- Author: Chris M. Webb
Huanglongbing (HLB) the deadly disease carried by the Asian citrus psyllid has recently been detected in Los Angeles County.
UCCE Ventura County Farm Advisor Ben Faber, stresses that people are responsible for much of the movement of ACP. On their own, this insect roughly the size of a grain of rice, can travel about a mile over their lifetime.
The health of citrus trees, and the health of our local citrus industry, largely depends on the responsible handling and movement of plant materials and fruit. This is of particular importance when traveling out of the county, state or country.
Please see the message below from the CDFA (California Department of Food and Agriculture).
CITRUS DISEASE HUANGLONGBING DETECTED IN HACIENDA HEIGHTS AREA OF LOS ANGELES COUNTY
SACRAMENTO, March 30, 2012 – The California Department of Food and Agriculture (CDFA) and the United States Department of Agriculture (USDA) today confirmed the state’s first detection of the citrus disease known as huanglongbing (HLB), or citrus greening. The disease was detected in an Asian citrus psyllid sample and plant material taken from a lemon/pummelo tree in a residential neighborhood in the Hacienda Heights area of Los Angeles County.
HLB is a bacterial disease that attacks the vascular system of plants. It does not pose a threat to humans or animals. The Asian citrus psyllid can spread the bacteria as the pest feeds on citrus trees and other plants. Once a tree is infected, there is no cure; it typically declines and dies within a few years.
“Citrus is not just a part of California’s agricultural economy; it’s a cherished part of our landscape and our shared history,” said CDFA Secretary Karen Ross. “CDFA is moving swiftly to protect the state’s citrus growers as well as our residential trees and the many prized citrus plantings in our parks and other public lands. We have been planning and preparing for this scenario with our growers and our colleagues at the federal and local levels since before the Asian citrus psyllid was first detected here in 2008.”
Officials are making arrangements to remove and dispose of the infected tree and conduct treatment of citrus trees within 800 meters of the find site. By taking these steps, a critical reservoir of disease and its vectors will be removed, which is essential. More information about the program will be provided at an informational open house scheduled for Thursday, April 5, at the Industry Hills Expo Center, The Avalon Room, 16200 Temple Avenue, City of Industry, from 5:30 to 7:00 pm.
Treatment for HLB will be conducted with the oversight of the California Environmental Protection Agency (Cal-EPA) and will be conducted safely, with advance and follow-up notices provided to residents in the treatment area.
An intensive survey of local citrus trees and psyllids is underway to determine the source and extent of the HLB infestation. Planning has begun for a quarantine of the infested area to limit the spread of the disease by restricting the movement of citrus trees, citrus plant parts, green waste, and all citrus fruit except what is commercially cleaned and packed. As part of the quarantine, citrus and closely related plants at nurseries in the area will be placed on hold.
Residents of quarantine areas are urged not to remove or share citrus fruit, trees, clippings/grafts or related plant material. Citrus fruit may be harvested and consumed on-site.
CDFA, in partnership with the USDA, local agricultural commissioners and the citrus industry, continues to pursue a strategy of controlling the spread of Asian citrus psyllids while researchers work to find a cure for the disease.
HLB is known to be present in Mexico and in parts of the southern U.S. Florida first detected the pest in 1998 and the disease in 2005, and the two have now been detected in all 30 citrus-producing counties in that state. The University of Florida estimates the disease has tallied more than 6,600 lost jobs, $1.3 billion in lost revenue to growers and $3.6 billion in lost economic activity. The pest and the disease are also present in Texas, Louisiana, Georgia and South Carolina. The states of Arizona, Mississippi and Alabama have detected the pest but not the disease.
The Asian citrus psyllid was first detected in California in 2008, and quarantines are now in place in Ventura, San Diego, Imperial, Orange, Los Angeles, Santa Barbara, San Bernardino and Riverside counties. If Californians believe they have seen evidence of HLB in local citrus trees, they are asked to please call CDFA’s toll-free pest hotline at 1-800-491-1899. For more information on the Asian citrus psyllid and HLB visit: http://www.cdfa.ca.gov/phpps/acp/
- Author: Chris M. Webb
On April 20, 2012 California State University, Channel Islands will host a symposium titled, ‘Agriculture in the Golden State: Challenges in Feeding California in the 21st Century.’
Strong and sustainable agricultural production is important to all of us, and to our future. UCCE Ventura County researchers Oleg Daugovish and Ben Faber will speak at the symposium.
From the event organizers:
"California is the nation’s top agricultural producer generating over $30 billion annually. However, the ability of growers to feed California and beyond is continually being challenged by the introductions of new insect pests, drug resistant pathogens, and environmental concerns at the urban-agricultural interface. CI sits within one of the top ten agriculturally important counties in California, which produces much of the States’ strawberries, raspberries, citrus, and avocados. Given our location, it is important that everyone learn about the issues affecting agriculture locally and statewide."
To learn more about this year's symposium, or to register please visit this page of the CSU Channel Islands website.
