- Author: Surendra K. Dara
Micro-sprinklers in strawberries. Photo by Surendra Dara
Strawberry is an important commercial crop in California primarily grown on the Central Coast in Watsonville, Santa Maria, and Oxnard production areas. Strawberry crop requires 24-29” of irrigation water for a typical production season based on fall plantings. Irrigation is primarily administered through drip tapes installed under plastic mulch during bed preparation. In addition to the drip irrigation throughout the crop life, supplemental irrigation through overhead aluminum sprinklers is administered during the first few weeks after transplanting. Overhead irrigation is practiced to leach out salts from the root zone and to support the establishment of new transplants. Strawberries are sensitive to salinity and this supplemental irrigation is believed to reduce or prevent salt injury. In the Oxnard area, overhead aluminum sprinkler irrigation is considered very important to prevent dry conditions which could result from Santa Ana winds. However, overhead aluminum sprinkler irrigation requires a significant amount of water and can be an inefficient system. Evaporation, limited surface area for water penetration due to plastic mulch on the beds, and potential run off are some of the disadvantages associated with this overhead sprinkler system.
Water is an important resource for growing plants and it has become scarce due to epic drought conditions in California. Conserving water through improved irrigation practices is a critical area for maintaining acreage of a lucrative commodity such as strawberry. Micro-sprinklers, which are commonly used in orchard systems could offer an efficient alternative to conventional aluminum sprinklers. Micro-sprinklers, established on strawberry beds, can deliver water in a more targeted manner with minimum or no run off. They could also help modify the microclimate in the strawberry canopy and create humid conditions that discourage spider mite pest populations and promote predatory mites which are sensitive to dry conditions.
A study was conducted at Manzanita Berry Farms in Santa Maria during 2014-2015 production season to evaluate the potential of micro-sprinklers in strawberry production. Objectives of this study included i) conservation of irrigation resources without affecting strawberry plant growth and fruit yield, ii) impact on pest and predatory mite populations, and iii) impact on powdery mildew and botrytis fruit rot.
Experimental design
A block of strawberry (variety BG-6.3024 planted on 6 November, 2014) was divided into two parts with beds aligned from south to north direction. The west half of the block was assigned for micro-sprinklers and the east half for the grower standard with aluminum sprinklers. Each block had about 60 beds (about 306-365' long) and aluminum sprinklers were established in furrows every 40' (7-8 beds in between) while micro-sprinklers were established on every third bed. Micro-sprinklers were placed 16' apart (on every fourth bed) and had a 15' spacing within a bed. Within each treatment section six 20' long plots were marked to measure plant, pest, and disease parameters.
Installing micro-sprinkler system (Field crew at Manzanita Berry Farms, Santa Maria)
Micro-sprinkler (left) and grower standard with aluminum sprinklers (right) sections of the field
Data collection and results
Irrigation – Conventional sprinkler irrigation was made 14 times from 6 to 29 November, 2015 at a rate of 125 gallons per minute while micro-sprinkler irrigation was made 1-3 day interval at a rate of 40 gallons per minute using 35 PSI pressure. During this period, aluminum sprinklers delivered 120,000 gallons of water over 16 hours of total irrigation while micro-sprinklers delivered 81,600 over 34 hours of total irrigation. This translates to 32% of water saving in just 3 weeks and could be more in situations where overhead irrigation is administered for extended periods. Micro-sprinkler irrigation was continued for 15 min twice a week for the rest of the production period. Distribution uniformity could not be measured in grower standard treatment in this study, but it is believed to be between 50-60% at 70 PSI based on other studies. Distribution uniformity for the micro-sprinklers was 74% at 35 PSI when measured on 16 January, 2015. When electrical conductivity (EC) was measured on January 1 and February 1, 2015, it varied between 0.47 and 0.49 dS/m in grower standard treatment and was at 0.54 dS/m in micro-sprinkler treatment. Although EC in micro-sprinkler plots was significantly higher (P < 0.0007) than in grower standard plots, it was within the safe limit of 0.7 dS/m.
