- Author: Chris M. Webb
Ventura County UCCE Farm Advisor, Ben Faber gives advice on how to identify and treat root rot in avocados.
How to identify root rot and treat it?
The canopy is thinning. The leaves are small and yellow. There is dieback in the canopy, with leafless tips on the branches. You dig around under the canopy in the wetted area of the sprinkler and you can’t find roots within 6 inches of the soil surface or if you do find them, they are black. There is little mulch under the tree. There are weeds growing under the tree. All these are signs of root rot disease. But it is also a sign of lack of water, because that is what is happening – there are no roots to take up water. At this point, gardeners may unfortunately water the tree more, which only makes conditions worse for a diseased tree; adding more water to a tree that can not easily take it up, creates asphyxiation conditions.
So what do you do if you have disease? First of all, make sure you are irrigating to the needs of the tree by checking soil moisture before irrigating and ensuring the tree is not receiving supplemental water from another area such as a lawn sprinkler. Add and maintain a good thick layer of woody mulch under the canopy. Adding gypsum (15-20 pounds per tree), evenly spread under the canopy, can also help. There are fungicides available from retail nurseries, but reviewing and modifying irrigation practices and maintaining a mulch layer are the two most important things you can do.
Read on for details on mulch and irrigation.
Mulch and avocados?
“I just raked up all the leaves under the avocado and it looks so nice,” you say. 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. Commercial 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 6 inches away from the trunk to avoid collar rot, which can be caused by keeping a moist mulch against the trunk.
How to irrigate avocados
Mature avocado trees may be large above ground, but they have very shallow roots mostly in the top 8 inches of soil. The tree therefore does not have access to a large volume of stored water. As opposed to a deep-rooted walnut, avocados require frequent, small amounts of water. A young tree in the summer might need multiple applications per week, but because the root system is small, each application may only be 5-20 gallons. An older tree with its wider rooting pattern may go a week to a month between irrigations depending on the weather and rainfall. Proper irrigation is the best way to keep the avocado from getting root rot. Both over and under irrigation can induce the conditions for root rot, although over irrigation is more common. And remember, it is not just the amount applied at an irrigation, but the timing that is important, as well. Because you are managing such a shallow root system, just poking your finger into the root system will tell you if there is adequate moisture there before you irrigate again.
- Author: Chris M. Webb
As with many things in life, chances for long-term success with citrus are increased with knowledge and planning. Even the size of the plant put in the ground has an impact on long-term growth and return on investment. Ventura County UCCE Farm Advisor, Ben Faber shares his knowledge with us.
What size plant should I buy?
The longer the plant has been in the container, the longer it takes for the plant to adjust to the soil after it has been planted. The smaller the plant, the more rapid the growth once it is put in the ground and survives -- a 5 gallon container- grown lemon will have outgrown the 15 gallon container in 3 years. This has been shown consistently with all manner of container grown plants……..and they are cheaper.
One vital consideration is the type of variety to plant. Please remember to use only rootstocks that are California-grown certified trees that are known to be free of disease. It is illegal to bring in citrus trees or cuttings into California from other states or countries because they may be infected with disease or insects.
There are many different rootstocks available to growers. Choose rootstock based on characteristics that are important to the growing site, such as greater nematode resistance, salt resistance, disease resistance, etc. The retail nursery typically sells whatever rootstock the wholesale nursery propagates. Wholesale nurseries do not all use the same rootstocks, but use those that they feel grow best for them. In some cases, a retail nursery may be able to special order a rootstock for a special situation. You can always ask.
There is one choice that the buyer can make, though – whether the rootstock is dwarfing or not. The ‘Flying Dragon’ rootstock creates small tree, under 6 feet and it is very slow growing. It especially lends itself to container culture.
For home growers, another important consideration is where to plant the trees. Irrigation needs are an important piece of this puzzle. Keep the following in mind while looking for a planting location:
Growing citrus in a lawn
Trees don’t belong in lawns. In California, we irrigate. Do you irrigate to the needs of the lawn or to the tree? Frequently, lawns are irrigated by timers, putting a short burst of water on. Trees like a deep watering. Shallow watering leads to an accumulation of salts in the tree’s root zone and salt burn results. If possible, keep a 6-foot turf-free area around the trunk. And best of all, irrigate the tree separately from the turf and ensure the lawn sprinklers do not wet the trunk, which can lead to crown rot in the tree.
