Arpaia M.L.; Kahn T.L.; El Otmani M.; Coggins C.W.Jr; Demason D.A.; O'connell N.V.; Pehrson J.E.Jr, 1991: Pre harvest rind stain of valencia orange histochemical and developmental characterization. Scientia Horticulturae (amsterdam). 46(3-4): 261-274
Pre-harvest rindstain of California [USA] cultivar 'Valencia' orange Citrus sinensis has economic significance since fresh fruit marketability is reduced. Quantification of the incidence of rindstain as related to tree quadrant has allowed us to designate quadrants where rindstain was most likely to occur (upper outside SW) or least likely (lower inside NE) to occur. Growth and development characteristics of fruit from the two quadrants were measured throughout fruit development. Significant differences in percent weight loss between fruit from the SW and NE quadrants occurred at color break and at commercial maturity. Structural and histochemical changes in flavedo tissue of fruit from SW or NE tree quadrants were monitored over the course of fruit development and maturation. First evidence of periderm formation occurred in October, coincident with observed changes in histochemical staining for lipids. These differences were increasingly evident as the fruit approached horticultural maturity and visual symptoms of rindstain developed. The development of a pronounced periderm in affected fruit suggests that rindstain is due to a physical trauma, although we do not believe it is caused by wind.
This from Mary Lu Arpaia in response from a Central Valley problem that cropped up recently. Fruit looked on the tree, but after getting it into the packing house, it started showing these symptoms
Here is her summation of the abstract above:
1) Fruit were predisposed to this problem as early as colorbreak. We found this out by doing some elaborate fruit manipulations in the field in the fall and looking at symptoms in the spring.
2) Symptoms really started to appear about this time of year and then progressively worse
3) There was a loose correlation to presence of citrus thrips in the previous year
4) Fruit isolations did not find much of anything but weak saprophytic fungi.
5) At this point, it's not clear what a grower can do to prevent it.
Rindstain on Ruby Red Grapefruit in the Hemet area was noted in the 1990's and the observation there was possible moisture from dew or rain focusing sunlight to cause the condition. So it's not really from even a general observation./h2>
- Author: Oleg Daugovish
When Richard Smith tells you that he is impressed with efficacy of an organic herbicide you better take notice. Richard shared his results on this blog site last year and showed good weed control with 'Suppress' from Westbridge. This OMRI approved herbicide is a mix of caprylic and capric acids and is a contact material that interferes with plant cells membranes causing leakage and desiccation.
It looked like a good fit for organic plasticulture systems such as strawberry that have wet weedy furrows which are difficult to access with mechanical tools because of proximity to plastic. We placed a trial in a very weedy field that also had one of the SoCal classics–yellow nutsedge. 'Suppress' at 6 and 9% by volume was applied to well-established weeds just before strawberry planting.
The effects of application were noticeable in minutes. We learned that:
Both 6 and 9% rates provided nearly 100% control of common lambsquarter (predominant species) and other occasional broadleaved weeds.
About 10-15% of common purslane plants survived and yellow nutsedge seemed unaffected by application. However, biomass of both purslane and nutsedge were significantly reduced, suggesting that production of seed and tubers for the two weed species, respectively, may be delayed.
Good coverage was important and some of the horizontally–inclined leaves of broadleaf weeds likely intercepted the herbicide deposition to vertically inclined nutsedge shoots.
When we simulated drift by over-spraying strawberry, it responded just like any broadleaf perennial plant—the canopy wilted and dried but in 3 weeks the new leaves developed from the crown. This was also true for the neighboring bindweed that lost above ground canopy but had new growth within a month after 'Suppress' application.
Since perennial weeds or those in soil seedbank are not controlled, repeated applications are needed with obvious caution of avoiding the spray drift to the crop.
Recently some 'W. Murcott' mandarins were shown to me. Brown spots in the core of the fruit. Another problem caused by drought and lack of leaching rains. Endoxerosis, also called internal decline, yellow tip, dry and blossom end decline is often confused with Alternaria rot which frequently accompanies or follows it. Internal tissues back of the stylar end break down, dry and become pinkish or brownish in color. Gum commonly forms in the core and either in or nest to the rind. Green fruits lose luster and frequently but not always develop a yellow color in circular areas surround the stylar end. The cut fru9i shows the gummy pinkish to brownish mass of partially dried and collapsed tissue. Gumming may even extend into the twig bearing the affected fruit. When the fruit turns color, the malady is more difficult to detect without cutting.
The cause is believed to be related to water and the physiological conditions within the tree and fruit and temperature conditions in the air and soil influencing transpiration and water stress. It is suggested therefore that water condones in the soil be kept as favorable for tree heath as possible and pick on time so that they are not over mature.
From: The Citrus Industry, Volume IV, Editor: Walter Reuther, UC Press
In other words, make sure to leach the root zone of accumulated salts from previous irrigations and pray for rain.
Craig Kallsen in Kern County says he often sees this in young mandarins especially on the south and west sides of the canopy, to the point that growers will not even bother to harvest this fruit until the trees are older. The fruit just transpires so much water when it's not shaded that the fruit just dries out.
If my Latin serves me right: endo - inside, xeric - dry. Dry Inside.
- Author: CA Dept Food
Two additional trees in San Gabriel have tested positive for Huanglongbing. The two trees, an orange and a kumquat, are on separate properties but are both within the core area in San Gabriel where 10 diseased trees were confirmed last summer. Given the close proximity, there will not be a quarantine expansion.
One of the HLB-positive trees has already been removed and California Department of Food and Agriculture officials are in the process of contacting the other homeowner to schedule tree removal. Agriculture officials are working quickly in the area.
Citrus trees in San Gabriel had already been treated for the Asian citrus psyllid within the last few weeks as part of CDFA's routine HLB response. Asian citrus psyllid populations are closely monitored in areas where HLB has been detected and treatments occur if there is a noted increase in population size. Since trees have been recently protected, no additional treatments will take place at this time. Instead, CDFA will focus on sampling extensively in the area. Much of the area has already been sampled and CDFA's lab has identified all samples from San Gabriel as high priority.
The Citrus Pest & Disease Prevention Program is working with the Los Angeles County Agricultural Commissioner's office and CDFA to develop a multi-lingual informational flier to notify residents of the significance of these finds and potential implications to other citrus trees in the area. CDFA staff will distribute this information as they go door-to-door sampling and surveying.
More information will be shared as it is available. In the meantime, the citrus industry is encouraged to keep a critical eye on all plant material moving into or out of your groves. Remove all leaves and stems, shake out picking bags, inspect harvesting equipment and educate fieldworkers. Additionally, get on board with area-wide treatments. Collectively, as a team, we can all save our citrus trees.
Residents in the area who think they may have seen ACP or symptoms of HLB on their trees are urged to call CDFA's Pest Hotline at 1-800-491-1899 or your local agricultural commissioner's office.
These official UC-approved guidelines for pest monitoring techniques, pesticide use, and nonpesticide alternatives for agricultural crops are essential tools for anyone making pest management decisions in the field. This 124-page guideline covers citrus fruit.
A hard copy version of these guidelines can be purchased as Publication 3441P.
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