Ventura County UCCE Farm Advisor Ben Faber shares with us some of his citrus tree knowledge.

Heat affects different types and varieties of citrus differently. Heat determines when fruit ripens and how sweet it will be.  Grapefruit has one of the highest heat requirements of all citrus.  Grown along the coast it will be sour, but in the Central Valley it can be decidedly sweet.  A Pixie mandarin along the coast will be 6-8 weeks later in ripening than the Valley and will hang on the tree much longer.  Acid fruits like lemon and ‘Bearss’ lime have low heat requirements and are well adapted to the coast.  The everblooming characteristics of lemons and limes are accentuated along the coast where there may be continuous cropping with lemon blooms year round.

High temperatures can have a negative effect on citrus.  Coastal citrus may suddenly drop fruit when temperatures swing from the cool 60’s to the 90’s as often happens with Santa Ana conditions.  Sudden warm weather can cause fruit to split, induce flower and leaf drop, and cause sudden burn to both the fruit and tree.  These problems are compounded by dry soil moisture and problems can be reduced if there is adequate moisture present during the heat wave.  In hot environments, some citrus like navels produce less fruit.

Lemons

There have been two earlier posting on this blog about the Asian Citrus Psyllid (ACP)and the potential crippling impact for citrus in California caused by the Huanglongbing vector (aka citrus greening disease) this insect carries. Please read the Introduction to the Asian Citrus Psyllid and Asian Citrus Psyllid: Lessons from Florida for additional information about this pest.

We are entering the time of year in which the ACP becomes most active. Make sure to check your trees regularly for signs of this insect. The Introduction to the Asian Citrus Psyllid post provides detailed photos and descriptions of how to determine if this species is on your trees. If you see this psyllid, call the California Department of Food and Agriculture at 1-800-491-1899 right away.

I recently asked Ventura County UCCE Farm Advisor Ben Faber what I should share about the ACP. He said to remind people how important it is to make sure to declare plant items when crossing the border. It is people who are spreading this around.

Recently UC Agriculture and Natural Resources’ News and Information group released a video demonstrating for the general public how to detect Asian Citrus psyllids on their garden trees. The video is available at:

http://news.ucanr.org/newsstorymain.cfm?story=1233

In addition, our office has a supply of bookmarks that contain photos and instructions for identifying both ACP and trees struck by Huanglongbing. They are available in both English and Spanish. Please contact our office if you would like some.

ACP infestation

ACP feeding damage

Distorted leaves from ACP

Ventura County UCCE Farm Advisor, Ben Faber shares his knowledge of avocados. Today’s topic:

The avocado is an amazing fruit.  It grows on a tree and comes to maturity, reaches certain oil content and a stage at which it will ripen, but does not ripen on the tree.  It needs to be removed from the tree before it will soften.  If the fruit is removed before it has reached maturity it will not soften, and will remain rubbery and inedible.  One of the problems is that the fruit will hang on the tree for an extended period of time and it is hard to know when they are mature.  Avocados are not like apricots where you have about 2 weeks to get the fruit off before it falls off. As the fruit stays on the tree in gradually develops more and more oil content and has a richer flavor.

If the fruit stays on the tree too long, the oil can develop an almost rancid flavor, however.  So it is good to know when the best, acceptable flavor is achieved.  Avocado varieties fall into general seasonal periods when they are mature –‘Fuerte’ in winter, ‘Hass’ in spring/summer, ‘Lamb-Hass’ in summer/fall.  Or you can pick a fruit and put it on the counter and watch to see if it softens evenly.  If it does in a two week period, the rest on the tree are good to go.

Ventura County UCCE Farm Advisor, Ben Faber shares his knowledge of avocados. Today’s topic:

The most important thing you can do before planting is assess the pH of the soil before planting.  Avocados are very sensitive to soil pH greater than 7.  Their uptake of iron and zinc can be terribly compromised and they will suffer.  Correcting the soil pH prior to planting is the easiest way to approach the problem, rather than trying to correct it later when the tree is in the ground.  Otherwise, it becomes expensive and takes a long time to correct the problem without killing the tree.  Elemental sulfur (not popcorn sulfur) in pellets is the easiest way to accomplish this.  Watering and waiting for the sulfur to make the change and then checking to make sure the pH is really down takes about 6 months.

As for nutrients, though, the most commonly required ones are nitrogen and potassium.  These can be applied as either organic (fish, soybean, manure, etc.) or synthetic forms (urea, ammonium sulfate, potassium sulfate, etc.) or a combination.  The thing to remember is that the tree likes small, frequent amounts of nutrients because of its shallow root system.  And because it is a subtropical plant, it goes quiescent in the winter and when the soil is cold.  So nutrient applications like nitrogen are best applied when soils are warm, from spring though fall.

Newly-planted trees do not need supplemental nutrients, they are loaded up from the nursery and the young root system can easily burn until it gets established.  In the first year, use the equivalent of 1 ounce per tree of nitrogen in 4- 5 applications over the spring/fall.  The following year double that amount and do so for each succeeding year for the next 5 years.  The more small applications you make the less total nitrogen fertilizer you will use. Use the equivalent amount of nitrogen whether it is a synthetic source or an organic source.  Once the tree has started to develop a thick leaf mulch, it is possible to back off on nitrogen applications because now the mulch is contributing some of the nutrients.  In many garden situations where mulch is maintained, by year 10 the nutrient status is self-sustaining and nitrogen fertilizer may not be needed at all.  Just keep an eye on the leaf color to make sure it stays green, indicating adequate nitrogen.

When the avocado starts bearing fruit about year three, it may need potassium.  This is not necessary in all situations throughout the state, but the harvested avocado fruit contains twice as much potassium as nitrogen and when the fruit is removed the tree can start showing potassium deficiency symptoms.  This can be analyzed at a lab, but probably the best thing to do is just apply potassium sulfate at an equivalent rate to nitrogen or to use triple 15 fertilizer to meet both the nitrogen and potassium needs.  Organic growers can use organic potassium sulfate or kelp.  Although phosphorus is used by avocados, there are no documented cases in California where supplemental phosphorus needs to be applied.