Grower Notes and Pest News
The western tarnished plant bug or lygus bug (Lygus hesperus) continues to be a major pest of strawberry on the Central Coast. Most growers typically rely on chemical or biological pesticides to manage pest. Some growers also use tractor-mounted vacuums to remove the pest, but the western tarnished plant bug is a major concern as it causes significant losses to marketable yields by deforming developing berries. Considering the status of the pest, having additional control options is critical both to reduce yield losses and also to strengthen the current integrated pest management (IPM) strategies.
A solar-powered UV light trap was reported to be a potential tool for controlling a variety of coleopteran, lepidoptera, hemipteran and other pests including the western tarnished plant bug. To evaluate its role as a potential IPM tool for strawberry pests a study was in conducted in fall-planted organic and conventional strawberry fields in Santa Maria.
Specifications of the trap: UV light trap known as Solar Powered Pest Control Machine (Model GFS-8) is manufactured by GreenFuture Equipment based in Sacramento, CA. It has a 30W solar power panel and a 12V battery to power a dual color UV light bulb and a rotating grill/grid for two nights on one day of charging. The grill surrounds the light produces 3600 volts of electricity with a surface area of 2.37 sqft and electrocutes insects as they are attracted to the light. Each light trap is supposed to cover 3-4 acres of area. A rubber flap brushes off insects into the container in the bottom of the trap as the grill rotates periodically.
Solar-powered UV light traps in conventional (left) and organic (middle) fields and insects collected in the container (right)
Experimental set up: One light trap was set up in a conventional strawberry field on West Main St (Manzanita Berry Farms) and another one in an organic field on Solomon Rd (Eraud Farms) in late March, 2017. Contents of the container were collected each week in a bag, taken back to the laboratory, and pest and beneficial insects were categorized and enumerated. Observations were made on 13 sampling dates between 2 May and 26 July, 2017.
Results: There were several groups of beneficial and pest insects were found attracted to the light trap. However, the western tarnished plant bugs were not seen throughout the observation period although field scouting indicated their presence. In general, the western tarnished plant bug infestations were lower this year and grower was able to manage pest populations by regular vacuuming. Pesticides were not used to control this pest during this period.
Among the pest insects trapped, corn earworm (Helicoverpa zea) adults were the only ones known to be a pest of strawberry in California. Insects that are generally recognized as pests included tiger moths, owlet moths, corn earworm adults, eucalyptus moths, sphinx moths, and mosquitoes while the beneficial insects included crane flies, lady beetles, parasitic wasps, neuropterons (such as lace wings), and soldier beetles. Some crane flies are important in the ecosystem as a prey for some animals and birds or through the activity of the larvae on decaying organic matter in the soil. However, their impact in strawberry is unknown.
Number of various pes (above) and benefifcial (below) insects collected on each sampling date
All pest and beneficial insects collected on different sampling dates (blue line: organic, orange line: conventional)
The number of both pest and beneficial insects was higher in the organic field than in the conventional field. Seasonal average of all insects per sampling date was 177 for the organic field and 98 for the conventional field. The proportion of the beneficial insects was about 27 in the organic field and 5 in the conventional field.
Seasonal average of various insects collected (Click on the image for a bigger version)
Although the role of UV light traps as a control option for the western tarnished plant bug could not be determined, it appeared to be a good tool for trapping corn earworm adults and other moths. This light trap could probably be useful for managing lepidopteran pests in strawberry or other corps.
Acknowledgements: Thanks to Dave Peck for his collaboration, GreenFuture Equipment for donating the light traps, and Maria Murrietta, Tamas Zold, and Chris Martinez for their technical assistance.
California offers ideal weather conditions for both nursery plant and strawberry fruit production. Variations in weather conditions in three strawberry production regions in California complement fruit production from each other and help avoid market glut. The warmer Oxnard area, the milder Santa Maria area, and the colder Watsonville area with minimal overlapping of their peak fruit production seasons allow yearlong strawberry production.
