Commercial Strawberry Farm Research Articles

Strawberry field trial in Australia demonstrates improvements to fruit yield and quality control conformity, from application of two biostimulant complexes

ABSTRACT Strawberry (Fragaria x ananassa) is a popular fruit consumed for its desirable flavour, aroma and colour and is considered a functional food due to its antioxidant properties. Noting the need for farmers to increase productivity to meet increasing consumer demands, this study aimed to explore the potential of biostimulants to enhance strawberry cultivation. Herein, a field trial was conducted on a commercial strawberry farm, wherein 1944 strawberry plants received fertigation supplementation with either a control solution (nutrients only) or nutrients combined with one of two biostimulant complexes (BCs). Biostimulant complex 1 (BC1) was composed of molasses, Aloe vera extract and fish-hydrolysate, and biostimulant complex 2 (BC2) was composed of potassium silicate and potassium phosphite. Results indicated that BC1 maintained total yields but increased the sellable proportion and decreased the proportion of waste. In contrast, BC2 increased total yields with both sellable yields and waste increased. No significant changes were observed for indicators of consumer preference (flavour, aroma and fruit colour), however, on-average large increases were observed to indicators of fruit antioxidant properties (phenolic and flavonoid content). Accordingly, these results support the utilisation of biostimulants as a strategy to improve strawberry on-farm productivity without compromising consumer quality measures.

Multidisciplinary evaluation of plant growth promoting rhizobacteria on soil microbiome and strawberry quality

The natural soil environment is considered one of the most diverse habitats containing numerous bacteria, fungi, and larger organisms such as nematodes, insects, or rodents. Rhizosphere bacteria play vital roles in plant nutrition and the growth promotion of their host plant. The aim of this study was to evaluate the effects of three plant growth-promoting rhizobacteria (PGPR), Bacillus subtilis, Bacillus amyloliquefaciens, and Pseudomonas monteilii for their potential role as a biofertilizer. The effect of the PGPR was examined at a commercial strawberry farm in Dayton, Oregon. The PGPR were applied to the soil of the strawberry (Fragaria × ananassa cultivar Hood) plants in two different concentrations of PGPR, T1 (0.24% PGPR) and T2 (0.48% PGPR), and C (no PGPR). A total of 450 samples from August 2020 to May 2021 were collected, and microbiome sequencing based on the V4 region of the 16S rRNA gene was conducted. The strawberry quality was measured by sensory evaluation, total acidity (TA), total soluble solids (TSS), color (lightness and chroma), and volatile compounds. Application of the PGPR significantly increased the populations of Bacillus and Pseudomonas and promoted the growth of nitrogen-fixing bacteria. The TSS and color evaluation showed that the PGPR presumptively behaved as a ripening enhancer. The PGPR contributed to the production of fruit-related volatile compounds, while the sensory evaluation did not show significant differences among the three groups. The major finding of this study suggests that the consortium of the three PGPR have a potential role as a biofertilizer by supporting the growth of other microorganisms (nitrogen-fixing bacteria) as part of a synergetic effect and strawberry quality such as sweetness and volatile compounds.

Precision Agriculture Using Soil Sensor Driven Machine Learning for Smart Strawberry Production.

Ubiquitous sensor networks collecting real-time data have been adopted in many industrial settings. This paper describes the second stage of an end-to-end system integrating modern hardware and software tools for precise monitoring and control of soil conditions. In the proposed framework, the data are collected by the sensor network distributed in the soil of a commercial strawberry farm to infer the ultimate physicochemical characteristics of the fruit at the point of harvest around the sensor locations. Empirical and statistical models are jointly investigated in the form of neural networks and Gaussian process regression models to predict the most significant physicochemical qualities of strawberry. Color, for instance, either by itself or when combined with the soluble solids content (sweetness), can be predicted within as little as 9% and 14% of their expected range of values, respectively. This level of accuracy will ultimately enable the implementation of the next phase in controlling the soil conditions where data-driven quality and resource-use trade-offs can be realized for sustainable and high-quality strawberry production.

