Farmers often use private and public labs, crop advisors, or fertilizer dealers to determine fertilizer needs for crops, with recommendations and resulting costs from these sources having the potential to vary greatly. Twelve on-farm trials across the state of Utah in alfalfa (Medicago sativa), small grain forage, and silage corn (Zea mays) were established in 2021 to compare fertilizer recommendations from five labs and a nonfertilized control, two public labs (Utah State University and University of Idaho), and three commercial labs in the Western United States, with some sites being replicated in 2022-2023. A baseline soil sample from each field was split and sent to multiple labs for analysis and corresponding nutrient rates recommended by each lab applied at each site. Fertilizer recommendations from the five laboratories varied greatly, both for types of nutrients and rates recommended, with differences between highest and lowest treatment costs ranging from $528 to $2024 ha(-1) across sites. Crop yield and forage quality data were collected from sites from 2021 to 2023, with fertilizer treatments having little to no impact at four silage corn or five alfalfa sites. Yield was increased by at least one private and university lab at all three small grain forage sites and crude protein content was increased at sites with multiple years of data. Fertilizer treatments occasionally improved forage yield and quality but not crop market value. The results of this study demonstrate that growers should be aware when selecting fertilizer recommendations, and opportunities exist for better public-private coordination of science-based recommendations.

There are many resources that farmers use to determine fertilizer needs for crops such as private and public laboratories, crop advisors, and fertilizer dealers. These resources provide recommendations for a specific crop that can vary greatly. An experiment established in 2021 at 12 sites in Utah and Wyoming in alfalfa (Medicago sativa), small grain forage, and corn (Zea mays) tested and compared fertilizer recommendations from five labs. The recommendations tested were from two public labs (Utah State University and the University of Idaho) and three commercial labs located in the western United States. A composite soil sample split and sent to multiple labs for analysis revealed high variability in reported soil test results and recommendations, both for types and rates of nutrients. Differences in soil test results were influenced by analytical methods used by each lab to measure nutrient levels and the accuracy of their analyses. Much of the variability in fertilizer recommendations was likely due to the recommendation approaches used by each lab, with soil test values having some influence. When the recommendations were applied in field trials, fertilizer applications increased soil concentrations of some nutrients (phosphorus [P], potassium [K], sulfur [S], and zinc [Zn]) at 21%-57% of sites, depending on the recommendation source, but the rates required and application costs varied greatly among sites and treatments. Applying higher fertilizer rates can sometimes raise soil nutrient levels, but results vary by nutrient and conditions, and the approach is often not cost-effective.

Kochia (Bassia scoparia) has emerged as a troublesome weed in the western U.S. This paper reviews the history, background, and current status of kochia resistance to herbicides in the western U.S., providing insights into the knowledge gaps and future research needs.

In water limited environments, alfalfa (Medicago sativa) is often criticized for its high water use, prompting interest in optimizing irrigation technologies, deficit irrigation, and drought-tolerant genetics. However, potential cumulative benefits from combining water-saving strategies have not been previously identified. This study evaluated the independent and combined effects of five irrigation technologies (low-elevation Nelson advantage, low-elevation precision application, low-elevation spray application, mid-elevation spray application, and mobile drip irrigation), four irrigation doses (growers' typical full dose, a 25 % reduction, and two 50 % reductions, uniform and growth stated-targeted), and two alfalfa varieties (growers' conventional and drought- tolerant) across three Utah sites from 2020 to 2022. No interaction effects were found among these factors, indicating that stacking multiple water-saving strategies did not enhance yield or forage quality. Low-elevation sprinkler technologies generally outperformed mid-elevation and mobile drip irrigation, though results varied by environment. Deficit irrigation at 25 % reduction often maintained yields similar to growers' Full irrigation dose, while 50 % reductions consistently decreased yield by 22-54 %. However, deficit irrigation improved forage quality and water use efficiency. Decision tree models revealed that maximizing relative feed value-adjusted water use efficiency primarily depended on matching irrigation dose and technology to site-specific climate demand rather than applying Full irrigation. These findings suggest that moderate deficit irrigation and low- elevation sprinkler technologies can improve forage quality and water resource efficiency without substantial yield loss that occurs with 50 % deficit irrigation.

