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

A portion of Placer County has been placed under quarantine for Asian citrus psyllid (ACP) following the detection of multiple life stages on citrus trees within the City of Lincoln. 

The quarantine zone in Placer County measures 118 square miles, bordered on the north by Riosa Road; on the south by the Roseville City Limit; on the west by Brewer Road; and on the east by Fowler Road. The quarantine map for Placer County is available online at: https://www.cdfa.ca.gov/plant/acp/regulation.html#maps. Please check this link for future quarantine expansions in this county, should they occur. Quarantines in new counties will be announced separately.

This is a case where an individual moved infested trees from a quarantine zone into a clean county and ended up moving psyllid with the trees.  This is how so many of our current pests are moving around - Shot Hole Borer, 1000 Cankers of Walnut, Emerald Borer, Gold Spotted Borer.  On and on, we are the culprits of our own destruction.  Pretty soon every pest known to plants will be everywhere.  Sorry for the rant.

The International Citrus Conference was just held and about 1,500 people came from all over the world to share their experiences and research in citrus.  It included marketers, growers, government officials and researchers who all had citrus as their interest.  It was remarkable the volume of information, everything from world production figures and marketing, new varieties, breeding technology, plant diseases and pests, water management and of course HLB and ACP, probably the two most fearsome world-wide problems. 

On the whole it was most hopeful to realize how much has been accomplished in the last several years to deal with the threat of HLB.  The biology of ACP is better understood in different situations, the disease progression in different citrus species is being recognized as being more or less aggressive, and how to manage the insect and disease are better understood.  Unfortunately, new threats (however none as mush as HLB) are being identified, such as citrus longhorn beetle.  Oh, my.

Read the Abstracts at:

http://www.icc2016.com/abstract/book-of-abstracts

What this means is that there is different feeding behavior on different scion varieties that is unaffected by the rootstocks used in this study. This does not mean "a" rootstock can not have an effect, just that the ones used in this trial did not.

EFFECT OF DIFFERENT CITRUS SCION AND ROOTSTOCKS

COMBINATION ON FEEDING OF Diaphorina citri

Alves GA1, Beloti VH1, Carvalho SA2 & Yamamoto PT1

1Escola Superior de Agricultura ‘Luiz de Queiroz'/

Universidade de São Paulo, Piracicaba, SP, Brazil; 2Instituto

Agronômico (IAC), Centro de Citricultura, Cordeirópolis, SP,

Brazil; e-mail: gralves@usp.br

The Asian citrus psyllid (ACP) is the vector of bacteria associated to the huanglongbing and has a host range of more than 50 species of the Rutaceae family. The knowledge about the feeding behavior in different hosts can show useful aspects for future studies of plant resistance and ACP management. Therefore, was evaluated the effect of different combinations of scion and rootstock of citrus in the feeding of ACP adults. For this, we tested Valencia, Pera and Hamlin sweet orange, Ponkan mandarin and Sicilian lemon grafted on Rangpur lime and Sunki mandarin rootstocks.

The flushes were individualized with cages made of transparent plastic cup and “voile” tissue. To collect the honeydew, discs of filter paper were placed at the base of each flush. The adults fed for a period of 72 h. After this, the discs were removed and immersed on the ninhydrin solution. After 24 h, the drops area of honeydew was determined using the Quant software. The feeding was more intense on sweet orange varieties, with a highest value observed to Valencia (0.902 cm2) and the smaller area to Ponkan mandarin(0.269 cm2). Unlike observed for scion varieties, when different rootstocks for the same scion variety were tested, no difference was observed in the consumption of ACP.

Rootstocks can have a tremendous effect, but not in this case with the rootstocks used