The University of California’s Early Detection Monitoring Manual for Quagga and Zebra Mussels publication defines aquatic invasive species (AIS) as ”non-native aquatic organisms that have caused, or likely will cause economic or ecological harm or impacts to human health (pg 1).”

Written by Ventura County UCCE’s Carolynn Culver and Monique Myers and Los Angeles County UCCE’s Sabrina Drill and Valerie Borel, this publication gives great background information while providing clear guidelines and instructions for monitoring small lakes, reservoirs and streams in California and is designed especially for citizen volunteer and monitoring groups.  We hope that early detection of these species in California’s waterways will reduce their negative impacts.  From the manual:

The sooner a population is detected, the more time there will be to take action and the higher the likelihood of successful eradication. Responding to an infestation at an early stage is also referred to as rapid response. Rapid response plans for AIS in general, and quagga/zebra mussels in particular, are being developed and updated in California (pg 1).”

For more information about these invasive species, check out the California Department of Fish and Game website at http://www.dfg.ca.gov/invasives/quaggamussel/.  Anyone interested in monitoring a water body is encouraged to contact your local Fish and Game authorities to coordinate efforts.

The Early Detection Monitoring Manual for Quagga and Zebra Mussels is available for viewing in the Ventura UCCE office (please call first to make sure) and for purchase online at http://anrcatalog.ucdavis.edu/. Use promo code PRVEN56 at checkout to receive a 10% discount. For orders of five or more, please contact our office for bulk discount rates.

Today, Ventura County UCCE’s Maren Mochizuki explains the routine maintenance required to keep CIMIS weather stations functioning accurately.

Data from CIMIS stations, please see previous post for details, provide accurate weather data to aid growers in irrigation planning and scheduling.  To ensure that each individual station measures and records accurately, monthly maintenance is performed at all stations.

For the CIMIS station at the Hansen Agricultural Center in Santa Paula, Staff Research Associate Maren Mochizuki checks the functioning of all the sensors.  She also checks the calibration of the relative humidity sensor using a psychrometer.  A psychrometer has one thermometer exposed to ambient air and another thermometer attached to a wick that is saturated with distilled water; a battery-powered fan forces air past the wick to evaporate the water and cool the temperature measured by the thermometer.

Using a conversion table, we can estimate the relative humidity based on the difference between the ambient temperature and the wetted temperature.  Drier air means more evaporation and a larger temperature difference between the two thermometers.  If the difference between the relative humidity calculated by the psychrometer reading and the station sensor is greater than 5%, the station sensor requires re-calibration.  The station is an inviting perch for birds so we also hose it down monthly to keep it clean.

inside of CIMIS station

psychrometer

Ventura County UCCE Farm Advisor, Ben Faber gives advice on how to identify and treat root rot in avocados.

How to identify root rot and treat it?

The canopy is thinning.  The leaves are small and yellow.  There is dieback in the canopy, with leafless tips on the branches.  You dig around under the canopy in the wetted area of the sprinkler and you can’t find roots within 6 inches of the soil surface or if you do find them, they are black.  There is little mulch under the tree.  There are weeds growing under the tree.  All these are signs of root rot disease.  But it is also a sign of lack of water, because that is what is happening – there are no roots to take up water.  At this point, gardeners may unfortunately water the tree more, which only makes conditions worse for a diseased tree; adding more water to a tree that can not easily take it up, creates asphyxiation conditions.

So what do you do if you have disease?  First of all, make sure you are irrigating to the needs of the tree by checking soil moisture before irrigating and ensuring the tree is not receiving supplemental water from another area such as a lawn sprinkler.  Add and maintain a good thick layer of woody mulch under the canopy.  Adding gypsum (15-20 pounds per tree), evenly spread under the canopy, can also help.  There are fungicides available from retail nurseries, but reviewing and modifying irrigation practices and maintaining a mulch layer are the two most important things you can do.

Read on for details on mulch and irrigation.

Mulch and avocados?

“I just raked up all the leaves under the avocado and it looks so nice,” you say.  PUT THEM RIGHT BACK.  The avocado is shallow-rooted and really depends on the natural leaf mulch to protect its roots.  In fact, the roots will actually colonize the rotted leaves as if it were soil.  This mulch is also a first line of defense against root rot.  The decomposing leaves create a hostile environment to the microorganism that causes the disease.  The mulch also helps to reduce evaporative loss of water and therefore reduces water needs.  Commercial growers will actually spread mulch in cases where trees are too young to produce adequate leaf drop for mulch or in windy areas where mulch has blown away.  The key to remember is that the mulch should be kept at least 6 inches away from the trunk to avoid collar rot, which can be caused by keeping a moist mulch against the trunk.

How to irrigate avocados

Mature avocado trees may be large above ground, but they have very shallow roots mostly in the top 8 inches of soil.  The tree therefore does not have access to a large volume of stored water.  As opposed to a deep-rooted walnut, avocados require frequent, small amounts of water.  A young tree in the summer might need multiple applications per week, but because the root system is small, each application may only be 5-20 gallons.  An older tree with its wider rooting pattern may go a week to a month between irrigations depending on the weather and rainfall.  Proper irrigation is the best way to keep the avocado from getting root rot.  Both over and under irrigation can induce the conditions for root rot, although over irrigation is more common.  And remember, it is not just the amount applied at an irrigation, but the timing that is important, as well.  Because you are managing such a shallow root system, just poking your finger into the root system will tell you if there is adequate moisture there before you irrigate again.

Ventura County UCCE staff research associate, Maren Mochizuki explains how weather data is collected and shared.

The California State Irrigation Management Information System (CIMIS) is a program of the California State Department of Water Resources Office of Water Use Efficiency.

CIMIS consists of a network of more than 120 weather stations throughout California that measure parameters such as air and soil temperature, precipitation or rainfall, wind speed, relative humidity, amount of solar radiation, and much more.  This data is recorded every minute at most stations; data from some stations are available from as far back as 1982!

Growers use this data to aid in irrigation planning and scheduling for their crops but data from any of the stations is available free to the public the day after the data has been recorded.

To find stations nearest to you and to view a sample report with data from the last seven days, please visit: http://wwwcimis.water.ca.gov/cimis/frontSampDailyReport.do

Photos of CIMIS station