Location: Horticultural Crops Production and Genetic Improvement Research Unit
2021 Annual Report
Objectives
Irrigation and nutrient management are key factors that impact sustainable and profitable production of high-quality small fruit and nursery crops. The goal of this project is to develop new approaches that integrate water and nutrient management methods with other environmental and cultural constraints to improve the quantity and quality of berry, wine grape, and nursery crops grown in the Pacific Northwest (PNW) while protecting the environment.
Objective 1: Determine requirements for high-quality berry crop production through monitoring and management of water, nutrients, and soil. [NP 305, Component 1, Problem Statement 1B]
• Subobjective 1A: Adapt and refine remote sensing technology to monitor water and nutrient deficits and determine irrigation and fertilizer needs in berry crops.
• Subobjective 1B: Assess the feasibility of using deficit or pulsed-drip irrigation to increase water use efficiency and protect regional water quality in berry crops.
• Subobjective 1C: Develop new fertigation and soil management practices to increase production and fruit quality in blueberry.
Objective 2: Develop approaches to manage vineyard canopies, soils, and nutrients for improved grape production, plant health, and fruit quality. [NP 305, Component 1, Problem Statement 1B]
• Subobjective 2A: Develop an integrated nitrogen (N) management approach encompassing N use in both the vineyard and winery to identify the most effective and efficient manner to manage N inputs to improve wine quality and protect water quality.
• Subobjective 2B: Examine how canopy architecture, vine density, and crop load interact to identify the most efficient use of sunlight and soil water resources to improve production efficiency of Pinot noir.
• Subobjective 2C: Understand how N management practices influence beneficial arbuscular mycorrhizal fungi (AMF) in grapevines to develop more sustainable methods for farming grapes.
• Subobjective 2D: Determine the impact of rootstocks on root development and AMF colonization when challenged by the northern root knot nematode.
Objective 3: Evaluate the impact of management practices for water and nutrients on tolerance to abiotic and biotic stress in specialty crops. [NP 305, Component 1, Problem Statement 1C]
• Subobjective 3A: Develop new management practices and disease control measures to minimize pathogen damage and losses for woody nursery plants.
• Subobjective 3B: Define salinity thresholds for specialty crops so growers can reduce losses of planting stock, mitigate salinity impacts on quality, and broaden the use of more salt tolerant species in systems considered marginal for production of other crops.
• Subobjective 3C: Develop and evaluate water and nutrient management practices for specialty crops grown in soilless substrates.
Approach
Experiments will be conducted in the greenhouse and field on small fruit (blueberry, raspberry, strawberry, grapevines) and other specialty crops including nursery crops (Rhododendron, Vaccinium, Basil), and in growth chambers on root pathogens. For Obj. 1 we will develop remote sensing based crop coefficients and water stress indices for irrigation of blueberry and raspberry, and will test the following hypotheses: Deficit irrigation will reduce water use but have no effect on yield or fruit quality when it is applied at early stages of fruit development or after harvest in blueberry or raspberry; Pulsed-drip irrigation will reduce water use and increase yield and production relative to conventional irrigation in blueberry and raspberry; Application of P and B by fertigation will result in greater yield and fruit quality than granular or foliar fertilizers in blueberry; Biostimulants are most effective when applied at low rates and during peaks in root production. For Obj. 2 we will test these hypotheses: Maintaining low N status in the vineyard will enhance wine composition as compared to boosting N supply in the vineyard; Varying N supply to Pinot noir alters berry and wine phenolic composition to a greater extent than P or K; Altering the VSP trellis to increase canopy solar exposure at midday will increase productivity but not alter ripening or fruit quality in Pinot noir; Soil and foliar applied N in vineyards reduces AMF colonization and P uptake; Nitrogen inhibition of AMF colonization in grape roots increases with N dose; Nitrogen is a more potent inhibitor of AMF as vine P increases; Root development and AMF colonization differ among rootstock genotypes when northern root knot nematode is present. We will test the following hypotheses for Obj. 3: Critical temperatures for vegetative growth and zoospore formation of Phytophthora isolates will be similar within a species; fungicide sensitivity of Phytophthora is greatest at the optimal temperature for growth; Root rot induced by flooding is more severe than rot under moisture conditions common in nurseries; Reducing water availability minimizes root damage caused by Phytophthora in rhododendron; Increasing N increases root damage caused by Phytophthora in rhododendron; Crop tolerance to salinity will differ among production systems; Southern highbush blueberry plants have different substrate needs than northern highbush blueberry; Strategies to improve water distribution in substrates will increase growth and production in blueberry. Measurements and techniques used in these studies will include standard approaches to measure plant growth, biomass, and yield, plant water status (pressure chamber, porometer), photosynthesis (gas-exchange), fruit quality (refractometry, titratation, HPLC, sensory perception), root production and mycorrhizal colonization (soil cores, microscopy), soil pH and EC, soil water content (TDR, tensiometers), plant and soil nutrients (CNS analyzer, ICP), and pathogen growth (microbiological media) and root damage (visual ratings). We will also utilize multi-spectral cameras and drones to develop new methods to measure plant water status.
