Weedy rice is of the same species as cultivated rice, Oryza, and is a common rice weed exhibiting allopathic characteristics. Incorporation of allelopathic traits from weedy rice into cultivated rice may have a positive impact on rice yield. The overall objective of this study was to characterize weedy rice accessions based on the allelopathic potential to suppress barnyardgrass. These accessions, once discovered, may be used in identifying phenotypic traits and genes associated with their weed suppressive trait. Ten weedy rice accessions, and five rice cultivars (Rex, CL163,Rondo, PI312777, PI338046) were screened using a stair-step technique. The allelopathic potential was calculated based on the percent inhibition of barnyardgrass. The best performing accessions were phenotyped for root characteristics in a lab setting. Lastly, 30 SSR markers were used to evaluate the weedy rice to identify markers associated with the trait. Accessions identified in this study should be considered in the development of weed-suppressive rice cultivars.

In an effort to reduce application costs and to integrate plant health management strategies in soybean, growers may combine POST herbicides with foliar fertilizers or cytokinin mixtures. Field experiments were conducted at the Delta Research and Extension Center in Stoneville, MS in 2015 and 2016 to evaluate soybean [Glycine max (L.) Merr.] injury, weed control, and agronomic performance when combining blended or single-nutrient foliar fertilizers with POST herbicide applications. Field experiments were also conducted at the Delta Research and Extension Center in Stoneville, MS in 2015 and 2016 to evaluate the influence of cytokinin mixtures on soybean injury and weed control when combined with common POST soybean herbicides.

Off-target herbicide movement onto rice is an annual problem in rice-producing areas within Mississippi. In Mississippi, rice is routinely drill‐seeded in April to early May. Because these dates often coincide with preplant and/or preemergence (PRE) herbicide applications to corn (Zea mays L.), cotton (Gossypium hirsutum L.), and soybean [Glycine max (L.) Merr.], drift onto neighboring rice crops is likely to occur. Although the effects of off-target movement of paraquat on rice may not be visibly apparent, the potential effect on rough rice yield could be detrimental. Field research was conducted at the Delta Research and Extension Center in Stoneville, MS, in 2019, 2020, and 2021 to characterize rice response to exposure to a range of sub-lethal concentrations of paraquat during the vegetative and reproductive growth phases. Other field experiments characterized rice response to exposure to a sub-lethal concentration of paraquat at different stages of reproductive growth. A final field experiment evaluated rice response and barnyardgrass control with labeled herbicides after exposure to a sub-lethal concentration of paraquat.

Water level declines in the Mississippi River Valley Alluvial Aquifer (MRVAA) are attributed largely to withdrawals for rice (Oryza sativa L.) irrigation. This study was performed to determine if alternative irrigation strategies for rice could reduce withdrawal from the MRVAA without having an adverse effect on grain yield, grain quality, control of barnyardgrass, and profitability. Research was conducted in Stoneville, MS and 19 on-farm locations across the Delta region of Mississippi from 2014 through 2017 to determine the irrigation threshold for alternate wetting and drying (AWD) rice irrigation, the effect of AWD management on barnyardgrass control, and effects of irrigation water management practice, i.e., conventional flood via cascade (CONV), multiple side inlet (MSI), and MSI coupled with AWD, on aquifer withdrawal, rough rice grain yield, irrigation water use efficiency (IWUE), and net returns above irrigation costs. An AWD threshold of -20 cm below the soil surface had no adverse effect on grain yield or grain quality, reduced irrigation applied by 50%, and improved IWUE by 45% compared to a continuous flood (CF). Control of barnyardgrass in AWD was either maintained or improved compared to CF for both Clearfield and conventional rice production systems. At the production scale, up to 39% less water was applied to AWD compared to CONV and MSI. Rice grain yield for AWD was not different from either CONV or MSI, despite substantial reductions in water use. Relative to standard irrigation strategies, AWD maintained or increased net returns up to $238 ha-1 for pumping depths from 5.5 m to 122 m and diesel prices from $0.42 L-1 to $0.98 L-1. Irrigation water use efficiency was up to 59% greater for AWD relative to conventional systems due to the positive effects of the former on water use while maintaining yield. These data demonstrate that AWD can reduce withdrawal from the MRVAA while maintaining or improving yield and net returns relative to irrigation strategies currently employed across the midsouthern USA rice belt.

The aim of the present diploma thesis is to widen knowledge of the chemical regulation of weeds in row crops. To establish the effectiveness of herbicides, we set up a small lot at a carefully chosen spot in the potato-growing region near Strakonice. We conducted a comparison of the effects of three herbicide combinations on two potato varieties (Red Anna, Laura). Two combinations proved pre-emergent (Afalon 45 SC+Command 36 SC; Sencor 70 WG+Command 36 SC), one post-emergent (Titus 25 WG). Subsequently, we evaluated economic costs on weeds regulation and suggested preliminary measures to be taken.