Spring weed control in established alfalfa (Medicago sativa L.) has historically relied heavily on paraquat. However, new regulatory safety measures introduced to ensure the safe use of paraquat may deter growers from relying on paraquat. Field studies were conducted in Idaho and Utah in 2023 and 2024 to assess weed control, alfalfa recovery, forage accumulation, and nutritive value following treatment with carfentrazone, saflufenacil, pyraflufen, tiafenacil, diuron + hexazinone, glyphosate, and paraquat. The main goal was to assess whether carfentrazone, saflufenacil, pyraflufen, tiafenacil, and diuron + hexazinone could be viable alternative herbicides to paraquat that growers can use for weed control in the spring in established alfalfa. Although carfentrazone, saflufenacil, and tiafenacil caused greater alfalfa injury and height reduction within the first 3 weeks after herbicide application, the alfalfa recovered within 6 weeks after herbicide application. At the Idaho site, all the evaluated herbicides provided similar or better weed control than paraquat, and there was no difference in alfalfa hay forage accumulation or nutritive value among the herbicide treatments, especially when compared with paraquat treatment. At the Utah site, saflufenacil and diuron + hexazinone reduced alfalfa hay forage accumulation when compared with the paraquat treatment, suggesting that farmers would have to wait longer to allow alfalfa to recover after applying saflufenacil or diuron + hexazinone. Overall, these results show that carfentrazone, pyraflufen, saflufenacil, and tiafenacil are promising alternatives to paraquat for weed burndown in alfalfa.

Determining the amount and timing of irrigation events using scientific irrigation scheduling (SIS) may help optimize water use. Soil moisture sensors, commercial irrigation schedulers, and water balance programs are common SIS tools. These three methods were evaluated to test their impact on alfalfa (Medicago sativa) mass, nutritive value, and irrigation productivity, in comparison to experience-based irrigation depths chosen by cooperating growers. Trials were conducted at 10 farms across central Utah in 2019. Trials were repeated at nine of these farms in 2020 and six in 2021. Alfalfa mass was measured in a total of 47 cuttings from across all these fields over 3 years. The three SIS methods only impacted alfalfa mass in five cuttings, and it occurred inconsistently at various fields and years. Three cuttings had improved mass with SIS methods and two had reduced production. Forage nutritive value was more often impacted by SIS method than mass, but impacts were rarely large enough to change forage market value. Applied water was lower with most SIS methods than the grower control in 2019 and 2021 but not 2020. This was influenced heavily by the drought conditions and water restrictions during the latter 2 years of this study. As one of the first studies to directly compare how four irrigation scheduling methods for center pivots affect crop production and irrigation levels, results indicated that all three SIS approaches had comparable performance, and in some situations (especially wet years) could reduce applied water by 6%-25% without impacting alfalfa mass or nutritive value.

Drought-tolerant (DT) corn (Zea mays L.) hybrids are developed to provide crop protection from plant water stress in areas prone to drought like the Intermountain West. These regions also face challenges from weeds because of the wide range of developmental and physiological mechanisms possessed by weeds that give an ecological advantage under increased temperature and water stress. Many weeds have developed resistance to some herbicides; therefore, understanding weed interactions with DT corn is important in developing sustainable strategies for management in water-stressed environments. A two-season field experiment was conducted to evaluate the critical period of weed control (CPWC) in DT versus drought-susceptible (DS) corn hybrids exposed to optimal and reduced irrigation in Utah. Treatment combinations of the two corn hybrids, two irrigation levels, and time of weed removal were arranged in a split-split plot design with each treatment replicated four times. Exponential decay and asymptotic regression models were used to determine the CPWC based on an estimated 5% relative yield loss in corn. Up to 5% and 42% yield differences were observed between weed-free and weedy plots throughout the 2021 and 2022 field seasons, respectively. The beginning and end of CPWC differed between the two corn hybrids as well as between the two irrigation levels in both seasons. CPWC was 19.5 and 28 d for DT corn under optimal irrigation in 2021 and 2022, respectively. CPWC was increased for DS corn with optimal irrigation to 52 and 35 d in 2021 and 2022, respectively. A similar result was observed with reduced irrigation for each hybrid (5 and 48.5 d for DT corn and 35 and 50 d for DS corn in 2021 and 2022, respectively). The results suggest that use of DT corn may help reduce the need for more intensive weed management because it reduces the CPWC.

