- 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.
- Author: Neil O'Connel
Installing tree wraps on young trees provides protection to the trunk from applications of herbicides during weed management operations. Additionally, the wraps minimize light interception by trunk tissue thereby reducing sucker growth. During hot weather tree wraps provide shade to the trunk and reduce the incidence of sunburn. With the increasing incidence of earwigs, damage to young trees and the tendency for the insect to congregate under the wraps, tree wraps are being removed in some cases. Recent laboratory data from Dr. Beth Grafton-Cardwell (confirmed by observations in the field) suggests that as the season progresses adults become less and less interested in feeding on leaves (peak of feeding in March and April, declines to next to nothing by June). So, a management consideration would be to check the earwigs in the wraps in the summer, and if there are only adults present there is less concern than if there are immatures present. Another point would be to consider treatment with an insecticide such as Lorsban if wraps are to be left on for sunburn protection.
If wraps are removed a uniform coating of sun protective material should be applied to the trunk to protect against sun damage. Trunk surfaces should be monitored to ensure that a uniform coating is in place. Sun damage to unprotected trunk tissue can result in partial or complete girdling of the tree.
- Author: Ben Faber
Jane Delahoyde, a PCA here in Ventura, recently found an unusual scale in lemon here. It is barnacle scale with a typically long Latin name - Ceroplastes cirripediformis. It is unlikely to be any worse than other scales, but it's something to keep our eyes on. This is one of the soft scales, often called wax scales because of the wax they produce. It turns out that this has been described as being in Southern California for years, but some years they are just more present. For more on "Wax" scales see the Texas A&M site
https://insects.tamu.edu/fieldguide/aimg110.html
or our UC IPM website
http://ucipm.ucdavis.edu/PMG/PESTNOTES/pn7408.html
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