First Report of Direct Damage Caused by the Stubby-Root Nematode, Nanidorus minor, to Strawberry (Fragaria x ananassa), in Florida.

In 2019-2022, declining symptoms were observed in two commercial strawberry farms in Hillsborough County, Florida. The fields in the two farms consisted of raised beds covered by plastic mulch. Both were fumigated with a mixture of 1,3-dichloropropene (40%) + chloropicrin (60%) before planting. Samples collected from large patches with declining plants were infested with stubby-root nematodes. No sting and root-knot nematode species were detected. The results of morphological and molecular analyses indicated that the stubby-root nematode populations were representative of the species Nanidorus minor. The two cultivars 'Florida Brilliance' and 'Florida Sensation' in the two fields included plants with stubby root symptoms showing a reduction in the size of the root system and arrested growth and elongation of the feeder roots on the first strawberry crop. The nematode population densities in the two fields increased at the end of strawberry season and averaged 66 and 96 specimens in 200 cm3 soil. In one of the fields, a second strawberry crop was established as in the previous year using the same practices (fumigation and raised beds covered with plastic). However, in this field the population of N. minor declined and did not reach damaging levels at the end of the season on the second strawberry crop. The factors causing the decline of the nematode population were not elucidated. This is the first report of a direct damaging effect of N. minor to strawberry.

Deep learning-based postharvest strawberry bruise detection under UV and incandescent light

Bruising is one of the major defects of strawberries. Strawberry bruised areas are often visible as flattened, sunken, and discolored. Postharvest strawberries can be bruised by compression, impact, or vibration forces during harvesting, transportation, and packinghouse operations. These bruises make strawberries more vulnerable to rot or disease, thus shortening their shelf life. Bruises can also cause consumers to abandon purchase decisions. Therefore, inspecting strawberry bruises is an important procedure for commercial strawberry farms to guarantee the high quality of strawberries sent to the market. A novel technique was developed in this study to detect bruises on strawberry images captured by a color camera under incandescent and ultraviolet (UV) light. Mask Region-Based Convolutional Neural Networks (Mask R-CNN), a deep learning method, was utilized for the strawberry bruise detection. Four bruise severities were classified according to the estimated bruise ratio of every single strawberry (Minor Bruise, Light Bruise, Moderate Bruise, and Severe Bruise). The results showed that Mask R-CNN could accurately detect whether a strawberry is bruised or not under both lighting conditions. However, the strawberry bruise severity classification accuracy of the proposed machine vision technique was improved significantly under UV light compared to incandescent light. For whole strawberry bruise detection under UV light, the F1 score for detecting strawberry bruises was 0.99, and the highest F1 score for whole strawberry bruise severity classification was 0.92 for Minor Bruise. This strawberry bruise detection system can assist farmers in detecting bruised strawberries on the processing line or an automated strawberry harvester, improve the quality of strawberries that are sent to the market, and avoid shortening the shelf life of fresh strawberries.

A novel dataset for wireless soil monitoring of a strawberry harvest and respective evaluation of physicochemical qualities

The paper presents a complete collection of data and its preliminary statistical analysis obtained from the first phase of a large soil study on how to improve strawberry production and achieve sustainable and high-quality harvests through sensor-assisted real-time field monitoring. Six real-time loggers were placed in an operational commercial strawberry farm in Central Florida for the entirety of a harvest season from soil preparation to planting to harvesting. Along with temporally high-resolution soil sensory measurements including water content, electrical conductivity, and temperature, strawberries were harvested from each of the six locations on three separate occasions for their objective physicochemical characteristics to be monitored and recorded in a food chemistry lab. The primary goal of this paper is to introduce the dataset to the food science and engineering research community and present the results of its preliminary statistical analysis in identifying which factors correlate with one another. Based on the findings of this paper, while there exists a weak correlation between the quality of the harvest and the water content of the soil immediately preceding it, there were several cases where statistically significant differences exist between the soil sensory measurements from different locations which did not replicate the same differences in their corresponding harvest qualities.