Weather influences on strawberry have been well documented in various strawberry producing regions across the world (Palencia et al., 2013; Li et al., 2010; Waister et al., 1972). Examples of key weather parameters correlated with strawberry yield include temperature, precipitation, solar radiation, relative humidity, and wind speed. Crop growth is weather dependent, thus, it is a common practice to estimate fruit yield based on weather variables. Since strawberry production spreads across 4–5 months, evaluating relationships between meteorological parameters and strawberry yield can provide valuable information and early indications of yield estimations that growers can utilize to their advantage. Objective of this research was to evaluate correlations of meteorological parameters on strawberry yield for Santa Maria region and to develop weather based statistical yield forecasting models for strawberries.
Strawberry yield data
Daily strawberry yield data for the Santa Maria region was obtained from published sources (California Strawberry Commission). This information is publically available and is originally compiled from the United States Department of Agriculture Market News/Fruits & Vegetables website. Daily strawberry yield data for the month of April through July were aggregated to weekly values. For this analysis we used weekly strawberry yield data for 2009 through 2015.
Weather data were obtained from the California Irrigation Management Information System (http://www.cimis.water.ca.gov/), a network of over 145 automated weather stations in California. Specific meteorological parameters used in this study were net radiation, air temperature (minimum and maximum), relative humidity (minimum and maximum), dew point temperature, soil temperature (minimum and maximum), vapor pressure (minimum and maximum), reference evapotranspiration, and average wind speed.
Weekly values of meteorological parameters from October of the year prior to harvest to February of current year of strawberry harvest were correlated with weekly strawberry yield from April through July and tested for significance. Each meteorological variable was correlated with strawberry yields from April to July. This thorough correlation analysis was done in order to understand influence of meteorological parameters on strawberry yield on a more detailed basis.
Fall and winter weather conditions during the vegetative growth period of strawberry have a significant influence on the fruit yields in the following spring and summer for the Santa Maria region. Results show that net radiation, relative humidity, vapor pressure, wind speed, and temperature showed significant correlations with strawberry yields at various temporal scales. In general, it was evident that many meteorological parameters during the early stages of strawberry growth and development phase exhibit statistically significant correlation with strawberry yields during the peak fruit production period. This finding is consistent with the findings of Lobell et al. (2006) for strawberry and other crops in California.
Table 1. Correlation matrix of monthly meteorological parameters and strawberry yields that were statistically significant.
Statistical yield model
Weather parameters that showed significant correlations were used to develop strawberry yield forecasting model. Instead of using weather parameters as explanatory variables, they were transformed into principal components to develop yield–forecasting models.
Figure 1 shows observed versus predicted yields for April (top) and June (bottom)
It is important to note that there are limitations on how much variability in yield data that can be explained by meteorological parameters as many other factors such as management practices, pests, diseases, varieties, other stress factors can also influence yield variability. Additionally, historic strawberry yield data provided an average estimate for the region and might not represent accurate observations.
These results demonstrate the potential to predict strawberry yield using weather variables relevant to the Santa Maria strawberry growing region. In order to make these results usable for decision–making, it could be refined to be utilized at the field scale. Additionally, skills of these models can be further improved by combining weather parameters and relevant physiological parameters of strawberry at the field scale.
A full version of this article (Pathak et al., 2016) can be viewed at: https://www.hindawi.com/journals/amete/2016/9525204/
Palencia, P., F. Martínez, J.J. Medina, and J. López– Medina. 2013. Strawberry yield efficiency and its correlation with temperature and solar radiation. Hortic. Bras.31(1): 93–99
Li, H., T. Li, R.J. Gordon, S.K. Asiedu, and K. Hu. 2010. Strawberry plant fruiting efficiency and its correlation with solar irradiance, temperature and reflectance water index variation. Environ. Exp. Bot. 68, 165–174.
Waister, P. D. 1972. Wind as a limitation on the growth and yield of strawberries. hort. Sci. 47: 411 – 418.
Lobell, D.B., K. Cahill, and C. Field. 2006. Weather–based yield forecasts developed for 12 California crops. California Agriculture, 60(4): 211–215.