Cumulative volume of water delivered in micro-sprinkler and grower standard sections of the field. There was a saving of 38,400 gallons per acre in just about three weeks.
Yield – Total and marketable berry yield data were collected 2-3 times a week between 7 February and 12 June, 2015 for a total of 34 sampling dates. There was no significant difference in total or marketable berries (P > 0.05) when the seasonal averages for grower standard and micro-sprinkler plots were compared. During the observation period, 44,322 gr (97.7 lb) and 43,452 gr (95.8 lb) of marketable berries/plot were produced in grower standard and micro-sprinkler treatments, respectively.
Plots were covered with netting for exclusive harvest data collection.
Marketable berry yields per plot in micro-sprinkler and grower standard sections from February to June, 2015
Total strawberry yields (marketable and unmarketable) per plot during the study period.
Plant canopy and health– Growth was recorded by measuring the width of the plant canopy across and along the bed from 20 random plants per plot on the 6th of each month from January to March, 2015. Plant health was monitored at the same time by on a scale of 0 to 5 where 0 = dead, 1 = weak, 2 = moderate-low, 3 = moderate-high, 4 = good, and 5 = very good. Plants in micro-sprinkler treatment had significantly smaller canopy in January (P = 0.004) and February (P =0.0006), but caught up with the grower standard by March (P = 0.14). Plant health rating during this period also followed a similar trend, but the differences were significant only in February (P = 0.02).
Size of the plant canopy and plant health condition from January to March, 2015.
Both micro-sprinkler and grower standard plants look equally healthy and productive (Photo taken on 26 May, 2015)
Twospotted spider mite and predatory mite – One mid-tier leaflet was sampled from each of the 10 random plants within each plot and the number of eggs, nymphs, adult pest and predatory mites were counted using a mite brushing machine. Sampling was made once a month from February to April, 2015, but due to sparse numbers and uneven distribution useful data could not be obtained.
Powdery mildew– One trifoliate leaf from 20 random plants within each plot were collected and checked under microscope for mycelial growth and powdery mildew severity was rated on a 0 to 4 scale where 0 = absent, 1 = 1-25%, 2 = 26-50%, 3 = 51-75%, and 4 = 76-100% of leaf area with infection. Sampling was made on 15 April and 16 and 24 June, 2015. Powdery mildew severity was significantly less in micro-sprinkler treatment on 15 April (P = 0.009) and June 24 (P = 0.01).
Severity of powdery mildew on three observation dates.
Botrytis fruit rot – Berries harvested from each plot were kept at room temperature in plastic clamshell boxes and disease severity was measured 3 and 5 days after harvest using the 0 to 4 scale used for powdery mildew. Observations were made on 26 March, 13 April, 22 May, and 16 June, 2015. In general, botrytis fruit was less severe in micro-sprinkler treatment, but significant difference were seen 3 days after harvest for samples collected on 22 May and 16 June (P = 0.02).
Severity of botrytis fruit rot when observations were taken 3 and 5 days after harvest.
Conclusions
Micro-sprinkler system contributed to a significant reduction in overhead irrigation water without affecting the marketable berry yield. With less pressure required to deliver water through micro-sprinklers, they could also contribute to energy savings. EC value of below 0.7 dS/m suggests that micro-sprinklers were as effective as aluminum sprinklers in leaching out salts. Due to the lack of sufficient mite infestations, the benefit of micro-sprinklers in spider mite management could not be determined. Data also suggest that powdery mildew and botrytis fruit rot could be reduced by micro-sprinklers, but additional studies are required to confirm these preliminary observations. An initial estimate by the vendor suggests that equipment and handling costs of the micro-sprinklers are more or less similar to those of the aluminum sprinklers.
