- Author: Tunnyalee Martin and Cheryl Wilen
Sometimes an invasive pest takes a while to become invasive. The Invasive Species Council of California defines an invasive species as “non-native organisms which cause economic or environmental harm.” So, until a species not originally from the area actually causes harm, it doesn't get the title of invasive.
Take the Italian white snail, also known as the white garden snail. In San Diego, it caused extensive damage to agricultural plants in the early 1900s but was considered eradicated after a massive control program in the 1920s. However, it was found again in San Diego County in the 1980s but it did not damage agricultural crops or gardens. Instead the snails lived off of weeds in neglected fields. Now it appears to be moving slowly from these fields to fruit tree orchards and avocado groves as well as landscapes. The Italian white snail feeds on decaying organic matter and living plants, damaging leaves, flowers, and fruit. Another fear is it being found in cut flower growing areas or in nurseries where it could become an export issue.
White or light tan, the Italian white snail is about the size of a dime or nickel when fully grown. It may or may not have brown markings on the outside of the shell. The inside shell color near the opening is light colored (compared to the milk snail, which looks similar but has a dark inside shell). Italian white snails are most noticeable during the day and when it is hot, because the snails climb up on fence posts, walls, weeds and other vegetation and congregate in large numbers.
In California, the Italian white snail is only officially found in San Diego County. However, it could easily move to new areas because of its small size, which makes it hard to detect, and tendency to attach to many kinds of surfaces such as truck beds. Also, because land snails are hermaphroditic—each snail has both male and female reproductive organs—it only takes any two snails to reproduce!
Californians can help in the fight against invasive species by learning and participating during California Invasive Species Action Week, June 2–10.
- Author: Ben Faber
Problem: There was a Valencia farmer in Ojai, farming on a rocky loam. More rocky than loam, on a 10 % slope, where he had been spraying the weeds down, the soil had gradually washed away and all he had left was scattered cobbles.
Solution: He planted a winter cover crop to protect the soil from erosion. He weed whipped it three times a year because that's all he could afford.
Result: After two years he had stopped the erosion, and there was actually a little duff layer forming in the orchard from the decomposing ground cover.
Problem: But now that wonderful cover crop and the cover it provided had attracted gophers that were chewing on the trees and because of inattention had killed a few of them. He couldn't trap fast enough.
Solution: He brought in a ‘Jack Russell' terrier that did a marvelous job at keeping the beasts down.
Problem: About the same time he noticed that he was getting gobs of snails that were getting into the trees. Even though he had lifted the skirts and painted copper on the trunks, they were still getting into the trees. He couldn't keep up with the winter weeds.
Solution: He brought in weeder geese to help with the ground cover and chickens to help with the snails and they worked.
Problem: Now the terrier is distracted by the fowl and is killing the chicks and goslings, as well as the gophers. In fact, he would prefer chasing the fowlings to going after gophers.
Solution: He tied a tether ball around the terrier's neck which slowed it down enough so that the young ones could get away.
Problem: Also with the introduction of birds, he also brought in coyotes which killed the larger birds.
Solution: He brought in a ‘Queensland Heeler' which is a bred that is noted for killing dingos in Australia. They are short-legged, barrel chested dogs that roll over on their back and pretend to be dead and when the coyote comes sniffing around, it grabs the coyote's neck and kills it.
Problem: What's next in this cause and effect chain of events?
This is a true story, but in today's world because of Food Safety and Good Agricultural Practices Certification would not happen with all these animals in the orchard, but something like it happens every time we overturn the flow of events. This is not the only scenario that is played out in agriculture. But hey, that's what a good grower is doing, managing a somewhat chaotic chain of events.
- Author: Ben Faber
When it starts to rain, things start happening. Growers come in with some interesting specimens. Wet, high leaf mulch environments create a special world that brings out some interesting creatures like slime molds and land planaria.
Land planaria are large, ‘slimy,' flatworms that reach ¾-12 ½ inches in length and 1/8 inch wide. Unlike their parasite relatives the tapeworms, these flatworms are free living predators of earthworms, slugs, snails and soil arthropods. Originally brought to the United States in the soil of potted plants transported from Indo-China, land planaria were first found in American greenhouses in 1901. As residents of potted plants, they were transported into new areas, established themselves in green houses, and eventually moved out to adjacent areas. Today land planaria are found in the natural environment of several states including: Alabama, California, Florida, Georgia, Illinois, Kentucky, Louisiana, Massachusetts, Mississippi, New Jersey, New York, North Carolina, Ohio, Oklahoma, South Carolina, Tennessee, and Texas.
Land planaria are brown-gray to yellowish in color with a series of long, dark stripes starting at the head. As a planarian ages the stripes become one long line, reaching the tip of the body. They have a triangular-shaped head and a long flattened body. Some have eyespots. The ‘slimy' appearance of planarians is due to a continual secretion of a mucus-type material. The mucus helps the planarian maintain body moisture, move, and is a defense mechanism due to its horrible taste. Land planaria are able to survive freezing weather conditions by resting in protected areas where boards or fallen trees cover rooted plants. During warmer seasons they are found under logs, rocks, woodpiles, plant debris and occasionally caves, but are rarely found in rural areas. They go where the nursery plants went. Oddly, they are rarely found in mulch-rich avocado orchards because most avocado orchards have few earthworms. Go look. Most avocados came from nurseries where potting mixes were fumigated or pasteurized before being sent out to the field and earthworms didn't go with the trees.
Throughout the fall and winter, planarians move outside their protective areas at night to hunt for earthworms that come to the soil surface after rainstorms subside. They prefer dark areas, cool temperatures and require high humidity. A humid environment is essential because death occurs quickly if a planarian losses 45% of its body moisture.
The inside of a land planaria is quite simple. They do not have a skeleton, circulatory, respiratory or digestive system. The nervous system consists of a mass of nerve tissue in the head attached to longer nerves in the body, arranged in a ladder shape.
Locomotion is made possible by the “creeping sole”; a strip of hairs going down the middle of the underside of the body and mucus secretion glands. The secretion glands deposit a layer of mucus that the hairs push against to move the planarians body across a surface.
Land planaria can reproduce in two ways. When land planarians reproduce by mating, they place eggs in cocoons that are red in color. After 24 hours, the cocoon turns black and the eggs continue to develop. Young planarians hatch and leave the cocoons within 21 days. If a land planaria reproduces without mating, the parent moves across the ground and attaches the tip of its tail to a rock or piece of wood. Once the tail is attached, the flatworm moves forward and the tip of the tail remains on the substrate. The tip of the tail left by the parent develops a head within 10 days and a young planarian is formed. A parent deposits the tip of its tail once or twice a month.
Land planaria primarily consume earthworms and other small soil organisms. They have one opening on the underside of their body that serves for both intake and elimination. The mouth extends and penetrates the body of a prey item when the planarian is attacking. Digestive mucus and the circular muscles within the mouth contract causing a sucking motion that allows the planarian to feed. The victim is slowly reduced into small particles that are consumed. Land planarians can survive for several weeks without food. If little prey is available, they will become cannibalistic or use their own reproductive tissue as a food source.
The only economic problem associated with land planarians is their ability to destroy entire earthworm populations in a greenhouse. Land planarians can disturb property owners who find them and their trails of mucus disgusting or annoying. The number of land planarians in an area usually is small and control is not recommended. In fact, it takes just the right sort of environment to consistently see them, like an irrigated garden with lots of hiding places or an orchard near a garden.
Photo: Univ. of Florida