It’s probably no surprise that California is the leading grower of strawberries in the U.S., producing almost 1.7 billion pounds of berries and more than 90 percent of the crop. With various climates throughout the state, California strawberries are grown year-round, with spring months bringing the highest volume of berries harvested and winter the least. With yields of over 40,000 pounds per acre and almost 40,000 acres in production on more than 400 farms, California’s strawberry growers lead the pack.
Approximately two-thirds of the strawberry acreage in the U.S. is in California. Although California and to some degree Florida, are the only real players for wholesale marketing and distribution of fresh strawberries in the U.S. today, the game may be changing as interest in reestablishing local food systems grows. Additionally, research devoted to regional strawberry production has been expanding in recent years.
One factor impacting California production is the loss of traditional strawberry acreage to growing populations. Regulations are changing too, forcing familiar growing practices, such as use of methyl bromide fumigant, to finally be phased out, leaving researchers and growers seeking solutions to keep productivity high despite cultivation challenges. Two recent grants from the U.S. Department of Agriculture’s National Institute of Food and Agriculture (NIFA), announced in late August, are allowing University of California researchers to study biofumigation and to develop new disease-resistant strawberry cultivars.
Methyl bromide had been permitted for use in California’s strawberry fields for soil fumigation purposes until the end of 2016. It had been the primary method for control of pathogens, pests and weeds. With new regulations in place, alternative chemical control products have been used, but many of these are also facing challenges, including evolving air quality and buffer zone rules. Strawberries require regular moisture, so droughts and limited water availability present more challenges in the state. Finding ecofriendly alternatives is crucial for California growers.
In the “normal” course of commercial strawberry production, soils are chemically fumigated, wide beds are made, plastic is laid and nursery-grown transplants are planted in double rows. Plastic liners keep berries off of the soil, provide some protection from disease and pests and warm the soil, extending the growing season. Chemical fertilizers are applied using various methods: injection into the soil, side dressing rows for distribution when it rains or plants are watered or via irrigation systems. Overhead irrigation systems are often used to provide frost protection and irrigation. Microsprinklers and drip irrigation are being used by some growers for conservation purposes and plant disease control. Water salinity can be a problem and needs to be monitored.
The California berry season starts in Watsonville, just south of San Jose, then moves down the coast to Santa Maria and finally to Oxnard, just north of Los Angeles. Production is year-round in all five strawberry-producing regions, including some production near San Diego and interior valley areas. The three primary fresh-market regions produce during the spring and early summer, allowing little room for out-of-state competitors, as California’s yields and growing season allow distribution of its berries nationwide almost year-round.
The mild climate extends the strawberry production season in each locale over several months, a big difference from the four- to six-week season typically seen in New York or Pennsylvania, two states whose production ranks in the top 10 strawberry-growing states, but which fall well below that of California or even Florida. Oregon is the third largest strawberry producer, but most of its berries are grown for the processing market.
Two recent grants, funded by the USDA’s NIFA, are assisting University of California researchers in finding new naturally disease-resistant cultivars for California growers and advancing the study of biofumigation practices. The grants, announced in August, will help California growers continue to produce high yields of berries and do so more sustainably.
Although California’s strawberry farmers and researchers continue to innovate to make production more sustainable, it is not ideal to rely on one state to produce a food crop for the nation. With many consumers now focusing on local or regional food systems, along with a desire to purchase from small farmers and to source certified organic foods, the National Strawberry Sustainability Initiative (NSSI) conducted research studies from 2013 to 2015. Its mission is “to move sustainable production forward through innovation, application of new technology, demonstration, outreach/extension and education, ultimately resulting in increased sustainable production and supply of strawberries to American consumers.”
The NSSI collaboration includes university researchers and extension educators whose projects range from cultivar breeding to plant pest and disease controls, food safety to reducing storage losses. By enhancing strawberry production in states other than California and by finding more sustainable growing alternatives for those California growers, the NSSI’s goal is to optimize strawberry sustainability via local production practices. Because the strawberry demand is growing each year, growth outside of major strawberry production areas can occur without negatively impacting existing commercial growers.
Other studies, such as the ongoing TunnelBerries project (https://www.tunnelberries.org/), have researchers in the Northeast and Midwest searching for ways to extend the strawberry season, make it more productive and making strawberries a more viable crop for area growers. Growing berries under cover and experimenting with day neutral and ever-bearing varieties, rather than relying solely on the June-bearing or short-day varieties normally grown in these regions, are two primary methods of yield increase and season extension.
Kevin Schooley, executive director of the North American Strawberry Growers Association, presented an overview of some challenges facing California, Florida and Mexico growers, along with a look at production changes occurring in other regions of the U.S. and Canada in early 2017. His presentation gave a glimpse at some of the regional strawberry markets being developed and the innovative growing systems that are allowing extended season production and yield increases.
June-bearing strawberries initiate flower buds during cool temperatures and short days. When days grow warmer and longer, they focus on producing vegetative growth and runners, through which they propagate new plants.
Day-neutral strawberries fruit the first year of planting, while June-bearers do not. They also have a longer growing season, producing flowers even when days grow short and do not produce an abundance of runners. Newer cultivar development has increased the yield and fruit size of these plants, making commercial production in cold climate regions possible. Day-neutral strawberries can continue to produce flowers in longer-day environments, although warmer soil or air temperatures will impact this, as will a lack of moisture.
