Subtropical Fruit Crops Research & Education
University of California
Subtropical Fruit Crops Research & Education

Posts Tagged: subtropical crops

A New Posting of the Topics in Subtropics Newsletter

Here's the Fall newsletter of Topics in Subtropics, and it is on time.  Winter hasn't started yet, but get ready.

And the topics are:

  • Real-Time Sensor for Early Detection of Citrus Huanglongbing (HLB)
  • The 2016 International Citrus Conference
  • UC Riverside Scientists Evaluate Trunk Injections of Pesticides for The Management of Ambrosia Beetles in California Avocados
  • An Overview of Mango
  • Water Based Latex Paint as a Means to Track Ambrosia Beetle Activity on Infested Trees

To subscribe:


avocado body rot2
avocado body rot2

Posted on Friday, December 9, 2016 at 8:57 AM
Tags: avocado (283), fruit trees (5), mango (4), subtropical crops (8)

Dealing with Drought

It ain't over yet, and this last week we had a wonderful 2 day meeting with folks who have dealt with drought in many different ways.  Here are presentations made by people from Israel, Australia and California.  Soon the actual videos will be available, but now see the powerpoints.!presentations-and-documents/niui7

 The grower panels are wonderful, but are not uploaded at this point



Session I: California Response to Drought

9:15am // Overview of California Drought Response

9:30am // El Nino Forecast for California and Possible Impacts on Irrigated Agriculture


Session II: Technology of Water Management

9:45am // Soil Water Sensing

10:15am // ETc Estimates - Weather Stations (CIMIS), surface renewal

11:00am // Salinity Measurement

11:30am // Consideration In Selecting Water Stress Indicators

12:00pm // Precision Water and Fertility Management During Deficit Irrigation


Session III: Alternative Water Supplies

1:30pm // Irrigation With Recycled and Desalinated Water

2:00pm // Effects of Irrigation With Poor Quality Water on the Soil - California Experience

2:30pm // Effects of Irrigation With Poor Quality Water on the Soil - Israeli Experience

3:00pm // The Challenge of Sustainable Irrigation with Water High in Salts: Lessons from Dates, Olives and Grapevines


Session IV: Water Management Strategies During Drought

3:45pm // Water Management Strategies during Drought - Australian Experience

4:15pm // Irrigation Planning/Budgeting - ETo Forecasting, Deficit Irrigation Concepts, Crop and Irrigation Variability

4:45pm // Cultivation Under Protective Structures to Save Water





Session V: Technology Demonstrations​

8:00am // Irrigation Scheduling - Australian Experience - IrriSAT Approach (IrriSAT Supporting Materials)

8:30am // Using the Pressure Chamber for Drought Mangagement Decisions

9:00am // Irrigation System Evaluation

9:30am // Salinity Mapping for Water Management


Session VI: Conncurrent Breakout Groups

10:30am // Citrus - Israeli Experience: Long Term Effects of Deficit Irrigation, Salinity, and Rootstocks on Orchard Productivity

10:30am // Grapes - Table and Wine Grape Irrigation Scheduling

10:30 // Deciduous Nut Crops - Irrigation and Crop Load Interactions

10:30// Almond Irrigation, the Israeli Experience

11:15am // Olives - Israeli Experience: Cultivation Under Limited Water Availability

11:15am // Grapes - Wine Grapes Irrigation - Coastal Vineyards

11:15am // Deciduous Nut Crops - Almond Irrigation - Israeli Experience

1:00pm // Avocado - Israeli Experience

1:00pm // Grapes - Wine Grapes Irrigation: San Joaqin Valley

1:00pm // Deciduous Nut Crops - California Experience

1:30pm // Deciduous Nut Crops - Pistachios Irrigation

1:45 // Subtropical Crops - California Experience

1:45 // Grapes - Irrigation, the San Joaquin Valley

2:00pm // Deciduous Nut Crops - Walnut Irrigation

2:30pm // Grower Panels

3:15pm // Concluding Remarks

water movement
water movement

Posted on Saturday, January 16, 2016 at 7:30 AM
Tags: avocado (283), citrus (327), deciduous crops (2), drought (41), grapes (2), irrigation (78), subtropical crops (8), water (49)

Think Cover Crops When it Rains, But You Gotta Think

Soil likes to be covered at all times.  It doesn't “want” to be exposed to the elements, so you either cover it (plants, asphalt, paper etc.) or it will cover it for you with plants (weeds).  If it can't be covered fast enough, it disappears – erodes.  This can be from wind or rain or just natural movement down slope.  Plants that are managed for other than their agricultural return are called cover crops, although they can also have a crop that is saleable. Often weeds can be managed to be a cover crop, as well.