Pathak, T.B., Dara, S.K., Biscaro, A. 2016. Evaluating correlations and development of meteorology based yield forecasting model for strawberry. Advances in Meteorology, vol. 2016, article ID 9525204. doi:10.1155/2016/9525204
Species of the genus Entomophthora cause epizootics in various insects around the world, but such infections are less common in California. Burger and Swain (1918) reported Entomophthora chromaphidis infections in the walnut aphid, Chromaphis juglandicola, in Southern California. With infections as high as 95%, the fungus was a significant mortality factor in aphid populations. In 2011, nearly a century after the epizootics in the walnut aphid, a single strawberry aphid, Chaetosiphon fragaefolii, was found infected with a species of Entomophthora in an organic strawberry field (Eraud Farms) in Santa Maria. The strawberry aphid is an occasional and minor pest in strawberry in California.
Entomophthora planchoniana infection in strawberry aphid
Attempts to in vitro culture the fungus were unsuccessful, but microscopic measurements of conidial size and shape indicate that the causal agent could be Entomophthora planchoniana. Bell-shaped conidia measured 17.3 μm or micrometers (14.8-20.1) long and 14.6 μm (12.7-17.7) wide (based on the measurements of 100 conidia) and had a broad base (papilla) and a pointed apex. Conidia also appeared to have 4-6 nuclei.
E. planchoniana and E. chromaphidis are closely related and were previously considered as synonymous species (MacLeod et al., 1976; Waterhouse and Brady, 1982). Humber and Feng (1991) later described these two as separate species due to the variation in conidial size, geographic distribution, host range, in vitro culturing techniques, and other characteristics. While E. planchoniana is commonly found in Europe, E. chromaphidis is reported elsewhere.
The following are the characters of E. chormaphidis and E. planchoniana from Keller's (2002) description of 22 species of Entomophthora.
First found in walnut aphids in California. Primary conidia are 11-14 μm long and 10-11 μm wide with 4-6 nuclei and contain a single large oil globule. Resting spores are 30 μm. Insect host is attached to the plant surface with fungal rhizoids (bundles of modified hyphal bodies).
First found on unidentified aphids on elder in western Europe. Primary conidia are 15-20 μm long and 12-16 μm wide with 4-11 nuclei [species description has 4-11 and key has 5-9 nuclei in Keller (2002)]. Resting spores are 31-38 μm. The fungus produces rhizoids to attach the host insect to the plant surface.
Keller (2002) noted an overlap in the number of nuclei between these two species and suggested the size of primary conidia as the distinguishing character. Hence the fungus found in the strawberry study is considered E. planchoniana, which was first reported in 1948 in the strawberry aphid, then known as Pentatrichopus fragariae (Petch, 1948; Leatherdale, 1970). Cédola and Greco (2010) reported E. planchoniana as a major mortality factor of the strawberry aphid in Argentina.
Life cycle of E. planchoniana
The infection process starts when a conidium (single spore) comes in contact with the insect cuticle, produces a germ tube and gains entry into the insect body with the help of a penetration peg and cuticle degrading enzymes. The fungus multiplies inside the insect body as protoplasts (cells without a cell wall) and invade the tissues. Vegetative growth stops when nutrients are depleted and the insect is dead. The fungus then produces conidiophores that emerge from the cuticle, produce bell-shaped primary conidia that are forcibly discharged. A halo of protoplasm (cellular contents) is often seen around the primary conidium, which may either produce the germ tube to cause infection or a secondary conidium. Secondary conidia are smaller than primary conidia, have rounded or less pointed apices, and more rounded basal papillae.
This is the first report of the occurrence of E. planchoniana in the strawberry aphid in California. Although strawberry aphid is not an important pest in California and only one infected aphid was found, this finding is important to record the distribution of E. planchoniana.
Burger, O. F. and A. F. Swain. 1918. Observations on a fungus enemy of the walnut aphis in Southern California. J. Econ. Entomol. 11: 278-289.
Cédola C. and N. Greco. 2010. Presence of the aphid, Chaetosiphon fragefolii, on strawberry in Argentina. J. Ins. Sci. 10: 1-9.