Non-Chemical Soil Fumigation for Sustainable Strawberry Production in Southern Italy

In intensive strawberry production, monoculture is a common practice worldwide; however, prolonged replanting can cause plant disorders and jeopardize profitable cultivation of this highly valuable crop. To mitigate replanting problems, the strawberry industry is still highly dependent on chemical fumigation. Given the increasing regulatory restrictions and concerns about human and environmental risks from fumigants use, there is a growing interest in the adoption of effective, non-chemical alternatives. Two non-chemical soil fumigation practices, i.e., anaerobic soil disinfestation (ASD) and bio-fumigation with biocide plants (BIOFUM), were tested against chemical fumigation by chloropicrin + 1,3-dichloropropene mixture (STANDARD) and untreated (UNTREAT) control in a 2-year trial established in a commercial strawberry farm in Southern Italy (40°25′ N, 16°42′ E). Overall, the alternative practices provided consistently better results than UNTREAT; whereas, compared to STANDARD, their performance was significantly different in the two years: in 2018/19 season the alternative practices registered a 20% (ASD) and 39% (BIOFUM) marketable yield loss compared to STANDARD, while in the 2019/20 season yield differences were not significant. Although both practices appear promising as eco-friendly alternatives to chemical fumigation, in this short-term trial ASD performed better than BIOFUM both in terms of yield and fruit size, resulting in a more advanced stage for practical adoption.

Silicon builds resilience in strawberry plants against both strawberry powdery mildew Podosphaera aphanis and two-spotted spider mites Tetranychus urticae.

Silicon is found in all plants and the accumulation of silicon can improve plant tolerance to biotic stress. Strawberry powdery mildew (Podosphaera aphanis) and two-spotted spider mite (Tetranychus urticae) are both detrimental to strawberry production worldwide. Two field trials were done on a UK commercial strawberry farm in 2014 and 2015, to assess the effects of silicon nutrient applied via the fertigation system on P. aphanis and T. urticae. The silicon treatments decreased the severity of both P. aphanis and T. urticae in two consecutive years on different cultivars. The percentage leaf area infected with P. aphanis mycelium from silicon treated plants were 2.19 (in 2014) and 0.41 (in 2015) compared with 3.08 (in 2014) and 0.57 (in 2015) from the untreated plants. The etiology of the pathogen as measured by the Area Under the Disease Progress Curve from silicon (with and without fungicides) treatments was 152.7 compared with 217.5 from non-silicon (with and without fungicides) treatments for the overall period of 2014–2015. The average numbers of T. urticae recorded on strawberry leaves were 1.43 (in 2014) and 1.83 (in 2015) in plants treated with silicon compared with 8.82 (in 2014) and 6.69 (in 2015) in untreated plants. The silicon contents of the leaves from the silicon alone treatment were 26.8 μg mg-1 (in 2014) and 22.2 μg mg-1 (in 2015) compared with 19.7 μg mg-1 (in 2014) and 21.4 μg mg-1 (in 2015) from the untreated. The silicon nutrient root application contributed to improved plant resilience against P. aphanis and T. urticae. Silicon could play an important role in broad spectrum control of pests and diseases in commercial strawberry production.

Fluopyram as a rescue nematicide for managing sting nematode (Belonolaimus longicaudatus) on commercial strawberry in Florida

The sting nematode (Belonolaimus longicaudatus) is one of the most economically damaging pests of strawberry in Florida. In this study we evaluated in-season application of fluopyram for management of B. longicaudatus populations at nine commercial strawberry farms. In-crop application of fluopyram reduced B. longicaudatus population densities in soil by the end of the growing season in four out of six of the commercial strawberry farms where B. longicaudatus was detected during the growing season. At the four sites, relative suppression of B. longicaudatus by fluopyram ranged from 54 to 96%. Despite significant suppression of B. longicaudatus population densities in soil, in-crop application of fluopyram did not result in greater strawberry plant vigour by the end of the growing season. Overall, in-crop application of fluopyram shows considerable potential to reduce B. longicaudatus populations on strawberry in Florida.