We are looking at a possibly wet winter and many tree crops grown on hillsides and sloping ground are prone to soil erosion.  Covers can be grown year round, but that usually means they require water all year round.  That means they need an irrigation system dedicated to their needs.  It also means having extra water which may be limiting.

A winter cover crop that grows out in the winter, does its thing (although that “thing” can include lots of other things, e.g. insectary, nutrients, water retention, etc.), and then dies or goes dormant, can be ideal.  It also requires less water than a permanent cover.

But there is a big problem here. Establishment of an introduced cover still requires water.  Rainfall in Southern California is erratic and there may be early rains to germinate seed, but it may not be consistent enough to get the plants established.  In fact, they may die for lack of further rain or be delayed.

Delayed germination means that soil is cooler and there is less growth. The real growth may occur after there has been sufficient rainfall by January and February when the soils are cooler and there is even less chance for growth

So when rainfall is doing its worst, there's no effective cover.  Or what cover there is, is what has germinated from “native” seed.  It may not have the characteristics you want for management: low stature, low entanglement with the trees, low water use, holds the soil without holding up harvest, etc.

So what do you do?  There are several approaches. You can move the sprinklers out into the middles and irrigate up the seed.  If you are in a limited water situation, you can do alternate middles, not cover cropping the whole area, or every third middle.  Whatever it takes to break the surface flow of water.  Or you can turn to mulching.  Put down sufficient mulch in a middle or every other middle to break overland water flow. 

Cover cropping is easier than mulching, but it takes water and timing.

Below are two websites with descriptions of cover crops and how to distinguish them from “weeds”.  Often a good cover can be the residential weeds. A low–lying cover allows pickers in to get lemons without mess and fear of snakes.  It also means that it can be more easily treated (mowed, weed whipped) at the end of the rainy season to reduce fire hazard.



1)      Characteristics of different cover crops

2)      Weed identification from the UC IPM

citrus with cover
citrus with cover

Posted on Tuesday, September 29, 2015 at 3:09 PM
Tags: avocado (283), citrus (327), cover crops (3), erosion (5), rain (17), subtropical crops (8)

Avocados and Salts

Some call it tip burn which is often what you see on an avocado as it goes into flowering.  The areas where avocado are grown typically have a lot of salts in the water, but also specific salts like sodium and chloride.  Over the irrigation season (which is all year long there is little or no rain), the salts in the water/soil are taken up by the tree.  In adequate rainfall years, there is enough water to leach those accumulated salts from the root system.  When we go for several years with low rainfall and we keep irrigating with the poor quality irrigation water, the trees develop die back at the tips and is conditions worsen more and more of the leaf is called.  This can get to the point where you can not call it die back any longer.  It's called leaf drop.  I've recently seen a number of orchards that are completely defoliated.  No leaves.  We have had a number of homeowner calls asking what the problem is and what they can do about it.  The damage is done and those leaves are not coming back.  It's possible to reduce the damage if one acts early on by applying more water than is usually applied to aid the leaching process, but if it is poor quality water, there will still be damage, but possibly not defoliation.  With high priced water or where water is being rationed, many growers and homeowners do not have themake the option of putting on the excess water.  There is no chemical or equipment that is going to make the situation better.  When you trees defoliating, you want to cut out those that are diseased or you know have been poor producers and put what water you have on the remaining trees in better condition.

