In California, field bindweed survives in both irrigated and dryland environments, and it grows through much of the year in annual and perennial cropping systems as well as non-crop areas like roadsides . This species causes yield loss, reduces water use efficiency, disrupts irrigation infrastructure, impedes crop harvest, and creates multiple flushes of growth each growing season . These factors contribute to ongoing problems in California orchard systems. Field bindweed has a reproductive biology that includes sexual reproduction with large flowers and hard-coated seeds as well as asexual reproduction with an extensive root system, and this biology has helped it thwart many common weed management programs across California orchard systems . Because it is difficult to control, orchard weed managers often use several weed management operations against field bindweed each year, especially repeated application of systemic herbicides like glyphosate in mature orchards . Repeated applications of contact herbicides like glufosinate, paraquat, or PPO inhibitors are also common in young orchards where crop safety is a larger concern when using systemic herbicides. In fact, repeated herbicide applications are common in a variety of cropping systems . Systemic herbicides offer the apparent benefit of translocation to the extensive root system of field bindweed . However, translocation of some herbicides to field bindweed roots can be limited, and repeated herbicide applications have the potential to select for herbicide resistance . Furthermore, vertical farm equipment field bindweed frequently demonstrates capacity for regrowth following systemic herbicide applications, even when factors such as application timing, herbicide mixtures, or spray adjuvants are optimized .
Mechanical management practices that disturb the soil and underground tissues could likewise be more efficacious against field bindweed relative to mechanical practices that only affect above ground tissues . These practices, however, frequently allow regrowth from root cuttings, adventitious roots, or perennial buds . The light environment in young orchards compared to shady, mature orchards is more conducive to field bindweed . However, many young orchard trees are susceptible to injury from the systemic herbicides and intensive mechanical management practices that are commonly used against field bindweed . The compounded challenges of managing field bindweed in young orchards necessitate deeper understanding of how this species persists and can be managed in unique orchard environments. This knowledge could then inform more sustainable integrated pest management strategies with greater efficacy while reducing reliance on glyphosate and other systemic herbicides and increasing the number of management practices that are known to be safe for young trees . Integrated pest management relies, in part, on information about pest life cycles and phenology and how they relate to cropping system context. The development of integrated management programs for field bindweed necessitates greater understanding of this species’ population ecology, particularly within the context of current cropping system practices and limitations . Current management programs react to the presence of field bindweed vegetation, but integrated management programs could better account for the specific ways that this species reproduces and create site-specific management that targets the most susceptible life cycle stages . Recent advances in soil seed bank management highlight the importance of understanding all kinds of plant propagules and how these propagules differentially contribute to weed populations .
Given its relatively complex life history, field bindweed could be a useful study system for understanding perennial weed reproduction and its importance to integrated pest management. This species reproduces with both sexual and asexual propagules, creating a persistent seed bank as well as perennial roots and buds . Perfect, self-incompatible flowers bear hard, dormant seeds that maintain genetic diversity within the soil seed bank . Significant resources are also allocated towards prolific root systems, and individual plants can create underground systems that are several meters in diameter . The morphology and biomass of these root systems are influenced by light, cultivation, and other cropping system cultural factors . However, field bindweed exhibits varying degrees of phenotypic plasticity despite its morphological diversity . Integrated management programs could be strengthened by improved knowledge of how this diversity contributes to field bindweed survival in the face of varied management. Despite the importance of reproductive allocation and diversity, direct quantification of field bindweed reproduction remains challenging due to the inaccessibility of root structures and dehiscence of mature seeds .There is a need for research that addresses these challenges to help us answer questions about field bindweed reproduction in ways that contribute to commercially-relevant management. We are particularly interested in how weed management practices in orchards differentially affect above ground and below ground tissues in order to better understand how each contributes to field bindweed persistence in orchard cropping systems . Additionally, we focus on time to first flowering as a practically important reproductive trait, because it can help determine when to schedule sequential weed management treatments and how species adapt to changing environmental conditions .