Progress Report
Research was continued in support of Sub-objective 1A, to investigate new remote imaging techniques for assessing the need for irrigation in blueberry and raspberry and to better prepare each industry against future water uncertainties. Two years of remote images were collected at least monthly from commercial field sites located throughout Washington State using a low-altitude, unmanned aerial system (UAS or drone) equipped with a multispectral and a thermal imaging camera. The images were processed and analyzed for normalized difference vegetation index (NDVI) and canopy temperature. While physiologically-based indicators can only be measured in a limited number of plants, remote imagery collected with the UAS was a quick and easy method to provide information on every plant on the farm. Fields were mapped on a block-by-block basis, providing an invaluable tool for water management. The NDVI images provided clear information on development of the canopy in the fields and to estimate the irrigation needs at each site. Thermal images were also useful, particularly for assessing spatial variability in water status of the fields. For example, thermal imaging revealed that large sections of a 4.5-ha field were under-irrigated. Although there was no visual evidence of drought stress in these plants (i.e., no wilting), it turned out that many of the drip emitters located in the under-irrigated sections were plugged. Such information enables growers to quickly identify problems with their irrigation systems. Growers can also use the images to determine whether they are scheduling irrigations properly or need to add more water to the field.
Field trials were continued in support of Sub-objective 1B, in order to evaluate new practices for reducing irrigation water use in berry crops, including deficit irrigation and pulsed drip irrigation. Results indicated that reducing irrigation during early stages of fruit development or after harvest has minimal effect on yield or fruit quality in blueberry. Applying irrigation in a series of small pulses, on the other hand, increased soil water availability relative to conventional irrigation in raspberry and, by the second year, increased total production by 7%, or 1230 kg/ha. Production followed a similar trend in the following year and increased by 1209 kg/ha with pulsing. Based on recent market prices for processed raspberries, the increase in production with pulsed drip was equivalent to $2,460/ha per year. Much of this increase occurred during the latter three to four weeks of the harvest season and was primarily due to larger fruit size with pulsing in year two and to more berries per plant in year three. Pulsed drip also increased canopy cover by nearly 12% in year two and resulted in larger and more floricanes per plant in year three. Based on these results, pulsed drip irrigation appears to be a promising method for improving production of red raspberries. A similar trial was initiated this year in blueberry. Use of deficit irrigation would lead to immediate water savings, and when coupled with remote sensing technology, could enable growers and irrigation managers to optimize on-farm and regional water use. When managed properly, pulsing could increase plant growth and production relative to applying water all at once each day or two and can greatly reduce runoff, evaporation, and leaching.