AbstractBackgroundMixtures with birdsfoot trefoil (BFT) increase herbage intake in grazing cattle. We hypothesized that BFT spatially separated from grasses would increase preferential grazing of BFT and herbage intake compared to grass and BFT in mixed rows.MethodsBinary mixtures of BFT were established with orchardgrass, meadow bromegrass, tall fescue, and perennial ryegrass in alternating and in mixed rows. Pastures were rotationally stocked with Jersey heifers, and herbage mass, intake, and preferential grazing were estimated.ResultsPlanting BFT in alternating rows did not affect herbage mass, intake, or BFT preference. Regardless of spatial arrangement, pasture production averaged 4116 kg ha−1 per rotation, of which 32% was BFT. BFT comprised 39% of herbage intake in alternating and mixed rows, 7% greater (p = 0.001) than offered, indicating partial preference for BFT. Greatest preferential grazing of BFT was in tall fescue and orchardgrass mixtures, but less than commonly reported for legumes grown in more contrasting spatial arrangements with cool‐season grasses.ConclusionsGrazing heifers showed partial preference for BFT over grass. However, the lack of an effect of spatial arrangement on herbage mass, herbage intake, and diet preference indicates that spatial arrangements greater than alternating rows may be needed to increase overall herbage intake.

The host-generalist two-spotted spider mite [Tetranychus urticae (Acari: Tetranychidae); TSM] and host-specialist Banks grass mite [Oligonychus pratensis (Acari: Tetranychidae); BGM] are common pests of corn (Zea mays L.) in the arid western United States. Climate warming and decreased precipitation may promote conditions favoured by these spider mites. However, rapid evolution of spider mite resistance to commercially available acaricides is driving the need for alternative solutions for managing outbreaks. Planting of drought-tolerant corn hybrids has been proposed to be a dual-purpose strategy for mitigating water deficits for irrigation and reducing leaf conditions favourable for BGM outbreaks. However, understanding of the mechanisms responsible for reducing the BGM in the field is lacking and determining whether outbreaks of the TSM can also be averted using drought-tolerant corn is a pressing concern. We conducted a 2-year field study testing a drought-tolerant corn hybrid and an analogous drought-susceptible hybrid under water-stress, with artificially infested spider mite populations. Drought-tolerant corn had larger stem diameter, more massive cobs, and greater leaf water mass compared to the drought-susceptible corn under water stress. We also found that the BGM populations were reduced on drought-tolerant plants under water-stress, as expected, but we found an opposite trend in the TSM. Lastly, water-stressed leaves were warmer, transpired less, and had higher carbon concentration, which contributed to larger investment in eggs and growth in the BGM. We anticipate that further evaluation of irrigation and crop drought-tolerance in management of agriculture systems for multiple pest species will be increasingly impactful in arid regions.