California orchards are unique cropping systems that require dedicated development of integrated management programs, especially given the distinctive biology of field bindweed and the specific challenges of weed management in young orchards. Our overall aim is to use information about the reproductive biology of field bindweed to support improved ecological management of this species with practices that are feasible in California orchards. The experiments described in this study evaluated field bindweed flowering and biomass production using field and potted plant experiments. Our approach was to determine how a variety of common and prospective weed management practices in young orchards affect field bindweed reproductive resource allocation. In the field experiment, we tested various chemical and mechanical weed management practices to identify effects on field bindweed flowering timing and aboveground biomass production at timings relevant for commercial orchard production. In the potted plant experiment, we evaluated different mechanical disturbance treatments on field bindweed collected from different source populations to describe responses in flowering timing or root:shoot biomass ratios. Together, these experiments were designed to provide insight into how the distinctive reproductive morphology of field bindweed behaves and responds to orchard weed management programs.A field plot experiment was designed to evaluate how in situ field bindweed alters its reproductive response to various commercial management practices. A potted plant experiment was designed to create a common environment for testing field bindweed from a variety of source environments, as well as to provide opportunity for detailed assessment of root biomass. Together, these complementary experiments allowed us to use a broader array of methods for observing the reproductive response of field bindweed to management. Field experiment. The field experiment was a small plot study arranged in a randomized complete block design with four repetitions in each replicate. Various management programs were applied to 4.6 by 6.1 m rectangular plots in fallow fields with endemic field bindweed infestations. The whole experiment was replicated three times in time, each with a different experimental timing that coincides with different management periods for California orchard growers. Each of the replicates took place in separate fallow fields at the Plant Sciences Field Facility at UC Davis in Davis, CA . These fields consist of Yolo silt loam and had a history of orchards, agronomic crops, and field bindweed infestation before being fallowed. Field bindweed grows nearly year-round in central California, commercial indoor growing systems with a period of senescence in the winter months only; these replicate timings were chosen to mimic some of the primary periods where agricultural weed management practices already occur within that window. The first replicate was performed in the fall of 2020, to coincide with post harvest weed management timing in nut orchards . The second replicate was performed in early summer 2021, coincidental with weed management that targets summer weed emergence in orchards, especially in young orchards where there may be a greater need to manage small weeds and prevent weed establishment given a relative lack of registered herbicide options. Finally, the third replicate was performed in the mid-summer of 2021, at the timing of preharvest weed management in orchards. Management programs tested in this experiment involved sequential management steps, as is often necessary for growers dealing with field bindweed. Each of the treatments received discing and culti-packing as the first management step in order to eliminate emerged bindweed vegetation, as well as to create a uniform soil surface for treatment application. This tillage step occurred on August 19, 2020, March 25, 2021, and May 4, 2021 at each of the three replicates, respectively. The fields were subsequently monitored for bindweed reemergence, and mechanical and chemical treatments were applied to the replicates when stem regrowth reached approximately 10-15 cm in length, approximately when sequential weed management would be applied commercially.
Treatments were applied on September 15, 2020, April 20, 2021, and June 3, 2021. There were seven treatments, including one non-treated control, three herbicide treatments, and three mechanical treatments. The three herbicide treatments were broadcast glyphosate, strip-applied glyphosate, and glufosinate. Both herbicides are widely used for field bindweed management in California, but they have contrasting systemic or contact actions. The broadcast glyphosate was applied at a rate of 2.8 L ha-1 across the entire plot. The strips were applied at a rate of 5.6 L treated ha-1 in two 1.15 m-wide strips in the plot, leaving two 1.15 m-wide non-treated strips in the same plot. The glyphosate strips treatment usedthe same total amount of herbicide as the broadcast treatment, and this treatment was designed to evaluate potential impacts of glyphosate translocation when applied in strips as is common in orchards. The glufosinate treatment used 3.9 L ha-1 of Rely 280 . Each of the herbicide treatments was applied using a CO2 propelled backpack sprayer equipped with a three-nozzle boom and 80015XRVS nozzles and calibrated to apply 187 L ha-1 spray volume, based on 3.2 km hr-1 ground speed and 50.8 cm nozzle spacing. The three mechanical treatments were rototilling, flail mowing, and string trimming. These three treatments were chosen because they affect field bindweed roots and shoots differently, with rototilling representing deeper disturbance compared to string trimming and flail mowing. Each plot was monitored weekly for 10 weeks following treatment application. The first five plants to emerge in each plot were marked with stakes. In the glyphosate strip plots only, these first-to-emerge plants were in the non-treated strips within each plot. Individual plant subsamples were evaluated throughout the experiment. We used flower counts to determine average time to first flowering in each plot. No flowering was observed in the first replicate, likely since it was relatively late in the 2020 growing season, and we did not include that replicate in flower timing analysis. At the end of the 10-week observation period, we collected the above ground portion of the marked plants, dried them in a forced air oven, and weighed the dry biomass. Pot experiment. The potted plant experiment involved propagating field bindweed plants from several source populations into pots and subjecting them to different mechanical disturbance treatments. The plants were propagated vegetatively from annual crop, perennial crop, and non-agricultural home environments. The experiment used a factorial design with three disturbance treatments, including non-treated, clipping, and simulated tillage, and four field bindweed populations. Plants were collected in late 2020 from an almond orchard near Corning, California , an almond orchard in the Wolfskill Experimental Orchard near Winters, California , an annual crop field in Davis, California , and a vacant lot in Davis, California . Several dozen plants cuttings, each including both root and shoot tissue, were collected at each site and transplanted into greenhouse pots. Plant populations were maintained in the greenhouse and re-transplanted twice into new pots over a six-month period. Re-transplanting included shoot trimming to minimize powdery mildew pressure, ensure uniform plant size, and control for any legacy effects from respective environmental conditions at the time of collection. After growing in the greenhouse, we transplanted plants into 12 L pots on outdoor benches. Each pot was filled with greenhouse soil . Plants were uniformly trimmed to have 10 cm of root and 10 cm of shoot length, and only one plant was transplanted per pot. Pots were watered daily with drip irrigation. We replicated the experiment twice, and there were six repetitions of each population-treatment combination in each replicate. Transplanting occurred on April 29, 2021 for the first replicate and on May 26, 2021 for the second replicate.