- Posted By: Chris M. Webb
- Written by: Ben Faber
A Frost Primer
Definitions:
Dry-bulb temperature: the temperature of the air as measured with a thermometer.
Wet-bulb temperature: the temperature that the tree will likely sense due to evaporative cooling of the leaves.
Dew point temperature: the air temperature required for condensation (dew or frost) to occur. This is an indication of the amount of humidity in the air. The higher the dew point, the lower the rate of cooling. As dew forms, the water releases heat (heat of condensation), and the temperature levels out.
A high dew point -- above 40 degrees
A moderate dew point -- between 25 - 40 degrees
A low dew point -- between 10 - 25 degrees.
"Cold night": any night at or below 32 degrees F.
"Key stations": weather stations with at least a ma/min thermometer and a thermograph in a white box facing north.
Temperature inversion: an atmospheric layer in which temperature increases with altitude. High temperatures during the day promote the formation of the inversion.
"Temperature ceiling": height to which heated air rises during orchard heating. The lower the ceiling, the stronger the inversion and a greater amount of heat can be obtained from wind machines and orchard heating.
Radiation freeze (frost): local cooling due to rapid heat loss from plant and soil surfaces under clear skies and light or no wind conditions. Daytime temperatures are usually in the 45-55 degree range which causes the formation of a nighttime inversion. Any significant breeze will cause temperatures to rise due to mixing of the inversion.
Advective freeze: cooling of a wide area by dry polar air. Typically the temperature is at or below 32 degrees for 2 or more days. The temperature ceiling is high or non-existent. This was what we got in December 1990.
1 gram of water = 1 calorie/degree of temperature change (°C)
1 gram of water = 79 calories released on freezing
1 gram of water = 607 calories consumed when evaporated
Gauging Wind Speed
Effect of air movement |
Wind force (mph) |
Terms used in forecasts |
Calm; smoke rises vertically |
less than 1 |
|
Wind direction shown by smoke drift |
1 - 3 |
light |
Wind felt on face, leaves rustle |
4 - 7 |
|
Leaves and small twigs in constant motion |
8 - 12 |
gentle |
Raises dust and loose paper; small branches move |
13 - 18 |
moderate |
Small trees in leaf begin to sway |
19 - 24 |
fresh |
Large branches in motion |
25 - 31 |
|
Whole trees in motion |
32 - 38 |
strong |
Breaks twigs and weak branches |
39 - 54 |
gale |
- Posted By: Chris M. Webb
- Written by: Ben Faber
How Frosts and Freezes Occur
Before considering the methods of frost protection, one should understand the conditions under which low temperatures occur. To differentiate between the two major sources of the cold, the terms local radiation frost and freeze are used.
Local radiation frosts are caused by a cooling of the objects on the earth's surface during the night. This loss of heat from the foliage and soil is called radiation. Heat accumulated from sunshine during the day is radiated to the sky during the night. The cooled objects chill the surrounding air and usually the coldest zone is near the ground surface. Air temperatures are warmer as one goes higher until a height is reached where they area art a maximum for that locations. This is called the ceiling. The temperature and height of the ceiling is different for each plane and situation.
When the ceiling is low, warm air is nearer the ground than when the ceiling is high/ This phenomenon, occurring frequently in Southern California, is called temperature inversion and accounts for this areas; ability to protect its orchards.
Colder air settles near the ground and then moves (flows) down the slope to still lower ground resulting in what is called the drift.
Terrain features and winds influence its direction and velocity. A strong drift maintains air temperatures higher than those existing when little or no drift is present
The other type of freezing weather occurs when a large mass of cold air moves in from the north. Fortunately, these freezes have not occurred frequently, about every 10 years. Under freeze conditions, temperatures usually go below those experienced during local radiation frosts. When this cold air moves in, high ground is no warmer than lower ground and there is little or no ceiling. Orchard protection at such times is difficult.
General Cultural Practices
Three to four degrees F of higher temperatures can mean the difference between a bad burn and death of a tree. The following practices can help protect your orchard from frost damage; they all have in common some method of retaining heat in the orchard.
During the day, an orchard soil acts as a reservoir for heat absorbed from the sun. Some of this heat returns back into the atmosphere during the day and at night (reradiation), warming the orchard. Moist soils will store more heat and are better heat conductors than dry ones, and a compacted soil - one that forms a firm surface - is a better conductor of heat than a soil that has been recently cultivated. Therefore, when there is danger of frost, do not cultivate your orchard soil, but do keep it moist to a depth of at least one foot.
The insulating effect of weeds, sod and leaf litter between the rows reduces soil absorption of heat during the day and reduces reradiation. In an experiment, an orchard that was weed-free with a compacted soil showed 3.8° F more warmth than an orchard with sod. The same experiment demonstrated that an orchard with rain compacted soil was warmer than one that had been recently cultivated. If you have a ground cover, mow as short as possible to minimize the insulating effect.
