University of California Cooperative Extension • Tulare County



Vol. 1, Issue 6 September 2004

8:30 Registration

9:00 IPM Demonstration in Tulare County

Neil O’Connell, UC Cooperative Extension, Tulare County

9:30 Frost Protection Strategy-When to Turn On/Off Wind Machines, Water

Dr. Rick Synder, UC Davis

10:00 What You Do In The Field Influences Fruit Quality

Dr. Mary Lu Arpaia, Kearney Agricultural Research & Extension Center

10:30 Break

10:45 Management of Citrus Nematode

Dr Mike McKenry, Kearney Agricultural Research & Extension Center

11:15 The Efficacy of Insecticides for Various Citrus Pests & The Current Status of Citrus Peelminer Research

Dr. Beth Grafton Cardwell, Kearney Agricultural Research & Extension Center

Continuing education credit has been requested

Dieback

Shoot dieback was seen throughout the county beginning in July. Dieback was seen in Cara Cara navels, Washington navel, Lane Late Navel, and Valencias. Frequently much of the dieback was located in the top of the tree or the south and west quadrants of the tree. Gumming was generally associated with the dieback. Leaves on affected shoots dried and remained in place.

Sudden wilting and dying back of leaves and small branches has been reported for many years in California citrus. Gumming has been reported with the dieback. It generally occurs in late summer following hot dry conditions. No pathogen has been associated with the condition. It might be confused with citrus blast; however blast is associated with cool moist conditions and is the result of the activity of the organism Pseudomonas syringae. Dieback in the spring in new flush growth with warming air temperature is known as Tulare County dieback and is not the result of a pathogen. The dieback in a shoot following hot dry conditions generally is self limiting and the dieback stops at the origin of the shoot; it does not generally progress into larger branches. The condition is thought to result from a temporary water deficit in the tree. As weather conditions moderate the potential for this condition should decline.

Splitting in Navel Oranges

September is typically the period when reports of splitting in navel oranges increases. The split begins at the navel where the tissue is thinner and often a check or a very small rupture of the tissue has occurred. The split progresses vertically from this point. Frequently the earliest of the split fruit will color prematurely and on close inspection will exhibit a black discoloration that progresses from the navel into the core of the fruit. This condition is referred to as black heart which is the result of a pathogen, Alternaria citri. Frequently drosophila fruit flies are attracted to the area. Another insect, navel orangeworm, may lay its eggs on the affected tissue, with larvae of the insect found later infesting the navel end of the fruit.

Woolly Whitefly

Infestations of this insect have been detected in backyard citrus trees in the city of Bakersfield. This pest produces copious amounts of honeydew, the deposits of honeydew later being a site for sooty mold fungus. Reductions in yield and fruit quality are likely results of infestations of this insect. Wooly whitefly was detected in Santa Barbara in 1979 and in Ventura County in 1980, and then invaded commercial citrus throughout Southern California, including orchards in the Escondido, Pauma Valley and Fallbrook areas. Three species of imported parasites had significant effect on infestations of the whitefly and were able to establish biological control in some locations. How well these same parasites would do in the climate of the valley and how effective they would be will have to be established. No infestations in commercial citrus in Kern County have been detected at this point.

Texas Citrus Mite

Last fall this mite was detected in high numbers in some orchards in Kern County, in the Edison, General Beale and Belridge areas. Reportedly, it had been in the Belridge area at very low numbers for two years prior to that. It was first detected in Coachella Valley citrus in 1990 and in the Filmore region of Ventura County in 2000 according to David Haviland, Cooperative Extension entomologist. Populations often reach peak numbers in the fall when significant leaf drop may occur as well as dieback. Warm fall conditions, deficit irrigation and dust influenced some of the worst outbreaks of the mite in Kern County. Numbers of mites have been significantly lower this spring and summer in the infested properties. Chemical treatments were applied in a significant number of the infested orchards where leaf drop was occurring and were effective if applied before cool weather set in. Infestations of a new pest sometimes exhibit a rapid increase in numbers as this mite did, with a subsequent dramatic decline in numbers. Infested properties will be closely monitored for a resurgence of the mite this fall.

Weed Management

Recently enacted regulations regarding use of certain preemergence herbicides in citrus within a groundwater protection area (gpa) require certain cultural procedures for a restricted material permit for application of the herbicide(s). For most citrus locations within the county in a gpa this requirement involves incorporation of the herbicide by water or mechanical means. A substitute for the use of the restricted material for weed management would be the use of a postemergence material such as glyphosate. In order to minimize weed growth during the winter, the postemergence material would have to be applied as late as possible before sustained rainfall prohibits entry or, if the ground allows it, application during the winter depending on weed growth. The amount of fall/winter weed growth will relate to the resident seed load present in the orchard which will vary depending upon the number of years of fall preemergence herbicide applications. For young orchards the load would be expected to be considerably greater than for a mature orchard.

Hypoderma Decline of Lemons

This problem was first observed in April of 2000 in the Terra Bella area in a mature block of lemons. Symptoms included shoot dieback with leaves remaining in place with gum formation. In some cases cracking of bark with gumming was seen on large branches even scaffolds, and in worst cases, cracking and gumming on the trunk down to the bud union. The organism was identified to be a wood rotting organism, a species not previously

reported to be a problem in citrus. Additional blocks of lemons were detected in other parts of the county. The problem appears to have been restricted to lemons and to mature trees. The same decline was detected in Ventura and Riverside counties shortly after the identification in Tulare County. In some cases growers had been unsuccessfully treating the affected trees thinking it was gummosis caused by the Phytophthora fungus. Screening of potential chemicals for efficacy in controlling Hypoderma have been of very limited success to this point. Management procedures that are thought to be of value are pruning out affected areas in late spring or early summer after the period of rain and fog when moisture is not present for reinfection of cut surfaces. Prunings should not be left in the orchard but removed and burned. The organism is capable of continuing to be active in pruned material left in the orchard. Pruning cuts should be made beyond the visibly affected areas into healthy tissue. Infected branches when cut show a staining of the wood where the organism has invaded the area. The fungus is thought to gain entrance through cracks in the bark perhaps as a result of freeze damage or sunburn but the means of entry and rate of spread in the tree has not been determined. Additional research is ongoing to investigate the biology of the organism and to further investigate the efficacy of chemicals and the benefit of cultural operations. Surveying for additional lemon orchards in Tulare and Ventura counties that might be affected by the fungus is continuing.

Neil O’Connell

Farm Advisor

Neil O’Connell

Farm Advisor

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Citrus Notes

FALL CITRUS MEETING

Wednesday, October 20, 2004

University of California

Cooperative Extension

Tulare County

4437B S Laspina St

Tulare, CA 93274-9537

Nonprofit Org

US Postage Paid

Visalia, CA 93277

Permit No. 240

Fall Citrus Meeting

Wednesday, October 20th

8:30 A.M. - 12:00

Agricultural Auditorium

4437 South Laspina Street, Tulare

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