Citrus can be grown in containers. Ben offers the following suggestions for the best results:
Container grown citrus
Citrus grows well in containers, especially if you choose varieties like ‘Meyer’ lemon which is a less aggressive tree or use ‘Flying Dragon’ dwarfing rootstock on one of the other citrus varieties. There is a long history of orangeries in Europe, where full sized trees were grown outside in containers in the warm weather and then moved into large greenhouses when it got cold. Half barrels and terra cotta pots can be used, but if a large container is used and you want to be able move it, put the container on some wheels first. Fill the container with a good quality potting mix and plant your tree. Containers dry out much faster the soil grown trees, so stay on top of the irrigation. When irrigating, make sure water comes out of the bottom of the pot to avoid salt accumulation in the root zone. Prune as necessary to keep the canopy in balance with the pot or pot up to the next size.
Additional information can be found on the Ventura County UCCE website.
- Author: Chris M. Webb
Ventura County UCCE Staff Research Associate Maren Mochizuki shares with us how monitoring spore traps in avocado orchards can lead to better understanding and management of disease.
An important component of integrated pest management is frequent monitoring to understand which, if any, pests are present and at what time of year. In collaboration with Akif Eskalen a researcher at UC Riverside, Ben Faber, Ventura County UCCE Farm Advisor and Maren Mochizuki, Ventura County UCCE Staff Research Associate are sampling in three avocado orchards in Ventura and Santa Barbara counties using traps that catch spores, reproductive structures for many disease-causing organisms in avocado such as Dothiorella and Phytophthora
The spore traps consist of glass microscope slides suspended at two heights in the avocado tree canopy. Every two weeks, we remove the slide and replace it with a fresh one; researchers at UC Riverside examine and identify the spores under a microscope. We hope to improve our understanding of the life cycles of these spore-producing organisms for more effective disease management.
Young avocado tree killed by Dothiorella canker,
White, powdery exudates from a Dothiorella canker
Healthy green avocado foliage (right) next to the pale, yellow foliage of a tree with Phytophthora root rot
- Author: Chris M. Webb
Below you will find a summary of what we did last month. By no means does this summary capture all that we accomplished or began, but it gives a nice glimpse of what we do.
1. Research Activities
This is a sampling of the research activity conducted in June.
- Established an experiment testing an herbicide for management of yellow nutsedge, a major weed in production agriculture costing Ventura County growers thousands of dollars annually to control. For more information on nutsedge and its impact, please read previous blog posts.
- Established an experiment testing an organic method of soil disinfestations by creating anaerobic conditions in strawberry beds and monitoring effects on plant pathogen Verticillium dahliae. This research makes direct contributions by addressing the issue of seeking alternatives to fumigants such as methyl bromide.
- Finished four field trials that evaluate management options for four pests detrimental to the strawberry industry. Management strategies included physical, thermal and chemical control measures.
- Initiated a project with CA Dept. of Food and Agriculture and local strawberry growers to introduce a biocontrol agent for Lygus bug, the #1 insect pest for strawberries and significant for other row crops.
- We are continuing research on minimizing irrigation needs for strawberries, which addresses both economic and environmental issues.
2. Educational Activities
This is a sampling of the educational activities conducted in June.
A. Grower/Clientele Education
- Jim Downer presented sessions at a regional meeting on nutrition of palms and diseases of shade trees. 100 in attendance.
- Ben Faber participated in a program at UC Riverside on Asian Citrus Psyllid (ACP), which poses a significant threat to the citrus industry. It was clear that fruit from affected areas coming into Ventura County packing houses could be a host for the psyllid. Ben spoke to Henry Gonzales about this and as a result the import of lemons from Imperial County (quarantine area) to Ventura for repacking has been restricted to reduce the likelihood of introducing the pest here. Both Faber and Rose Hayden-Smith participated in a meeting that brought packers together with the Ag Commissioner, where they hammered out a solution/agreement.
- Ben Faber delivered two grower workshops, one on avocado irrigation and the other on techniques to reduce surface water contamination.
- Rose Hayden-Smith presented her research on gardening and community development at a City of Minneapolis/IATP event attended by more than 100 people. She also presented a two-hour workshop on Victory Gardens, past and present, to a sold-out audience in Minneapolis. She offered a talk on gardening trends and public policy in Oxnard to an audience of 75. Earlier in the month, she facilitated an Urban Agriculture Symposium for 175 people in Chicago, which generated public policy recommendations for the USDA.
