- Author: Ben Faber
There have been some complaints about satsuma mandarin fruit having problems. These are prone to a rind/skin/peel breakdown when the fruit is not picked promptly. It's not clear what the cause is - wet winter, warm winter - but it is less of a problem if the fruit is picked when it is mature. A lot of the time in southern California, satsumas will develop good flavor and sweetness, but for lack of cool weather, they don't turn bright orange, a hallmark of the fruit. So growers will leave the fruit on longer, hoping for color, but the fruit becomes over mature, and more susceptible to breakdown. This weakening of the peel then opens it up to infection by fungi, such as Alternaria. In warm winters, the peel matures more rapidly and is more susceptible. Early maturing varieties like ‘Okitsuwase' are especially prone to breakdown later in the season, since their rind matures earlier. They end up being a mess, as can be seen in the photo below.
Navels can have a similar problem in these winters with erratic rainfall. Common wisdom is you don't irrigate in the winter, right? Wrong. With no, low and widely spaced rain events, the tree roots dry out, and rewet with rain. Navels are building their sugar in the winter and they become suction balls for water as the sugar increases. The fruit will continue to grow as the tree takes up water. When the roots run out of water, and then are suddenly rewetted during this period, the fruit can suck up water so rapidly that the skin cant expand fast enough and will split. So this is what happens with uneven irrigation or rainfall this time of year. One of those abiotic problems in citrus.
- Author: Ben Faber
Something hit the citrus trees of Riverside in late December 2017. Some vandal spraying herbicide? It was too widespread. It was all over town, orchards and backyards. It was on the north and east sides of trees. It didn't happen in Ventura or Santa Barbara. It probably happened to a lot of other plant species, but our correspondent had eyes only for citrus.
It sure looks like it could have been a cold, freezing wind, but on closer consultation with our Citrus Specialist, Peggy Mauk who also directs the Agricultural Operations at UC Riverside – it was the demon wind. The Satan Wind. The Santa Ana that dried out the trees that had not gotten sufficient water to cool themselves and had dried out on the windward side of the tree and orchard. Burned, in effect. This is the side of the orchard that dries out the most. It's what's called the “clothes line” effect. The margins that dry first because of the greater exposure to wind, sun and usually lower humidity. In this case, way lower. And by the time the damage was noticed a week later, the winds had been forgotten. Expect more water stress in our future.
- Author: Ben Faber
In the citrus world there is a relative tolerance to the bacteria that causes Huanglongbing, or Citrus Greening. Grapefruit and some orange varieties are very sensitive and some mandarin varieties are much more tolerant, meaning they live longer in the presence of the bacteria. Work is being done to use mandarin juice as a substitute for the traditional glass of orange juice. A recent bulletin out from the University of Florida has this news. This does not mean that Asian Citrus Psyllid and Huanglongbing are any less of a threat to citrus at this point. Just a way of prolonging an industry until true solutions can be found.
GAINESVILLE, Fla. — Some people like to wake up and drink a glass of fresh Florida orange juice. With the greening disease ravaging Florida's citrus industry, University of Florida Institute of Food and Agricultural Sciences researchers want to make orange juice from disease-tolerant fruit.
Huanglongbing (HLB), or citrus greening as it's commonly called, has destroyed 80 percent of citrus in Florida, a state where citrus is an $8.6 billion-a-year industry, according to UF/IFAS research. About 90 percent of the state's oranges are used to make orange juice, UF/IFAS researchers say.
So it's critical that scientists find sources for orange juice upon which consumers can rely. UF/IFAS researchers have found some mandarins that are tolerant to citrus greening.
In a newly published study, UF/IFAS researchers also found that consumers sense little, if any difference in the smell and taste of certain specific mandarins, compared to oranges.
“We found out what makes orange taste like orange and mandarin taste like mandarin, even though they are very close species,” said Yu Wang, a UF/IFAS assistant professor of food science and human nutrition and lead author of the study.
“If we use greening-tolerant mandarin for orange-juice making, the first thing we need to know is the difference between them,” Wang said. “This will provide more possibilities and flexibilities for the citrus industry in particular in the HLB era.”
In the past, researchers used traditional methods such as gas chromatography-mass spectrometry to study the flavor differences in orange and mandarin, Wang said. But people's senses of taste and smell are much more sensitive than analytical equipment, so scientists integrated sniffing into the study, she said.
It's important to remember that oranges are descendants of mandarin and pummelos, said Fred Gmitter, a UF/IFAS horticultural sciences professor and co-author of the study. So there's already a lot of mandarin's genetic makeup in an orange.
The problem is that oranges are very sensitive to citrus greening, Gmitter said.
“While we find other selections in the breeding program, mostly mandarin, hold of up a lot better against greening, we are finding some of these selections produce fruit that more closely resemble orange in appearance,” Gmitter said. “But more importantly, here, that they also very closely resemble orange in flavor.”
