Hairy buttercup and cutleaf evening-primrose control using halauxifen-methyl based programs in Mississippi and Oklahoma winter wheat (Triticum aestivum)

Hairy buttercup and cutleaf evening-primrose are winter annual weeds that have become more problematic for winter wheat growers in the Southern Great Plains and the Mid-Southern United States in recent years. Little research exists to base recommendations for controlling hairy buttercup in wheat, and little research has been published on cutleaf evening-primrose control in recent years. With growing concerns of increased herbicide resistance among winter annual weeds, incorporating new herbicide sites of action has become necessary. The objective of this study was to assess halauxifen-methyl as a novel herbicide to control these two problematic winter annual broadleaf weeds in winter wheat in Mississippi and Oklahoma. Studies were conducted across four site-years in Mississippi and one site-year in Oklahoma comparing fifteen herbicide programs with and without halauxifen-methyl. Hairy buttercup and cutleaf evening-primrose control was the greatest when a synthetic auxin was combined with an acetolactate synthase (ALS) inhibiting herbicide. Treatments including halauxifen-methyl resulted in the greatest control of hairy buttercup, whereas a synthetic auxin herbicide plus chlorsulfuron and metsulfuron resulted in the greatest control of cutleaf evening-primrose. Halauxifen-methyl is an effective addition for control of winter annual broadleaf weeds like hairy buttercup and cutleaf evening-primrose in winter wheat.

Preplant and Residual Herbicide Application Timings for Weed Control in No-Till Soybean

Timely herbicide applications for no-till soybean can be challenging given the diverse communities of both winter and summer annual weeds that are often present. Research was conducted to compare various approaches for nonselective and preplant weed control for no-till soybean. Nonselective herbicide application timings of fall (with and without a residual herbicide) followed by early-spring (4 wk before planting), late-spring (1 to 2 wk before planting), or sequential-spring applications (4 wk before planting and at planting) were compared. Spring applications also included a residual herbicide. For consistent control of winter annual weeds, two herbicide applications were needed, either a fall application followed by a spring application or sequential-spring applications. When a fall herbicide application did not include a residual herbicide, greater winter annual weed control resulted from early- or sequential-spring treatments. However, application timings that effectively controlled winter annual weeds did not effectively control summer annual weeds that have a prolonged emergence period. Palmer amaranth and large crabgrass control at 4 wk after planting was better when the spring residual treatment (chlorimuron plus metribuzin) was applied 1 to 2 wk before planting or at planting, compared with 4 wk before planting. Results indicate that in order to optimize control, herbicide application programs in soybean should coincide with seasonal growth cycles of winter and summer annual weeds.

Response of 110 Kentucky Bluegrass Varieties and Winter Annual Weeds to Methiozolin

Methiozolin is a new isoxazoline herbicide that has scarcely been tested in Kentucky bluegrass turf. A field trial was conducted in Blacksburg, VA, to determine response of 110 Kentucky bluegrass varieties and winter annual weeds to sequential fall applications of methiozolin. At 1.5 and 6 mo after initial treatment (MAIT), Kentucky bluegrass injury I30values (predicted methiozolin rate that causes 30% Kentucky bluegrass injury) ranged between 3.4 to more than 10 times the recommended methiozolin rate for annual bluegrass control. Methiozolin at all rates reduced cover of annual bluegrass, common chickweed, corn speedwell, hairy bittercress, mouseear chickweed, and Persian speedwell but increased cover of parsley-piert. For all varieties, methiozolin at 2 kg ai ha−1increased Kentucky bluegrass cover, turf quality, and turf normalized difference vegetation index (NDVI) relative to the nontreated check at 6 MAIT. Kentucky bluegrass relative cover change (RCC) was attributed primarily to weed control but was inversely correlated with methiozolin rates because of increased weed control and reduced Kentucky bluegrass growth. Despite the decline in RCC with increasing methiozolin rates, most Kentucky bluegrass varieties treated with the highest methiozolin rate (6 kg ha−1) still had greater Kentucky bluegrass cover than the nontreated check at 6 MAIT. Results from this study indicate that two fall applications of methiozolin at rates beyond that previously reported for annual bluegrass control can safely be applied to a broad range of Kentucky bluegrass varieties spanning most of the known genetic classifications.

Winter Annual Weed Suppression in Rye–Vetch Cover Crop Mixtures

Winter annual weeds can interfere directly with crops and serve as alternative hosts for important pests, particularly in reduced tillage systems. Field experiments were conducted on loamy sand soils at two sites in Holt, MI, between 2008 and 2011 to evaluate the relative effects of cereal rye, hairy vetch, and rye–vetch mixture cover crops on the biomass and density of winter annual weed communities. All cover crop treatments significantly reduced total weed biomass compared with a no-cover-crop control, with suppression ranging from 71 to 91% for vetch to 95 to 98% for rye. In all trials, the density of nonmustard family broadleaf weeds was either not suppressed or suppressed equally by all cover crop treatments. In contrast, the density of mustard family weed species was suppressed more by rye and rye–vetch mixtures than by vetch. Cover crops were more consistently suppressive of weed dry weight per plant than of weed density, with rye-containing cover crops generally more suppressive than vetch. Overall, rye was most effective at suppressing winter annual weeds; however, rye–vetch mixtures can match the level of control achieved by rye, in addition to providing a potential source of fixed nitrogen for subsequent cash crops.