The size of the tree canopy in many ways determines the amount of reradiated heat that is captured by the trees. A large, dense canopy can intercept more heat leaving the orchard than a small, sparse one. A healthy tree has been shown to have a higher canopy temperature than a sparsely-foliated tree. For example, lemon trees with sieve-tube necrosis are frequently more frost-damaged than healthy ones, partly because of the sparseness of the foliage. Proper pest and disease control, irrigation and fertilization are all important in maintaining a healthy tree more resistant to frost damage.
A most important factor in determining how damaging a frost may be is the time of year which it occurs - early or late winter. If the frost comes early, before temperatures have a chance to drop gradually, trees have not had time to acclimate themselves, and the damage can be severe. If, however the frost hits later in the season (after a period of gradual temperature decline), trees can develop a cold hardiness and better tolerate the cold weather. To this end, late applications of nitrogen that cause excessive growth may delay this acclimation , thereby further reducing the tree's cold tolerance.
In most cases, frost protection can be improved by improving air drainage. Brush, tall weeds and trees can impede the movement of cold air out of an orchard. Remove these obstacles (or at least mow the weeds or prune up windbreaks), creating channels for air movement.
Managing Irrigation Water for Tree Protection
Irrigation water releases two types of heat when applied during a frosty night: the heat released by going from the water temperature at the nozzle down to 32° F (0° C), and another type called the heat of fusion, which is how most of the warming energy is released. This is the energy that is obtained by water going from a liquid to a solid state. For every degree of temperature drop (Celsius), there is one calorie of heat released per gram of water. A gram of water with a nozzle-exiting temperature of 65°F will release about 18 calories of heat when it cools to 32°F, but in changing from liquid to ice, 79 calories are released. The more ice that is made, the more heat is released. This heat helps raise the temperature of the orchard.
In furrow irrigation it is best to place the furrows as close to the dripline as possible and make the furrows as wide as possible to increase the transfer of heat into the air. With sprinklers, the more output the better. At Lake Alfred, Florida, the guidelines call for at least 20 gph sprinklers, with lower rates giving less effect. If you do not have the capacity to irrigate your entire orchard, it is advisable to choose one area and protect it, rather than stopping in the middle of the night to irrigate another area. This is because the resultant evaporative cooling will take 607 calories per gram of water, and this heat loss comes at the expense of the leaf. Therefore, an area where the water has been turned off prematurely will rapidly cool.
The rate of cooling is related to the dewpoint. A high dewpoint indicates moist air, and a low dewpoint relatively dry air. The drier the air, the more rapid the cooling. When temperatures are low with extremely dry air conditions, irrigation can be a hazard to trees. If the predicted dewpoint is well below (at least more than 5 °F) the predicted minimum temperature, sprinklers can cause excessive evaporative cooling. With evaporative cooling, orchards with running water can actually be cooler than dry orchards. Therefore, if trees are sprinkled and ice forms, in order to protect the trees, the sprinklers should continue in operation until the ice begins to melt. To be certain, sprinklers can continue until the ice is completely melted.
Use of Wind Machines
In most situations, wind machines can be both effective and economical in providing protection; however, in some situations, as we found in the advective freeze (cold polar winds) of 1990, they can exacerbate the situation. The dry cold air drawn in by the machines will intensify the cold damage.
The San Joaquin Valley and Southern California more commonly have radiation frosts (heat loss under conditions of clear skies and light wind conditions) which commonly have a temperature inversion. For a machine to do its job properly, this temperature inversion is needed so that warmer temperatures at higher elevation can be mixed with cold air near the ground.
The number, power requirement and area protected vary with terrain and manufacturer's brand. Generally 7 to 10 brake horsepower are required per acre, more in cold spots, less if there is a slope. They should be started before temperatures drop below 35°F, since it is difficult for a wind machine to warm an orchard that has dropped below this critical temperature.
Ice-nucleating Bacteria
For some years, it has been known that bacteria residing on cold-sensitive plants initiate ice formation. The ice formed in or on the plants spreads rapidly, causing mechanical injury. Copper-containing sprays that are applied 10 days before cold weather, kill off these bacteria and allow enough time for their decomposition. By controlling the ice-nucleating bacteria (INB), tests have shown temperatures may drop 2-4°F below critical levels without plants showing damage.
- Author: Chris M. Webb
A new volume of Topics in Subtropics is now available.
This newsletter is a collaborate effort of UCCE Farm Advisors throughout the state. Topics in this issue include:
- Organic Herbicides: Do they work? – An interesting research summary on organic herbicide products currently available. Suggestions for maximizing results are included.
- Snake Oil: Horticultural Myths and Legends – Practical tips for avoiding products that do not provide benefit or can possibly cause harm.
- Success Story Before There is a Problem – Ben Faber describes a common pest in Turkey that causes much damage to a wide range of plants, including citrus. Tropinota hirta Poda (Coleoptera, Scarabaeidae, Cetoniinae) feeds on flowers and reproductive plant parts, resulting in no fruit formation. While this beetle is has not yet been found in the United States, knowledge of potential method for control is already stateside.
To access this addition, as well as previous additions, of Topics in Subtropics please visit this page of our website.