The study is published in the Journal of Agricultural and Food Chemistry:
https://pubs.acs.org/doi/abs/10.1021/acs.jafc.7b04968?src=recsys
Brad Buck
UF|IFAS
- Author: Ben Faber
HLB confirmations The number of trees in Southern California confirmed to be infected with HLB has risen to 347, distributed across 16 communities in four counties. So far, all are in residential plantings, not in commercial groves. As HLB detections increase and spread closer to commercial citrus, it is a good time to consider removing citrus trees that are uncared for or not worth the resources required to protect them from ACP and HLB. The distribution of HLB confirmations, updated weekly, can be found on https://citrusinsider.org/maps/. Winter ACP area-wide cycle As a reminder, due to the Thomas Fire the treatment window for psyllid management areas in West Ventura and the Ojai Valley (PMAs 44-50) was delayed until Feb. 23-March 16. If you wish to confirm your treatment window or interim treatment percentages, or obtain referrals for pest-control or tree-removal services, please contact your grower liaisons, Sandra Zwaal and Cressida Silvers. Low- or no-cost tree removal assistance can also be obtained through California Citrus Mutual's Citrus Matters ACT NOW program. More information can be found at https://citrusmatters.cropscience.bayer.us/commercial-grower/act-program. HLB in the news ABC7 news and The San Bernardino Sun recently picked up a story regarding a San Bernardino County nursery caught up in the HLB quarantine, which led to destruction of its inventory of citrus trees. ABC News7 article with clip: http://abc7.com/food/ie-nurserys-citrus-trees-to-be-destroyed-by-ca-agriculture-department/2959173/ The Sun article: https://www.sbsun.com/2018/01/19/more-than-4000-citrus-trees-destroyed-while-disagreement-between-bloomington-nurseries-state-continues/ Meetings UC Riverside & Citrus Research Board Citrus Day for the Industry will be on Tuesday, Feb. 6, at UC Riverside. The deadline to register is Jan. 30. Registration is $35 and includes lunch. Online registration is available at https://form.jotform.com/80016278039152. Click here to download the program. The Citrus Pest and Disease Prevention Committee's operations and outreach subcommittees will meet Wednesday, Feb. 7, at the Mission Inn Hotel in Riverside. Attendance is free. The CDFA website with agenda, venue, and webinar information is at https://www.cdfa.ca.gov/citruscommittee/. If you have any questions, please contact one of the grower liaisons: Cressida Silvers (805) 284-3310 Sandra Zwaal (949) 636-7089 |
- Author: Ben Faber
No rain for several years may have let citrus growers think that brown rot control is not important. But it still is and it's just coming out after a few inches of rain earlier this January. This is not the brown rot of stone fruits caused by Monilina fungus but a pathogen, completely different – Phytophthora spp.
Symptoms appear primarily on mature or nearly mature fruit. Initially, the firm, leathery lesions sometimes have a water-soaked appearance. Lesions are tan to olive brown, have a pungent odor, and may turn soft from secondary infections. Infected fruit eventually drop. Occasionally, twigs, leaves, and blossoms are infected, turning brown and dying.
Brown rot is caused by multiple species of Phytophthora when conditions are cool and wet. Brown rot develops mainly on fruit growing near the ground when Phytophthora spores from the soil are splashed onto the tree skirts during rainstorms; infections develop under continued wet conditions. Fruit in the early stage of the disease may go unnoticed at harvest and infect other fruit during storage.
Brown rot management primarily relies on prevention. Pruning tree skirts 24 or more inches above the ground can significantly reduce brown rot.
One spray of copper fungicide between October and December before or just after the first rain may provide protection throughout the wet season. When rainfall is excessive, you may have to repeat the spray in January or February. Spray the skirts to about 4 feet above ground. Spraying the ground underneath the trees also reduces brown rot infections. In addition to copper, other products effective against brown rot include the phosphonate and phenylamide fungicides. Phosphonates are applied as foliar and fruit or soil treatments, whereas phenylamides are applied as soil treatments for brown rot control. For soil applications, microsprinkler irrigation applications may be used.
Recently, oxathiapiprolin (Orondis®) was registered for use on citrus in California. Orondis® is an outstanding alternative for Phytophthora control that may be applied as chemigation or foliar application. However, foliar applications are preferred for preventing brown rot.
Postharvest Packinghouse Treatments to Prevent Fruit Decay
Potassium phosphite fungicides may be applied in aqueous dilutions to fruit alone or in combination with other postharvest fungicide treatments to manage nonvisible infections that occurred before harvest or protect fruit from brown rot infection after harvest during storage, distribution, and marketing. Use high-volume flooder or dip treatments for maximum coverage of fruit. Heated (125–136°F) fungicide solutions optimize performance of the potassium phosphite treatment.
More citrus brown rot information is at:
http://ipm.ucanr.edu/PMG/r107100711.html
Packers should check the Global MRL Database for all country MRLs at https://globalmrl.com/db#pesticides/query.
Photos of brown rot on different citrus varieties - lemon, mandarin, orange