Chris Martinez and rest of the field crew, Manzanita Berry Farms, Santa Maria after transplanting
Acknowledgements: Thanks to Dave Peck, Manzanita Berry Farms for his collaboration, Chris Martinez for his field assistance, Manzanita field crew for help with planting, irrigation, and yield data collection, Danilu Ramirez, Fritz Light, and Tamas Zold for their technical assistance, and RDO Water and Netafim for partial funding of the study.
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Reference:
Dara. S. K. 2012. Salt injury in strawberries. UCCE eNewsletter, Strawberries and Vegetables. http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=6820
- Author: Surendra K. Dara
Some Santa Maria strawberry growers experienced heavy infestations of whiteflies last year and there are already reports of infestations in some fields this year. Greenhouse whitefly, Trialeurodes vaporariorum has been a common strawberry pest in California for the past few years occasionally reaching high infestation levels that require targeted treatments. It used to be a concern mainly in the Oxnard area. Presence of the cut-back strawberries for second year production aid prolonged presence of whiteflies in the area and contribute to the early season infestations in new plantings.
Life stages of the greenhouse whitefly: Eggs darken when they are close to hatching. First instar nymphs are mobile and called crawlers. Later instars are immobile. Fourth instar nymphs are called pupae and characterized by long, waxy filaments. Adults have waxy, white wings. Black sooty mold grows on the honeydew secreted by whiteflies. (Photos by Jack Kelly Clark, Frank Zalom, and Surendra Dara)
Direct and indirect damage: Whitefly feeding affects plant growth and reduces yield and fruit quality. As they consume large quantities of plant sap, whiteflies excrete sticky honeydew deposited on the plant. Fungi of a few genera develop as black sooty mold on the honeydew covered surfaces. Sooty mold interferes with photosynthesis and affects plant growth. It also reduces the quality of the fruit.
Disease transmission: Greenhouse whiteflies are also important as vectors of pallidosis-related decline of strawberries. So, growers should be watching for symptoms of the disease which can be mistaken for nutritional deficiencies or abiotic disorders.
Pallidosis-related decline of strawberry is a viral disease caused by Strawberry pallidosis associated virus(SPaV) or Beet pseudo yellow virus(BPYV) along with non-whitefly transmitted viruses. Disease is not caused by SPaV or BPYV alone, but by the infection of SPaV or BPYV along with any of several non-whitefly transmitted viruses.
Symptoms of the disease include stunted plant growth, purple to red foliage, and brittle roots with reduced rootlets. Disease causes severe yield loss.
Whiteflies can cause a significant reduction in strawberry yield through direct feeding and indirectly through sooty mold and as viral disease vectors.
Biology: Greenhouse whitefly is about 1 mm long and has four membranous wings with white, powdery wax coating. Wings are held parallel to the top of the body. Eggs are small, elongated and attached to the lower leaf surface with a short pedicel. They are pale yellowish green to brown and turn dark with maturity. Eggs hatch and go through four nymphal instars before becoming adults. Immatures are oval, flat and often semitransparent. First instars are called crawlers which move around in search of ideal feeding sites on the underside of leaves. Later nymphal stages are immobile. Fourth instar nymphs are called pupa and have long, waxy lateral filaments and red eyes.
Management: Low population densities of whiteflies are usually controlled by the natural enemy complex in strawberries and pesticide treatments for other pests. Heavy infestations require timely treatments to prevent population build up. Monitor whitefly populations by using yellow sticky cards (1 per 10 acres) and counting their numbers on 20 mid-tier leaflets per each quarter of the field.
Refer to http://www.ipm.ucdavis.edu/PMG/r734301011.html for additional details on greenhouse whiteflies and their management.
My field trials: Among the control options that I evaluated, spiromesifen (Oberon) provided good control in a 2009 trial. In my 2012 large plot field trial, acetamiprid (Assail) alone at full label rate and acetamiprid at half the label rate along with the entomopathogenic fungus, Beauveria bassiana (BotaniGard 22 WP) provided a better control than other treatments.