Irrigation is a critical resource in meeting the global demand for food, feed, fiber, and fuel. One water optimization method with high potential and interest is the use of more efficient irrigation systems. In many areas where pivots are used, the most common sprinkler package is mid-elevation sprinkler application (MESA), which typically has application efficiencies near 80%. Low-energy precision application (LEPA) and mobile drip irrigation (MDI) can have greater than 95% application efficiency. The objective of this research was to evaluate the ability of LEPA and MDI to maintain crop yield and quality in alfalfa (Medicago sativa L.) and silage corn (Zea mays L.), at similar and reduced irrigation rates as MESA. The intent of the reduced rate was to determine if the decreased application losses with LEPA and MDI could result in sustained crop production with a 20% irrigation rate reduction. Actual reductions ranged from 5% to 55% depending on system and site due to equipment constraints. Data from two farms in Utah during 2018-2020 provided evidence that these systems can often maintain yield and forage quality with 5%-55% less applied water. However, there were also many instances where yield was reduced by LEPA and MDI, even with similar application rates to MESA. This indicates that the two higher efficiency systems will not save water in all cases and that the application system must be carefully evaluated in small on-farm trials over multiple years for its ability to succeed in specific field conditions. Low-energy precision application (LEPA) and mobile drip irrigation (MDI) have high but inconsistent potential to maintain yield with less water than mid-elevation sprinkler application.Low-elevation sprinklers did not consistently benefit alfalfa and corn production with full or reduced irrigation.MDI often had severe rate reductions due to tubing flaws and thereby severed reduced alfalfa-corn production.Growers considering LEPA and MDI should test in small areas over multiple seasons to validate performance.

Dactylis glomerata L., orchardgrass or cocksfoot, is frequently planted as a companion crop in perennial forage legumes such as alfalfa (Medicago sativa L.). However, many commercial orchardgrass cultivars flower earlier than legumes, resulting in a reduction in grass yield and nutritional value if harvested to maximize the legume. Additionally, during orchardgrass seed production over years, later flowering can gradually shift to earlier flowering. In this study, we employed parental selection based on half-sib family (HS-family) trait values for dry matter yield (DMY) and heading date (HD), and augmented it with marker-assisted selection to enrich for late-heading-associated alleles in six vernalization and flowering time candidate genes. The parent population resulted from polycrossing three late-heading orchardgrass germplasm sources and evaluating 94 HS-families. HDs differed by years and locations for both the parent and HS-family populations. Of the 313 single-nucleotide polymorphisms (SNPs) identified within the candidate genes, 16 were associated with HD with a range of effects from 0.48 to 3.37 days to heading. An SNP detected across multiple years and locations in this study was also found in a previous study, within the intron of the Constans 1 gene (DgCO1). DMY was not highly significant in this study, highlighting a large environmental effect alongside lower variation across the HS-families. However, parental plants fixed for the SNP within DgCO1 showed a trend to later heading as well as higher DMY.

Several short-term studies have investigated 4R (right source, rate, time, and place) N management for dryland wheat (Triticum aestivum L.) production and profitability, but few long-term studies exist in the United States or abroad. This study evaluated long-term impacts of several aspects of 4R N management on dryland hard red wheat yield, protein, and return to N. Experiments were conducted at Nephi and Blue Creek, UT, during 1995-2007. Fourteen N treatments evaluated performance of starter fertilizer, fall applications of anhydrous ammonia (AA) with and without nitrapyrin (AA-Nitrapyrin and AA, respectively), and several split applications in the fall and spring. Across years, winter wheat required N to increase yield, protein, and returns at both sites. Applying 56 kg N ha-1 as AA in the fall usually produced the best return to N compared to other N treatments. Starter N (6 kg N ha-1) at fall planting rarely increased yield, protein, or returns at either site. Across both sites, nitrapyrin increased mean annual yield by 0.6 Mg ha-1 and mean return to N by $150 ha-1. Spring application of N was rarely required and only increased yield in 13% of the years. Results indicate that nitrapryin is often needed with fall AA applications to optimize yield and returns and that starter N or extra N in the spring are rarely economical in dryland wheat in Utah and possibly the greater Intermountain West. Further, N rate had the most influence among 4Rs on wheat production and should be the focus of future efforts to improve 4R stewardship. Few long-term studies have compared various 4R (right source, rate, time, and place) nitrogen aspects for dryland wheat-fallow systems. Across 13 years, fall fertilizer N was needed to optimize production and economics in dryland wheat-fallow system. Starter N and spring N applications rarely improved wheat yield, protein, or return to N. Nitrapyrin added to anhydrous ammonia increased mean annual yield by 0.6 Mg ha-1 and mean return to N by $150 ha-1. N rate had the most influence among 4Rs on wheat production and should be focus of future 4R stewardship efforts.

