- Author: Ben Faber
- Author: Craig Kallsen
- Author: Akif Eskalen
Dry Root Rot is a pretty fantastic disease symptom that is usually seen in lemon, but can be seen in orange, as well.
Craig Kallsen, UCCE Citrus Advisor in Kern Co. comments on a disease sample:
I have seen a lot of dry root rot over the years. It usually is something that damages or weakens the root system which allows a Fusarium species to colonize the rootstock. It is very common in older lemon groves that froze at some point in their past. Also common in groves that suffered a lot of gopher damage or where the wraps got too hot in the sun burning the bark and cambium. I have also seen it in cases of fertilizer or other soil-applied chemical burn. I have no doubt that graft incompatibility could do it too.
Akif Eskalen, UCCE Plant Pathology Specialist chimes in on a disease sample submitted:
As you can see from the attached picture there is a weird callus formation and symptoms of incompatibility at the graft union which I think is the primary cause of decline. We didn't observe any discoloration in the scion, however rootstock was completely discolored where we isolated Fusarium solani the causal fungus of Dry Root Rot. Dry root rot caused by either Fusarium solani and/or Fusarium spp. When there is a disconnection at the graft union, the phloem can not transfer enough carbohydrate to the rootstock to feed feeder roots. Fusarium fungal species are present in the soil and they can attack and easily colonize on starch depleted roots and cause DRR.
We still don't know what is causing the graft incompatibility on these plants. That needs to be investigated.
It's still not clear how and why citrus becomes affected.
- Author: Ben Faber
Per CDFA:
One adult (female) Asian Citrus Psyllid was identified from a trap in Hollister CA. Delimitation trapping will commence, along with visual survey, treatment and quarantine activities, following the newly approved Northern California protocol.
- Author: Ben Faber
Just so we don't forget, but there are a lot more threats to California than ACP and PSHB. There's a lot more where they came from. Here's one that has landed in Florida that could easily with the shipment of infested plants arrive in California.
Myllocerus undecimpustulatus undatus Marshall, the Sri Lankan weevil, is a plant pest with a wide range of hosts. The Sri Lankan weevil was first detected in 2000 in Florida. By May, 2006 it was found in 12 counties in that State. The Sri Lankan weevil has a wide host range of over 150 plant species including native, ornamental, vegetable and fruit species. Some host plant examples include Citrus spp., citrus; Conocarpus erectus, green buttonwood; Bauhinia x blakeana, Hong Kong orchid tree; Chrysobalanus icaco, cocoplum;Phoenix roebellenii, pygmy date palm; Prunus persica, peach; Lagerstroemia indica, crepe myrtle;Capsicum spp., pepper; Litchi chinensis, lychee; Muntingia calabura, strawberry tree; and Solanum melongena, eggplant. It is unclear what the larval host plants are, but they have been reared in the laboratory on pepper, eggplant, cotton, carrot, and sweet potato roots.
The damage adults cause to foliage can be significant in the ornamental industry and to young citrus trees they can be lethal. The most disturbing aspect of this pest is that it has a larval stage that feeds on roots and is difficult to detect and treat with traditional insecticides. This pest behavior is very much like of the introduced Diaprepes root weevil which is found in certain areas of the Southern California coast. The possible distribution of the pest is for much of coastal California
Various life stages of the Sri Lankan Weevil.
- Author: Ben Faber
Along the mighty Santa Clara River are planted many lemons and once upon a time many Valencia orange trees. There's lots of wild life along the river which causes some issues with food safety. One of the many creatures are rats and when things dry up they start foraging further and further for food. They really like citrus and can cause a lot of damage. What I first thought was sun burn damage turned out to be rat feeding on the bark and cambium of these lemon trees. The damage wasn't in the right position to be sunburn damage. Inside the canopy, often on the north facing branch.
- Author: Ben Faber
Mark Hoddle of UC Riverside Entomology Department has intorduced a second species of natural enemy of Asian Citrus Psyllid (ACP), Diaphoencyrtus aligarhensis, imported from Punjab, Pakistan. It was officially released December 16, 2014 at the Biological Control Grove at UCR. It is anticipated that this natural enemy will be complimentary to Tamarixia radiata, a parasatoid that also attacks ACP nymphs that was released in California in 2011. It's thought that it might occupy slightly different environments where it might be more successful than Tamarixia.