Non Technical Summary
Field crops in Utah have primarily been represented by alfalfa, corn, and small grains. A new field crop, industrial hemp (Cannabis sativa), was grown as a federally-recognized commodity in Utah in 2019. Damage from herbivorous arthropods can cause major economic yield losses for growers of field crops if left unchecked. Traditionally, pest management in field crops has relied on insecticide applications for pest suppression. However, reliance on insecticides has resulted in unintended consequences including resistance to overused insecticides, non-target suppression of beneficials (predators, parasitoids, and pollinators), and other environmental and human health concerns. Integrated pest management (IPM) provides a way to have a multifaceted approach to manage arthropods and assist in addressing the judicious use of insecticide applications. One of the first steps in an IPM program is validating the identification of a pest. In a new system like hemp, it is important for growers and agricultural professionals to know which arthropods are pests and what beneficials are present that may assist in pest suppression. Therefore, for hemp there is a need to establish a species list of arthropods associated with this crop in Utah. In addition, it is important that growers and agricultural professionals of hemp and established crops (i.e., alfalfa and com) continue to be educated on target pests and conservation of beneficial species. A way to prevent pest outbreaks is through the selection of plant varieties that have traits to deter arthropod feeding, slow development, or are generally toxic to the pest (e.g., genetically modified Bt-crops like corn). Screening plants in search of pest susceptibility, tolerance and resistance can assist growers in variety selection and anticipated pest pressure as a result of planting susceptible varieties. Despite best attempts to prevent pest outbreaks, herbivores may still damage crops and reach abundances equaling or exceeding established economic thresholds where management is recommended. Insecticides offer relatively quick pest suppression in field crops, however, growers have limited options considering loss of products to public pressure, misuse, federal bans (e.g., Furadan used as a weevil treatment in alfalfa), and resistance. For some field crops, like alfalfa, grower perception is that traditional products (e.g., organophosphates and pyrethroids) are providing mixed results, yet it is not clear if this is a result of resistance, timing, or other factors. By understanding the mechanism, growers can develop a pesticide resistance management program, better time applications, and generally adjust management practices to ensure pest suppression. Taken together, an IPM approach is key for herbivorous arthropod management. Identifying the needs for each crop to establish best practices and determining how to address the need are important next steps. It is clear that for new crops, like hemp, a basic framework of IPM including identification of pests and the relationship of pests with the crop are needed. For other well established crops (i.e., alfalfa and com), a reevaluation of IPM is needed considering the impact of climate variability on plant-pest interactions, and the extended use of traditional pesticide use on pests where in some cases appear to be having mixed results. Here, IPM for new and established field crops in Utah are evaluated.
Animal Health Component
Research Effort Categories
Goals / Objectives
The objectives are to:1) conduct on-farm surveys to determine the composition of arthropods on field crops,2) conduct greenhouse trials to compare susceptibility of varieties to arthropod herbivory,3) evaluate the effect of insecticides on arthropod pests and beneficials,4) conduct outreach on field crops to provide resources enabling growers to implement IPM practices.
Hemp farms will be identified, and variables impacting arthropod presence will be collected (e.g, farm size, management practices, etc.). At each farm, inspections and collections of arthropod pests and beneficials will occur starting after plant establishment. Visual inspections for plant symptoms will be collected and/or beating tray/vacuum will capture subsequent causal pest (if any). Detailed sampling of a random selection of four plant-rows representing two edge and two middle locations (where each section is approximately 4.5 meters long, and the edge section is 9 meters from the edge) using vacuum collection (reverse leaf blower with catch bag) for approximately one minute per section. Arthropod samples will be stored in a freezer, until each sample is sorted for identification. Pest arthropod identification will be based on plant symptoms and identification keys.Hemp cultivar selection will involve experiments conducted in secure facilities at the USU Research Greenhouses in Logan, UT. The Crop Physiology Lab will provide young, sterile transplants (approx. 