The effectiveness of frequent compost application in improving soil health is well-documented. Less is known on the long-term effects of infrequent compost application to semiarid soils. Compost made of dairy manure and straw bedding was applied once in a dryland organic hard red winter wheat (Triticum aestivum L. emend. Thell.)-fallow system at 50 Mg ha(-1) dry wt. in 1994 in a randomized complete block design with three replicates. Twenty-eight years later, yields in composted plots (1.4 Mg ha(-1)) remained higher (p < 0.1) than in control plots (0.79 Mg ha(-1)). Plant-available P, acid phosphatase activity (ACP), and total N were higher in composted plots by 143%, 37%, and 29%. Soil organic carbon (SOC) and dehydrogenase enzyme activity were greater by 25% and 20% with compost compared to the control, as were aggregate stability determined using SLAKES method, autoclave-extractable protein, and CO2-96 h by 143%, 22%, and 16%. Soil extractable K and Zn also increased with compost application. The interaction of ACP and estimated evapotranspiration (ET) emerged as a pivotal factor in explaining the variation in yield. These findings suggest that growers may see some yield improvements from periodic compost applications to dryland organic winter wheat-fallow systems. This strategy could help rebuild SOC and partially counter the challenges of low and variable precipitation.

This research evaluated several methods to help reduce pivot ruts or wheel tracks on pivots. On-farm trials were established at nine site-years with corn (Zea mays L.), alfalfa (Medicago sativa L.) and wheat (Triticum aestivum L.) during 2020-2022 in Utah and Idaho. The eight-boom design (i.e., Advantage booms) had mostly positive crop responses but did not reduce wheel track depth. The part circle (PC) method provided much shallower tracks at one site, but it also lowered crop yield. At other sites there were minimal effects to yield and quality with the PC method, but the early-season, shallow wheel tracks did not usually last through the heaviest time of irrigating. The low energy precision application (LEPA) method was the most reliable method for maintaining crop yield and quality, while improving wheel tracks. The single boom method often maintained crop quality, but it also often reduced yield, and did not improve wheel tracks compared with the nontreated controls. The polyacrylamide had few effects on crop yield and quality, or wheel track depth. There was no approach in the study that maintained yield and reduced pivot track depth compared with no treatment in every scenario, but the LEPA method displayed the greatest potential for uniformly irrigating the area near the wheel track to maintain crop yield and quality, while minimizing water entering the track, to help reduce burdensome pivot ruts. Thus, LEPA may be one of the most effective sprinkler modifications for reducing pivot tracks and adequately irrigating the area around the track. This research evaluated how several sprinkler modifications and a soil conditioner help reduce pivot ruts or wheel tracks on pivot irrigation systems. On-farm research trials were established at six fields with corn, alfalfa, and wheat during 2020-2022 in Utah and Idaho. The eight-boom sprinkler modification had mostly positive crop responses but did not reduce wheel track depth. The part circle (PC) sprinkler method sometimes reduced wheel rut depth but came at the expense of lost crop production. The low energy precision application (LEPA) sprinkler method was the most reliable method for maintaining crop yield and quality, while improving wheel tracks. The single boom method often reduced yield and did not improve wheel tracks compared with the nontreated tracks. The polyacrylamide soil conditioner had few effects on crop yield and quality, or wheel track depth. There was no approach in the study that maintained yield and reduced pivot track depth compared with no treatment in every scenario, but the LEPA method displayed the greatest potential for uniformly irrigating the area near the wheel track and maintaining crop yield and quality. Thus, LEPA may be one of the most effective tools for reducing pivot tracks and adequately irrigating the area around the track.

