- Author: Ben Faber
So if you have lemons, read this. And if we have rain, really read this. I think because we prune lemons so much, this is more of a lemon problem, because I've never heard of other citrus getting it. It is a wood decay fungus on a lot of other tree species, though. Does anyone know what "sambuci" translates as?
Chlorotic, undersized, sparse leaves and branch dieback are common symptoms of wood decay fungi infecting roots, the basal trunk (root crown), or limbs. These fungi include Armillaria mellea, Hyphoderma sambuci, Ganoderma spp., and Oxyporus spp. These fungi are called white rots because they often cause decayed wood to become soft and white or yellow. Brown rots, such as those caused by Antrodia sinuosa and Coniophora spp., primarily decay cellulose and hemicellulose. They leave behind the brownish wood lignin, which is usually dry and crumbly.
Wood decay fungi produce fruiting bodies on the bark, root crown, or stumps or growing from soil near trunks. Fruiting bodies may be obvious toadstool- or umbrella-shaped mushrooms like those of Armillaria spp. or large and shelflike as with Ganoderma spp. Oxyporus spp. produce bracket-shaped, seashell-shaped, or thin and pale fruit bodies. Some decay fungi, such as Antrodia and Hyphoderma spp., form relatively inconspicuous crusts on infected bark. Fruiting bodies produce numerous tiny spores that spread in wind or splashing water.
Decay fungi initiate infections when their spores contact injured tissue on living trees, such as wounds from pruning, vertebrate chewing, or infection sites of Phytophthora or other pathogens. Decay fungi can colonize stumps and infect through root grafts to adjacent trees. Spores landing on dead limbs initiate infections that spread to the attached living wood. Most decay fungi are saprophytes that can only grow on severely stressed or injured hosts, or they must first produce substantial inoculum on dead wood.
Avoid wood decay by providing trees with good growing conditions and optimal cultural care to promote vigorous tree growth. Protect bark from injury. Avoid making large wounds (such as pruning cuts), especially during the rainy or foggy season. When a tree is cut down or disease is spreading from an infected tree (such as by root contact), remove the entire tree—including the stump and major roots.
If it rains or we finally have some Valley/Tule Fog or if we have a winter with heavy dew and you have lemons, read further about Hyphoderma sambuci.
Hyphoderma gummosis is reported in the field only on lemon. It occurs in the San Joaquin Valley and coastal growing areas. This wood decay fungus causes branch wilting and dieback that ultimately results in tree death. It cannot infect its host through intact bark. To initiate infections, it requires injuries such as pruning wounds. Spores colonize exposed wood and during moist conditions produce new infections. A crust of pink to white fungal growth of Hyphoderma sambuci appears around infected wounds after wet weather.
Provide good cultural care that encourages vigorous tree growth. Prevent irrigation water from directly wetting bark. Avoid wounding bark. When pruning trees, wait at least one month after the end of the rainy season before making cuts, because Hyphoderma basidiospores require moist conditions to survive and cause infections. Prune out all infected wood during dry conditions and remove it from the orchard.
Plant Shield is a product of an antagnonistic fungus - Trichoderma harzianum- that can be painted on wounds to prevent this gummosis. It's best to just avoid pruning in wet weather, though.
photo: Crusty pink fruiting bodies and wet area on lemon branch
- Author: Ben Faber
Hats Off.
The Orange County Master Gardeners have lived up to their name with their website information on citrus. It's a truly impressive information site for not only homeowners, but also growers:
http://mgorange.ucanr.edu/Edible_Plants/?uid=108&ds=530
The “Citrus Problem Diagnosis Chart” is especially work perusing:
- Author: Sonia Rios
Dr. Gary Bender, UC Cooperative Extension (UCCE) Farm Advisor Emeritus, is the lead instructor for a six-week course entitled “Avocado Production for New Growers.” Co-instructor, Sonia Rios, current subtropical Farm Advisor, Riverside/San Diego Counties will also be teaching in the course. The course is designed for new avocado growers, as well as those interested in learning more about avocado production best practices and meeting fellow growers.
The six-week course consists of six, two-hour sessions and will be held in Fallbrook, CA this year. The fee for the course is $105 and includes two avocado books, an IPM book and a post-harvest handbook. Final dates and the location will be announced soon. The always fills up, so please register A.S.A.P.
