- 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
You come on a leaf with the margins munched on. It's got to be a beetle or a looper or some insect doing the damage, right? Not necessarily. It's not time to drag out the Raid. Look at the damage closely. In the photos below you can see the dead leaf margins caused by either salt damage or more likely leaf blight. Leaf blight is a disease that shows up with water stress and is caused by a fungus, one of the Botryoshpaerias. It causes an uneven marginal necrosis that goes along the margin in a somewhat irregular pattern and often not at the leaf tip. In this case it does affect the leaf tip, and since salt burn and leaf blight are caused by the same conditions of water stress, it's probably a bit of both.
Lepidopteran larvae will more commonly feed in a smooth pattern, not the rough pattern seen here. Now with this dead tissue, the wind blows it out, and what's left is the uneven margin. No it's not time to spray an insecticide. It's time to reflect on irrigation. There's a lot of this damage out there now. On avocados, citrus, landscape plants. It's going away until the leaves drop and are replaced with new ones, that will hopefully be well hydrated by rain and proper irrigation.
Top photo is salt/leaf blight damage
Bottom is necrotic tissue that the wind has blown out
- Author: Ben Faber
So I got an email with an attached set of photos showing a number of 18 month avocado trees that had broken at the ground line in a wind storm. It looked something like an incompatibility between scion and rootstock, since below the graft union the rootstock girth was substantially smaller than the scion. The problem is, I'd never heard of this between ‘Hass' and ‘Dusa' and the combination has been around for at least 15 years in trials.
So it was time to go out to the orchard and see the setting in which the trees had failed. And there was the answer. All of the trees had been planted too deeply. The trunk sleeves had been buried and the graft union was below grade and had been infected by disease organisms. The crown roots are the most active physiologically and that union area is a weak spot. Burying it encourages disease and a weak union.
The trees had been planted with an auger and over time the trees had settled into the soft earth and had been buried. The first time I had ever seen something like this was in Guatemala and Costa Rica. There growers had created these massive 3 x 3 X 3 foot holes and amended them 50% with compost. And over time, the trees had settled as the compost decomposed and the unions were covered with dirt. Occasionally you see people moving too fast when they are planting and this shows up in a few trees, not usually a whole orchard.
The lesson here, is that if you are going to err on plant depth, plant high. A few exposed roots won't hurt, and the settling problem doesn't become a problem. Of course it's best to plant just right.
Broken Trunks
The Buried Avocado Graft Union
- Author: Ben Faber
It ain't over yet, and this last week we had a wonderful 2 day meeting with folks who have dealt with drought in many different ways. Here are presentations made by people from Israel, Australia and California. Soon the actual videos will be available, but now see the powerpoints.
http://www.droughtmgt.com/#!presentations-and-documents/niui7
The grower panels are wonderful, but are not uploaded at this point
DAY I: UNDERSTANDING IRRIGATION WATER MANAGEMENT
Session I: California Response to Drought
9:15am // Overview of California Drought Response
9:30am // El Nino Forecast for California and Possible Impacts on Irrigated Agriculture
Session II: Technology of Water Management
9:45am // Soil Water Sensing
10:15am // ETc Estimates - Weather Stations (CIMIS), surface renewal
11:00am // Salinity Measurement
11:30am // Consideration In Selecting Water Stress Indicators
12:00pm // Precision Water and Fertility Management During Deficit Irrigation
Session III: Alternative Water Supplies
1:30pm // Irrigation With Recycled and Desalinated Water
2:00pm // Effects of Irrigation With Poor Quality Water on the Soil - California Experience
2:30pm // Effects of Irrigation With Poor Quality Water on the Soil - Israeli Experience
3:00pm // The Challenge of Sustainable Irrigation with Water High in Salts: Lessons from Dates, Olives and Grapevines
Session IV: Water Management Strategies During Drought
3:45pm // Water Management Strategies during Drought - Australian Experience
4:45pm // Cultivation Under Protective Structures to Save Water
Day II: WATER MANAGEMENT FOR INDIVIDUAL CROPS & GROWER EXPERIENCES
Session V: Technology Demonstrations​
8:00am // Irrigation Scheduling - Australian Experience - IrriSAT Approach (IrriSAT Supporting Materials)
8:30am // Using the Pressure Chamber for Drought Mangagement Decisions
9:00am // Irrigation System Evaluation
9:30am // Salinity Mapping for Water Management
Session VI: Conncurrent Breakout Groups
