The latest Arizona Vegetable Integrated Pest Management (IPM) Update from the University of Arizona Cooperative Extension in Yuma, Ariz.

Movento registered again

By John Palumbo, UA Research Scientist and Extension Specialist

On Oct. 15, 2010, the Environmental Protection Agency (EPA) announced that Movento (spirotetramat) has been registered for a second time.

Movento was first registered by EPA in June 2008, but EPA issued a cancellation order for the Movento registration in April 2010 that made it unlawful for the manufacturer, Bayer CropScience, to sell or distribute the product.

The cancellation order allowed for the use, sale, or distribution of existing supplies of Movento in the possession of retailers, distributors, and end-users under the provisions of the previously-approved label.

The previous Movento registration was terminated because of a judicial action related to a procedural failure by EPA – a failure to publish a notice of receipt of the spirotetramat registration application in the Federal Register.

The new registration has been anticipated for several months. A statement issued by the EPA's Office of Pesticide Programs said, " After evaluating the application for registration and comments received from the publication of the notice of receipt for registration, EPA has determined that spirotetramat does not pose an unreasonable risk of adverse effects to human health or the environment if used according to the label directions and, as such, meets the Federal Insecticide, Fungicide, and Rodenticide Act standard for registration.”

Spirotetramat is registered for citrus, grapes, pome fruit, stone fruit, tree nuts, hops, Christmas tree plantations, and certain vegetables including potatoes.

The new registration will be available in the marketplace for the next growing season. It is our understanding that pending state approval by the Arizona Department of Agriculture, local growers may purchase inventory and use Movento under the new label.

Contact Palumbo: (928) 782-3836 or [email protected].

Fusarium wilt on lettuce

By Mike Matheron, UA Extension Plant Pathologist

Since the first detection of Fusarium wilt on lettuce in Arizona during the 2001-02 growing season, the disease has been found yearly in lettuce fields from mid-October through early January.

This year is no exception. The first confirmed appearance of Fusarium wilt on lettuce was recorded the week of Oct. 11.

The primary diagnostic features of this disease include yellowing of leaves, plant wilting, and a brown-to-black necrosis of the internal taproot and crown tissue. 

Disease incidence can range from a few plants to large areas or zones of infected plants within a field. Plants can become infected and display symptoms at any age; ranging from young plants just after thinning to those ready for harvest.

The symptoms of Fusarium wilt resemble two other lettuce diseases: ammonia toxicity and the early stages of lettuce drop. 

To confirm disease identity, bring plant samples to Mike Matheron at the Yuma Agricultural Center (YAC) in Yuma for analysis. The confirmation of disease identity is achieved by isolation and identification of the causal fungus of Fusarium wilt of lettuce, Fusarium oxysporum, f. sp. lactucae, from symptomatic root tissue.

Disease development is strongly affected by the planting date and the type of lettuce grown. The main determinant of disease severity with respect to the planting date is soil temperature.

Experimental data demonstrated that lettuce planted in early September resulted in high levels of Fusarium wilt. Plantings in mid-October or early December in the same naturally-infested field sustained moderately low and trace levels of disease, respectively.

Of the many crisp head and romaine cultivars tested, crisp head cultivars generally were significantly more susceptible to Fusarium wilt than romaine lettuce.

The lettuce Fusarium wilt pathogen can survive in the soil for many years so minimizing the spread of infested soil within and especially between fields is of paramount importance. 

Two comprehensive research reports are available from Matheron concerning disease development and management of Fusarium wilt of lettuce.

Contact Matheron: (928) 726-6856 or [email protected].

Adjuvants and lettuce herbicides

By Barry Tickes, UA Area Agriculture Agent

Adjuvant is a broad term for anything added to a herbicide that helps with performance or handling.

Adjuvants can be added by the manufacturer for a variety of purposes including improving solubility, shelf life, handling, compatibility, stability, and other characteristics. Most people think of an adjuvant as products they add to the spray tank.

The most common adjuvants are surfactants or surface-active agents used to improve spreading and/or the absorption of the applied solution. Other uses for adjuvants include deposition agents, drift control agents, anti-foam agents, buffering agents, compatibility agents, water conditioners, tank cleaners, and others.

Adjuvants are rarely used with soil applied herbicides. There has been interest in using adjuvants with two soil-applied herbicides in lettuce to improve weed control.

The intent is to use an adjuvant to increase the movement of Prefar down into the soil or to reduce the movement of Kerb too far into the soil.

Prefar (bensulide) is normally applied to the soil surface and incorporated with water. It adheres well to the surface and can be difficult to move down to the germinating weed seed in many fine textured soils.

Some growers and pest control advisers have used non-ionic surfactants, crop oil concentrates, or other specialty adjuvants to improve movement into the soil and have reported improved weed control.

Results of our trials have been variable. We have not measured a consistent improvement in weed control from any of the tested adjuvants.

Kerb (pronamide), on the other hand, does not adhere well to the soil and can often be leached below germinating weed seeds by irrigation water before germination. Adjuvants used to increase the adsorption of products to foliage and soil have been tested with Kerb to reduce leaching. Results have been variable and inconclusive.

Contact Tickes: (928) 580-9902 or [email protected].

Vegetable IPM video archive

By Marco Peña, UA research specialist

On April 26, 2010, the “How Herbicides Work" field day was held at the UA YAC. Barry Tickes and students from the applied weed science class PLS 300 explained the different herbicide modes of action directly from the experimental plots.

We are frequently so busy spraying gardens and crops for weed control that it is easy to forget how these products really work. By attending this meeting, participants learned that seedling root and shoot growth inhibitors kill weeds by affecting mitosis, the process in cell division by which the nucleus divides - causing what is called "pruned roots" in the treated plants. This makes weeds suffer from lack of water and nutrients.

The students showed epinasty, a symptom caused by growth regulators and explained how weeds turn white by the action of pigment inhibitors.

Tickes also showed the symptoms of a cell membrane disruptor application which have mostly contact activity. He said these herbicides produce a dark green, water-soaked appearance on the leaves which means the cell membranes were destroyed and the leaking of intercellular fluids which causes necrosis.

Watch the videos on how herbicides work by visiting the Vegetable IPM Video Archive located at http://ag.arizona.edu/crops/vegetables/videos.html.

This archive also has videos on insect management, evaluation methods, and insecticide trials conducted by researchers at the UA YAC. Plant pathology videos will be added in the future.

Contact: Marco Peña at (928)782-3836 or [email protected].