Humber, R. A. and M.-G. Feng. 1991. Entomophthora chromaphidis (Entomophthorales): the correct identification of an aphid pathogen in the pacific northwest and elsewhere. Mycotaxon 41: 497-504.
Leatherdale, D. 1970. The arthropod hosts of entomogenous fungi in Britain. Entomophaga 15: 419-435.
MacLeod, D. M., E. Müller-Kögler, and N. Wilding. 1976. Entomophthora species with E. muscae-like conidia. Mycologia 68: 1-29.
Petch, T. 1948. A revised list of British entomogenous fungi. Trans. Brit. Mycol. Soc. 31: 286-304.
Waterhouse, G. M. and B. L. Brady. 1982. Key to the species of Entomophthora sensu lato. Bull. Brit. Mycol. Soc. 16: 113-143.
Evaluating beneficial microbe-based products for their impact on strawberry plant growth, health, and fruit yield
Various soilborne, fruit and foliar diseases can affect strawberry crop and fruit yields. Chemical fumigants and a variety of fungicides are typically used for managing the disease issues. In addition to the environmental and human health concerns with chemical control options there is a need to improve current disease management with alternatives that include beneficial microbes. Previous studies showed some promise with some of the treatments, but additional studies are required to evaluate the efficacy, which is more evident especially when there is disease incidence.
A study was conducted in summer-planted conventional strawberries in 2016 at Manzanita Berry Farms to evaluate the impact of various beneficial microbial treatments on plant growth, health, and fruit yield. Untreated control and the grower standard practice (Healthy Soil treatment) were compared with MycoApply EndoMaxx (Glomus intraradices, G. aggregatum, G. mosseae, and G. etunicatum), Actinovate AG (Streptomyces lydicus WYEC 108), and Inocucor Garden Solution (Saccharomyces cerevisiae and Bacillus subtilis) applied in the following treatments:
1. Untreated control
2. Grower Standard-Healthy Soil; transplant dip in Switch 63 WG 5 oz in 100 gal
3. MycoApply EndoMaxx 2 gpa transplant dip (TD)
4. MycoApply EndoMaxx 2 gpa drip at planting (DrP)
5. MycoApply EndoMaxx 2 gpa transplant dip + 2 gpa drip at planting
6. MycoApply EndoMaxx 4 gpa transplant dip
7. MycoApply EndoMaxx 4 gpa drip at planting
8. MycoApply EndoMaxx 4 gpa transplant dip + 4 gpa drip at planting
9. Actinovate AG 6 oz/ac transplant dip + 6 oz drip at planting + 6 oz drip monthly (DrM)
10. Inocucor Garden Solution 1 gpa drip at planting + 1 gpa drip monthly
Transplanting was done on 21 May, 2016 with appropriate treatments administered at the time of planting and thereafter. Study had two blocks of 10 strawberry beds (300' long) and treatments were randomly applied to a bed within each block. Two 15' long plots were marked within each bed for sampling. Canopy growth was measured on June 21, July 5 and 20; powdery mildew severity on August 3, September 1, October 10 and November 16; botrytis severity 3 and 5 days after harvest (DAH) for berries harvested on September 13 and 27, and October 11 and 18; and dead and dying plants were counted on September 16 and October 23. Yield data were collected from August 20 to November 18. Powdery mildew and botrytis fruit rot severity was measured on a scale of 0 to 4 where 0=No disease, 1=1-25%, 2=26-50%, 3=51-75%, and 4=76-100% severity. Data were analyzed and means were separated using LSD test.
Strawberry field and plots on June 9 (above) and August 31 (below).
Two sampling plots were set up within each bed to collect plant growth, health, and yield data.
Canopy growth: MycoApply EndoMaxxat 2 gpa either as a transplant dip with or without drip application at planting appeared to promote significantly higher growth (P <0.0001) than MycoApply EndoMaxx at 2 and 4 gpa as drip at planting, untreated control, and grower standard. Inoculating the entire transplant with Glomus spp. through a dip appears to be better than application through drip irrigation system.
