Although many pests constrain rice production, weeds are considered to be the major barrier to achieving optimal yields. A predictive model based on naturally occurring mixed-species infestations in the field would enable growers to target the specific weed group that is the greatest contributor to yield loss, but as of now no such models are available. In 2013 and 2014, two empirical hyperbolic models were tested using the relative cover at canopy closure of groups of weed species as independent variables: grasses, sedges, broadleaves, grasses and sedges combined, grasses and broadleaves combined, and all weed species combined. Models were calibrated using data from experiments conducted at the California Rice Experiment Station, in Biggs, CA, and validated across four sites over 2 years, for a total of 7 site-year combinations. Of the three major weed groups, grasses, sedges, and broadleaves, the only groups positively related to yield loss in the multispecies infestation were grasses. At the model calibration site, grasses and sedges combined best predicted yield loss (corrected Akaike information criterion [AICc] = −21.5) in 2013, and grasses alone best predicted yield loss (AICc = −19.0) in 2014. Across the validation sites, the model using grasses and sedges combined was the best predictor in 5 out of 7 site-years. Accuracy of the predicted values at the model validation sites ranged from 6% mean average error to 17% mean average error. No single model and set of parameters accurately predicted losses across all years and locations, but relative cover of grasses and sedges combined at canopy closure was the best estimate over the most sites and years. Nomenclature: Rice, Oryza sativa L.

Control of weeds in cultivated crops is a pivotal component in successful crop production allowing higher yield and higher quality. In rice‐growing regions worldwide, weedy rice (Oryza sativa f. spontanea Rosh.) is a weed related to cultivated rice which infests rice fields. With populations across the globe evolving a suite of phenotypic traits characteristic of weeds and of cultivated rice, varying hypotheses exist on the origin of weedy rice. Here, we investigated the genetic diversity and possible origin of weedy rice in California using 98 simple sequence repeat (SSR) markers and an Rc gene‐specific marker. By employing phylogenetic clustering analysis, we show that four to five genetically distinct biotypes of weedy rice exist in California. Analysis of population structure and genetic distance among individuals reveals diverse evolutionary origins of California weedy rice biotypes, with ancestry derived from indica, aus, and japonica cultivated rice as well as possible contributions from weedy rice from the southern United States and wild rice. Because this diverse parentage primarily consists of weedy, wild, and cultivated rice not found in California, most existing weedy rice biotypes likely originated outside California.

Over the last 10 yr, California has experienced a series of ever-worsening droughts. Rice, traditionally a flooded crop, has come under increasing scrutiny with respect to its water use, leading to proposals to evaluate alternative irrigation systems. For growers, weed competition is one of the most limiting factors to maintaining high yields, so understanding the shifts among species in weed communities under the proposed alternative irrigation systems is vital. A field study was conducted from 2012 to 2014 to compare weed population and growth dynamics with three irrigation systems: (1) a conventional water-seeded control system (WS-Control), with a permanent flood of 10 to 15 cm from planting until 1 mo prior to harvest; (2) a water-seeded alternate wet and dry system (WS-AWD), with the field flooded from planting until canopy closure, after which floodwater was allowed to subside and the field was reflooded when the soil volumetric water content reached 35%; and (3) a drill-seeded alternate wet and dry system (DS-AWD), with rice drill seeded and then flush irrigated to establish the crop, after which the field was flooded until canopy closure and then underwent an alternate wet and dry (AWD) treatment similar to WS-AWD. In the AWD treatments, there were two drying periods, neither of which occurred after the heading stage. The dynamics of major weed species were evaluated using plant density counts (2012) and relative cover and biomass (2013 and 2014). Grasses (sprangletop and watergrass species) dominated the DS-AWD system; sedges, broadleaves, and grasses dominated both WS systems. The WS-AWD system increased smallflower umbrella sedge relative cover at canopy closure, relative dry weight at harvest, and percent frequency when compared with the WS-Control system. Yields did not differ across treatments when weeds were controlled (P > 0.05); in the absence of herbicides, yields in the WS-AWD were equivalent to the WS-Control (ranging from 40 to 65% of the herbicide-treated yields) and zero in the DS-AWD due to weed pressure. Nomenclature: bearded sprangletop, Leptochloa fusca (L.) Kunth N. Snow; ducksalad, Heteranthera rotundifolia (Kunth) Griseb.; redstem, Ammannia coccinea Rottb.; ricefield bulrush, Schoenoplectus mucronatus (L.) Palla; smallflower umbrella sedge, Cyperus difformis L.; rice (Oryza sativa L.).