10:30am // Citrus - Israeli Experience: Long Term Effects of Deficit Irrigation, Salinity, and Rootstocks on Orchard Productivity
10:30am // Grapes - Table and Wine Grape Irrigation Scheduling
10:30 // Deciduous Nut Crops - Irrigation and Crop Load Interactions
10:30// Almond Irrigation, the Israeli Experience
11:15am // Olives - Israeli Experience: Cultivation Under Limited Water Availability
11:15am // Grapes - Wine Grapes Irrigation - Coastal Vineyards
11:15am // Deciduous Nut Crops - Almond Irrigation - Israeli Experience
1:00pm // Avocado - Israeli Experience
1:00pm // Grapes - Wine Grapes Irrigation: San Joaqin Valley
1:00pm // Deciduous Nut Crops - California Experience
1:30pm // Deciduous Nut Crops - Pistachios Irrigation
1:45 // Subtropical Crops - California Experience
1:45 // Grapes - Irrigation, the San Joaquin Valley
2:00pm // Deciduous Nut Crops - Walnut Irrigation
2:30pm // Grower Panels
3:15pm // Concluding Remarks
- Author: Elizabeth Fichtner
Elizabeth Fichtner1, Dani Lightle2, Dan Flynn3, Rodrigo Krugner4
UC Cooperative Extension (UCCE) Tulare1, Kings1, Glenn2, Tehama2, and Butte2 Counties, UC Davis Olive Center3, USDA, Agricultural Research Service, San Joaquin Valley Agricultural Sciences Center4
The recent outbreak of the plant bacterium Xylella fastidiosa in southern Italy illustrates the potential for introduced organisms to incite widespread havoc in a short time. Xylella fastidiosa has been found in association with a new disease called olive quick decline syndrome (OQDS), which is affecting over 20,000 acres of olive in the Apulia region of Italy. Symptoms of OQDS include extensive branch and twig dieback, yellow and brown lesions on leaf tips and margins, vascular discoloration, and subsequent tree mortality. In southern Italy, the main insect vector of X. fastidiosa is the spittlebug Philaenus spumarius, which is known to occur in California. While research is underway to determine if the bacterium is responsible for causing OQDS, establishment of X. fastidiosa in Europe leaves growers and researchers asking where it came from. Genetic techniques used to compare pathogen populations have led researchers to hypothesize that the isolates of X. fastidiosa (strain CoDiRO) associated with OQDS, may have originated in Costa Rica. Marking the first European find of X. fastidiosa outside of Italy, the bacterium also was found on ornamental coffee plants at a retail market near Paris in April 2015; the plants had been imported to Europe from Honduras (3). In July 2015, X. fastidiosa was identified on ornamental plants on the French island of Corsica and on the mainland in October 2015 (2). The X. fastidiosa subspecies found in Corsica (subspecies multiplex) is different from that associated with OQDS in Italy (subspecies pauca) (2).
The European Commission has imposed several regulatory actions to prevent further spread and introduction of X. fastidiosa into the European Union, including a specific ban on import of coffee plants from Honduras and Costa Rica; eradication measures in Italy and France; and the potential for strict eradication measures aimed at new outbreaks or finds of the bacterium, including removal and destruction of infected plants, and all host plants within a radius of 100 m. (1)
The new introductions of X. fastidiosa to Europe illustrate the potential for long distance dispersal of the bacterium and a vulnerability of California agriculture to invasion by new organisms. The United States Department of Agriculture-Animal and Plant Health Inspection Service-Plant Protection and Quarantine's (USDA-APHIS-PPQ) New Pest Advisory Group (NPAG) is assessing the biology and potential economic and environmental impacts that the strain CoDiRO may pose to the United States to recommend potential regulatory strategies (Tara Holz, personal communication). NPAG is designed to inform Federal decision makers regarding potential regulatory actions that may be appropriate to prevent pest introduction.Previous USDA-led research has found X. fastidiosa in California olive trees, but the endemic bacterium has only limited association with disease and is a different subspecies than the CoRiDO strain associated with the OQDS in Italy.
California olive growers and industry stakeholders are encouraged to contact UCCE Farm Advisors to report trees displaying symptoms of OQDS.
References
1. European Commission Press Release, April 28, 2015: http://europa.eu/rapid/press-release_IP-15-4887_en.htm
2. European and Mediterranean Plant Protection Organization. 2015. First reports of Xylella fastidiosa in EPPO region-Special Alert. http://www.eppo.int/QUARANTINE/special_topics/Xylella_fastidiosa/Xylella_fastidiosa.htm
3. French Ministry of Agriculture Food and Safety Press Release, April 29, 2015: http://translate.google.com/translate?hl=en&sl=fr&tl=en&u=http%3A%2F%2Fagriculture.gouv.fr%2Fstephane-le-foll-salue-la-mise-en-place-de-mesures-europeennes-de-prevention-contre-la-bacterie-xylella
