- 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
Huanglongbing or Citrus Greening caused by Asian Citrus Psyllid and its associated bacterium Candidatus Liberibacter A. causes misshapened fruit and causes the fruit to have a green portion on the skin. Hence the name citrus greening. More commonly in Southern California where we have warmer winters than in the Central Valley, without the cold we can often get some green fruit. It's the cold that brings on the color of fruit. Especially fruit on the inside of the tree or on the side of the fruit not facing the sun. Also fruit that hangs on the tree and is over-mature can regreen, losing its yellow or orange color depending on lemon or orange/mandarin. In this case, we had some fruit brought into the office that was both old and has matured in our warm winter this year. So the whole tree is covered with fruit that has either green spots or green sides.
- Author: Ben Faber
How to Manage PestsUC Pest Management Guidelines
I have had a number of requests to identify fruit spotting on lemons. It turns out to be Septoria fungus which can show up on leaves, stems and fruit. The key to this is to make sure there is a fungicide on the tree in the fall before the wet weather kicks in
CitrusSeptoria SpotPathogen: Septoria citri(Reviewed 9/08, updated 9/08) In this Guideline: SymptomsEarly symptoms of Septoria spot appear as small, light tan to reddish brown pits on fruit, 0.04 to 0.08 inch (1 to 2 mm) in diameter, which usually do not extend beyond the oil-bearing tissue. Advanced lesions are blackish, sunken, extend into the albedo (white spongy inner part of rind), and are up to 0.8 to 1.2 inch (20 to 30 mm) in diameter. Dark brown to black fruiting bodies often develop in these lesions, which usually do not extend beyond the oil-bearing tissue. The spots are much more conspicuous after the fruit has changed from green to yellow or orange. Small spots may develop into large, brown blotches during storage or long-distance transportation. Septoria citri may also cause similar spotting on leaves or twigs that are weakened by frost or pests. Comments on the DiseaseThe Septoria fungus causes spotting of Valencia oranges, late-season navel oranges, and occasionally of lemons and grapefruit. It occurs in the San Joaquin Valley and interior districts of southern California during cool, moist weather. Infections begin when Septoria conidia are transported throughout the tree by rainfall. The spores germinate with additional moisture from rain or dews and commonly infect cold-injured fruit tissue and mechanical injuries. The damage to the rind lowers the grade of the fruit and results in culling. Septoria spot may be confused with copper injury and other abiotic and biotic agents. ManagementApply a preventive copper spray in late fall or early winter, just before or after the first rain. In years with heavy rainfall, additional applications may be necessary. For California oranges (Navels and Valencias) shipped to Korea:
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- Author: Ben Faber
Edema may be caused by any agent that stimulates an abnormal increase in the size and number of a group of inner cells. Edema can be induced by (1) spraying with some chemicals such as ammoniacal copper carbonate in an oil emulsion, (2) injuries resulting from wind-blown sand particles and sucking insects, (3) high light intensity (over 2000 foot-candles) for ivy geraniums, and (4) accumulation of water in the intercellular spaces.
The most common cause of edema is the presence of abundant, warm soil water and a cool, moist atmosphere. Under these conditions the roots absorb water at a rate faster than is lost through transpiration. Excess water accumulates in the leaf, some parenchyma cells enlarge and block the stomatal openings through which water vapor is normally released from the plant; thereby contributing to further water retention in the leaf. If this condition persists, the enlarged cells divide, differentiate a cork cambium, and develop elongate cork cells externally to form a periderm. The rupture of the epidermis by the enlarged inner cells and the periderm account for the raised, crusty appearance of older edema spots and also corky veins.
Changes in weather and cultural practices of growing plants usually will avoid edema. To reduce the risk of edema occurrence, the following may be helpful:
1. Avoid irrigation or watering during cool, overcast humid weather. For potted plants in greenhouses, remove saucers under pots, or discard any water that remains in the saucer 30 minutes after watering. Irrigate or water when air temperature are rising or humidity is low.
2. In greenhouses: a) reduce the humidity of the air by venting and increasing heat; b) improve air circulation; c) increase light intensity; d) space the plants farther apart; e) for potted plants use a well-drained potting medium for potted plants and avoid standing water in saucers under the pots.
3. Avoid overfertilizing, especially when the plants are growing slowly, such as during the winter months. Maintain fertility based on a soil test. Avoid low levels of potassium and calcium.
4. Avoid cultivars that are highly susceptible to edema under your growing conditions.
Photo:
The black spots on the fruit start out as a clear exudate. The same for the brown spots on the leaves.
/span>- Author: Ben Faber
Citrus is a messy botany. It loves to cross with anything and in so doing creates very complex ancestry. C-35 rootstock is a citrange and was created for its tolerance to cold, but is also good in Phytophthora situations and creates a slightly smaller tree. Oddly, it is deciduous, a cross between Poncirus and Citrus. It's a trifoliate hybrid. 'Meyer' lemon is the same mess, a cross between a lemon and an orange/mandarin. You would think these two messed up cousins might do well, but in several instances there is an incompatibility. 'Meyer' has been grown successfully on 'Macrophylla' and 'Yuma Ponderosa', both of which are also complex hybrids.