The ability to change direction is essential to any animal that moves around in a complex, 3D environment. In this study we present the first 3D description of body positions during gliding turns in a mammalian gliding specialist, the southern flying squirrel, Glaucomys volans. In addition, we used these kinematic data to estimate the aerodynamic forces generated by the animals and rotational velocities and accelerations of the body while turning. These results were compared with similar measurements of flying squirrels during straight glides. The two individuals used in this study differed significantly in limb position asymmetries between the two sides of their bodies and also were significantly different in measures of turning performance. The individual with better performance used limb positions consistent with a primarily lift-based turning mechanism (banked turn), whereas the individual with poorer performance used limb positions consistent with a primarily drag-based turning mechanism (crabbed turn). Both individuals employed limb movements continuously through the gliding turn, but these movements did not have any consistent relationships with body rotations or lateral acceleration. As compared with straight glides, squirrels used significantly higher angles of attack and had lower lift-to-drag ratios, but did not differ in glide angle. Contrary to the typical view of maneuvering during gliding as a simple, static form of locomotion, the results presented here indicate that mammalian gliding is a complex behavior comprising the interplay of many components of limb position and wing shape that affect the balance of forces that control the turn.

Weedy rice (Oryza sativa f. spontanea Roshev.) has recently become a significant botanical pest in California rice (Oryza sativa L.) production systems. The conspecificity of this pest with cultivated rice, Oryza sativa (L.), negates the use of selective herbicides, rendering the development of non-chemical methods a necessary component of creating management strategies for this weed. Experiments were conducted to determine the emergence and early growth responses of O. sativa spontanea to flooding soil and burial conditions. Treatment combinations of four flooding depths (0, 5, 10, and 15 cm) and four burial depths (1.3, 2.5, 5, and 10 cm) were applied to test the emergence of five O. sativa spontanea accessions as well as ‘M-206’, a commonly used rice cultivar in California, for comparison. Results revealed that burial depth had a significant effect on seedling emergence. There was a 43-91% decrease in emergence between seedlings buried at 1.3 and 2.5 cm depending on the flooding depth and accession, and an absence of emergence from seedlings buried at or below 5 cm. Flooding depth did not affect emergence, but there was a significant interaction between burial and flooding treatments. There was no significant difference between total O. sativa spontanea emergence from the soil and water surfaces regardless of burial or flooding depths, implying that once the various accessions have emerged from the soil they will also emerge from the floodwater. Most accessions had similar total emergence compared to M-206 cultivated rice, but produced more dry weight than M-206 when planted at 1.3 cm in the soil. The results of this experiment can be used to inform stakeholders of the flooding conditions necessary as well as soil burial depths that will promote or inhibit the emergence of California O. sativa spontanea accessions from the weed seedbank.