Powdery mildew: Disease incidence and severity was low during the observation period. When the average of four observations period was compared, the grower standard, MycoApply Endomaxx at 2 and 4 gpa as drip at planting, and the Actinovate treatments had the lowest incidence (P = 0.0271).
Botrytis fruit rot: There was no difference (P >0.05) among the treatments on botrytis when the mold growth on fruit was compared 3 and 5 days after harvest.
Unknown issue: Some wilting and dead plants were found throughout the field during the study. Although symptoms suggested some kind of wilt, laboratory testing did not identify any pathogens. The total number of dead and dying plants was the lowest in Actinovate treatment, but it was significantly different (P = 0.0429) only from the grower standard Healthy Soil treatment.
*Means followed by the same or no letter are not significantly different at the P value indicated in the table.
Fruit yield: There were no statistically significant difference among the treatments and the seasonal total of marketable yield varied between 66 lb/plot in the grower standard and about 76 lb/plot in MycoApply EndoMaxx applied as a transplant dip at 4 gpa.
Total and marketable berry yields and their proportion among different treatments.
We need to continue to evaluate beneficial microbial products and their potential benefit in improve crop health and yields.
Acknowledgements: Thanks to Chris Martinez and Tamas Zold for technical assistance, and Valent USA and Inocucor Technologies for the financial support of the study.
Life stages of spotted-wing drosophila (Photos by Elizabeth Beers, Washington State University)
Spotted-wing drosophila (SWD), Drosophila suzukii is an invasive pest that attacks many cultivated and wild fruits. With the help of a strong, saw-like ovipositor or egg laying appendage, SWD is able to deposit eggs in ripe and occasionally in unripe or developing fruit unlike other Drosophila spp., commonly known as vinegar flies or fruit flies, that attack ripe or fallen fruit. Larvae develop in the fruit and pupation occurs either in or outside the fruit. Blueberry, caneberries, cherry, peach, and strawberry are some of the commercially important fruit crops that are at a risk of SWD damage.
Monitoring with lures, application of pesticides, use of exclusion netting, and sanitation are some of the control practices currently adopted in organic and conventional crops. Among the microbial control options, entomopathogenic fungi such as Beauveria bassiana, Isaria fumosorosea, and Metarhizium brunneum (=M. anisopliae) against adults and entomopathogenic nematodes such as Heterorhabditis spp. and Steinernema spp. against pupae in the soil can be potential choices. A few lab studies that evaluated these options showed limited efficacy of the most except for B. bassiana treatments in Italy and M. brunneum in Oregon that appeared promising (Gargani et al., 2013; Cuthbertson et al., 2014; Woltz et al., 2015). Biocontrol potential with predators and parasitoids is also limited based on current research data (Haye et al., 2015; Renkema et al, 2015; Woltz et al., 2015).
In light of limited microbial and biocontrol control agents, a recent outbreak of fungal epizootics in SWD on fig offers a potential natural control option. SWD populations in a small fig orchard in Clinton, Mississippi were infected by a fungus in June, 2017. Unusually cool and wet conditions caused epizootics of a fungus, which was later identified by Connecticut Agricultural Experiment Station scientists as Entomophthora muscae or a closely related species. SWD first appeared in blueberry, blackberry, and mulberry plots of this orchard in 2012 and infestations on figs were noticed only in 2017. Other SWD hosts that are grown at this orchard include grapes, pears, and strawberries. Having a variety of hosts with extended availability of fruits could have supported SWD populations at this location.
