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Arizona Veg IPM: spring melons, plant resistance-tolerance, backpack sprayer calibration

Annual pest activity and insecticide surveys help support the industry’s efforts in addressing state and federal regulatory issues by providing real world information on insect pest status and insecticide usage; The terms resistance and tolerance are often used interchangeably yet the definitions denote a significant difference; Increasingly sophisticated equipment has made pesticide application more precise than ever before. 

The latest Arizona Vegetable Integrated Pest Management Update from the University of Arizona (UA) Cooperative Extension in Yuma, Ariz. released June 1, 2011.

Insect losses, insecticide usage in spring melons

By John Palumbo, UA Research Scientist and Extension Specialist

The UA Vegetable IPM Team has conducted annual surveys though interactive workshops since 2005 that document insect pest activity and insecticide usage in cantaloupes, mixed melons, and watermelons. Overall, the information provided by pest control advisers (PCAs) and growers during the workshops can be very useful to the melon industry for a number of reasons.

First, the data is extremely helpful in supporting the industry’s efforts in addressing state and federal regulatory issues by providing real world information on insect pest status and insecticides usage that otherwise would not be available. This type of information is invaluable for supporting product re-registrations, plus demonstrating the importance of a particular pest or insecticides necessary for supporting Section 18 and SLN requests.

Secondly, from an academic perspective, survey results often provide us with a historic record of insect occurrences that allows us to identify trends in pest activity and insecticide use, and can be useful for prioritizing our research and extension activities.

Finally, for PCAs, it can translate their efforts into economic terms for their clientele and confirms their value to the melon industry by showing the importance of key insect pests and cost-effective management under desert growing conditions.

For example, results from these surveys over the past six years show:

1 - costs associated with spray applications and management fees have increased steadily;

2 - two-spotted spider mites are clearly a major pest of desert watermelons, but seldom attain pest status or require control in cantaloupes;

3 - the older, broadly toxic insecticides are slowly being replaced with newer, softer, reduced-risk chemistries.

The information generated from the surveys is not surprising to growers and PCAs. However, these surveys document important pest information useful to those less involved with the day-to-day activities of IPM in desert melons.

To view a complete summary of the Lettuce Insect Losses and Insecticide Usage surveys in Arizona spring melons from 2005-2010, click on this link.

Contact Palumbo: (928) 928-782-3836 or

Plant resistance or tolerance to disease

Plant resistance or tolerance to disease

By Mike Matheron, UA Extension Plant Pathologist

An extremely valuable weapon in the battle to manage plant diseases can originate from the genetic composition of the plant. This plant genetic disease management tool is commonly referred to as resistance or tolerance. These terms are often used interchangeably; however, the definitions of each term denote a significant difference.

Resistance is defined as the ability of a plant to exclude or overcome the effect of a plant pathogen, whereas tolerance is the ability of a plant infected by a pathogen to grow without dying or sustaining serious injury or yield loss.

Resistance focuses on infection prevention. Tolerance permits the plant to grow without serious injury or yield loss after infection. Disease resistance and tolerance are not all or nothing conditions.

For example, resistance can range from its highest level, which we call immunity, through degrees of useful resistance, and finally to its lowest level, when a plant is highly susceptible to a particular pathogen. Also, resistance and tolerance usually are specific to one or a few diseases at most, and not a broad range of plant ailments.

The mechanisms within plants that create disease resistance and tolerance are many and varied. Successful suppression of pathogen activity by a plant is tied to how a particular pathogen gains entrance into a plant to initiate disease and also how a plant defends itself from that infection by one or more physiological (biochemical) or morphological (structural) changes.

One key advantage of genetic resistance or tolerance is this disease management tool will be active for the life of the plant, whereas a crop protection product, if available for managing a particular disease, has to be applied more than once to suppress the disease over a long period of time.

Also, disease management controlled by plant genetics often targets diseases for which no other known effective disease management tools are known. Building disease resistance or tolerance into plants is an ongoing activity of plant breeders, using classical as well as modern genetic manipulation techniques, to achieve this goal.