An Approximated, Control Affine Model for a Strawberry Field Scouting Robot Considering Wheel–Terrain Interaction

SummaryRecently, autonomous field robots have been investigated as a labor-reducing means to scout through commercial strawberry fields for disease detection or fruit harvesting. To achieve accurate over-bed and cross-bed motions, it is preferred to design the motion controller based on a precise dynamic model. Here, a dynamic model is developed for a custom-designed strawberry field robot considering terramechanic wheel–terrain interaction. Different from existing models, a torus geometry is considered for the wheels. In order to obtain a control affine model, the longitudinal force is curve-fitted using a polynomial function of the slip/skid ratio, while the lateral force is curve-fitted using an exponential function of both the slip/skid ratio and slip angle. An extended Kalman filter (EKF) is then developed to estimate the unknown parameters in the approximated model such that the state variables propagated by such a model can match experimental data. The approximated model and the EKF-based parameter estimation method are then validated in a commercial strawberry farm.

Identification and field evaluation of (E)‐11,13‐tetradecadienal as sex pheromone of the strawberry tortrix (Acleris comariana)

AbstractThe strawberry tortrix (Acleris comariana Lienig and Zeller) (Lepidoptera: Tortricidae), is a major pest of strawberry in Denmark and southern Sweden. Chemical and electrophysiological analyses revealed a single compound, (E)‐11,13‐tetradecadienal (E11,13‐14:Ald), in gland extracts of females eliciting a strong antennal response in conspecific males. Also (Z)‐11,13‐tetradecadienal (Z11,13‐14:Ald) was found to be antennally active, but not detected in gland extracts. The corresponding alcohol and acetate of E11,13‐14:Ald, which are biologically active in other Acleris species, were not produced by females and did not trigger electrophysiological response in males. Trapping experiments at a commercial strawberry farm in southern Sweden showed that E11,13‐14:Ald and Z11,13‐14:Ald, alone or in combination, attracted large numbers of males. Trap catches increased with increasing dose of E11,13‐14:Ald, with traps baited with 100 µg and 1,000 µg being most attractive. Our results confirm the widespread use of E11,13‐14:Ald as a key sex pheromone component in the genus Acleris. The identification of a highly attractive sex pheromone is a first step in developing pheromone‐based methods for monitoring and control of A. comariana in European strawberry production.

Multiphase Scouting Control of an Agricultural Field Robot With Reachability Analyses

Accurate path scouting control of an autonomous agricultural robot is substantially influenced by terrain variability, field patterns, and uncertainties in sensed information. Based on conventional farming techniques, the targeted test crop of strawberries grows in semi-structured environments. Thus in this study, the proposed scouting control architecture comprises of three distinct portions and in each portion different sensors are used. Based on range finder (RF) information, the first region uses a proportional-integral-derivative (PID) controller with logic steps to account for undesirable pop-up events. In the other two portions, vision-based robust controllers are developed, in which a new bound is derived for the focal length uncertainty in vision. Stabilities of the controllers are proven and the reachabilities are analyzed to guarantee that the final state of each portion is within a desired initial region of the next portion controller. The proposed multiphase scouting control is successfully validated for our custom-designed robot in a commercial strawberry farm.

Early detection of arthropod-induced stress in strawberry using innovative remote sensing technology

