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Arizona Veg IPM: insecticide use, lettuce drop, pigweed and the lysimeter

Arizona Veg IPM: insecticide use, lettuce drop, pigweed and the lysimeter

Pyrethroids, applied as foliar sprays and chemigations, are consistently the most commonly used insecticide class in desert head lettuce; Pigweeds are easily identified by physical characteristics but one species of pigweed can hybridize with another and become less distinguishable; A lysimeter is a device to measure the amount of evapotranspiration - the sum of evaporation and plant transpiration. 

The latest Arizona Vegetable Integrated Pest Management Update from the University of Arizona (UA) Cooperative Extension in Yuma, Ariz. released May 17, 2011.

2010-2011 insecticide usage in head lettuce

By John Palumbo, UA Research Scientist and Extension Specialist

Results from the recent Lettuce Insect Losses Workshop reveal some interesting trends in insecticide usage on desert head lettuce. Data was summarized from pest control advisers (PCAs) and grower surveys completed over the past seven years.

When compared by class of chemistry using the IRAC mode of action classification system, the pyrethroids, applied as foliar sprays and chemigations, have consistently been the most commonly used insecticide class by far. Over the past few years the usage has been declining, but only slightly.

The spinosyns (Radiant and Success) are the second most commonly used class of insecticides, where the usage increased this season compared.

In contrast, estimates of diamide usage (Coragen, Voliam Xpress, Vetica) showed that PCAs used almost 20 percent less of these products in 2010 and 2011.

Not surprising, Ketoenol usage (Movento) was up about 40 percent compared to 2010 and neonicotinoid usage remained about the same.

The usage of the broadly toxic, old chemistry (organophosphates /carbamate/endosulfan) on head lettuce acreage continued to decline in 2010 and 2011; relative to the newer, selective reduced-risk products which overall increased considerably this season.

The most commonly used insecticides in fall and spring lettuce also correspond to the key pests that typically occur throughout the season.

To view a summary of the insecticide usage by chemical class over the past seven seasons, as well as the 15 most commonly used insecticides on head lettuce in 2010-2011, click on this link - Insecticide Use AZ Head Lettuce 2005-11.

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

Management considerations for lettuce drop

Management considerations for lettuce drop

By Mike Matheron, UA Extension Plant Pathologist

This subject may be a distant memory at this time for those that deal with this disease in the desert southwest. However, in a few short months lettuce plantings will be in place and lettuce drop will be a concern.

Management of lettuce drop was discussed at the just completed 2011 Desert Agricultural Conference. The slides used for this presentation are available for your examination here: "Lettuce Drop: Current and Future Management Considerations"

Contact Matheron: (928) 726-6856 or



By Barry Tickes, UA Area Agriculture Agent

Pigweeds are some of the most common summer annual broadleaf weeds in the low deserts. Although they are often lumped together, there are four different species of pigweed common here and more than 10 species that occur as weeds in California and Arizona. The growth habits and response to herbicides are similar.

It is easy to identify the pigweeds by physical characteristics but one species of pigweed can hybridize with another and become less distinguishable.

Palmer amaranth, Amaranthus palmeri, is probably the most common pigweed species found in this region. It is very aggressive, fast growing, and can become six-feet tall or higher if uncontrolled. It has one thick stem and several lateral branches.

The leaves are lance shaped, hairless, and have distinctive white veins on the underside. It has flowering tassels that become stiff and spiny. This species has become resistant to Glyphosate in many parts of the county.

Redroot pigweed, Amaranthus retroflexus, is probably the second most common pigweed species. It is shorter and the seed heads are smaller, in clusters, and have stiff spine-like scales. It has leaf hairs on the margins. The veins and lower stems are often reddish. This species will hybridize with palmer amaranth and become less distinguishable.

Tumble pigweed, Amaranthus albus, is very different from palmer and redroot pigweed. It grows lower to the ground and has many branches that turn upright. The leaves are much smaller and narrower. The numerous stems are light green rather than red.

The seed heads are small, spiny, and at the base of the leaves rather than in long terminal spikes. When mature, the branches are sticky, stiff bristles that break off at the ground and “tumble” with the wind.

Prostrate Pigweed, Amaranthus blitoides, is very similar to tumble pigweed but the stems are more prostrate, grow close to the ground, and form mats. The stems and leaves are smaller and reddish rather than light green.

Contact Tickes: (928) 580-9902 or

What is a lysimeter?

What is a lysimeter?

By Marco Pena, UA Research Specialist

While sampling for whitefly at the University of Arizona Yuma Ag Center (YAC) I saw this huge block of soil suspended in a tank. When I asked what it was I was told a "lysimeter." Obviously my next question was what is a lysimeter?

A lysimeter is a device which can be used to measure the amount of evapotranspiration - the sum of evaporation and plant transpiration. By recording the amount of precipitation that an area receives and the amount lost through the soil and its vegetation, we can calculate the water lost by evapotranspiration.

There are two types of lysimeters: weighing and non-weighing.

YAC researchers are conducting projects with weighing lysimeters. A weighing lysimeter, which in this case is a big square tank with weight cells on each corner, shows the amount of water that crops use and the loss of water as vapor through stomata.

This is done by constantly weighing the block of soil in a field to detect losses of soil moisture. The crop, in this case cauliflower, is grown in the soil tank which allows the estimation of crop needs.

The rainfall input and water lost through the soil is also calculated. The data is constantly collected and automatically sent to the computers at the YAC. Also the relation between the weather and water usage by different crops is established using the AZMET weather stations.

Finally the water that infiltrates below the root system is collected, then pumped out of the tank, and analyzed for various elements.

For more information, contact Charles Sanchez at the YAC at (928)782-3836 or

Contact Pena: (928)782-3836 or

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