In the northern region of the northern Great Plains of North America, the relative abundance of dandelion in field crops has increased over the past two decades, and farmers need information to help them to better manage this species and slow its spread. A study was conducted to determine the emergence timing of dandelion from both rootstock and seed, and to investigate the efficacy of preseeding (spring) versus postharvest (autumn) herbicide treatments on dandelion in spring wheat fields. Emergence of dandelion plants from rootstock was very early (mean time to 50% emergence [E50] of 430 growing degree days [GDD] Tbase 0 C), while seedling emergence was much later (mean E50 of 980 GDD). Dandelion does not have a persistent seed bank, and seedling emergence occurred only after dandelion plants arising from rootstock flowered and shed seed. Herbicide treatments that included glyphosate plus florasulam, glyphosate plus tribenuron, or higher rates of glyphosate alone (≥675 g ae ha−1), provided high levels of dandelion control. Autumn herbicide applications were more effective than spring applications for reducing dandelion infestation levels (both aboveground biomass and density). Autumn herbicide applications came after peak emergence timing for dandelion plants emerging both from rootstock and from seed. Because dandelion is a simple perennial, population spread must be limited by controlling seedlings. Autumn herbicide applications provide control of dandelion seedlings and therefore, should limit dandelion population spread.

An experiment was conducted in 1998 and 1999 in southeastern Pennsylvania to examine the effect of tillage and soybean row spacing on burcucumber emergence and growth. A second experiment evaluated postemergence (POST) soybean herbicides on burcucumber control. In the tillage and row spacing study, a glyphosate-resistant soybean variety was planted in no-till and reduced-tillage systems in 38- and 76-cm row spacings. In the POST herbicide experiment, chlorimuron, glyphosate, CGA-277476, thifensulfuron, and several combinations of these herbicides were applied at two different POST application timings in 38-cm row soybean planted in a reduced-tillage system. In the tillage and row spacing study, burcucumber emergence was greatest starting in late May through mid-June and mostly ceased by early July, regardless of tillage system or row spacing. Although there was no difference in germination period in either tillage system, preplant tillage increased the number of emerged plants by 110% in 1997 and 70% in 1998 compared to the no-till system. Row spacing had no effect on burcucumber emergence or biomass production. In general, most POST herbicide programs controlled burcucumber, and there was no difference between early POST and mid-POST application timings. Chlorimuron at 13 g ai/ha, chlorimuron plus thifensulfuron, glyphosate, glyphosate plus chlorimuron, and glyphosate plus CGA-277476 provided 87% or greater control of burcucumber 12 wk after planting. These herbicides reduced burcucumber density and biomass by more than 56% in 1997 and 96% in 1998.

Producers in the semi-arid Great Plains are starting to grow corn in sequence with winter wheat and proso millet. However, volunteer proso millet (hereafter referred to as proso) is difficult to control in corn with conventional practices. This study characterized growth and interference of proso in corn to aid producers in developing control strategies. Proso seedlings began emerging May 18 with 78% of seasonal emergence occurring by June 22; initial proso emergence occurred within 2 wk of corn emergence in all years. Seed production was related to time of emergence; proso seedlings emerging in mid-May produced approximately 2,800 seeds per plant, whereas seedlings emerging 4 wk later produced 88% fewer seeds. Controlling proso in late June prevented loss of corn grain yield caused by competition. When corn was planted in early May, the height difference between corn and proso was sufficient to allow postemergence-directed applications of graminicides for proso control. Corn yield was highest when planted in early May.