Dead or immobilized SWD (above) and sporulating cadavers (below) from Entomophthora muscae infections. Photos by Tom Mann, Mississippi Museum of Natural Science, Jackson, MS
Conidia at different stages of development on conidiphores (left) and discharged conidia (right). Photos by DeWei Li, Connecticut Agricultural Experiment Station, Windsor, CT
Unlike B. bassiana, I. fumosorosea, and M. brunneum (Phylum Ascomycota: Class Sordariomycetes: Order Hypocreales), Entomophthora spp. belong to a different fungal group (Phylum Zygomycota: Class Entomophthoromycetes: Order Entomophthorales). Entomophthora spp. cause disease outbreaks in their host populations when environmental conditions are favorable with high humidity and low temperature aided by high host densities. Entomophthora muscae is considered to be a species complex infecting a variety of dipteran families including Drosophilidae (Goldstein, 1927; MacLeod et al., 1976; Gryganskyi et al., 2013). However, it appeared to be less pathogenic to the common fruit fly, Drosophila melanogaster compared to other dipteran species (Steinkraus and Kramer, 1987).
Entomopathogenic fungi typically take 3-5 days to kill their hosts. Infection process typically starts when host insect comes in contact with the conidia (asexual spores) of the fungus (Brobyn and Wilding, 1983). Primary conidia either produce a germ-tube that penetrates through the host cuticle or produce secondary conidia (which later produce germ-tubes) or hyphae. Both enzymatic degradation of cuticle and mechanical pressure by the penetration peg of the germ-tube aid in fungus gaining entry into the host body. Hyphal bodies are formed inside the host, invade the fat bodies and other tissues, and eventually cause death of the host insect. The fungus later emerges from the intersegmental membranes and conidiophores or spore bearing structures produce conidia that are dispersed to continue the infection cycle. Infected flies become sluggish and typically fly to the higher parts of the plant canopy where they become attached to plant surfaces with rhizoids (peg like structures that emerge from the ventral or lower side of the insect body) and sticky secretions (Steinkraus and Kramer, 1987). This process increases the chances of disease spread as insect cadavers are securely attached to plant surfaces and infective conidia are dispersed from a higher elevation in the canopy. When host populations diminish and during the winter months, entomophthoralean fungi may produce environmentally resilient resting spores to survive cold winters (Eilenberg and Michelsen, 1999) or survive as hyphal bodies in the dead (Keller, 1987) or winter hosts (Klingen et al., 2008). Other overwintering options for these fungi include infections in their host insects on winter crops (Dara and Semtner, 2001) or infections in alternative host insects (Eilenberg et al., 2013).
Entomophthoralean fungi are difficult to culture in vitro and do not have the biopesticide potential as the hypocrealean fungi. However, they can be significant mortality factors in some areas and bring down high host populations. Neozygites fresenii epizootics in cotton aphid, Aphis gossypii (Steinkraus et al., 1995), Entomophaga maimaiga in gypsy moth, Lymantria dispar (Hajek and Elkinton, 1991), and Pandora neoaphidis in green peach aphid, Myzus persicae populations (Dara and Semtner, 2007) are some of the examples for the natural control of insects by entomophthoralean fungi.
Anecdotal reports indicated outbreaks of a possible entomophthoralean fungus in aphids on some vegetables in California, but there are no published reports of fungal outbreaks except for a study in the 1980s. Mullens et al. (1987) reported E. muscae epizootics in house fly (Musca domestica), little house fly (Fannia canicularis), and predatory fly (Ophyra aenescens) populations in Southern California poultry facilities. Similarly, E. muscae infections in adult onion fly (Delia antiqua) and seed corn maggot (D. platura) caused significant population reductions in Michigan (Carruthers et al., 1985). In a recent study in North Carolina, E. muscae infected both cabbage maggot (D. radicum) and a predatory fly (Coenosia tigrina).
The extent of E. muscae epizootics in Mississippi populations of SWD show promise for the natural control of this pest. While large scale in vitro production of the fungus may not be practical at this moment, small scale production in vivo or a specialized culture medium is possible for laboratory and greenhouse studies. In vivo culturing of entomophthoralean fungi and releasing infected live arthropods was successful for a large scale release of Neozygites tanajoa for controlling the cassava green mite, Mononychellus tanajoae in West Africa (Hountondji et al., 2002) and a small scale release of P. neoaphidis for controlling M. persicae in Virginia (Dara and Semtner, 2006). Future studies will shed light on the potential of E. muscae in SWD integrated pest management.
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