There are 4,000 species of earthworms grouped into five families and distributed all over the world. Some grow uo to 3 feet long, while others are only a few tenths of inches. We call them nightcrawlers, field worms, manure worms, red worms and some people call them little diggers.
In California, we have some native species of earthworms, but in many cases non-native introduced species have come to dominate. The predominant native species belong to the Argilophilus and Diplocardia while many of the non-native are of European in origin in the Lumbricidae family. Many of these non-natives were probably introduced by settlers bringing plants from home, which had soil containing the worms. A survey of California earthworms by the US Forest Service can be found at:
This is a wonderful description of earthworm biology and their occurrence in the landscape.
When digging in citrus orchards, it is common to find earthworms in the wetted mulch under tree canopies. Many of our citrus orchards were initially established by “balled and burlap” nursery trees that brought worms along with the soil. In the case of many avocado orchards, on the other hand, it can be rare to find earthworms in orchards. Most avocado orchards have been established since the 1970s when potting mixes and plastic liners were the standard practice and worms were not part of the planting media. Even though there is a thick leaf mulch in avocado orchards, the worms have not been introduced, and it is rare to find them.
Numerous investigators have pointed out the beneficial effects of earthworms on soil properties. One of the first of these observers was Charles Darwin who published Earthworms and Vegetable Mould in 1881. He remarked on the great quantity of soil the worms can move in a year. He estimated that the earthworms in some of his pastures could form a new layer of soil 7 inches thick in thirty years, or that they brought up about 20 tons of soil per acre, enough to form a layer 0.2-inch-deep each year.
Earthworms, where they flourish, are important agents in mixing the dead surface litter with the main body of the soil. They drag the leaves and other litter down into their burrows where soil microorganisms also begin digesting the material. Some earthworms can burrow as deeply as 5 to 6 feet, but most concentrate in the top 6 to 8 inches of soil.
The worm subsists on organic matter such as leaves and dead roots near the soil surface. The earthworm ingests soil particles along with the organic matter and grinds up the organic matter in a gizzard just as a chicken does. This is excreted in what we call worm casts. The castings differ chemically from the rest of the soil, as they are richer in nitrogen, potassium and other mineral constituents.
Castings are a natural by-product of worms. When added to normal soils in gardens or lawns, they provide the same kinds of benefits as other bulky organic fertilizers. Castings today are not commonly used as fertilizer by commercial plant growers because of their cost relative to other fertilizers. However, castings are used by some organic growers and are sold commercially as a soil amendment or planting medium for ornamental plants grown in pots.
The physical soil churning process also has several important effects:
-Organic residues are more rapidly degraded with the release of elements such as nitrogen, sulfur and other nutrients.
-Some of the inorganic soil minerals tend to be solubilized by the digestive process.
-Extensive burrowing improves soil aeration.
-Burrowing can improve water penetration into soils
-The earthworm carries surface nutrients from the soil surface and imports them into the root zone of the plant.
Although earthworms are considered beneficial to soil productivity, few valid studies have been made to determine whether their presence will significantly improve plant growth. This may seem odd since many of us have learned from childhood that worms are good. It is something like the chicken and the egg analogy. The conditions that are conducive to earthworms are also ideal for plants. Both plants and worms need temperatures between 60 and 100 degrees F for good growth; both need water, but not too much or little; they both require oxygen for respiration; and they do not like soils that are too acid or basic or too salty. By correcting soil conditions that are unfavorable for one will also improve the outlook for the other. The earthworm is a natural component of the soil population. If the soil is properly managed this natural population will thrive. In this sense, the presence or absence or earthworms can be an indicator of the "fertility" of one's soil.
A recent auction in South Africa was selling 'Maluma' variety of avocado for $92 a tree. That is more than the average price of avocado nursery trees in that country and a lot more than what is paid in California or Florida. That variety has suddenly gotten a huge demand because of its sales characteristics accounting for 13% of the tree sales from one nursery there.
This is a phenomenon that is going on world-wide not just for 'Maluma'. According to a CA nursery producer, the 'Maluma' sale is really a reflection of the world-wide demand for avocado trees and not necessarily this South African variety. Avocado acreage is expanding world-wide. So far 'Maluma' has a US import license, but has not been grown in CA, so we don't know its performance characteristics. That should change soon according to the nurseryman.
Related story: South Africa: Maluma Day to challenge avocado sector's “convenient position”:
Why eat terrible fruit when you can eat wonderful California fruit, or should be able to? All too often fruit which is shipped for several weeks from far off groves arrives distressed and put into cold storage here and then this is mishandled at the retailer. What the consumer ends up with is postharvest damage. Fruit that has been held too long in cold storage at the wrong temperature and you get fruit like that pictured below. Barely edible if you eat around the black stuff.
In January, I bought a bag of 4 fruit from the local store. When it had ripened, I cut open all 4 fruit and saw cold damage. I took them back to the store and they gave me another bag. When ripe, I cut them open and found the same damage. Took them back and they gave me another bag. Same thing. Took them back and asked for my money back. The produce manager said I was the only one to complain. It's a good store to back their product, but I wonder if they ever complained to their supplier. And what about the other buyers?
California can grow great fruit year-round. Some of it could be the old 'Fuerte' which is a great eating winter fruit or a 'Reed' or 'Nabal' in the summer. And some people just really like 'Zutano' or 'Bacon'. We all don't like the same taste. Add some variety to life. I was reminded of this the other day when I went to look at a recently planted 'Reed' orchard. When asked why, the grower said she loved the fruit and had a buyer for all her fruit. That's what it takes when you don't grow 'Hass', finding the market for some of these unusual varieties. Or find a packer that will take a chance on your fruit.
There's been a call for a long time on the part of growers to sell their greenskins, but the consumer needs to be taught what a good piece of fruit taste like at the right time of year. There have been lots of advocates for variety for a long time, and now that consumers have turned into 'foodies' it's time to feed them. They don't want to go to the store and buy a bad piece of fruit. And then throw it out. Instead they should go back to the store and demand a good piece of fruit.
End of rant.
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The government of Ecuador has requested the U.S. allow avocado to be imported into the continental United States. APHIS has drafted a pathway-initiated risk assessment for this request. The draft document is available for 30 days for stakeholders to review and provide comments.
The document and instructions for submitting comments may be accessed through the APHIS Plant Import Information Web page, or this link: