The use of POST herbicides has been limited in sweet corn because of the narrow spectrum of weed control or potential crop injury. Field experiments were conducted to evaluate the 4-hydroxyphenyl pyruvate dioxygenase (HPPD)-inhibiting herbicides mesotrione, tembotrione, and topramezone applied POST in sweet corn at three locations. Efficacy of mesotrione, tembotrione, and topramezone applied alone or mixed with atrazine was compared to other labeled POST herbicides following PRE S-metolachlor. Giant foxtail control was greater with tembotrione or topramezone than mesotrione alone or mixed with atrazine. Common lambsquarters, velvetleaf, and common ragweed were controlled 98% or greater with the HPPD-inhibiting herbicides when mixed with atrazine. Tolerance of six sweet corn hybrids was determined in the field when treated with 1× and 2× rates of these herbicides mixed with atrazine. Tolerance of six sweet corn hybrids to these herbicides was determined in the greenhouse when treated with 0.5, 1, 2, 4, 8, and 16 times the labeled rate. Differential hybrid tolerance to each herbicide was observed in both the field and greenhouse evaluations. Tembotrione killed ‘Merit’ in both evaluations. Excluding Merit, hybrids generally had good tolerance to tembotrione and topramezone in the field, but had differential tolerance to mesotrione. With the exception of Merit, hybrids generally had greater tolerance to tembotrione than topramezone and less tolerance to mesotrione in the greenhouse. These HPPD-inhibiting herbicides provide POST weed control, but the potential for sweet corn injury varies among the herbicides and hybrids and warrants further characterization.
Management of perennial weeds is a major concern in reduced-tillage cropping systems. Field research was conducted at Nashua, IA, from 1977 through 1990 to evaluate the long-term impacts of tillage and cropping patterns on perennial weed populations in corn and soybean production. Continuous corn and a corn/soybean rotation were conducted utilizing moldboard plow, chisel plow, ridge tillage, and no-tillage systems. The research area was free of established perennial weed species at the initiation of the experiment in 1977. Hemp dogbane was observed by 1980, with the greatest densities in no-tillage. By 1990, continuous corn had greater hemp dogbane densities with no-tillage than other tillage system by crop rotation treatments. American germander densities were not affected by tillage systems in 1980 and 1981, but by 1990, corn/soybean rotations had greater densities in moldboard plow than other tillage systems. Field bindweed developed primarily in the corn/soybean rotations with the greatest densities occurring in no-tillage. Greater and more diverse populations of perennial weeds developed in reduced-tillage systems than in the moldboard plow system. However, practices used to control annual weeds and environmental factors interacted with tillage to regulate perennial weed populations.
Effects of several factors on reproductive performance were evaluated. Mean performance and number of observations were for days from parturition to first service, 93 and 7730; days from first to successful service, 35 and 11,751; days open, 123 and 8571; gestation length, 280 and 13,612; and calving interval, 400 and 8524. Data covered 52 yr during which no detectable trends in calving interval occurred; other variables changed slightly. Jerseys had 8 fewer d from parturition to first service, 16 fewer d from first service to conception, 8 fewer d open, and 8-d shorter calving intervals than did Guernseys and Holsteins, which did not differ. Cows freshening in warm rather than cool weather suffered by 7, 7, 12, and 13 d for these variables. Repeatabilities ranged from .05 to .12; heritabilities were .05 and .06. Nonmaternal estimate of heritability of gestation length was .22. Phenotypic and genetic correlations between days from parturition to first service and calving interval were .48 and .87; for days open and calving interval, they were .97 and .96. Although days from first to successful service were essentially uncorrelated with days open and calving interval phenotypically (.05), genetic correlations were greater than 1.0 and estimated as unity. Results show no discrepancy between estimates for measures of reproductive performance in a subtropical environment and numerous studies in temperate areas. Large studies from subtropical areas are sparse; essentially none concerns long-term trends.
Agriculture in the Upper Midwest of the USA is characterized by a short growing season and unsustainable farming practices including low-diversity cropping systems and high fertilizer inputs. One method to reduce the magnitude of these problems is by integrating a winter annual into the summer-annual-dominant cropping system. For this reason, pennycress (Thlaspi arvense) has garnered interest in the agricultural community due to its winter annual growth habit and potential for industrial oil production, making it an ecologically and economically desirable crop. Despite decades of research focusing on pennycress as an agricultural weed, little is known about its best management practices as an intentionally cultivated crop. The majority of agronomic research has occurred within the past 10 years, and there are major gaps in knowledge that need to be addressed prior to the widespread integration of pennycress on the landscape. Here we review relevant agronomic research on pennycress as a winter annual crop in the areas of sowing requirements, harvest, seed oil content, seed oil quality, cropping strategies, ecosystem services, and germplasm development. The major points are as follows: (1) there is little consensus regarding basic agronomic practices (i.e., seeding rate, row spacing, nutrient requirements, and harvest strategy); (2) pennycress can be integrated into a corn (Zea mays)soybean (Glycine max) rotation, but further research on system management is required to maximize crop productivity and oilseed yields; (3) pennycress provides essential ecosystem services to the landscape in early spring when vegetation is scarce; (4) breeding efforts are required to remove detrimental weedy characteristics, such as silicle shatter and high sinigrin content, from the germplasm. We conclude that pennycress shows great promise as an emergent crop; however, current adoption is limited by a lack of conclusive knowledge regarding management practices and future research is required over a multitude of topics.
Dissipation of atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐s‐triazine) in a Webster clay loam soil (fine loamy, mixed, mesic Typic Haplaquoll), and Estherville sandy loam (sandy, mixed, mesic typic Hapludoll) was determined over a concentration range of 5 to 5000 mg kg−1 in field and laboratory experiments. Over the first 6 mo in the clay loam soil, the persistence of atrazine (based on percent of applied) was greater for the high‐rate treatments than the low‐rate treatments. However, in the laboratory, there was no effect of concentration on dissipation; the amount of atrazine degraded increased proportionally with the increase of concentration. In the sandy loam, persistence was greater at high concentration in both field and laboratory studies. Mineralization was the most important pathway for the dissipation of atrazine at all concentrations in the clay loam soil and from 5 to 500 mg kg−1 in the sandy loam. It was postulated that soil microorganisms were able to use the N or C from the s‐triazine ring. Atrazine at 500 and 5000 mg kg−1 may have increased soil microbial growth and activity and thus increased the degradation of atrazine based on the increase in soil respiration in the clay loam soil. Degradation pathways in both soils apparently were not influenced by concentration. Ring cleavage and hydrolysis were the major metabolic pathways in both soils, with dealkylation of less importance. Addition of a dairy manure amendment increased the rate of atrazine mineralization, while corn meal decreased and (NH4)2HPO4 amendments prevented mineralization.
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