultivar tolerance to the parasite. Data collection included measurement of carrot processing qualities such as root length, root diameter, and fresh weight, as well as quantification of carrot leaf biomass and swamp dodder biomass. Carrot processing qualities were reduced the most in carrots infected 14 d after emergence (DAE). Carrots infected 70 DAE were similar to the noninfected carrots for all processing qualities. Carrot cultivars differed in tolerance of swamp dodder parasitism. All parameters for cultivar tolerance were significantly reduced by swamp dodder infection; however, ‘Enterprise’, ‘Sweet Bites’, ‘Sugar Snax 54’, ‘Topcut 93’, and ‘Mokum’ were most tolerant of parasitism and exhibited minimal reductions in root length, diameter, and fresh weight compared with other cultivars. ‘7626B’, ‘Bolero’, ‘Legend’, and ‘Imperial Cuts’ cultivars grew poorly when parasitized.