Glyphosate-resistant (GR) alfalfa (Medicago sativa L.) has been widely adopted in the United States. Exceptional tolerance of GR alfalfa to glyphosate application has been reported as a strength of this technology; however, growers have recently reported potential crop injury under specific environmental conditions. The purpose of this study was to document and characterize the injury and determine best management practices for avoiding injury to GR alfalfa in the Intermountain West. The effects of glyphosate rate and application timing during various seasons were investigated at 24 sites over 5 years, measuring the impact on alfalfa crop height and biomass yield. Summer glyphosate applications did not injure alfalfa. However, spring applications reduced crop height at 76% of sites and biomass yield at 62% of sites. At responsive sites, low (869 g ae ha(-1)) and high (1739 g ae ha(-1)) glyphosate rates reduced yield by 0.53 and 1.06 Mg ha(-1), respectively. Alfalfa treated with high rates in the late spring, when 15-20 cm tall, had mean yield reductions of 16%-17% compared with untreated alfalfa. These results suggest that glyphosate applications made at tall crop heights or high rates on GR alfalfa are more likely to reduce crop height and yield in the Intermountain West compared with earlier applications at lower rates. We recommend that spring applications using low glyphosate rates occur before alfalfa is 10 cm tall to mitigate the risk of injury. If a high glyphosate rate is necessary, then an application should be made before alfalfa is greater than 5 cm tall.

Abstract Megachile rotundata F. is the primary commercial pollinator for alfalfa seed production in North America. Managed M. rotundata populations are susceptible to several mortality factors including attack by parasitoids. One such parasitoid, Melittobia acasta Walker, is a multivoltine wasp whose infestations can decimate bee stocks. Details of M. acasta life history using M. rotundata as a host are needed to develop control strategies. Our objectives were (i) to describe the M. acasta life cycle using M. rotundata prepupae as hosts and (ii) to determine the M. acasta developmental base temperature and propose a degree-day model. First, 150–300 M. acasta adults were introduced to 60 M. rotundata prepupae (10–20 wasp females/4 bee prepupae) upon which they oviposited. Progeny development (at 30 °C) was monitored through adulthood. We identified 12 distinct phases of the M. acasta life cycle that were observed among samples over an average of 19.5 days. Second, vials each containing a M. rotundata prepupa with M. acasta eggs were positioned across a temperature gradient bar (2 vials per temperature). In repeated trials, wasp development was tracked from egg to adult where a mean development time for 30 °C was found to be 13 days. A linear regression analysis determined the lower developmental temperature threshold to be 8.55 °C. Application of this base temperature in a degree-day model revealed an average of 305.8-degree-day accumulation from egg to adult. These results provide a framework to assist bee managers in devising M. acasta control strategies and timing their implementation.

Insufficient dry matter intake (DMI) of pasture by dairy cattle is a major factor limiting growth and milk production; however, it has been hypothesized that some dairy breeds may be more efficient grazers than others. This study was conducted to determine whether dairy breed types differ in DMI and feed efficiency when grazing either grass monoculture or grass-legume mixed pastures. The experiment compared 4 different dairy breed types (Jersey, Holstein, Holstein-Jersey crossbreds, and Montbéliarde-Swedish Red-Holstein 3-breed crossbreds) and 2 levels of pasture type [grass monoculture (MONO) and grass-birdsfoot trefoil (BFT) mixture (MX)] for a total of 8 treatments. Pastures were rotationally stocked with groups of 4 prepubertal heifers for 105 d for 3 yr, and DMI was determined from herbage disappearance. Feed conversion efficiency (FCE) and residual feed intake (RFI) were then derived from DMI, and heifer body weights (BW) and normalized to animal units (AU) as 40% metabolic mature BW of the corresponding dairy breed type to account for inherent differences in size and growth rates. We observed differences in DMI and feed efficiency among breed types and between pasture types. On average, Holsteins had the greatest overall DMI (4.4 kg/AU), followed by intermediate DMI by the crossbreds (4.0 kg/AU), and Jerseys had the least DMI (3.6 kg/AU). Heifers grazing MX pastures had on average 22% greater DMI than those grazing MONO, but heifers on grass monocultures were more efficient in converting DMI to BW gain (i.e., RFI/AU of 0.27 and -0.27, respectively; more negative RFI numbers indicate less DMI to achieve the expected gains). Overall, Jerseys had the most favorable feed efficiency; however, ranking of Holsteins and crossbreds depended upon the feed efficiency metric. This study is one of the first to compare the interaction of dairy breed and pasture quality on grazing efficiency. However, the lack of a breed type × pasture type interaction for DMI, FCE, or RFI indicated that none of these dairy breed types were better adapted than another breed type to pastures with contrasting levels of nutritive value.