Topics include:
- Introduction to Agriculture in San Diego County, History of Avocado Production in California
- Botany, Flowering, Varieties, Harvest Dates, Rootstocks
- Irrigation Systems, Irrigation Scheduling, Salinity Management
- Fertilization, Organic Production
- Weed, Insect and Mite Control, Disease Control
- Ag Waiver Water School Training (Dr. Loretta Bates)
- Canopy Management, Tree Spacing, Frost Management
- Field trip to High Density Trial grove and a commercial grove
For more information, contact Erin Thompson at 858.822.7919 or enthompson@ucanr.edu.
- Author: Ben Faber
Here is a system of avocado pruning that seems to be working for the grower. He has been keeping his 12 year old ‘Hass' planted on 16 x 16 to 8 feet high by pruning out center limbs each year. He leaves some to flower and fruit the next year, then removes those with the fruit once they pass maturity in January. The cost of the pruning and chipping is about the value of the fruit that is harvested off those limbs. On older trees that were planted in the 1970's are treated in a similar manner. The trees were scaffolded to 5 feet and once tamed, have been allowed to grow in a similar fashion as the 12 year old trees. Both tree ages are productive throughout the canopy. In the spring, the trees are size picked from the ground with picking poles and as necessary with short ladders. In the summer they are stripped. The key is yearly pruning. I have been somewhat disenchanted with this style in the past because the centers would fill up so fast. In this case, the trees are kept short to keep light throughout the tree and the yearly pruning keeps opening it up.
Photos:
12 year old center pruned trees
Center prune
Fruit hanging in the interior
40 year old, scaffolded then center pruned trees
- Author: Ben Faber
Transpiration is essentially a function of the amount of leaves present. With no leaves, there is no transpiration and no water use. The extreme case is tree removal. If canopies are pruned there is reduced water use. The more canopy reduction, the more transpiration reduction. Most citrus produces terminal flowers, so there is also a reduction in yield, but there is also typically an increase in fruit size as competitive fruit growing points are removed. There is a balance between yield reduction and tree water use, but typically a 25% canopy reduction results in a 25% decrease in tree water use (Romero, 2006).
The severity of the drought will determine how drastic the canopy should be trimmed. The trees can be skeletonized so that only the main structural branches are left. The tree is whitewashed to prevent sunburn and the water is turned off. As the tree gradually leafs out, the water is gradually reapplied in small amounts. It's important to check soil moisture to make sure the tree do not get too much or too little water. The trees if pruned in the winter will often flower a year later in the spring, but normal production will often take three years for the trees to recover their previous yields.
Skeletonizing should first be practiced on orchards that are the poorest producing. In those areas that get too much wind and have lots of wind scarring or elevated water use, those areas that are most prone to frost damage, those areas that have been always problematic, such as fruit theft. In areas that are healthy and a new variety has been contemplated, this is the time to topwork and replace that old variety. In areas that have been poor producing from disease, this is the time to get rid of those trees.
Canopy sprays of kaolinite clay have shown some promise in reducing transpiration with negligible yield reduction (Skewes, 2013; Wright, 2000). If these are used, they should be done under the advisement of the packing house to make sure the clay can be removed in the packing house.
With a reduced canopy, there are often other benefits besides water reduction. There is better spray coverage for pest control. There is also reduced fertilizer use. New growth is normally coming from nutrients that are now being mined by a large root system and fertilizer applications can be significantly reduced or eliminated altogether for a year until fruit set recommences.
Citations
Kerns, D. and G. Wright. 2000. Protective and Yield Enhancement qualities of yield of kaolin on lemon. In: Eds. G. Wright and D. Kilby, AZ1178: "2000 Citrus and Deciduous Fruit and Nut Research Report," College of Agriculture and Life Sciences, University of Arizona. http://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1178_3.pdf
Skewes, M. 2013 Citrus Drought Survival and Recovery Trial. HAL Project Number CT08014 (16/12/2013). SARDI. http://pir.sa.gov.au/__data/assets/pdf_file/0004/238414/SARDI-Citrus-Drought-Survival-Recovery-Trial.pdf
Navel trees skelotinized and topworked, ready for rain and more profits in the future.