- Author: Ben Faber
In 1911, the avocado was a relatively new crop in Southern California and the great USDA plant explorer Wilson Popenoe (pronounced POP e Noe according to Jack Shepherd), describes avocado culture and its problems
https://www.biodiversitylibrary.org/item/137628#page/31/mode/thumb
This is from the first volume ever of the Pomona Journal of Economic Botany which also has a nice description of "wither tip" of citrus in Santa Paula.
https://www.biodiversitylibrary.org/item/137628#page/5/mode/1up
- Author: Travis Bean
Although the main objective of herbicide use in avocado orchards (and all crops) is to manage weed populations, sometimes unintentional injury of the crop itself can occur when herbicides are incorrectly applied. Herbicide injury in avocado can reduce yield, decrease fruit, reduce plant vigor, increase susceptibility to diseases and pests, and sometimes result in plant death. Common situations resulting in injury include spray drift, tank contamination, application of the wrong herbicide or rates, and herbicide carryover from a previous crop. The extent of herbicide damage on avocado can vary widely according to factors such as herbicide mechanism of action (MOA) and application rate, route of exposure, plant size and growth stage, soil properties, and weather.
Herbicide injury can be difficult to diagnose properly and is often confused with disease, insect damage, nutrient deficiencies, and other environmental stresses. It is recommended that trained researchers or Pest Control Advisers, who may utilize plant tissue, make diagnoses or soil samples along with plant symptoms, injury progression, and other plant species affected, orchard herbicide use history, weather conditions, and other factors to confirm or rule out injury from herbicides or other causes.
Where the injury occurs can also be an indication of herbicide injury. For example, if injury is on just one side of a tree or trees near another field, it may be an indication of spray drift. If it occurs only along the edge of the skirts, it may be a hint that an uneven ground spray was applied.
The majority of herbicides for use in avocado orchards in California fall into eight MOAs as defined by the Weed Science Society of America. MOAs describe the specific biological processes that are disrupted by a group of herbicides. These processes control the growth and development of plants and when interfered with, can result in plant injury or death.
Table 1: Common herbicides used in avocado, their mechanism of action, and possible injury symptoms
WSSA Group |
Mechanism of Action |
MOA description1 |
Example herbicides |
Possible injury symptoms1 |
1 |
Acetyl CoA Carboxylase (ACCase) Inhibitors |
Inhibits lipid creation in grasses, preventing production of plant cell membranes |
Fluazifop-P-Butyl (Fusilade DX), Sethoxydim (Poast) |
Chlorosis, necrotic spots, leaf crinkling, leaf distortion |
3 |
Mitosis Inhibitors |
Inhibits cell division in germinating seedlings and lateral roots |
Oryzalin (Surflan) |
Thickened, shortened lower stems and small, crinkled leaves |
5 |
Photosystem II Inhibitors |
Prevents the transfer of energy generated during photosynthesis, causing a buildup of reactive molecules that damage chlorophyll and cell membranes |
Simazine (Princep 4L) |
Chlorosis, necrosis progressing from leaf margins toward the center of the leaves, foliar applications will appear as leaf burn |
9 |
Enolpyruvyl Shikimate-3-Phosphate (EPSP) Synthase Inhibitors |
Inhibits the production of three aromatic amino acids and the enzymes and proteins built from them |
Glyphosate (Roundup) |
Leaves of trees and vines become chlorotic 3 to 7 days after exposure, and margins of new leaves become necrotic |
12 |
Carotenoid Biosynthesis Inhibitors |
Inhibits production of carotenoid pigments, which harvest light and protect chlorophyll from reactive molecules |
Norflurazon (Solicam DF) |
Plant foliage turns white and appears bleached
|
14 |
Protoporphyrinogen Oxidase (PPO) Inhibitors |
Blocks the production of chlorophyll and causes a buildup of reactive molecules that damage existing chlorophyll, carotenoids, and cell membranes |
Oxyfluorfen (Goal 2XL), Carfentrazone (Shark EW), Flumioxazin (Chateau) |
Drift injury will appear as speckling on leaf tissue. The necrotic spots are sometimes surrounded by a reddish colored ring. Injury from soil applications or residues appears as a mottled chlorosis and necrosis. |
21 |
Cellulose Inhibitors |
Inhibit cell wall synthesis and plant growth |
Isoxaben (Gallery 75 DF) |
Chlorosis, necrosis, leaf crinkling, leaf distortion, purpling of the leaf, and stunting |
22 |
Photosystem I Inhibitors |
Disrupts photosynthesis, forming reactive molecules that destroy cell membranes |
Paraquat (Gramoxone SL) |
Drift injury will appear as speckling or necrotic spots on leaf tissue |
1Not a complete list. Symptoms listed are likely for established orchards. For detailed descriptions of MOAs and injury symptoms, as well as a searchable database of specific injury images (e.g., “chlorosis, necrosis, stem swelling, etc.” visit http://herbicidesymptoms.ipm.ucanr.edu.