Ever-bearing types of strawberries produce over a long season, but have three distinct periods of production of fruit. Flowers and fruit are produced in spring, in summer and again in the fall. Runners are few. Often, day-neutral and ever-bearing are used interchangeably.
These ever-bearing and day-neutral berries allow cold climate growers to produce berries into the summer and fall. Although production is not steady throughout the fruiting period, growers can feasibly extend their strawberry season and offer local berries throughout the region, even after June-bearing cultivars (early, mid and late season) have ceased production. Part of the research being done also involves customer response. Will consumers, used to having local strawberries only for a brief period of time, be receptive to purchasing local berries during an extended local season? Can these local berries compete with the year-round presence of strawberries from afar on retail shelves?
Although planting day-neutral or ever-bearing types and selecting a variety of June-bearing cultivars with different growing seasons can extend the harvest, growing strawberries in protected environments can provide even more options for extended production.
Low or high tunnels, as well as greenhouse production or even hydroponics, are all being studied. The TunnelBerries Project and the NSSI have information on these practices, geared toward growers in various regions. Visit their websites for resources, including cost analysis, cultivar selection, production guides and videos.
Disease, pest and weed concerns
Fumigation with methyl bromide or other chemicals has effectively controlled many pests, diseases and weeds for the commercial strawberry industry. Solar sanitization, crop rotation, hand weeding, selective herbicide and pesticide use, the use of various colored mulches to manage weeds, the use of soil amendments to optimize beneficial microbial populations and the use of beneficial insects are alternative means of control.
Strawberry diseases vary in importance depending on the growing region and its climate, the cultivars being grown and the growing system. Less than 10 percent of California’s strawberries are grown for more than one season. By growing strawberries as an annual, pest and disease pressures can be lessened and plant vigor and fruiting optimized.
Transplants are common sources of strawberry disease. Certified disease-free transplants are the best way for growers to guard against problems and reduce disease occurrence in their crop.
Diseases that require moisture are primary issues in strawberry production. Fungal disease such as botrytis (gray mold), anthracnose fruit rot or bacterial leaf spot are common concerns in many growing regions. Often, growing on plastic can promote moisture issues, particularly if regionally-adapted cultivars are not used. Overhead irrigation, working when berries are wet and infected crop debris all contribute to the transmitting of diseases, particularly during periods when excess moisture is present.
Botrytis is a disease of major concern in strawberries worldwide. Also known as gray mold, the infection impacts fruit both pre- and post-harvest. Spores are easily spread via water, air or contact, and infection can worsen as the flowering and fruiting season continues. Cold, wet weather provides optimum conditions for Botrytis cinerea, the fungal pathogen, to thrive.
For commercial growers in California, anthracnose fruit rot is a serious issue. This fungal pathogen, Colletotrichum acutatum, prefers warm, wet conditions and rapidly spreads via water to infect crop fruits, with losses over 50 percent in conducive conditions. Anthracnose species pathogens can also cause crown and runner rot. Black plastic may contribute to the ideal wet, warm environment around strawberry plants.
Phytophthora fragariae is another fungal disease of concern. It attacks the roots of the strawberry plant, can live for many years in the soil and spreads rapidly in cool, moist conditions. The disease causes plants to be stunted and to wilt. A diagnostic symptom is the presence of red discoloration in live white roots during the winter and spring.
Some pathogenic nematodes also cause disease in strawberries, causing severe root damage in infected plants.
Not all issues seen in strawberries are indicative of pathogens or pests. Sometimes, a nutrient deficiency, climatic conditions or even genetic issues cause plant symptoms and lack of productivity. A guide to identifying these concerns from the University of California is available at the university’s web site.
A variety of mites can cause infestation on strawberry plants. According to University of California IPM guidelines, more than one mite per leaflet can cause noticeable yield loss, whereas those with more than 75 mites/leaflet will suffer stunting and crop loss.
Black cutworm can cause some issues when it feeds on crowns, damaging the central growing point of plants.
Spotted wing drosophila (SWD) is an emerging pest, causing damage to healthy fruit, as well as to overripe fruit. Eggs are deposited just under the skin of the fruit. The maggots feed on the fruit as they develop. The injury to the fruit caused by SWD attracts other pests, such as the vinegar fly and can serve as a point of entry for other disease-causing pathogens.
Weeds can out-compete the young berry plants before they become established each season. Some weeds of concern for California growers include yellow nutsedge, Bermudagrass and bindweed. Yellow nutsedge is a perennial plant, which readily grows through plastic mulch. It spreads readily by tubers and traditionally has been controlled with fumigation.
Strawberries have become a year-round fruit, available continually in supermarkets. Whether good, bad or simply a fact of life, distributors would not be filling supermarket shelves if growing strawberries year-round was not a profitable enterprise. California’s predominance in the commercial strawberry market is a reality for a variety of reasons and it remains to be seen whether regionalized production can take a bite out of the monopoly California growers now have on the market.
For growers elsewhere seeking to add strawberries to their crop production, understanding how the wholesale market works and finding your niche in relation to the supply chain can help you determine the best way to grow and market your strawberries. With the help of regional cultivars, innovative growing practices and the demand for local foods, strawberries that are not California grown may become more common.