Stem and leaf blights are symptoms that appear for various reasons – high rainfall or humidity, spray burn, chewing insect infestation.  Here in California we can add other causes, such as drought and salinity burn.  These conditions can cause wounding of leaf and stems allowing entry of fungal spores that can cause leaf and stem dieback.  This condition is most common near the coast where weather conditions can change from mild and low temperatures to extremely high temperature with winds, such as the Santa Anas or the Sundowners in Santa Barbara.  Leaves suddenly dry out, causing cracking either at that time or when they are rehydrated with irrigation.  This allows spore entry into the wounds and permits the pathogen to grow in the dead tissue.  Symptoms appear 7 – 10 days after the stress.  These are decay fungi that create these spores and they are the ones that cause decay of dead tissue on the ground.  So their spores are everywhere. 

The greater part of a tree is dead – the woody part of the branches and trunk.  And it is dead tissue that these fungi are feeding on. Most trees will limit the growth of the fungus by sealing off the infection with gums of various sorts.  In that case, the disease is limited and you may only see a leaf or small branch dying back. In mature trees it is possible to see a small branch here and there that has died back, but the bulk of the canopy is still green.  It has been called “salt and pepper syndrome”, because of that speckled appearance.  In the case of young trees with their smaller root systems and a lesser ability to seal of the disease process, a whole tree can die.

Since this is a severe water stress or salt stress induced problem, the most important management issue is to watch the weather forecasts predicting unusual hot, dry weather and make sure the trees are adequately irrigated going into the stressful period. Shallow rooted trees like avocados are more prone to dry out rapidly in these high water demand situations, but it can be occur in other trees (citrus, apple, peach) and shrubs if the weather conditions are severe enough. With poor leaching due to low rainfall, this can be more of a problem

The only solution to the symptoms is to cut out the diseased parts to prevent its further spread. Once the disease starts spreading, the fungus can produce copious amounts of spores, which in the case of avocado can cause cankers and rots on the fruit.

Figure.  In the case of young trees, the whole tree may die from blight.

Here's a list of links for growers and homeowners on how to prepare for fire and in the case of fruit trees, how to treat them after they have burned and how to calculate the loss of a commercial fruit tree.

Tree and Vine Loss Calculators

Spread sheets to help you calculate loss

Calculate Cost of Fire Damage to Avocado and Citrus Trees

Information from Ben Faber, Soils and Water, Avocado and Minor Subtropicals Advisor

Living with Fire

Information on how to care for fire damaged trees from Ben Faber, Soils and Water, Avocado and Minor Subtropicals Advisor

Safe Landscapes Project

Information on fire ecology and fire safe landscaping for homeowners, developed by Sabrina Drill, Natural Resources Advisor

UC Center for Fire Research and Outreach

Information on fire science from UC experts. Includes information on how to make homes and other structures more fire resistant, developed by Steve Quarles, Statewide Wood Performance and Durability Advisor

Local Fire Departments - have regulatory information you may need

Ventura County
City of Ventura
City of Oxnard
City of Fillmore
City of Santa Paula

Santa Barbara County
City of Lompoc
City of Santa Barbara
City of Santa Maria

Publications Available From University of California ANR Catalog

You can find the publications listed below at theUniversity of California DANR Catalog site (In the ANR Search type fire) and order more than one publication at a time or you may click on one of the links below.if you purchase a priced publication enter the promotion code PRVEN56 at check-out. You'll receive a 10% discount on your order, and a portion of the sales will benefit local programs.

A Property Owner's Guide to Reducing Wildfire Threat - describes ways homeowners can reduce the threat of fire to their property. Cost $1.50

Home Landscaping for Fire - Incorporating fire safe concepts into your landscape is one of the most important ways you can help your home survive a wildfire. FREE

Landscaping Tips to Help Defend Your Home from Wildfire - You can have both a beautiful landscape and a defensible fire-safe zone. FREE

Recovering from Wildfire - discusses issues that family forest landowners should consider following a wildfire. Cost $5.00

WildFire: How Can We Live With It? (DVD) - This program contains general information about wildland fire in California. Cost $20.00

Companion Set: How Can We Live with Wildland Fire? (Publication and DVD) - What role does fire play in the natural cycle and what choices can we make about coping with wildland fire? Cost $27.50

How Can We Live with Wildland Fire? - What role does fire play in the natural cycle and what choices can we make about coping with wildland fire? Cost $10.00

Soil moisture sensors fall into two broad categories, volumetric and tensiometric methods. One tells you how much water is in the soil and the other tells you how tightly the soil holds on to the water.  Volumetric methods require a calibration of the sensor to the soil, whereas tensiometric is good to go when installed.  For both methods, the grower learns to keep soil moisture within a given range of values and, in theory, the plant is kept in a better condition with improved health and yields and potential improved irrigation efficiency. 