Event Abstract Back to Event Early detection of arthropod-induced stress in strawberry using innovative remote sensing technology Elvira S. De Lange1* and Christian Nansen1 1 University of California, Davis, United States Innovative imaging technologies are being promoted to automate and optimize crop scouting and detection of emerging pest outbreaks. Due to the large size of farm operations, pest monitoring is time consuming; pests are often detected late, allowing populations to increase. Early, accurate pest detection is key for effective management and control. Spectral imaging, or remote sensing, can be used to indirectly detect pest presence, through stress-induced changes in leaf reflectance (1). However, only a limited number of studies showed that leaf reflectance data could be used to differentiate between stressors (2, 3). We aim to develop a feasible, cost-effective, accurate method for early detection of stress induced by different pests in strawberry, using innovative airborne remote sensing technology. We hypothesized that herbivores with different feeding biology cause significantly different leaf reflectance responses. To address this hypothesis, potted strawberry plants were experimentally infested with three arthropod pests with different feeding modes: two-spotted spider mite, a sucking pest; silverleaf whitefly, a piercing-sucking pest; and beet armyworm, a chewing pest. Control plants remained non-infested. In a greenhouse setting, we acquired data on leaf reflectance over a 14-day period with a novel, greenhouse-suitable setting, containing a hyperspectral camera mounted onto a rail system. Furthermore, in a commercial strawberry field, we acquired data on leaf reflectance using the same hyperspectral camera, mounted on a drone (4). Leaf samples were collected and inspected for arthropod presence or absence. Results showed that in a greenhouse setting, leaf reflectance profiles differed between strawberry plants exposed to feeding by the different arthropod herbivores. In a field setting, leaf reflectance profiles differed between areas in the presence or absence of two-spotted spider mite. These results indicate that reflectance in specific wavelengths can be used to detect early pest infestations in strawberry. Current experiments involve expanded greenhouse trails, aiming to distinguish stress caused by biotic and abiotic stressors in strawberry. Also, we’re performing additional field trials at local strawberry farms. Ultimately, we aim to develop a remote sensing-based decision support tool for improved sustainable pest management on commercial strawberry farms. Acknowledgements We thank Alison Stewart, Machiko Murdock, Robert Starnes, April Van Hise, Keshav Singh, Charissa Tseng, Yasmeen Haider, and Rachel Purington (UC Davis) for technical assistance. We also thank Mark Edsall, Daniel Olivier (California Strawberry Commission) and Hillary Thomas (Naturipe Berry Growers), and the commercial growers who made their fields available. This research is supported by Western Sustainable Agriculture Research and Education (project SW17-060, http://www.westernsare.org/).

Characterization of Botrytis cinerea Isolates from Strawberry with Reduced Sensitivity to Polyoxin D Zinc Salt.

Polyoxin D is a Fungicide Resistance Action Committee (FRAC) code 19 fungicide that was recently registered for gray mold control of strawberry in the United States. In this study, we determined the sensitivity to polyoxin D zinc salt (hereafter, polyoxin D) of Botrytis cinerea isolates from 41 commercial strawberry farms in South Carolina, North Carolina, Maryland, Virginia, and Ohio and investigated the fitness of sensitive (S) and reduced sensitive (RS) isolates. Relative mycelial growth ranged between 0 and over 100% on malt extract agar amended with a discriminatory dose of polyoxin D at 5 μg/ml. Isolates that grew more than 70% at that dose were designated RS and were found in three of the five states. The 50% effective dose (EC50) values of three S and three RS isolates ranged from 0.59 to 2.27 and 4.6 to 5.8 μg/ml, respectively. The three RS isolates grew faster on detached tomato fruit treated with Ph-D WDG at recommended label dosage than S isolates (P < 0.008). In all, 25 randomly selected RS isolates exhibited reduced sporulation ability (P < 0.0001) and growth rate (P < 0.0001) but increased production of sclerotia (P < 0.0386) compared with 25 S isolates. Of 10 isolates tested per phenotype, the number of RS isolates producing sporulating lesions on apple, tomato, and strawberry was significantly lower compared with S isolates (P < 0.0001 for each fruit type). The results of this study indicate that resistance management is necessary for fungicides containing polyoxin D. To our knowledge, this is the first study demonstrating reduced sensitivity to FRAC 19 fungicides in B. cinerea isolates from the United States.