In support of Sub-objective 1C, trials investigating the value of fertigating with phosphorus (P) and boron (B) fertilizer in highbush blueberry were continued. Results indicate that fertigation and granular applications of P fertilizer increased the concentration of P in soil solution within the root zone, but neither had any effect on yield, berry weight, or berry firmness in either cultivar. These treatments also had no effect on leaf P. In fact, the concentration of P in the leaves was no different than it was prior to applying any P to the plants; however, granular P increased the concentration of P in the roots of both cultivars and tended to reduce root colonization by mycorrhizal fungi in ‘Bluecrop’. The soil at the site was high in clay and likely bound much of the applied P. Questions remain on whether blueberry requires less P than recommended or if alternative sources or rates of P fertilizer are needed. Leaf B, on the other hand, was significantly affected by the fertilizers and within the first year was sufficient with fertigation or foliar applications but low in the granular treatments and no different than those with no B. By the following year, leaf B remained low in treatments with no B and in one cultivar remained deficient with granular B. At this point, applying B by fertigation or as a foliar appears to be preferable over the use of granular B fertilizers. The project builds on our previous work on nitrogen and potassium and will be used to develop complete guidelines for fertigation of highbush blueberry. The results will help growers improve production in the crop and enhance fruit quality for consumers.
A trial was initiated in support of Sub-objective 1C, to assess the response of blueberry to biostimulants and ascertain how they function in new and mature plantings. Several different biostimulants were tested, including humic substances (humic and fulvic acids), extracts from Ascophyllum seaweed, and a mix of nitrogen-fixing bacteria (Azorhizobium caulinodans, Azoarcus indigens, and Azospirillium brasiliense). Fertigating with humic substances or seaweed extract increased growth of the plants relative to using the bacterial mix or nutrients only; however, the response was quite different between the two products. Plants grown with humic substances were greener and contained more N than those in the other treatments, while those grown with seaweed extract tended to be taller and more upright. Clearly, the use of these products can be beneficial during establishment of highbush blueberry, but more research is needed to determine exactly how they work and whether they are useful under all circumstances.
In support of Sub-objective 2A, field treatments with varying nitrogen were applied with grower collaborators and vine growth, nutrient status in leaf and petioles, water status and gas exchange measurements were completed. Crop yield parameters were measured and fruit was harvested and delivered to collaborators to make wine and monitor fermentations. Sensory analysis was completed by collaborators. Also in support of Sub-objective 2A, the first steps of spectral analysis on both berries and wines were completed.
In support of Sub-objective 2B, the baseline data was collected for soil moisture profiles, plant growth and yield, and water status. However, due to poor fruit set resulting from cool rainy weather at bloom, crop load was well below normal.
In support of Sub-objective 2C, all root samples were collected and cleared and stained for mycorrhizal colonization assays and nutrient status for the vines was determined. Research to evaluate the impact of soil and foliar nitrogen on mycorrhizal fungi and plant nutrition in controlled greenhouse conditions was conducted to further support Sub-objective 2C. Results showed that young vines did not respond in a similar fashion as older field-grown vines to added nitrogen and root colonization by mycorrhizal fungi was unaffected by nitrogen supplied to the soil or to the foliage.
In support of Sub-objective 2D, root samples were processed, root parameters were measured and roots were cleared and stained for mycorrhizal assays.
In support of Sub-objective 3A, research continued on establishing critical temperatures for growth, reproduction, and fungicide sensitivity of pathogens associated with root rot in nursery crops. Completed trials identified optimal, minimum, and maximum temperatures for growth. Researchers are currently analyzing data from growth studies and starting trials to assess temperature effects on pathogen reproduction and fungicide sensitivity. In further support of Sub-objective 3A, research continued to identify how substrate moisture alters the incidence and severity of root rot in nursery crops. Completed trials identified whether research techniques used in studying root rot are representative of what occurs under nursery conditions. Researchers are currently analyzing data and writing a manuscript and starting trials to assess whether irrigation practices that reduce water availability can alter disease.