The most common volumetric methods rely on utilizing the dielectric constants of the soil and water, with water’s dielectric constant being much greater than soils’.  The velocity of an electromagnetic wave or pulse depends on soil moisture content.  These sensors have become widely used because they have a good response time, do not require maintenance and can provide continuous readings, allowing for automation.  There are several different methodologies used: Time Domain Reflectometry,  Frequency Domain Reflectometry (Capacitance), Amplitude Domain Reflectometry (Impedance), Phase Transmission, and Time Domain Transmission.  There is quite a range in: (1) prices for these different devices, (2) requirements for calibration with soil moisture content, and (3) requirements for close soil contact.  Some devices are affected by the chemical nature of the soil.  Even if they are not calibrated they can be used as relative change in moisture content over time.

The tensiometric methods include: Tensiometers, Gypsum Blocks, Granular Matrix Sensors, Heat Dissipation and Soil Psychrometer.  These techniques require the sensor to come into equilibration with the soil moisture and generally are unaffected by soil salinity. Gypsum blocks and Granular Matrix are not very responsive in sandy soils and require good soil contact.  These methods are less affected by salinity and do not require soil calibration, because they are reflecting the soil moisture tension the roots are seeing.

All soil moisture sensors need to be placed in a position that represents the irrigated area.  They need to be placed in the active root zone where water is applied and taken up and must be near trees representative of the whole irrigated area.  They should not be next to a sick tree, a smaller tree compared to the other trees or be in an area that obstructs applied water (such as under a canopy that intercepts applied water).  It is always best to reinforce sensor values with manual field measurements with a soil probe to ensure that sensor placement and response is truly reflective of what is going on in the field, before completely relying on the sensor values.  As with all field equipment, occasional visual inspection of the field and sensor readings should be made to make sure the situation has not changed, such as an emitter has clogged or broken near the sensor.

Volumetric Sensors

+ Prices as of 2009

Tensiometric Sensors

 These sensors can be purchased individually and installed by the grower, or increasingly there are companies that provide a monitoring station that includes soil moisture, sensors for estimating plant evapotranspiration , data logger and software that determines an irrigation schedule for the crop.  Some of these systems are outright purchase and some are for lease.  In the future, there will be affordable satellite imagery that can help in irrigation scheduling, showing how rapidly this technology is changing.

If you can’t speak the language, you can’t follow the conversation.  Talk about adjuvants used in agriculture can be filled with unfamiliar terms like activator, non-ionic surfactant, penetrant, humectants, and buffers.  To help growers who want follow a sales pitch or discussion on adjuvants, the following article lists and describes common adjuvant categories by function.  This is the first of a series to help growers better understand adjuvants and their effective use.

There are two types of adjuvants – spray adjuvants and formulation adjuvants.  Spray adjuvants are packaged separate from pesticides.  Formulation adjuvants are mixed with the pesticide active ingredient during packaging and formulation.  This article is concerned specifically with spray adjuvants. 

Spray adjuvants are pesticides according to California Department of Pesticide Regulation (CDPR).  They must be registered.  Spray adjuvants are defined by CDPR as “a product solid in a separate package and intended to be used with another pesticide to aid the application or enhance the activity of the pesticide.”  Growers must report spray adjuvant use in their monthly pesticide use reports. 

There are two general categories of spray adjuvants: 1) activator adjuvants and 2) utility adjuvants.  Activator adjuvants directly enhance pesticide performance once the spray hits the plant target.  They include wetter-spreaders, stickers, penetrants, and humectants.  Utility adjuvants help make the spray application process go better.  This group includes defoamers, drift control agents, deposition aides, water conditioners, acidifiers, buffers, and colorants.  A single adjuvant product can be both an activator and a utility adjuvant.  For example, a product that contains a spreader/penetrant plus a buffer/acidifier is both an activator and utility adjuvant.

