That's a good question.  Some question whether they flourish now.  Southern California does not have the landscapes of apples, pears and peaches of Oregon, Michigan, Pennsylvania or even Fresno, but there are nice little niches of persimmon, low chill apple, and even blueberries that thrive in the lower winter chilling environments along the coast and in the south of California.

Here is an example of what might happen to this fruit industry here. A recent, detailed study extrapolate the accumulation of cold periods in Spain over the next 30 years and to the end of the century. This provides growers with important information on the viability of future  fruit cultivation in the various Spanish regions, as it allows them to know if there will be the necessary accumulated cold for the fruits to grow correctly or if they should relocate their crops to other areas.

The results obtained show a general reduction in the accumulation of cold in any future period for all the chilling models and scenarios considered. The reduction is especially significant at the end of the century, under the most pessimistic scenario. These results invite us to strongly commit, not only to adapt but also to mitigate climate change, something that would make an important difference. The probable reduction of cold would threaten the viability of some varieties of fruit trees in the near future, especially in regions where there is currently a low accumulation of cold and there are varieties that require a lot of it.

The study can be viewed at:

https://www.nat-hazards-earth-syst-sci.net/19/1087/2019/

Climate change discussions for California can be found at these websites:

https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=30513

https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=28175

https://www.energy.ca.gov/sites/default/files/2019-07/Reg%20Report-%20SUM-CCCA4-2018-007%20LosAngeles.pdf

An intriguing Santa Barbara apple study grower's observations are worth noting: https://ucanr.edu/blogs/Topics/index.cfm?start=1&tagname=apples

By the way the 'Moor Park'  apricot is not from Moorpark, CA, but from England and the variety has never done very well in Moorpark (http://www.ngr.ucdavis.edu/treedetails.cfm?v=997).

Here's the Fall newsletter of Topics in Subtropics, and it is on time.  Winter hasn't started yet, but get ready.

And the topics are:

• Real-Time Sensor for Early Detection of Citrus Huanglongbing (HLB)
• The 2016 International Citrus Conference
• UC Riverside Scientists Evaluate Trunk Injections of Pesticides for The Management of Ambrosia Beetles in California Avocados
• An Overview of Mango
• Water Based Latex Paint as a Means to Track Ambrosia Beetle Activity on Infested Trees

http://ceventura.ucanr.edu/newsletters/Topics_in_Subtropics66242.pdf

To subscribe:

http://ceventura.ucanr.edu/Com_Ag/Subtropical/

The drought has caused numerous conditions – physiological and pathological – that I have only seen in text books (see our newsletter article: http://ceventura.ucanr.edu/newsletters/Topics_in_Subtropics63007.pdf). But other phenomena are also occurring. Recently I saw a field of blackberries in full bloom and the other day a grower called in about a plum tree that was also in full bloom. What is going on? This is supposed to happen late winter/early spring. It turns out that often drought stress can supplant winter chill in some plant species. In this case, these two species are relatively low chill, meaning they don't require a lot of cold to break winter bud dormancy. The drought stress causes the buds to break dormancy.

This is similar to the “Verdelli” effect in lemons. This is a technique used to shift the period of optimum fruit production to a more profitable period, usually the summer when more lemons are used. In the case of plum and blackberry and other low chill deciduous tree crops, this would be pushing production into the coldest period of the year. It might work along the coast, but in the Central Valley it would probably just mean frozen fruit. But it's a possible method that we might play with.

Photo: October, 2016

The roof rat (Rattus rattus), sometimes called the black rat, is a common vertebrate pest in citrus, avocado and other yummy tree orchards. It builds leaf and twig nests in fruit trees or nearby trees, or it can nest in debris piles or thick mulch on the ground. This agile, sleek rat has a pointed muzzle, and a tail that is longer than the body and head combined.

Be sure to identify the species of rat present to avoid killing nontarget or protected species. Be aware that endangered native kangaroo rats (Dipodomys spp.) and the riparian woodrat (Neotoma fuscipes riparia) resemble pest rats, but are protected by law. Unlike the hairless, scale-covered tail of roof rats, the tails of kangaroo rats and the riparian woodrat are covered with fur. The riparian woodrat is active mostly during the day, and its tail is somewhat shorter than the combined length of its body and head. A kangaroo rat's tail is noticeably longer than its body and head combined. Kangaroo rats are nocturnal, but unlike Norway rats and roof rats, which move on all four legs, kangaroo rats hold their front legs off the ground and travel by hopping on their hind legs.

Rats gnaw on electrical wires, wooden structures, and fruit on trees. After harvest, they damage fruit in bins, chewing on the bins and leaving excrement. Rats are active throughout the year, and mostly at night.

To help manage rats, reduce shelter and nesting sites of rats. Eliminate debris and wood piles. Store materials neatly and off the ground. Thin and separate non-crop vegetation around orchards where feasible. Exclude rats from nearby structures by properly sealing entry ways.

Baits and rat-sized snap traps placed in trees are the most effective control measures. Rats are wary, tending to avoid baits and traps for at least a few days after their initial placement. Fasten traps to limbs and bait them with sweet fruit or nut meats, but do not set the traps until after bait is readily eaten. Secure anticoagulant wax blocks in a bait station before placing in trees on limbs 6 feet or more above the ground. Placing the wax blocks in a bait station will prevent chunks of the anticoagulant wax from dropping to the ground and creating a hazard.

Be aware that certain types of single-dose rat baits for use inside buildings are not labeled for use outdoors in orchards; these are hazardous to wildlife and should not be used.

For more on the subject see:

http://icwdm.org/handbook/allPDF/RO_B125.PDF

http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74106.html

and another blog:

http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=16880