The latest Arizona Vegetable Integrated Pest Management Update from the University of Arizona (UA) Cooperative Extension in Yuma, Ariz., released April 3, 2012.

Lettuce insect, disease, and weed losses workshop – April 11

By John Palumbo, UA Research Scientist and Extension Specialist

The 2012 Lettuce Insect, Disease, and Weed Losses Workshop will be conducted April 11 at the Yuma Agricultural Center in Yuma from noon to 2 p.m. Lunch will be provided.

This workshop has been invaluable to the Veg IPM Team since it allows us to develop accurate “real world” data on crop losses and pesticide usage which is important to the assessment of our integrated pest management (IPM) programs in Arizona.

Quantifiable measurements of pesticide use patterns, costs, target pests, and yield/quality losses due to key insect, disease, and weeds are the most objective tools for assessing change in systems. This data helps build relevant databases for measuring user behaviors and the adoption of new IPM technologies.

This is information important for several reasons.

First, specific data on pesticide use patterns and pest losses can be useful for providing information to the Environmental Protection Agency and other regulatory agencies in submitting Section 18 and 24c requests, plus support the tolerance of older active ingredients critical to the lettuce industry.

In addition, it can directly demonstrate the value of new pest control technologies and IPM tactics.

From an academic perspective, these databases can re-direct the efforts of the University of Arizona’s College of Agriculture and Life Sciences by providing key stakeholder input to our applied research and extension programs.

This “real world” input from the industry documents the relevancy of key pest problems and has become mandatory for competing for federal grants.

Finally, for pest control advisers (PCAs), it can translate their efforts into economic terms for clientele and confirms their value to the lettuce industry by showing the importance of key insect pests and cost-effective management in desert lettuce production.

We hope you can make it to the workshop and participate in this important process. Two Arizona/California CEUs have been requested.

More information on the workshop can be found here.

Remember: “when in doubt - scout.”

Contact Palumbo: (928) 782-3836 or jpalumbo@ag.arizona.edu.

Persistence of Sclerotinia

By Mike Matheron, UA Extension Plant Pathologist

The 2011-2012 winter lettuce production season is coming to a close in the desert southwest region of Arizona. Transitioning to warm weather crops, the presence of Sclerotinia drop in former lettuce fields may quickly fade from the memories of growers and PCAs.

Although the crop and the disease are now gone, the fungal pathogens Sclerotinia minor and Sclerotinia sclerotiorum are still present in these fields in the form of over seasoning structures called sclerotia.

These small fungal bodies, produced in large numbers on infected lettuce plants, were incorporated into the soil along with the remains of diseased lettuce plants and will allow both pathogens to carry over in the soil to await the planting of the next crop of lettuce or other susceptible crop.

How long sclerotia survive in the soil depends on several factors. High soil moisture and temperature greatly hasten the destruction. Increasing soil temperatures due to solar radiation, which peaks during July and August, combined with high soil moisture supplied by irrigation of warm-season crops, will help reduce the number of viable sclerotia in portions of the field, especially in furrows where the soil moisture is high.

Flooding of infested field soil for at least four weeks during the hottest months of July and August in the Yuma area has shown to destroy virtually all sclerotia of both fungal pathogens.

Contact Matheron: (928) 726-6856 or matheron@ag.arizona.edu.

Soil-applied herbicides

By Barry Tickes, UA Area Agriculture Agent

Foliar-applied herbicides almost always have more uniform activity on plants than soil applied herbicides. This is largely because the conditions that affect activity are more uniform above the soil than below the ground.

It is not uncommon to see inconsistent activity with soil-applied herbicides. It is also difficult to predict where and how long the effects of these herbicides will occur.

Many factors affect soil-applied herbicides. In this desert region where crops are intensively irrigated and the soils are low in organic matter, the most important variables affecting soil-applied herbicides are adsorption and volatility.

Adsorption is the process whereby herbicides are bound to soil particles. All herbicides have electrical charges that cause them to bind to positive or negative charges in soil or organic matter. This is similar to how metal is bound to a magnet. This is reported as the “absorptivity coefficient” (K) and is generally more important than water solubility in determining how herbicides move in the soil.

Many factors can affect adsorption. These include soil texture, pH, organic matter, and soil moisture. Although the soils here are generally low in organic matter, crop residues from crops grown previously in rotation can temporarily tie up many herbicides.

Soil moisture can also have a significant effect. Herbicides compete with water for binding sites on the soil and bind stronger to dry versus wet soils. Absorptivity and water solubility are usually inversely related. As solubility increases, binding to the soil decreases.

There are some exceptions to this. Notable include Gramoxone (Paraquat) and Glyphosate. These herbicides are highly water soluble but bind tightly to the soil. Herbicide volatility occurs when a herbicide changes from a liquid or solid form to a vapor.

This is affected primarily by vapor pressure and varies considerably for various herbicides. The higher the vapor pressure then the higher the volatility.

Some of the most volatile herbicides used in the Yuma area include Eptam, Banvel, MCPA, and 2,4-D. Some of the least volatile are Glyphosate, Gramoxone, Karmex, and Pursuit.

Contact Tickes: (928) 580-9902 or btickes@ag.arizona.edu