In general support of Sub-objective 3A, research evaluating factors altering horticultural crop root health continued as planned. Collaborative research was completed on numerous projects, including: identifying how temperature and moisture alter pathogenicity in raspberry root rot; comparing virulence of multiple pathogens associated with root rot in nursery grown Rhododendron; establishing how pathogens associated with root rot in nursery plants differ in sensitivity to fungicides; and improving methods for producing reliable inoculum of root rot pathogens. Collaborative research continued on quantifying fertilizer run-off from nursery crops and use of remote imaging for management of nursery plant nutrition and irrigation and evaluating environmental effects on spread of the boxwood blight pathogen.
Researchers initiated a trial in support of Sub-objective 3C to evaluate the effects of irrigation frequency (pulse length) and number of wetting points (number and distribution of emitters per pot) on growth, mineral nutrition, yield, and fruit quality of highbush blueberry in substrate. The study will provide new information on best irrigation practices for substrate production of blueberries and ultimately contribute to the feasibility of using this type of niche production.
Accomplishments
1. Variability in fungicide sensitivity and Phytophthora root rot in rhododendron nursery plants. Fungicides used by growers frequently fail to control Phytophthora root rot in rhododendron nursery plants, causing significant losses to the $42 million industry. ARS researchers in Corvallis, Oregon, determined three reasons why fungicide control of this disease might fail: (i) the fungicide is applied to the wrong portion of the plant for optimal control; (ii) there are differences in fungicide sensitivity among the many different soilborne Phytophthora spp. and isolates infecting rhododendron; and (iii) fungicide-insensitive isolates are present in the rhododendron nursery industry. This research provides valuable information for other researchers and industry in developing more effective disease control measures.
2. New guidelines extend the time window to monitor water stress in grapevines. The pressure chamber is the standard tool used to measure water stress in vineyards and other crops, but its application was limited by the one-hour time period when measurements were thought to reflect the maximal level of vine water stress experienced during the day. An ARS researcher in Corvallis, Oregon, and a graduate student from Oregon State University, evaluated when different measures obtained with the pressure chamber were stable at the maximal daily stress level in vineyards utilizing north-south oriented, vertical shoot positioning (VSP) trellis systems. The VSP system with north-south oriented rows is the most common training system used in wine grapes worldwide. Results obtained from multiple vineyards and a variety of conditions revealed that leaf water potential accurately reflected the maximal level of water stress for up to a four-hour time period beginning at solar noon in vineyards employing VSP systems. These findings are being utilized by researchers and growers to increase the number of vines or vineyard blocks that are monitored on a given day to improve sustainable water use in vineyards.
3. A new tool for preventing heat damage in blueberries. Heat damage is a persistent problem in blueberries and results in millions of dollars of fruit loss each year. Growers commonly report sunburn, softening, and discoloration of the berries when temperatures exceed 90 to 95 degrees Fahrenheit. An ARS researcher in Corvallis, Oregon, and collaborators from Oregon State University, and Washington State University determined that sprinkler irrigation was very effective at reducing heat damage and developed a model to identify the best time and frequency to operate these systems for cooling. This model is a valuable new tool that will help protect the blueberry industry against costly fruit losses during hot weather.
4. Strategies for dealing with drought in blueberries. Many blueberry growers are facing serious water limitations due to drought and increased demand for water by other sectors, and must often cut back on irrigation during drier years. To identify periods in which irrigation may be less critical for blueberries, an ARS researcher in Corvallis, Oregon, and collaborators from Oregon State University, evaluated the effects of soil water deficits during fruit development in a wide range of blueberry cultivars that ripen at various times between June and September. Water deficits applied during later stages of fruit development had the largest effects, particularly in cultivars that ripened later, but was less critical during early stages of fruit development, suggesting this may be a good time to reduce irrigation if needed. Results from the study will help blueberry growers increase the efficiency of irrigation water use and reduce losses of yield and fruit quality in years when water is limited.
