On typical days, the air near the ground is warmer than the air above it. This is because the atmosphere is heated from below as solar radiation warms the Earth's surface. A surface inversion occurs when the atmosphere at the earth's surface is colder than the layer above it. There are four common causes of surface inversions, some of which can occur at the same time. Remember - inversions flow like water:
Advection of cool air:
A slab of cool air slides into and under a warmer air mass. This "drainage inversion" can occur when there are sea breezes, cold fronts or when cool air drains downhill into warmer air.
Advection of warm air:
Warm air flows over cool surfaces and lower layers cool more rapidly than those above.
Shading from trees as well as from rolling terrain can cause an inversion to set in earlier and stay later.
Around sunset, the ground cools rapidly by radiating heat upwards into space. The air in contact with the ground cools by conduction, causing the lowest layer of air to be cooler than higher layers. Air within this "radiation inversion" tends to remains in place.
Radiation inversions create problems for spray operators because they can cause pesticide spray to:
- stay concentrated for long periods over the target,
- move with the cool air for many miles when the breeze picks up,
- drain down slopes and concentrate in low-lying regions,
- drift unpredictably as the inversion dissipates during the morning
Radiation inversions happen every day and should always be expected to begin 3-4 hours before sunset, reach their apex just before sunrise and then dissipate no longer than an hour or so after sunrise… unless one or more of the following conditions occur:
- There is continuous overcast, low and heavy cloud.
- There is continuous rain.
- Wind speed remains above 7 m/h for the whole period between sunset and sunrise - although even this isn't always true.
Field air temperatures are often very different from local or regional forecasts, so the most reliable method of detecting inversion conditions is to measure temperatures at, and several meters above, the ground. Spray operators can recognize a surface inversion when:
- there is a big difference between the daytime and night time temperatures,
- evening and night time wind speeds are considerably less than during the day,
- sounds seem to carry further,
- odors seem more intense,
- daytime cumulus clouds tend to collapse toward evening,
- overnight cloud cover is 25% or less,
- mist, fog, dew and frost occur
- smoke or dust hangs in the air and/or moves laterally in a sheet.
If you suspect there's an inversion, then don't spray. Often, it's right on the label.
Farm Advisor Mark Battany measuring inversions/h3>/h3>/h3>/h3>
Polyphagous Shothole Borer which is an ambrosia beetle that normally feeds on dead trees is going after live trees - over 100 species including sycamore, alder and coast live oak. It also goes after avocado. The California Avocado Commission has sponsored the placement of traps that have lures for PSHB. The traps are near avocado orchards but also likely spots where they might show up, such as campsite where people would bring firewood that might be infested with the beetle. The map here shows where the traps are located and where PSHB have been trapped. There are also traps in Santa Barbara County which are not yet shown on this map.
SACRAMENTO — An additional portion of Fresno County along its southern border with Tulare County has been placed under quarantine for the Asian citrus psyllid (ACP) following the detections of ACP in two locations in an unincorporated area of northern Tulare County near the City of Orange Cove. The quarantine expansion adds approximately 50 square miles to the existing quarantine for a total of 84 square miles in Fresno County. All of Tulare County remains under quarantine as a result of previous ACP detections.
The new quarantine area in Fresno County is bordered on the north by E Kings Canyon Road; on the south by the Fresno County Boundary Line; on the west by S Alta Avenue; and on the east by an unnamed creek. The quarantine map is available online at www.cdfa.ca.gov/plant/go/acp-qmaps.
The quarantine prohibits the movement of citrus and curry tree nursery stock out of the quarantine area and requires that all citrus fruit be free from ACP prior to moving out of the quarantine area. An exception may be made for nursery stock and budwood grown in USDA-approved structures which are designed to keep ACP and other insects out. Residents with backyard citrus trees in the quarantine area are asked not to transport citrus fruit or leaves, potted citrus trees, or curry leaves from the quarantine area.
ACP county-wide quarantines are now in place in Imperial, Los Angeles, Orange, Riverside, San Bernardino, San Diego, Santa Barbara, Tulare and Ventura counties, with portions of Fresno, Kern, Madera, San Joaquin, San Luis Obispo, and Santa Clara counties also under quarantine.
The ACP is an invasive species of grave concern because it can carry the disease huanglongbing (HLB), also known as citrus greening. All citrus and closely related species, such as curry trees, are susceptible hosts for both the insect and disease. There is no cure once a tree becomes infected; the diseased tree will decline in health and produce bitter, misshaped fruit until it dies. HLB has been detected just once in California – in 2012 on a single residential property in Hacienda Heights, Los Angeles County. This plant disease does not affect human health.
Residents in the area who think they may have seen ACP or symptoms of HLB on their citrus trees are urged to call CDFA's Invasive Species Hotline at 1-800-491-18991-800-491-1899 FREE. For more information on the ACP and HLB, please visit: www.cdfa.ca.gov/go/acp.
—California Department of Food and Agriculture
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.