How LEAF Is Addressing the County’s Medfly Infestation

-By Christine Young, Volunteer Blogger-

What is smaller than the flies you typically find at home, but devastating to California’s bountiful $59B agriculture industry? The Mediterranean fruit fly (Medfly). The good news is, the current medfly invasion isn’t triggering the widespread (and controversial) aerial spraying of insecticides that marked a California infestation decades ago. However, to stem the reach of these damaging pests, the agricultural community—including our gardeners here at the LEAF Urban Farm—are adjusting their planting strategies in response. 

Medflies can be costly to agriculture because they cause fruit to decay, making crops inedible and thus reducing yield for farmers. This time around, the invasive pests were initially found in Fremont and later on in Newark, Union City, Milpitas, Sunol, and Hayward. In response, the California Department of Food and Agriculture (CDFA) instituted a medfly quarantine that began on December 12, 2024, and will run through August 19, 2025, covering parts of Alameda and Santa Clara Counties. What this means for LEAF and home gardeners alike is, wild and cultivated fruits from affected areas cannot be transported outside of those areas. So, no sharing with friends and neighbors. However, it’s okay to consume or process (such as juice or cook) the fruits where they are picked. 

The CDFA has also prescribed a treatment plan for this medfly infestation that includes:

• Biological control, where sterile medflies are released around current and future detection sites to disrupt the flies’ breeding cycle. 

• Chemical control, where a protein bait spray containing an organic formulation of a pesticide called spinosad is applied within about 656 feet of current and future detection sites. 

• Physical control, which involves removal and disposal of host fruit from current and future detection sites, as well as properties within at least 328 feet of these locations.

“You cannot have a healthy planet without healthy soil,” says Elaine. “There’s a whole network of animals and insects that live in the soil. Most of it is invisible, such as microbes. There are also earthworms, snakes, and even frogs that bury in the soil—all of them contribute.”

Elaine added, “One of the practices to build healthy soil is to have a buffet of many types of plants rather than a monoculture approach where only one crop is planted in a given space. Polyculture farming encourages a diverse array of soil-based organisms to flourish. Encouraging beneficial carnivorous insects to visit the garden and eat the vegetarian insects is one way to create a natural balance.”

Shifting the Crop Mix at LEAF Urban Farm

At the LEAF Urban Farm, we’re continuing to take an active role to thwart the current medfly infestation. Our gardeners take pride in sharing the fruits of their labor with our community. However, based on the physical control guidelines, the farm unfortunately won’t be able to donate any produce from medfly host plants to local food banks or hand them out to volunteers while we remain under quarantine. Host plants include many traditional summertime favorites: all citrus, pome, and stone fruit trees; nut trees; berries; tomatoes; peppers; eggplants; melons; and cucumbers. There are a few exceptions that are safe to share, including California elderberry, potatoes, and okra. We’re also unable to accept gleaned fruits from our neighbors, as our fruit gleaning program is on hold while we remain under quarantine. (Fortunately, most vegetables can be accepted.)

Elaine, LEAF president, notes that reducing their food supply is one of the most effective ways to combat medflies. Based on this, LEAF gardeners are focusing their growing on plant families that aren’t attractive to the pests:

• Beet, which includes spinach, chard, and amaranth

• Brassicas, which include bok choy, broccoli, kale, and radishes

• Leafy greens such as arugula, chard, collards, endive, and mustard

• Legumes such as beans and peas

• Mint, which includes basil, oregano, thyme, and rosemary

• Onion, which includes chives

• Parsley, which includes carrot, cilantro, and fennel

• And miscellaneous items like corn, okra, bunching onions, and sorrel

  
  

A Tough Enemy to Battle 

Given their voracious appetite and ability to infest more than 250 different fruits, medflies represent a formidable agricultural enemy. Female medflies typically lay their eggs inside produce, usually 1 to 10 eggs per fruit, according to the CDFA. When those eggs hatch and become maggots, the maggots feed on the produce by tunneling through it, causing the affected fruits to rot. The maggots then leave and burrow into the ground to pupate. Adult medflies eventually emerge and mate, starting another lifecycle. So, you can see why those involved in California’s billion-dollar agricultural industry act quickly at the initial signs of an invasion. 

The state has had to deal with medflies periodically over the last several decades. According to a report in Smithsonian magazine, the first medfly in California was found in 1975. By 1980 and 1982, the state considered the issue a full-on outbreak. As anyone who was in the state might recall, the government opted to battle the pests via widespread overnight aerial spraying of an insecticide called malathion. Not surprisingly, this was a very controversial move. Residents (myself included!) would awaken to find the sticky substance blanketing everything outside. Despite official reassurances, there was plenty of concern about health ramifications. 

California stopped using malathion in 1990. These days, a more common protocol is to release sterile males into an affected environment, with hopes that the female medflies will mate with them and produce eggs that won’t hatch. 

Elaine expressed concern that it will be difficult to fully (and permanently) eradicate medflies. Since our state is home to so many of the fruits that these pests find attractive, it’s not surprising that we see them return time and again. But we can all do our part to help prevent medflies from becoming a permanent fixture, as they are in other warm-weather areas like Hawaii and parts of the Mediterranean, South America, and Australia. 

At LEAF, with our focus on regenerative agriculture practices, we are in a strong position to be part of the solution when a medfly infestation is detected in the region. 

Want to learn more about regenerative agriculture or try it out for yourself? Sign up for one of our events or volunteer at the LEAF Urban Farm.