5. New tissue nutrient test shows promise in grapevines. Grape growers use leaf blades, or petioles, collected during the growing season to diagnose vine nutritional status, but an earlier indicator of vine nutrient status is desired to give growers enough time to develop more efficient nutrient management plans for the year. An ARS researcher in Corvallis, Oregon, tested if dormant season pruning wood collected in the winter over four years could predict vine nutrient status in the subsequent growing season, as measured in leaf blades and petioles at bloom and veraison (when grapes turn red). Winter time pruning wood was an excellent predictor of vine phosphorus levels and a good predictor of potassium levels during the next growing season, but the winter samples were not effective in predicting vine nitrogen status. These promising results will be further tested as part of a nationwide study to find new tools for grape producers to better monitor nutrition.
6. Several Phytophthora species cause rhododendron root rot in nurseries. Rhododendrons are an important component of the ornamental nursery industry, but are prone to Phytophthora root rot, despite decades of research. One Phytophthora species, P. cinnamomi, was previously thought to be the primary pathogen causing rhododendron root rot. Recent research suggests there are several other Phytophthora species that may cause root rot, but little was known of their virulence and risk to the industry. ARS researchers in Corvallis, Oregon, and researchers at Oregon State University, determined that at least three other Phytophthora species isolated from Oregon nursery plants can cause similar disease severity as P. cinnamomic, but not all species are equally virulent. This research provides valuable information for other researchers and industry in developing more effective disease control measures.
7. Transport of nitrate from roots to shoots drives the growth promoting ability of grapevine rootstocks. Grapevine rootstocks are used in viticulture to control pests and also vine growth or size, which is related to their ability to both acquire nitrogen from soil and to transport it to the shoot. However, which of these two major mechanisms actually governs nitrogen accumulation in shoots is not understood. An ARS researcher in Corvallis, Oregon, and colleagues from Oregon State University, investigated nitrogen uptake and transport properties of two rootstocks that are known to differ in how well they promote scion growth in a series of studies in grafted Pinot noir grapevines. The results showed that the rootstock known to impart greater scion growth transported more nitrate to leaves resulting from greater water movement to individual leaves under low and high nitrate supply, while the less vigorous rootstock had greater root nitrate uptake capacity and allocated more biomass to roots when nitrogen was low. These findings indicate that growth promotion of scions by grapevine rootstocks appear to result from greater transport of nitrogen to shoots in the xylem as compared to greater uptake kinetics from soil.
8. Understanding optimal temperatures for occurrence of Raspberry root rot. The pathogen, Phytophthora rubi, causes significant losses to root rot in the Washington State red raspberry industry. This pathogen was previously assumed to be the most infective during winter when soil temperatures range from 5 to 10 C. However, recent research has reported that symptoms of root disease during summer were strongly associated with P. rubi. ARS researchers in Corvallis, Oregon, and researchers at Oregon State University, determined that P. rubi grew fastest and sporulated more heavily at 20 C than lower temperatures, but disease severity was similar at 15 and 20 C. These results indicate that P. rubi is more likely to infect during the spring and summer in this region when soil temperatures are between 15 to 20 C. This research provides valuable information for researchers and industry for timing effective disease control measures when the pathogen is most active.
9. Rethinking the use of mulch in blueberries. Many growers are using woven polypropylene ground cover, which is often referred to as “weed mat”, in commercial blueberry fields. Weed mat is very cost effective for weed control, but, unlike the previous industry standard of using sawdust mulch, it leads to a reduction in soil health and fruit production within a few years after planting. An ARS researcher in Corvallis, Oregon, and collaborators from Oregon State University, evaluated the potential of using a dual system, in which sawdust is placed underneath the weed mat. The dual system helped plant establishment and increased yield by as much as 20% in the second growing season. Furthermore, weed mat protected the sawdust layer from erosion by wind and rain and was more effective for weed control than sawdust alone. Although there is an extra upfront cost to the dual system, net returns are higher once factors such as labor, maintenance, and fruit sales are considered.