Influence of Winter Annual Weed Management and Crop Rotation on Soybean Cyst Nematode (Heterodera glycines) and Winter Annual Weeds: Years Four and Five

Certain winter annual weeds have been documented as alternative hosts to soybean cyst nematode (SCN), and infestations by such species are common in no-till production fields in the midwestern United States of Indiana, Ohio, and Illinois. The objective of this research was to determine the influence of crop rotation and winter annual weed management on winter weed growth, SCN population density, and crop yield. Two crop rotations (SS and soybean–corn rotation) and six winter annual weed-management systems (autumn-applied herbicide, spring-applied herbicide, autumn + spring applied herbicides, autumn-seeded Italian ryegrass, autumn-seeded wheat, and a nontreated check) were evaluated in long-term, no-tillage systems at West Lafayette, IN, and Vincennes, IN. In the fourth and fifth years of these experiments, the 2-yr corn–soybean rotation generally resulted in increased soybean yield, decreased winter annual weed growth, and reduced SCN population density compared with SS. Autumn or spring herbicide applications or both were a more effective option than cover crops at reducing winter annual weed density. Cover-crop systems generally did not differ from the nontreated check in winter weed density. Between years three and five, winter annual weed SCN hosts in nontreated check plots increased approximately threefold to levels as high as 102 and 245 plants m−2 at West Lafayette, IN, and Vincennes, IN, respectively, which are infestation levels at or above those commonly observed in production fields. However, controlling winter annual weeds did not influence crop yields or SCN population density. The results of these studies suggest that winter weed management, even at the high levels of weed infestation present in these studies, appears to have little value as a tool for SCN management in corn and soybean production systems in the midwestern United States.

Short Communication: Timing of stinkweed and shepherd's-purse recruitment affects biological characteristics of progeny

Van Acker, R. C. and Cici, S. Z. H. 2012. Short Communication: Timing of stinkweed and shepherd's-purserecruitment affects biological characteristics of progeny. Can. J. Plant Sci. 92: 933–936. The effect of recruitment timing (fall versus spring recruitment) on seed characteristics and performance of two common Canadian facultative winter annual weeds; stinkweed (Thlaspi arvense L.) and shepherd's-purse (Capsella bursa-pastoris L.) was investigated. Seed germination proportion was unaffected by maternal emergence timing but germination was faster for spring versus winter cohort seeds of stinkweed. Proportionally more seeds from winter (fall-recruited) cohorts were rendered non-viable by aging treatments, while for shepherd's purse, aging treatments broke dormancy instead of reducing viability and this was especially true for winter cohort seeds. For both weed species, spring cohort seeds produced earlier flowering plants with greater and lesser biomass allocation to reproductive tissues and roots, respectively. These results show the potential importance of germination timing and maternal effects on weed populations and demonstrate additional complexity in the nature of facultative winter annual weeds, in particular.

Buckwheat Residue Effects on Emergence and Growth of Weeds in Winter-Wheat (Triticum aestivum) Cropping Systems

Field and pot studies were conducted in Central New York to determine the potential weed-management benefits of a buckwheat cover crop grown before winter wheat. Specific objectives were to determine buckwheat residue effects on (1) emergence and growth of winter annual weeds; (2) wheat establishment and yield; and (3) emergence of summer annual weeds in the spring following overwinter seed burial. In a field study, buckwheat was sown at two timings (July or August), mowed, and either incorporated or left on the soil surface. Winter wheat was drilled into buckwheat residue in September and weed and crop growth were monitored. In a complementary pot study, four winter annual weeds were sown in soil removed from buckwheat and bare-soil plots at 0 or 15 d after incorporation and monitored for emergence and early growth. To assess buckwheat residue effects on spring emergence from overwintering seeds, seeds of three weed species were buried in buckwheat residue and bare-soil plots in the fall, exhumed in April, and evaluated for emergence. To investigate the mechanism for possible effects of buckwheat residue on overwintering seeds, two levels each of seed treatment (none or fungicide) and fertilization (none or 170 kg ha−1) were applied before burial. Buckwheat residue had no negative effect on wheat yields but suppressed emergence (22 to 72%) and growth (0 to 95%) of winter annual weeds, although effects were often small and inconsistent. Buckwheat residue had no effect on the emergence of buried weed seeds in spring. However, fungicide treatment enhanced the emergence of Powell amaranth seeds by 12.5 to 25.5% and of barnyardgrass seeds by 0 to 12%. Our results suggest that buckwheat residue can contribute to weed management in wheat cropping systems, but that further studies investigating the mechanistic basis for the inconsistent selective effects of buckwheat residue on weeds are needed before buckwheat use can be optimized.

Relative freezing tolerance of facultative winter annual weeds

Cici, S. Z. H. and Van Acker, R. C. 2011. Relative freezing tolerance of facultative winter annual weeds. Can. J. Plant Sci. 91: 759–763. To understand why some of the facultative winter annual weeds are more abundant in spring rather than both in fall and spring, we assessed the freezing tolerance and re-growth capacity of 12 species collected across Canada. Our study allowed us to classify these species in three broad categories based on their relative tolerance to freezing temperatures. Freezing scores and biomass reproduction after freezing were generally consistent with field observations. It was shown that early emergence of weeds in spring is not, however, systematically related to superior freezing tolerance.