References:
Al-Khatib, K. 2015. University of California Integrated Pest Management Herbicide Symptoms. http://herbicidesymptoms.ipm.ucanr.edu (accessed 09/05/18)
Faber, B.A., C.A. Wilen, B.D. Hanson. 2016. Weeds. Pages 107-124 in University of California Integrated Pest Management Guidelines for Avocado. http://ipm.ucanr.edu/PMG/selectnewpest.avocado.html (accessed 09/05/2018)
Sosnoskie, L.M., B.D. Hanson. 2013. Understanding herbicide mechanisms (modes) of action and how they apply to resistance management in orchards and vineyards. UC Weed Science Blog Post. http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=9383 (accessed 09/05/2018)
Weed Science Society of America. Summary of Herbicide Mechanism of Action
According to the Weed Science Society of America. https://wssa.net/wp-content/uploads/WSSA-Mechanism-of-Action.pdf (accessed 09/05/2018)
Photo: Sometimes weeds are tasty, like amaranth and purslane
- Author: Jim Downing , UC Agriculture and Natural Resources Lucien Crowder, UC Agriculture and Natural Resou
California avocados often are exposed to high temperatures after harvest, either in the field or during preconditioning (ethylene treatment), especially in summer. It's been known that long periods of high temperatures can delay ripening time and reduce fruit quality, but a new study indicates pronounced effects after only short periods of high temperature following harvest. Authors of the study concluded that it's important to maintain avocados at temperatures below 25°C following harvest and that the ideal temperature to ripen the fruit is 20°C. The authors also found that ripening below 20°C resulted in significantly longer ripening times and resulted in poorer coloration of the ripened fruit.
Mary Lu Arpaia, UC Cooperative Extension specialist, Jim Sievert and Sue Collin, staff research associates (retired) in the Department of Botany and Plant Sciences at UC Riverside, working with David Obenland, research physiologist with the USDA Agricultural Research Service, Parlier, studied for two seasons holding avocados from multiple harvest times for the first 24 or 48 hours of the ripening period at high temperatures (20°C to 35°C), with and without ethylene. In the third season, they made a detailed assessment of ripening temperatures (15°C to 25°C) on ripening time and fruit quality.
Results from the first two seasons showed that even a 24-hour exposure to temperatures of 25°C and above inhibits ripening and increases postharvest disorders such as stem end rot and body rot. In season 1, the incidence of stem end rot increased from 9.7% at 20°C to 32.3% at 35°C, and body rot increased from 3.9% to 20.2% for the same treatment comparison. Ethylene applied during the exposure period was ineffective in preventing the disorders.
In the third-season trial, temperature was also shown to be critical. Fruit ripened below 20°C took slightly longer to ripen. Additionally, the authors found that the ripened fruit at either 15°C or 18°C remained more green then fruit ripened at the higher temperatures. Avocados ripened above 20°C were more likely to develop pink discoloration in the mesocarp. Ripening temperature had no effect on overall likeability, or ratings of grassy or rich flavor.
- Author: Ben Faber
Got trees/brush to remove?
The CREW is ready to work:
With a decline in federal funding to work on Forest Service lands and elsewhere our local non-profit, The CREW is looking for work. They are great at getting all kinds of brush cleared, trees removed and as a non-profit their rates are reasonable. In hiring The CREW you are helping train a new generation of folks to use saws and work in the field.
If you have need for dead trees/limbs to be removed, one local resource is The C.R.E.W. - Concerned Resource & Environmental Workers. Since 1991 this Ojai-based nonprofit has provided paid employment to young people in conservation and forestry work. With a workforce trained in chainsaw use for fire abatement, The C.R.E.W. is available at a reasonable fee to take down trees and limbs in orchards. They also have a chipper.
The C.R.E.W. works throughout Ventura and Southern Santa Barbara counties. In fact, The C.R.E.W. was hired in 2016 by California Citrus Mutual to take out neglected orange trees on private property to limit growers' exposure to ACP/HLB.
If you're interested in learning more, contact Todd Homer at thomer@thecrew.org or call 805-649-8847.
CREW Equipment Ready
The CREW does great fire clearance.
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- Author: Ben Faber
One avocado tree, wholesale, recently sold for $92 in South Africa with 250 trees in a bunch costing about $23,000. They are ‘Maluma', of course, which means it is a new variety that has similar properties to the traditional ‘Hass', and might have some unusual properties like higher productivity, upright growth lending itself to higher planting density and fruit production inside the canopy protecting it from wind and sunburn (Fresh Fruit Portal, 2017).
At a traditional California tree spacing of 273 trees/ha, that would be $25,116 / ha. At some of the new high density spacings of 1 m x 1m, that is nearly a million dollars per hectare alone in trees, let alone the cost of the land and infrastructure. And that is just one hectare, not the multiples of hectares that growers are planting. There are growers investing in five, ten, twenty and more hectares per planting. Big investment.
One million dollars in trees. Nurseries are happy to hear this. If a grower in California or South Africa or Australia wants to plant a new orchard, they are told to get in line. And then, they need to wait for one or two years until the nursery can ramp up supply. I have gotten calls from China, Philippines, and Italy of all places for trees. Everyone wants to plant trees now, and this has been after a steady increase in world-wide planting that has gone on for the last 20 years. World-wide consumption has seen a steady increase over this time. World-wide, global marketing has assured a steady supply to local markets, regional markets and now all those consumers in far off places like North Dakota in the US, or other countries, such as Beijing and Moscow. French and German consumers have always been reliable importers of the fruit over the years. But now even traditional Italian foodies are eating the fruit.
What is driving this activity? Well, consumers, of course. They have caught the ‘avocado toast' bug. And the health benefits bug. It's all online and a lot of the claims are backed up by science (Scott et al, 2017). According to IndexBox (2017), a data compiling news service, the avocado market expanded at +5.6% per year from 2007 to 2016. Over the last six years, the market displayed a consistent growth; it accelerated sharply from Price of the fruit showed growth. Wholesale prices in 2016 totaled $13,797M, a growth by 23% over the previous year.
Read more at:
http://ceventura.ucanr.edu/news/Topics_in_Subtropics/