- Author: Ben Faber
I used to think that you could not add enough mulch into an orchard and cause any harm. Well, I've been proved wrong a number of times. Some people have gone overboard and put on three to five feet for some reason and it causes all manner of problems, the least of which is usually just getting around in the orchard. But organic matter is the energy source that drives a lot of positive good in an orchard. It provides nutrients for the plants, as well as the microbes that protect plant health, keeps weeds down and maintains an even soil moisture content.
In agriculture, mulch has been viewed as an important input to maintain good tree health, especially in avocado orchards. That has been true up until the introduction of Asian Citrus Psyllid (ACP) and Polyphagous Shot Hole Borer (PSHB, and a close relative Kuroshio Shot Hole Borer ((KSHB))) into California. These are insects that carry disease that are lethal to trees. The ACP can carry a bacteria that causes the death of citrus trees. It has been a major cause of tree death in Florida, as well as other parts of the world. It is severely threatening the industry in that State as it does in California. It also threatens all backyard citrus wherever they are found. PSHB, on the other hand, is another insect that carries a fungal disease that threatens not just one species of tree, such as avocado, but many native trees, such as coast live oak, sycamore, willow and many other native tree species.
Initially these pests were pretty much confined to the Los Angeles Basin and south, but ACP has moved into the Central Valley, and through Ventura up the coast. Its progress has been monitored by traps. PSHB has been found in parts of Ventura County, but it is not widespread, as far as we know at this point. Both insects can be easily moved by contaminated plant material. ACP can be found in infested leaves and on fruit. Moving that material increases the likelihood of spread. PSHB can be moved in wood where it makes its galleries. Moving wood and chips, can spread this pest/disease complex.
The way to help control the spread of these two pest and their disease causing organisms is to stop the spread of materials. This means don't move material from known infested areas, such as the LA Basin into Ventura. It means know where your mulch is sourced. Ideally, if you mulch, it should be with material found onsite. Chip the trees on your property and use it there. This is a threat not only to you, but your neighbors, as well. Be a good neighbor.
For more on ACP and PSHB/KSHB see:
http://eskalenlab.ucr.edu/avocado.html
http://eskalenlab.ucr.edu/distribution.html
http://eskalenlab.ucr.edu/handouts.html
http://ucanr.edu/sites/KACCitrusEntomology/Training_Materials/Educational_Materials/
Photos: ACP and PSHB
- Author: Ben Faber
A recent article in California Agriculture highlights something that we have found in raw organic materials that have been used in mulches for controlling Avocado Root Rot – Phytophthora cinnamomi. The most active stage of a material in the process of composting, is the initial one where all the bacteria and fungi are fighting to consume the easily decomposable sugars and light fraction organics. That's when the material heats up and various gases, such as ethylene, ammonia and others are released. This is the most competitive time in decomposition and Phytophthora just can't compete. In fact, it becomes a food source for the antagonistic fungi, since its cell wall is made of cellulose the material that many leaves are made of. In releasing exudates to decompose cellulose, the Phytophthora is decomposed, as well. As the cellulose is decomposed and disappears more resistant materials remain. A mature compost, is therefore a much more stable material than a raw one. It still has nutritional benefits, as well as physical effects on soil when it is incorporated, but has a lesser impact on Phytophthora.
Compost is used as a soil amendment, largely because it is relatively stable biologically and has nutritional/physical effects. Incorporating raw organic matter into the soil and then planting has its restrictions and should be done cautiously. But as a mulch (material applied to the soil surface) there are fewer problems, as long as some common sense is used. Like don't pile it up against plant stems which keeps moisture and conditions for disease around the plant crown. And there are several other qualifiers, such as don't apply it so thickly that the soil never dries out and becomes a problem in walking across it.
So, read this interesting story of what happens to Phytophthora when introduced into a mature compost:
This is also a great web site to read about other UC related agriculture and natural resource research. Sign up.
- Author: Ben Faber
I just raked up all the leaves under the avocado and it looks so nice. PUT THEM RIGHT BACK. The avocado is shallow-rooted and really depends on the natural leaf mulch to protect its roots. In fact the roots will actually colonize the rotted leaves as if it were soil. This mulch is also a first line of defense against root rot. The decomposing leaves create a hostile environment to the microorganism that causes the disease. The mulch also helps to reduce evaporative loss of water and therefore reduces water needs. Avocado growers will actually spread mulch in cases where trees are too young to produce adequate leaf drop for mulch or in windy areas where mulch has blown away. The key to remember is that the mulch should be kept at least six inches away from the trunk to avoid collar rot which can be causes by keeping a moist mulch against the trunk.
- Author: Ben Faber
Ground urban organic material that shows up in great trailers for use in agriculture has simple rules for its use. 1) It should be a material low in contaminants. If you can clearly see golf balls and plastic, send it back. Over time with decomposition it is only going to become clearer because all the organics go away and all you are left with is a mess to clean up. 2) If used as a mulch (applied to the surface of the soil), it should be as woody material as possible, because it is more persistent and lasts longer and the roots which adjust to the mulch layer are less likely to be disturbed. 3) If it is used as a material to be incorporated into the soil IT MUST BE COMPOSTED. This cannot be emphasized enough. With decomposition, gasses such as methane, ethylene and ammonia are released which are all toxic to roots and it heats up, also which is hard on roots- like it burns the heck out of them. This goes for the material used as a mulch, it should be kept at least 6 inches away from tree trunks so that gasses and heat don't burn the trunks. And 4) no organic material should be incorporated into the planting hole, composted or non. This is one of those myths (planting mix in planting holes) that have been foist on gardeners and farmers alike. If it is organic it is good? Any organic material incorporated into a planting hole is going to decompose over time, and then the soil settles, causing voids. Much better to plant into the mineral soil and mulch and let the worms move any nutrients from the organic surface material into the root zone.
And remember that fresh citrus leaves and stems can harbor Asian citrus psyllid. Dry that material out before moving it around so you don't spread the psyllid.
- Author: Ben Faber
With the proliferation of pests and disease that might appear in mulch used in orchards, it might appear that the practice will become more limited unless the material can be guaranteed to be safe. Polyphagous Shot Hole Borer and Asian citrus Psyllid are just two examples of pests that might appear in a mulch from an unknown origin. There are many other examples, though, and new threats keep coming. Composting is a process that can insure a quality product, but composts tend to be too expensive to be used as a mulch. There is a new solar processing technique that is being evaluated in the Central Valley that might produce a product that could be used as a mulch.
The proliferation of low-cost, high-efficiency and durable solar panels makes it possible to set up solar-powered composting systems that reduce reliance on alternative forms of power and avoid very expensive grid hook-up costs.
This type of technology lends itself to a more stable site layout, which can then utilise conveyors for material movement, further reducing reliance on diesel-powered equipment. A potato piler, a standard piece of equipment in the potato storage industry, is an ideal prototype for compost conveyors.
Static piles can easily be watered using simple irrigation systems that save water and further reduce diesel reliance. When combined with the already proven technology of a compost cap, reductions of VOCs and greenhouse gases can be substantial.