- Author: Ben Faber
The English often call a fruit seed other names, like pip. A large pit could be called a stone. Avocado usually has a seed, and if not it turns out to be a small fruit, called a "cuke". Well that's a different story. Sometimes little hard stones form in the flesh that are unrelated to germination. These stones are unpredictable and uncommon. A friend has said that if an avocado gives you a stone, turn it into a pearl. These stones are that rare. Art Schroeder from UCLA described them without much attribution to their cause, but gave them a good name - sclerocarpelosis. You can read his description in the 1981 California Avocado Society Yearbook which is available at Avocado Source:
http://www.avocadosource.com/CAS_Yearbooks/CAS_65_1981/CAS_1981_PG_125-132.pdf
Sclerocarpelosis in Avocado Fruit
C. A. Schroeder
Department of Biology, University of California, Los Angeles.
A rather unusual case of malformation in avocado fruit has been noted recently. The
aberrant tissue structure is not detectable from external examination of the fruit. Upon
cutting the mature or nearly mature fruit, the aberrant tissue becomes evident in the
form of a stony layer of various degrees of development located in the otherwise soft
fleshy pericarp wall. A tentative name of sclerocarpelosis is used to describe this
condition. The term sclero refers to hardness of the stone cells, or sclereids, which are
the basic structural elements involved. Carpel refers to the fruit wall, and osis implies a
disease or disturbance of the plant or plant tissue.
The fruit is sometimes affected to an extent that it becomes inedible. Still other fruits
may contain small clusters of stone cells which would not be detected even if eaten.
Extremely affected fruits can have a stony layer 1 to 5 mm in thickness completely
surrounding the seed. This structure is suggestive in many ways of a peach pit which
envelops the peach seed.
The affected fruits have been observed on several trees at various locations in a very
large (1300 acres) avocado planting in Orange County, California. The orchards
involved are situated on gently rolling hills. The major portion of the trees bearing
abnormal fruits are found in low elevations or "pockets" where the effects of local
radiation frosts were observed to severely affect the trees during the 1979-80 winter
season. Many of the trees exhibited responses to frost injury such as unusual resprouts
and development of main structural limbs at points near the soil, severe bark and
sunburn injury due to unusual exposure as the result of loss of leaf canopy by frost, and
a general weakened appearance of the entire tree in comparison with nearby unaffected
trees.
- Author: Ben Faber
Come Learn About Field Identification of Invasive Shot Hole Borers
We're holding two early December trainings on invasive polyphagous and Kuroshio shot hole borer biology, identification, surveillance, and management of infested trees and downed wood. We'll cover these topics in the classroom, then head outside to see infested trees and learn how to identify signs of shot hole borer damage, set up a monitoring program, and sample trees.
$30.00 Registration fee includes lunch, a ISHB Field Guide, and ISHB Demonstration Kit
Continuing Education Units from DPR have been requested, check back for updates.
Speakers include Sabrina Drill, UCCE Natural Resources Advisor; Bea Nobua-Behrmann, UCCE Research Scientist; Kim Corella, Forest Pest Specialist, CalFire; and Paul Rugman-Jones, Research Entomologist, UC Riverside.
Ventura County - Ojai - Dec.6
Meiners Oaks (Ojai) Class & Field Training at Saint Thomas Aquinas Church
Thursday December 6, 2018, 10am – 2:30pm
Los Angeles County - Gardena - Dec. 7th
Gardena Class & Field Training at Gardena Moneta Mason Lodge & Gardena Willows Wetland Preserve
Friday December 7, 2018, 10am – 3:00pm
- Author: Ben Faber
- Author: Mary Lu Arpaia
Of the many known varieties, they fall into three broad categories based on whether they are of the Mexican, Guatemalan or West Indian races of Persea americana, the avocado specie and the crosses that occur between these races. For example, ‘Hass' has the thick skin of the Guatemalan but turns black like a Mexican. Generally speaking, California varieties have been the result of crossing between the Mexican and Guatemalan races. West Indian race varieties are not common here because of their generally lower cold tolerance. There are lots of factors approaching the identification of an avocado and its origins, and here is a brief run down on those that need to be considered.
Grafted?
Is it a grafted tree, or is it a known variety with known characteristics which the tree can be compared to? Look for the change in bark texture at the base of the tree where the graft was made.
Leaf characteristics
When you crush the leaf, does it have an anise smell (Mexican) or not?
Is the leaf edger smooth (Hass) or wavy (Zutano)?
Is the color of the new leaves red and turn green (Mexican) or are green (Guatemalan)?
Canopy shape
Is it columnar (Bacon, Reed) or umbrella (Hass)?
Is the mature tree big (Hass) or under 20 feet in height (Holiday, Littlecado, Gwen)?
Fruit
Is the fruit round (Nabal), pear shaped (Fuerte), thin necked (Pinkerton) or broad shouldered (Lamb-Hass)
Is it thick skinned (Guatemalan) or thin skinned (Mexican)?
Is it green when ripe (Guatemalan) or black (Mexican)?
Is it big (more than 16 ounces; Daily 11 is 5 pounds) or small (Mexicola is 5 ounces)?
When is fruit maturity; winter, spring, summer or fall?
The combination of all these factors go into describing a variety and distinguishes it from other varieties. When varieties have mixed parentage, they will take on those characteristics of each parent, so often the lines of either Mexican or Guatemalan get blurred.
- 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