Contact Matheron: (928) 726-6856 or

Calibrating a backpack sprayer for herbicide spot applications

Calibrating a backpack sprayer for herbicide spot applications

By Barry Tickes, UA Area Agriculture Agent

Increasingly sophisticated equipment has made pesticide application more precise now than ever before. Knowledge of the exact spray volume is the basis for accurate applications.

Spray volume is determined by three variables: speed, pressure, and nozzle output. Many techniques and formulas are available for calculating the spray mix when these variables are known. Most of the newer equipment used for commercial applications contain computers that make these calculations.

Precision rapidly goes downhill, however, when people put on a backpack sprayer to selectively spot spray weeds in and around fields. When making spot applications by hand, only one of the three important variables needed to accurately calibrate the sprayer and nozzle output is often known.

Speed is often zero as the person spraying stops at each weed or patch of weeds. The pressure is often unknown as the applicator uses a hand crank to pump it up. A pressure gauge can be installed but rarely is. It is always best to calibrate the sprayer as precisely as possible although in practice this can be very difficult.

It is necessary, however, to get at least a general idea of spray volume when applying herbicides. Herbicide labels and nozzle charts can be very helpful. Many herbicide labels address the subject of spot spraying with hand sprayers and give guidelines on how to do this.

Several examples include:

Goal: “Apply uniformly to soil for pre-emergence weed control…and spray-to-wet basis for post emergence weed control.” The amount required to treat 1,000 square feet for specific rates are listed.

Gramoxone: “If the broadcast rate per acre is (chart) add the following amount of Gramoxone Inteon to one gallon of water.”

Roundup: Chart lists the amount to add to a certain volume of water, from one gallon to 100 gallons, in order to apply a certain percentage of herbicide. “Spray coverage should be uniform and complete…applications made on a spray-to-wet basis. Do not apply to point of runoff.”

Many other herbicide labels contain guidelines on spot spraying but many do not.

Nozzle charts can also be helpful. Nozzle type and size determine the spray volume, uniformity of the application, spray pattern, surface coverage, and other important factors.

There are several general types of spray nozzles used in agriculture. Flat fan, flood, hollow cone, and solid cone are the most common.

Flat fans are most commonly used to apply herbicides. These produce a flat ever spray. There are several sub types such as standard flat fan, even flat fan, low pressure flat fan, and extended flat fan.

Flood nozzles are used mainly for applying suspension fertilizers where clogging is a potential problem. These produce large droplets and are generally not suited for herbicide applications.

Hollow cones have a round orifice and produce a cone shaped pattern. These are generally used to apply insecticides or fungicides where complete coverage and penetration of the foliage is required and are generally not used for herbicides.

Solid cone nozzles produce a wider angle and bigger droplets. They are sometimes used for soil incorporated herbicides.

Once the nozzle type is selected, you can use a chart that lists spray volumes produced at certain pressures and speeds. There are several spray nozzle manufacturers. The two most common are The Spraying Systems Company (Tee Jet) and Delavan-Delta Inc.

Tee Jet is the most common in this area. The catalogue that includes the nozzle type and spray volume charts and an interactive nozzle selection guide can be reviewed online at

A spray volume of 20 to 30 gallons per acre is typical for herbicide applications. Foliar contact and soil applied herbicides (Gramoxone, Aim, Buctril, Prowl) generally work best at higher spray volumes. Systemic foliar applied herbicides (Glyphosate, Poast, Clarity) work best at lighter even volumes.

If pressure and speed are unknown, the applicator should try to simulate the coverage that would be produced from a ground application made by a sprayer set to apply this volume. This is a light even application. Something between a mist and a drench may be the most precise way to describe it. Herbicide labels often describe this as “spray-to-wet.”

Flat fan nozzles are available in several spray angles. The most common are 80 and 110 degrees. The angle will affect the proper height between the nozzle and the target. The 110 degree nozzles are designed for lower heights. The 80 degree nozzles are for higher boom heights.

Contact Tickes: (928) 580-9902 or

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