There are several categories based on product function within the general groups of activator and utility adjuvants.  Many adjuvants fit into multiple categories, as a particular set of ingredients may provide spreading and penetrating properties to a single packaged product. 

Wetter-Spreaders:  contains surface-active ingredients – surfactants -- that reduce the contact angle of the spray droplet on the target (see Figure 1.).  This allows the spray solution to contact more of the target surface.  Spreading is essentially an extension of the wetting process.  A spreader adjuvant allows the spray droplet to spread over a larger area of the target compared to a droplet with no spreader. 

Most pesticides are mixed with water and sprayed.  Wetter-spreaders behave differently in your spray tank based on their electrical charge in water.  Surfactants –the active ingredients in wetter-spreader adjuvant -- are further categorized as non-ionic, cationic, anionic, or amphoteric surfactants.  Why is this important to a grower?  When choosing an adjuvant to use with a water soluble ionic herbicide, you don’t want an adjuvant “tying up” your pesticide and reducing pest control.  For example, when mixed in the spray tank, a cationic spreader may bind to an anionic herbicide, possibly reducing the pesticide activity. If you use an adjuvant, make sure it matches the pesticide label adjuvant recommendation.   

Wetter-spreaders are surface active because they contain surfactant molecules that have a fat/wax loving (lipophilic) end and a water loving (hydrophilic) end.  Common ingredients include fatty amines, glucosides, alkyphols, alkylamine ethoxylates, polyethylene oxides, and organosilicones.

Stickers: contains non-evaporating ingredients that resist dislodging of the spray deposit from the target surface.  Common sticker ingredients include synthetic latex, low volatile oils, pinene polymer, water-soluble polymers, and resins.  The less water soluble the ingredients the lower the “wash off” potential of the pesticide deposit. 

Humectants: contains ingredients that reduce spray droplet evaporation before and after it reaches the

target.  Humectant materials include glycerin, various glycols, petroleum oils, vegetable oils, and urea.   

Penetrators:  contain ingredients that help the chemical enter the target plant once the spray is deposited.  Petroleum oils, vegetable oils, or modified vegetable oils are common penetrator ingredients.

Compatibility Agents:  commonly used to keep a homogeneous solution in a spray tank that contains multiple ingredients, usually including liquid fertilizer.

Defoamers: eliminate or suppress foam in the spray tank. 

Drift Control Agent:  used to reduce the percentage of spray droplets below a certain diameter in an application.  Small droplets are considered “driftable fines”.  The smaller the droplet, the farther it will move with wind.  Droplets with a diameter less than 150 mm are frequently characterized as “driftable”.  Drift control agent commonly include polyacrylamides and polysaccharides.  

Deposition agent: do not change spray droplet size, but improve the amount of pesticide deposited on the target – indirectly reducing drift -- or improve the uniformity of spray deposits. 

Water Conditioner: eliminates or reduces the interaction of ions in the spray solution with the pesticide.  For example, glyphosate efficacy can be reduced when hard water is used in the spray tank.  A range of materials including chelating agents, citric acids, and fertilizer salts such as ammonium sulfate and ammonium nitrate are used as water conditioners to improve glyphosate activity when the spray water source contains hard water.

Acidifier:  usually a dilute strong acid solution used to reduce spray water pH.  An acidifier will commonly not maintain – that is, buffer – the spray solution at a certain desired pH range.  Addition of an alkaline pesticide or fertilizer will increase the spray solution pH that was initially lowered by an acidifier.  

Buffer:  a product that will resist change in the spray solution pH.   Buffers will limit the change in solution pH when an acid or base are added to the tank.  A buffer/acidifier will reduce spray water pH AND hold the pH in a certain range.  How long the pH is held in a certain range when other pesticides or fertilizers are added differs between products.  The correct rate of buffer depends on the water source and materials in the tank.  Commonly used buffers are buffer/acidifiers using ingredients such as phosphates or organic acids.  

Colorants:  alters the color of the spray solution so that previous spray passes are visible to the applicator. 

So, there’s the general “line up” of adjuvant materials.  Once you know the players and their roles in the spray tank, you can begin to select the right material for the job.