Weedy rice is an emerging problem of cultivated rice in California. Infestations of weedy rice in cultivated rice result in yield loss and reduced grain quality. In this study, we aimed to evaluate growth and yield components of a widely grown cultivated rice variety in California in response to weedy rice competition. Greenhouse competition experiments in an additive design were conducted in 2017 and 2018 to determine the growth and yield components of ‘M-206’ rice and five weedy rice biotypes found in California at varying weed densities. M-206 rice initially grew at a faster relative growth rate of 0.53 cm−1 wk−1 under competitive conditions compared with 0.47 cm−1 wk−1 in the absence of weedy rice, but absolute and relative growth rates declined more rapidly under competitive conditions as plants approached maturity. At harvest, M-206 plant height was reduced 13% under competitive conditions, and M-206 tiller number was reduced 23% to 49%, depending on the weedy rice biotype it was competing with. Except for 100-grain weight, the growth traits and grain yield components of M-206 rice were reduced with increasing density of weedy rice. At the highest weed density measured, 40 plants m−2, M-206 rice had yield losses of 69% grain yield plant−1, 69% panicle weight, 59% fresh and dry biomass, 55% grain yield panicle−1, and 54% panicle number. The five evaluated weedy rice biotypes varied widely in early growth rates, height, biomass production, and grain yield, indicating differing competitive strategies. Most weedy rice biotypes produce plants with greater plant height, tiller number, panicle number, and above- and below-ground biomass compared with cultivated rice. Weedy rice biotypes produced 45% to 57% higher grain yield per plant than M-206 rice under competitive conditions.

Agronomic cropping systems in many regions face growing economic and management challenges as well as new regulations designed to address negative environmental and social externalities. At the same time, public support for agricultural education and extension is decreasing. Hence, new approaches are necessary to understand the most pressing on-farm issues and help prioritize critical needs. With a diversity of agronomic crops and new regulations for water and nitrogen, California is an important case study for other regions. The objective of this study was to identify major grower and industry concerns, management challenges, and motivations in making management decisions. In 2020, 483 growers, consultants, and allied industry of agronomic crop production responded to an online survey. The crops most widely grown by respondents included rice (Oryza sativa L.), alfalfa (Medicago sativa L.), wheat (Triticum aestivum L.), and corn (Zea mays L.). Four out of the five top concerns were related to water. Weed control and irrigation/water management were primary management challenges, though differences occurred by crop and region. The highest priorities considered in grower management decision-making were water, profitability, and land stewardship. Crop rotation benefits were a primary reason for growing agronomic crops, with profitability and tradition ranking closely behind. This study highlights opportunities to guide research and extension efforts based on critical needs identified by growers and industry, while also informing larger policy and institutional decisions regarding new programs and funding to address key issues in agronomic crop production.

Late watergrass is a competitive weed of rice that is well-adapted to both aerobic and anaerobic environments. Cultural controls such as a stale-seedbed and alternating from wet- to dry-seeding have been proposed as management options. However, the effects of these systems on its emergence and early growth are unknown. The objective of this study was to modify a previously-developed population-based threshold model (PBTM) to predict emergence and early growth under field conditions. In 2013, a series of experiments were conducted at the California Rice Experiment Station (CRES) in Biggs, CA to evaluate emergence and early growth of multiple-herbicide resistant and susceptible late watergrass at four burial depths (0.5, 2, 4, and 6 cm) under three irrigation regimes: Continuously Flooded (CF), Daily Flush (DF) and Intermittent Flush (IF). Resistant plants emerged at a significantly higher rate under the IF treatment (p < 0.05). Both biotypes showed decreasing emergence with increasing depth, and no plants emerged from the 4 or 6 cm depths in the CF treatment. Using the Gompertz growth curve, resistant plants had greater predicted growth rates (k), lower predicted maximum heights (h max ), and a shorter time to predicted maximum growth rate (t m ) than susceptible plants under the CF and DF treatments. Under the IF treatment, the susceptible plants had greater k, lower h max and shorter time to predicted t m . Information about burial depth and irrigation was incorporated into a previously-developed PBTM for late watergrass, and validated at the CRES in a field with a susceptible late watergrass population in 2013 and 2014, under two irrigation systems, CF and IF. Model fit was best in the CF treatments (average AIC = 199.05) compared to the IF treatments (average AIC = 208.6).