10. Optimizing inoculum production methods for infesting soil with Phytophthora species. Phytophthora root rot causes significant losses in many horticultural crops and research on this pathogen requires consistent and predictable production of viable pathogen inoculum. A common method used to produce inoculum of this pathogen can take six weeks to produce and often results in variability among batches of inoculum that can waste valuable resources and delay research progress. ARS researchers in Corvallis, Oregon, identified inoculum moisture content that reduces inoculum viability and used results to develop a new method that produces more reliable inoculum in a shorter time. This research is important to other researchers because it helps explain variability in soilborne Phytophthora inoculum production and storage, and provides a new method for producing inoculum more quickly.
Review Publications
Tian, T., Schreiner, R.P. 2021. Appropriate time of day to measure leaf and stem water potential in vineyards using vertical shoot positioning. American Journal of Enology and Viticulture. 72(1):64-72. https://doi.org/10.5344/ajev.2020.20020.
Strik, B.C., Davis, A.J., Bryla, D.R. 2020. Individual and combined use of sawdust and weed mat mulch in a new planting of northern highbush blueberry. II. Nutrient uptake and allocation. HortScience. 55(10):1614-1621. https://doi.org/10.21273/HORTSCI15271-20.
Yang, F., Bryla, D.R., Peters, T. 2021. An energy balance model for predicting berry temperature and scheduling sprinklers for cooling in northern highbush blueberry. HortScience. 56(4):447-453. https://doi.org/10.21273/HORTSCI15459-20.
Almutairi, K.F., Bryla, D.R., Strik, B.C. 2021. Sensitivity of northern highbush blueberry cultivars to soil water deficits during various stages of fruit development. HortScience. 56(2):154-162. https://doi.org/10.21273/HORTSCI15493-20.
Rossdeutsch, L., Schreiner, R.P., Skinkis, P.A., Deluc, L. 2021. Nitrate uptake and transport properties of two grapevine rootstocks with varying vigor. Frontiers in Plant Science. 11. Article 608813. https://doi.org/10.3389/fpls.2020.608813.
Yang, F., Bryla, D.R., Orr, S.T., Strik, B.C., Zhao, Y. 2020. Thermal cooling with sprinklers or microsprinklers reduces heat damage and improves fruit quality in northern highbush blueberry. HortScience. 55(8):1365-1371. https://doi.org/10.21273/HORTSCI15119-20.
Schreiner, R.P. 2021. Utility of dormant season pruning wood to predict nutrient status of grapevines. Journal of Plant Nutrition. 44(2):238-251. https://doi.org/10.1080/01904167.2020.1806311.
Strik, B.C., Davis, A.J., Bryla, D.R., Orr, S.T. 2020. Individual and combined use of sawdust and weed mat mulch in a new planting of northern highbush blueberry I. impacts on plant growth and soil and canopy temperature. HortScience. 55(8):1280-1287. https://doi.org/10.21273/HORTSCI15122-20.
Sacher, G.O., Scagel, C.F., Davis, E.A., Beck, B.R., Weiland, G.E. 2021. Virulence of five phytophthora species causing rhododendron root rot in Oregon. Plant Disease. https://doi.org/10.1094/PDIS-09-20-1873-RE.
Graham, K.A., Beck, B.R., Zasada, I.A., Scagel, C.F., Weiland, G.E. 2021. Growth, sporulation, and pathogenicity of the raspberry pathogen phytophthora rubi under different temperature and moisture regimes. Plant Disease. https://doi.org/10.1094/PDIS-09-20-1916-RE.
Weiland, G.E., Scagel, C.F., Grunwald, N.J., Davis, E.A., Beck, B.R. 2020. Phytophthora species differ in response to phosphorous acid and mefenoxam for the management of phytophthora root rot in rhododendron. Plant Disease. 105:1505-1514. https://doi.org/10.1094/PDIS-09-20-1960-RE.
Davis, E.A., Weiland, G.E., Scagel, C.F. 2021. Optimizing inoculum production methods for infesting soil with phytophthora species. Plant Disease. https://doi.org/10.1094/PDIS-12-20-2698-RE.