Toward precision irrigation for intensive strawberry cultivation

The Doñana area in Southwestern Spain has the largest concentration of strawberry producers in Europe. The annual yield, close to 300,000t, is mainly devoted to the international markets (more than 90%). Due to the high water demand of strawberries and to the environmental concerns of the destination countries, the maximization of water use efficiency is critical for the strawberry sector.Aiming at the efficient water use in the strawberry production, a comprehensive drip irrigation system has been designed, according to precision irrigation principles. The system has been developed based on a three stages methodology. First, the irrigation process carried out by farmers has been assessed to identify inefficiencies in the irrigation system and management. Their performances have been evaluated using indicators such as the Relative Irrigation Supply (RIS), Strawberry Irrigation Water Applied (SWA) and Strawberry Water Footprint Applied (SWFA). The second phase is focused in an accurate irrigation scheduling based in precise crop water requirements estimation and the optimum irrigation pulse design. Finally, the irrigation system has been designed with the prevailing wisdom of meets the needs of the crop in a timely manner and as efficiently and as spatially uniformly as possible. The most appropriate drip irrigation emitters for the particular conditions of the strawberry production in the study area have been selected. The rest of the on-farm irrigation technologies required to control the system have been integrated, including soil water sensors, smart water meters, programmers, electrovalves and weather station. This precision irrigation system has been installed in a commercial strawberry farm during the irrigation season 2013–2014.Also, an application for PC, mobiles and tablets has been developed to provide farmers practical information (e.g. irrigation times) for optimal irrigation scheduling.

Relationships between nematode diversity, plant biomass, nutrient cycling and soil suppressiveness in fumigated soils

Nematodes interact with many other organisms as participants in several links of the soil food web, playing important roles in essential soil processes. Due to their high abundance and diversity of responses to soil disturbance, nematodes are suitable indicators of soil condition. With the aim of inferring soil fumigation effects on agroecosystem functioning, soil nematode diversity, soil properties, plant growth, and soil suppressiveness were monitored in a commercial strawberry farm and its surroundings for two consecutive growing seasons in southern Spain. Our results show that nematode diversity was low in fumigated soils throughout the whole season and, although yearly recovery occurred within the treated fields, fumigated soils showed a permanent perturbed condition. The nematode community was more closely associated to nutrient cycling in non-cropped than in cropped soils, and the link between plant biomass and nematode community structure was weak. Non-treated furrows within the treated fields were a reservoir of both beneficial and plant-parasitic nematodes, but such difference between furrows and beds was not enough to maintain more suppressive soil assemblages in the furrows. Treated soils were less suppressive than unmanaged soils, and there was a positive and significant correlation between soil suppressiveness and soil food web structure and diversity.

Nematodes as indicators of fumigant effects on soil food webs in strawberry crops in Southern Spain

The phase-out of methyl bromide due to concerns regarding ozone depletion in the stratosphere has imposed the need of developing alternatives less aggressive to the environment. The use of 1,3-dichloropropene (1,3-D) and chloropicrin (Pic) has extended in the last years, and has become essential to maintain strawberry production in Southern Spain, the main producer within the EU. However, their uncertain effects on the environment have become a new obstacle for their future use, and scientific evaluation of their toxicity is necessary to assess their impact on the environment. In this paper, we use the nematode assemblage as indicator of the effects of 1,3-D, Pic and 1,3-D + Pic on non-target soil fauna, and to infer their effects on soil food web functioning in two commercial strawberry farms in Southern Spain. Although affected, the abundance of bacterial-feeding nematodes did not differ among treatments due to compensatory growth of opportunistic nematodes. Fungal-feeding nematodes were strongly reduced by the fumigants, probably due to direct fumigants toxicity and to alterations on the fungal decomposition channel. Taxa richness and soil food web indices were also affected by the treatments. The ratio fungal to bacterial-feeding nematode abundances is proposed as the best indicator of the short and medium term effects of fumigants on non-target soil organisms. Implications of such findings on soil food web functioning and recovery are discussed.