Many studies have examined individual water-saving management practices for corn (Zea mays L.), but few studies have looked at how combinations of practices might further enhance water optimization. The research objectives of this paper were to evaluate the impact of irrigation technology, irrigation rate, and crop genetics, as well as their interactions, on silage corn yield and forage quality. Trials were conducted in three Utah locations from 2019 through 2021. The results from five site-years indicated that the best water optimization practices varied by site-year. Low-elevation sprinklers commonly applied water more efficiently, with four of the five site-years having improved or equivalent yield compared to mid-elevation sprinklers. Irrigation rate reductions and yield losses were not proportional, as a 25% irrigation reduction resulted in better silage quality and a 7% average yield loss across site-years. Further, targeted deficit irrigation (less water during vegetation and more during maturation) was inferior to a uniform deficit during all growth stages. Drought-tolerant genetics often maintained but did not improve yield in extreme water stress environments compared to non-DT genetics. No cumulative benefits were observed when combining irrigation technology, rate, and DT genetics. Irrigation technology had the greatest potential of the three factors to optimize water use in silage corn production in the Western U.S. region.

Melittobia acasta Walker is one among other hymenopterous parasitoids of Megachile rotundata F. Commercial M. rotundata populations are employed to pollinate North American alfalfa for seed production. This wasp can be prolific when using M. rotundata as a host and can reduce or destroy bee stocks. Hundreds of M. acasta female offspring can develop in a single M. rotundata cell and disperse to infest other cells, producing thousands of more parasitoids. In this study, we determined (i) upon what bee life stages M. acasta females choose to lay eggs and if those eggs ultimately become adults and (ii) M. acasta female longevity when exposed to various resources within M. rotundata cells. We found that M. acasta females lay eggs on M. rotundata prepupae and pupae and that those eggs can hatch and survive to adulthood. Eggs are not laid on early instar bee larvae; eggs laid on adults do not survive. Average female life span is 5 days without feeding, 8-9 days if a pollen-nectar provision is available while the bee develops through larval stages, and 34 days if the wasp can feed on prepupal hemolymph. Wasp females can emerge from bee cells several days after trays of cells are taken to fields. Therefore, adult females could survive long enough for new bee offspring to become prepupae. Our findings support a better understanding of host life stage preference and the longevity of M. acasta females that can inform the timing of the implementation of possible control measures.

Alfalfa (Medicago sativa L.) is often grown in water-limited climates where available soil moisture is a key factor in determining the success or failure of new stand establishment. This study was conducted to determine optimal oat (Avena sativa L.) companion seeding rates for alfalfa establishment across a range of soil moisture levels. The effects of five oat seeding rates (0 [with and without herbicide], 11, 22, 45, and 89 kg ha(-1)) under five water levels on alfalfa stand establishment, forage yield, and nutritive value were evaluated at North Logan, UT, on a Millville silt loam soil (coarse-silty, carbonatic, mesic Typic Haploxeroll) in 2019 and 2020. When soil moisture was adequate, first cut alfalfa stem density increased twofold as oat seeding rates decreased from 89 to 11 kg ha(-1), but at low soil moisture levels stem density increased fivefold to sevenfold. At second cut, the only stem density differences that remained were at low irrigation. First cut forage yields were lowest in 0 kg ha(-1) treatments and increased with increasing oat seeding rates. The opposite was true at second cutting, where yields were greatest where no oat had been planted. Yield differences were more extreme as soil moisture was reduced. The highest oat seeding rate had comparable weed control effects to the herbicide. Generally, the presence of either oat or weeds reduced forage nutritive value when compared to alfalfa alone. Reducing oat seeding rates or eliminating the companion crop altogether appears to improve alfalfa stand establishment when soil moisture is limited.