This advice is good for other evergreen tree crops like citrus, although they are not as sensitive as avocado.  Avocado is an indication of how bad it really is.

avocado chloride damage
avocado chloride damage

Posted on Monday, February 23, 2015 at 7:09 AM
Tags: avocado (283), citrus (327), defoliation (3), leaf drop (1), salt damage (8), subtropical crops (8), tip burn (8)

White Sapote

The white sapote is a relative of citrus. However, it is too distant botanically for the fruit to resemble, be graft compatible, or hybridize with citrus. The white sapote should not be confused with other fruit termed sapote (aka zapote) which only signifies a soft, sweet fruit in the Nahuatl Indian language. The white sapote is a native of central Mexico and appears to be well adapted to any area in California in which oranges can be grown. The fruit is slightly larger than a baseball. The thin, smooth skin is green, yellow, or orange in color. The smooth textured pulp, contained around* 5 to 7 moderate sized seeds, is pleasantly flavored (banana + peach). For some tastes the fruit of many of the cultivars lacks sufficient acidity to offset the sweetness, nevertheless a market for fresh fruit would likely exist if it were not for its poor handling characteristics. No market has been established for preserved products such as jelly, juice or wine. The enormous productivity in combination with a potentially mature height of 30 to 50 feet and an extensive lateral root system make the white sapote a problematical choice for the home garden.


The citrus fruit family, Rutaceae, includes about 900 tropical and temperate species of which citrus are the most commercially important. Other less well known Casimiroa species having edible fruit are the woolly-leafed sapote (C. tetrameria) and matasano (C. sapote).

The seedling white sapote tree grows to 50 feet under ideal conditions; however, many grafted cultivars tend to grow more slowly and can be held between 15 and 20 feet.

The leaves are mostly evergreen, palmately compound with 5 to 6 inch leaflets, and sometimes hairy on the underside. The odorless greenish yellow flowers are 4 or 5 parted and born in axillary panicles The flowers are hermaphrodites; however, the stigmas may prematurely abort. Cross pollination sometimes improves fruit set. The 2 to 6 inch ovoid fruits are borne 6 to 9 months after pollination, generally in October and November. The fruit is soft when ripened and has a smooth consistency with a delicate banana flavor with hints of peach. In poorer varieties and overripe fruit, the bitter overtone predominates along with an unpleasant resinous flavor. Although tree ripened fruit has the best flavor, the fruit is readily bruised and damaged when ripe. Some cultivars can be picked early and ripened to good flavor while others become overly bitter.

Climatic requirements

The white sapote is hardy northward to Chico except for the desert areas. Frost damage occurs at about 22oF; however, young trees can be damaged at 30oF.

Soil Requirements

The white sapote prefers well draining soils but will tolerate almost any soil. For healthy trees, the pH should be between 5.5 and 7.5. Salty soil conditions should be avoided.

Cultural Requirements

Spacing and training

The terminal bud should be removed from young trees in order to encourage branching.


The white sapote prefers regular, deep watering. Shallow watering will encourage surface roots which can be a nuisance for the home gardener.


White sapotes prefer regular applications of nitrogen fertilizer. Minor nutrient deficiencies (not a major problem) can be treated as with citrus.


The main purpose of pruning is to control size and secondarily shape.

Pests and Diseases

In California the tree is generally pest free. Black scale, mealy bugs and aphids are occasional problems which are best checked by controlling ants. Snails will damage the fruit. Phytophthora and armillaria are not problems.


Seedlings are considered too variable to be reliable producers of good fruit. Clonal reproduction is normally done by grating and budding as with citrus. Grafted trees bear in 3 to 4 years.

Harvesting and Storage

The poor handling characteristics of the fruit have limited its commercial potential. The very thin skin provides little protection against bruising which is aggravated by the fact that if picked when underripe the fruit will not ripen to full flavor and pick up an unpalatable bitterness. Overripe fruit also becomes bitter. Careful selection of cultivars can mitigate these drawbacks.


Orchard costs should be approximately the same as oranges or less.


White sapotes are seldom available in markets. Development of better handling cultivars would appear to be essential if a market for fresh fruit is to be established. Just as important is the establishment of other uses, for example, those which would allow use of bruised fruits. One challenge is that the delicate flavor of white sapote is easily lost if mixed with other fruits such as lemon to provide a better acid, sweetness balance.


White sapote
White sapote

Posted on Wednesday, February 26, 2014 at 9:24 AM

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