- Monique Myers presented the Ventura County RESTOR Project at the National Marine Educators conference in Monterey.
- Monique Myers organized a focus group for Ventura City/County Planners and city storm water experts addressing low impact development and emergency safety issues.
- 4-H staff trained staff at Pt. Mugu and Port Hueneme Naval Bases in the basics of 4-H program management. Also trained new 4-H club leaders.
B. Youth Education
- Monique Myers directed/facilitated the last of 8 RESTOR teacher/student field trips to Ormond Beach (~70 students per trip). RESTOR is a grant-funded wetlands/ecological restoration program linking teachers and youth with science education and community service opportunities.
- Monique Myers led a RESTOR Project field trip with 28 student essay contest winners and their teachers on the NOAA research vessel Shearwater.
- 4-H held a Science, Engineering and Technology Day at the military base.
- 4-H held events at both military bases kicking off the new 4-H programs there.
- UCCE staff. Launched a UCCE/Farm Advisor blog http://ucanr.org/blogs/venturacountyucce/
- UCCE staff. Produced a new UCCE/Farm Advisor educational brochure.
- Daugovish, Oleg and Maren Mochizuki submitted a paper to HortTechnology detailing the potential for carbon dioxide to be taken up by raspberry plants to boost productivity instead of being released to the atmosphere as a greenhouse gas. We hope this method will gain attention as one of the ways to tackle a global issue on a local scale.
- Downer, James and Maren Mochizuki.
- Two manuscripts accepted to HortTechnology.
- Pruning landscape palms
- Diseases of palms.
- Two manuscripts accepted to HortTechnology.
- Downer, James. Landscape Notes – Landscaping Trees. Available at http://ceventura.ucdavis.edu/newsletterfiles/Landscape_Notes17660.pdf
- Downer, James: Article on mulches in Western Arborist Magazine.
- Downer, James, Article on a new pest, the Date Bug, in Southwest Trees and Turf Magazine.
- Faber, Ben and Newman, Julie, et al. 2009. Re-evaluation of the roles of honeybees and wind on pollination in avocado. J. of Hort Science and Biotech (84)3:255-260.
- Faber, Ben and Newman, Julie, et al. 2009. Farm Water Quality Planning Project – From Education to Implementation. Statewide Conf., Sacramento April 27-30.
- Faber, Ben. 2009. Cherry Vinegar Fly in Ventura County. VC Farm Bureau Newsletter 41(7): 2-3.
- Hayden-Smith, Rose, et al. Proceedings of the Chicago Urban Agriculture Symposium. Includes policy recommendations for the USDA and other cities relating to urban agriculture. http://www.chicagobotanic.org/wed/index.php
- Myers, Monique, et al. Differences in benthic cover inside and outside marine protected areas on the Great Barrier Reef: influence of protection or disturbance history? was published on-line (in advance of printing) this week in Aquatic Conservation. (http://www3.interscience.wiley.com/journal/84503925/issue)
- Newman, Julie. Wrote an article for Greenhouse Management & Production, a national grower magazine
- Monique Myers and Sabrina Drill won an Award of Merit from the 2009 Ecology Awards for their Quagga Mussel manual.
- Author: Chris M. Webb
Ventura County University of California Cooperative Extension’s (UCCE) Ben Faber is one of 62 people evaluating proposals for the United States Dep artment of Agriculture’s (USDA) "Farmers Market Promotion Program" (FMPP). This exciting program is implemented through a competitive grants process through the USDA Agricultural Marketing Service.
Approximately $5 million is allocated for FMPP for Fiscal Years 2009 and 2010 and $10 million for Fiscal Years 2011 and 2012. The maximum amount awarded for any one proposal cannot exceed $100,000.
The grants, authorized by the FMPP, are targeted to help improve and expand domestic farmers markets, roadside stands, community-supported agriculture programs, agri-tourism activities, and other direct producer-to-consumer market opportunities. More specifically the program is designed to help farmers markets promote and improve their services through grower/consumer education, advertising and supply purchases.
Entities eligible to apply include agricultural cooperatives, producer networks, producer associations, local governments, nonprofit corporations, public benefit corporations, economic development corporations, regional farmers market authorities and Tribal governments.
Follow this link to find additional information about the program, including projects funded in earlier years at http://www.ams.usda.gov/AMSv1.0/fmpp.
Related information, including marketing resources, can be found at the University of California’s Small Farm Center at http://www.sfc.ucdavis.edu/default.asp.