2009 Trial: Percent change in whitefly populations two weeks after the treatment. *Note that spirotetramat is not registered for strawberries.
2012 Trial: Average percent change in whitefly populations after three applications. There was a general decline in their numbers throughout the experiment.
- Author: Surendra Dara
Petals, sepals, and developing fruit damaged and darkened from freezing temperatures (Photos by Surendra Dara)
Fruit deformation as a result of low temperatures which affect pollination. Smaller achenes are formed and uneven development of the tissue around them results in misshapen fruit. Notice larger achenes in unaffected areas (Photo by Surendra Dara)
Unusual cold weather during the past few days is a concern for the strawberry growers. Second year crop and cultivars that produce early or late can influence the extent of impact experienced by the growers because injury depends on the stage of development.
Damage: Low temperatures could completely damage the flowers or injure developing fruit tissue resulting in misshapen fruit. Pollination is also affected if temperature drops below 60 oF (15 oC) during flowering. As a result, some achenes do not have a seed, remain small, and cause fruit distortion. Cold injury can also cause fruit with multiple tips. Distorted fruit from lygus bug damage have uniform sized achenes, but the achenes affected by cold injury are much smaller than those on unaffected parts of the fruit.
Protection: Sprinkler irrigation can protect the fruits from cold injury when there is no or low wind. Freezing water releases heat and protects the flowers and fruits as long as temperatures do not fall below 23 oF (-5 oC) on still nights or 25 oF (-4 oC) when wind speed is no more than 2 mph. If wind speed is more than 4 mph, sprinkler irrigation is not recommended. Sprinklers must be started before the temperatures drop to freezing levels and continued throughout that period.
The time to start irrigation for frost protection depends on the dew point. If the dew point is low, irrigation has to be started before the freezing temperature. The following table shows when irrigation should be commenced depending on the dew point.
Dew Point |
Temperature at which irrigation should start |
Dew Point |
Temperature at which irrigation should start |
32 oF (0.0 oC) |
32 oF (0.0 oC) |
23 oF (-5.0 oC) |
38 oF (3.3 oC) |
31 oF (-0.6 oC) |
33 oF (0.6 oC) |
22 oF (-5.6 oC) |
38 oF (3.3 oC) |
30 oF (-1.1 oC) |
34 oF (1.1 oC) |
21 oF (-6.1 oC) |
39 oF (3.9 oC) |
29 oF (-1.7 oC) |
34 oF (1.1 oC) |
20 oF (-6.7 oC) |
39 oF (3.9 oC) |
28 oF (-2.2 oC) |
35 oF (1.7 oC) |
19 oF (-7.2 oC) |
39 oF (3.9 oC) |
27 oF (-2.8 oC) |
35 oF (1.7 oC) |
18 oF (-7.8 oC) |
40 oF (4.4 oC) |
26 oF (-3.3 oC) |
36 oF (2.2 oC) |
17 oF (-8.3 oC) |
40 oF (4.4 oC) |
25 oF (-3.9 oC) |
37 oF (2.8 oC) |
16 oF (-8.9 oC) |
41 oF (5.0 oC) |
24 oF (-4.4 oC) |
37 oF (2.8 oC) |
15 oF (-9.4 oC) |
41 oF (5.0 oC) |
Water should be applied at 0.10-0.15 (0.25-0.4 cm) inches per hour through sprinklers to provide adequate protection. Discontinuing sprinkler irrigation during the frost period can cause more damage. If sprinkler equipment is in shortage, limit the area to be irrigated. Sprinkler irrigation to an upwind or uphill field may provide some protection to an adjacent field downwind or downhill.
Drip irrigation can also provide some protection by wetting 6-12 inch (15-30 cm) of soil before the frost period. Wet soil stores and releases more heat than the dry soil.
Reference
2008. Integrated pest management for strawberries. Second Edition. UC ANR Publication 3351.