Farmers have been complaining about the difficulty of finding people to pick fruits and vegetables. The problem has seeped to the cash register, where consumers face escalating costs. The problem may soon be solved - by robots.

The world has seen three agricultural revolutions: 10,000 years ago, when stationary farms replaced hunting-and-gathering societies. In the 18th century, when European agriculture shifted from the techniques of the past to embrace new methodologies like crop rotation and livestock utilization. And in the mid-20th century, when the Green Revolution increased yields, saving perhaps a billion people from starvation.

Now, we are entering a fourth - driven by robotics. The robot revolution is coming none too soon, as farmers find it increasingly difficult to hire affordable labor during the harvest season.

It is hard to find people who will undertake farm work. In the United States, a rising minimum wage and a dwindling birth rate in Mexico have reduced the potential supply of farm workers - forcing many growers to let fruit rot in the fields. In the U.K, the fall of the value of sterling in the wake of Brexit has made it increasingly difficult to recruit overseas workers.

The work is dangerous, characterized by tough physical demands and long hours in the sun. It is difficult and unpleasant, making it hard to attract workers even when farmers offer $50 an hour in California or $30 an hour in Florida.

The year 2017 saw an especially tight labor supply in California, which yields about half the U.S agricultural industry’s fresh fruits, vegetables and nuts. Immigration restrictions have been making it more difficult than ever to find workers, thanks to stepped-up federal government immigration sweeps in California. It is hard to attract people, with recruitment undermined by negative perceptions.

In the face of these challenges, the robots are on their way. Indoor farming opens the door to considerable technological improvement, with yields growing significantly to address the reduction of arable land and continuing population growth. Marrying many technologies to indoor farming will allow the growing, planting and harvesting of crops 24 hours a day, seven days a week, in all seasons - lengthening shelf life and avoiding bruising. The average yield per acre in indoor farms for vine crops like tomatoes and leafy greens is already 10 times higher than in their outdoor equivalent. With the increased introduction of technologies, indoor farming will be able to produce as much as 20 times more fruit, using up to 90 percent less water.

Robotic machinery is being tested to harvest apples and other crops. A mobile robot is able to examine crops for their health and conduct simple operations like pruning, and observing and controlling ripening profiles so a robot can cultivate crops like tomatoes continually and more efficiently than people.

Work is being conducted to develop small agricultural field products to attack weeds and perform other farm chores. Robotic harvesting vehicles are being tested in Florida and California to pick strawberries and perform labor-intensive tasks normally performed by dozens of farm workers.

Berries represent one of the most difficult challenges faced by farm technology. Harvesting soft fruit mechanically is not an easy task. Each berry needs to be located, even if it’s behind a leaf, assessed for ripeness, and then harvested and boxed with enormous care to avoid bruising. But recent developments in visual sensor technologies, machine leverage and autonomous propulsion have brought the goal within reach.

For example, a robotic arm has been developed to reach up from its place on a self-driving trolley to use 3D vision to grip a ripe berry between a pair of cushioned plastic paws. The gripper then snaps the fruit off its stalk, mimicking a human technique. The prototype’s results this far? One strawberry picked every four seconds, collecting between 70 percent and 100 percent of the ripe fruit - a result competitive with human pickers.

Another device being tested is a picker that delivers berries with a centimetre or so of stem still attached, extending shelf life. Robotic arms mounted on mobile platforms are aided by computer vision to identify ripe fruit, grade them to determine their size and quality, and pack them.

In California and Florida, new technologies are being prepared to launch, equipped with robotic arms that reach down to locate and pick every fruit, carrying it off by the stems to minimize damage. In another prototype, paddles gather up the plants’ leaves to expose the fruit; rotating grippers than snap the berries off the stalk.

The challenges are significant but so is the opportunity: A broader selection of foods, more widely available, less expensive — and a better fed population. The world of agriculture has come a long way from the horse and plough - and will continue to progress even further.