8 cm in height), representing four cultivars (selected from Abacus, BaOx, Cherry, Otto 2, T1 [Trump], or Tokyo), depending upon availability. Plants will be grown in standard potting media under greenhouse controlled conditions (25±2 °C, 60±5% RH, 16:8 hr (L:D) photoperiod) and fertigated. Experimental units will consist of a pot with a single plant, representing one replicate. Each treatment, each of four cultivars with arthropods (either/or mites, caterpillars) or a control (no arthropods), will be replicated 10 times. After 2 weeks of plant establishment in pots, 10 individuals of a specific pest (i.e., adult female mites or 1st instar caterpillars) from laboratory colonies will be introduced onto a single leaf of each plant. For mites, individuals will be transferred to leaves by vacuuming mites into filtered pipette tips. The pipette tips will then be secured to the upper leaf surface to allow mites to exit and settle on the leaves. At 1, 3, and 7 days post mite introduction, three leaves per plant (initial mite introduction leaf, middle, and upper leaf) will be selected to count mites and eggs. At 14 days post mite introduction, a destructive sample of leaves will be taken to evaluate mite growth (mites and eggs) on the entire plant. For caterpillars, individual first instar larvae will be transferred to leaves with a fine paint brush. At 1, 2, and 4-weeks post-larvae introduction, plants will be given feeding damage rankings, and larvae measured for growth stage. At 5-weeks post-introduction, larvae will be examined for pupation and tested for differences in size.To evaluate the effect of drought tolerant corn hybrids on the development of spider mites, a greenhouse experiment in a completely randomized design will be conducted at USU Research Greenhouse in Logan, UT. Experimental units will consist of plastic containers filled with potting soil mix. Six corn plants (of a given hybrid, drought tolerant or non-drought tolerant) will be seeded per container, where each container represents a replicate and each plant represents a subsample. Each treatment (mite × hybrid × irrigation) will be replicated four times. Plants will be kept under greenhouse-controlled conditions and fertigated. Drip tape will be used to irrigate the plants throughout the experiment. After six weeks, plants will be switched from fertigation to irrigation to establish optimal irrigation or water-stress levels. Soil sensors will be used to monitor the volumetric water content (VWC) of soil. All replicates (containers) will be irrigated evenly at the level equivalent to field capacity of potting soil (50-60 % VWC) for seven weeks after sowing. When plants are 8-weeks old, containers will be randomly assigned to either optimal irrigation (maintaining 50-60 % VWC at field capacity) or water-stress (reducing irrigation to 5-10 % VWC above permanent wilting point) treatments. When plants are 8-weeks old, two sticky barriers will be made with non-phytotoxic wax around the under- and upper-side of the 8th leaf. Each barrier will be positioned at 7.5 cm from the leaf center, creating a 15 cm long arena at the center of the leaf. Twenty adult female mites from laboratory colonies will be introduced into the leaf arena. Mites will be transferred to leaves by vacuuming as previously described. Leaf subsamples from two randomly selected plants per treatment will be collected at 1, 3, and 7 days post mite introduction. Each leaf sample will be inspected to count all mite stages.To investigate alfalfa pest susceptibility to insecticides, we will utilize standard bottle tests. Bioassays will be conducted in 1000 mL glass bottles containing 10-25 insects (alfalfa weevil or Lygus). Insecticides including chlorpyrifos, lambda-cypermethrin, indoxacarb, sulfoxaflor, will be evaluated. A series of concentrations (ranges within the pesticide label) will be tested for each insecticide with replicates being conducted for each concentration. A time-response survival curve for each of the insecticides used will be developed with each of the different insect pests. Time-response survival curves will be constructed by plotting time on the x-axis against percent mortality on the y-axis. A diagnostic dose is the lowest dose tested that caused 100% mortality between 30 and 60 min.To measure contact lethal insecticide concentrations, alfalfa foliage from sprayed plants will be used to expose insects to treated plants. Cages will be setup in the USU Research Greenhouse to have controlled conditions. Cages without insecticide treated alfalfa will represent the control. Six replicates will be assigned to each treatment and control, with a minimum of 25 insects per replicate. Percent insect mortality will be measured after 24 hrs of exposure in each treatment and control. Other sub-lethal and behavioral parameters (e.g., twitching, upright but not exploring cage, etc.) will also be recorded. Similarly, survival curves will be constructed for evaluation of insect sensitivity to insecticide applications.Commercial alfalfa fields (2-3 years old) will be selected. For alfalfa weevil sampling, we will use a sweep net which consists of swinging a canvas net from side-to-side in a 180-degree arc. We will take a series of 10 sweeps at three locations in the field. We will count the number of weevils after every 10 sweeps and calculate the average number per sweep. Weevils will be sampled once a week starting when alfalfa is approx. 25 cm tall and continue until the first alfalfa cut or when alfalfa weevil pupates (whichever comes first) since weevils have one generation per season. Stem sampling method (also known as the "shake-bucket method") will also be implemented when alfalfa stems are 8-10 inches tall. Stem sampling consists of clipping individual alfalfa stems at the soil surface and carefully placing stems top-side-down into a bucket. We will select 30 stems in a field and shake groups of five alfalfa stems at a time vigorously against the inside of the bucket to dislodge small larvae hidden in tight leaf whorls. We will count the number of weevil larvae collected and calculate the average number of larvae per stem. These data will be used to develop a phenological model to predict activity.The Utah Pests website will be used to deliver outreach materials. Project updates and subject matter (e.g., weevil chemical control options, resistance, spider mite management, etc.), as deemed relevant will be published through university and industry newsletters.