The Effects of Cultivar on the Arbuscular Mycorrhizal Fungi Symbiosis in Strawberries

Cultivar may cause variation in arbuscular mycorrhizal fungi (AMF) colonization levels leading to differences in shoot growth and runner formation, and in pathogen control in strawberries. However, a clear consensus has not been reached regarding the degree to which cultivar affects the formation of the symbiosis or its functioning. The study was conducted on four commercial strawberry farms in Minnesota and Wisconsin to compare, within a farm, mycorrhizal colonization and plant response among three strawberry cultivars: `Winona', `Anapolis' and `Jewel'. At each farm, two 6 × 6 meter plots of each cultivar were randomly selected. On each of three sampling dates, 4 whole plants and soil samples were collected from these plots in the 2003 field season. Roots were separated from shoots and leaves, and fresh and dry weights were taken. Leaves and soil were dried, weighed, and submitted for nutrient analysis. Soil nutrient analyses include phosphorus (Bray P), potassium, pH, buffer pH and organic matter. Leaf tissue analyses include P, K, Ca, Mg, Na, AL Fe, MN Zn, Cu, B, Pb, Ni, Cr, and Cd. Roots were collected, frozen, and prepared for scoring using methods adapted from Koske and Gemma (1989). Presence of mycorrhizal colonization is being scored using the methods of McGongle et al. (1990). Levels of mycorrhizal colonization among different strawberry cultivars will be compared. We will also use biomass measurements, to determine mycorrhizal effects on plant growth among different cultivars. Soil and leaf analysis data will be used to determine effects of AMF on plant nutrition and compare effects among cultivars.

Biological Control of Fungal Strawberry Diseases by Serratia plymuthica HRO-C48.

To develop a biological control product for commercial strawberry production, the chitinolytic rhizobacterium Serratia plymuthica strain HRO-C48 was evaluated for plant growth promotion of strawberries and biological control of the fungal pathogens Verticillium dahliae and Phytophthora cactorum. In phytochamber experiments, treatment with S. plymuthica HRO-C48 resulted in a statistically significant enhancement of plant growth dependent on the concentration of the bacterium that was applied. In greenhouse trials, bacterial treatment reduced the percentage of Verticillium wilt (18.5%) and Phytophthora root rot (33.4%). In three consecutive vegetation periods, field trials were carried out in soil naturally infested by both soilborne pathogens on commercial strawberry farms located in various regions of Germany. Dipping plants in a suspension of S. plymuthica prior to planting reduced Verticillium wilt compared with the nontreated control by 0 to 37.7%, with an average of 24.2%, whereas the increase of yield ranged from 156 to 394%, with an average of 296%. Bacterial treatment reduced Phy-tophthora root rot by 1.3 to 17.9%, with an average of 9.6%, and increased strawberry yield by 60% compared with the nontreated control. Under field conditions, strain HRO-C48 survived at approximately log10 3 to 7 CFU/g of root in the strawberry rhizosphere at 14 months after root application. Although results of the field trials were influenced by pathogen inoculum density, cropping history of the field site, and weather conditions, S. plymuthica HRO-C48 successfully controlled wilt and root rot of strawberry.

Strawberry Yield over Red versus Black Plastic Mulch

Plastic mulches are frequently used in raised‐bed culture of strawberry (Fragaria × ananassa Duch) to conserve water, control weeds with less herbicides, and keep fruit clean. The most commonly used plastic mulch color is black. It was hypothesized that a specially formulated red plastic mulch that reflects a higher far‐red to red photon ratio could regulate photosynthate allocation enough to increase yield of strawberry. Yields over the red plastic (SRM‐Red) were compared with those over standard black plastic in field experiments at a research center and on a commercial strawberry farm. Yield per plant and size per berry were greater over the red than over the black plastic at both locations. The yield advantage of red mulch relative to black occurred whether the red plastic was placed directly over the soil or over a layer of black plastic. It is concluded that strawberries were larger over the new red plastic mulch because reflected far‐red and red light affected phytochrome‐mediated allocation of photosynthate, and more was directed to developing fruit.