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

Insect pests of leafy vegetables, melons at stand establishment

By John Palumbo, UA Research Scientist and Extension Specialist

Most fall melon crops are in the ground and the planting of produce crops is not far behind.

In these fall crops, pest control advisers are likely to encounter insects that can cause serious economic losses to seedling crops during stand establishment. The insects include flea beetles, crickets (sometimes grasshoppers), darkling and rove beetles, and saltmarsh caterpillers.

Seedling crops at the cotyledon stage are most susceptible to the pests. Feeding by large numbers can devour much of the cotyledons or outright kill the small plant.

If left uncontrolled, larger seedling plants (2-4 leaf stage) can sustain significant feeding damage on newly emerged leaves. Not only can this feeding stunt plant growth, it can result in the lack of uniformity and maturity at harvest.

Host sources of beetle, cricket, and "wooly worm" infestations include numerous weeds, sudangrass, cotton, and alfalfa. As these summer host plants are harvested over the next several weeks, these seedling pests typically move to the next available host crop — lettuce, cole crops, and melons.

Fortunately, there are many registered insecticide alternatives available that can be applied via chemigation or foliar sprays to cost-effectively minimize the pest abundance and damage to produce and melons crops.

For more information on insect pests of leafy vegetables and melons at stand establishment, click on this online link: http://extension.arizona.edu/sites/extension.arizona.edu/files/resourcefile/resource/marcop/Pests%20at%20stand%20establishment.pdf.

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

Chemical barriers to plant diseases

By Mike Matheron, UA Extension Plant Pathologist

Plants are not susceptible to many potential pathogens for several reasons.

Structural characteristics of plants can provide various levels of resistance against potential plant pathogens. Also, various substances formed by plants present before infection provide disease defense mechanisms of a chemical rather than a structural nature.

Plants exude a variety of chemical substances from the surfaces of plant parts including leaves, stems, fruit, seeds and roots. These anti-microbial materials include phenolic compounds, tannins, and fatty-acid like chemicals.

Experiments show some of these compounds have an inhibitory action on certain pathogens. For example, toxic exudates on leaves of a specific variety of sugar beet are present in sufficient concentrations to inhibit spore germination of certain fungal pathogens.

Another compound caused resistance in certain types of tomato plants to powdery mildew by inhibiting spore germination.

Additionally, proteins and enzymes on plant surfaces have been shown to inactivate pathogen enzymes that are essential for disease development. These preformed compounds, together with structural defenses, often drive what we recognize as resistance to diseases in certain varieties or types of plants.

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

Update on the registration of Kerb for leaf lettuce

By Barry Tickes, UA Area Agriculture Agent

The herbicides Kerb (Pronamide), Prefar (Bensulide), and Balan (Benefin) have been used for pre-emergent control of broadleaf and grass weeds in lettuce for 40 years.

Poast (sethoxydim) and Select (clethodim) were registered for use on lettuce in the mid-to-late 1980s. These are effective only on grasses.

New herbicides have not been registered for use in lettuce. The older products have been used effectively for decades. The products are valuable. When used in combination along with tillage and hand labor, the products can achieve high levels of weed control demanded by lettuce growers.

Kerb is the most broad spectrum and widely used herbicide on lettuce. The results of an “Insect Losses Survey” conducted in Yuma, Ariz., in 2009 showed that 69 percent of the lettuce acreage was treated with Kerb, 42 percent with Prefar, and 33 percent with Balan.

Rohm & Haas first registered Kerb in 1969. The company was acquired by Dow AgroSciences in 2001. Kerb is currently labeled on head lettuce, endive, escarole, and radicchio, although the registration for leaf lettuce was removed in August 2009.

In 2009, 53 percent of the lettuce grown was head lettuce and 47 percent was leaf lettuce. This cancellation is expected to be temporary and is the result of regulatory action by the Environmental Protection Agency (EPA) and not because of any known problems with food safety or environmental contamination.

Kerb is still registered on other leafy vegetables including head lettuce, and has been used safely for decades on leaf lettuce. Early Kerb registrations did not differentiate between the types of lettuce. Most of the early work conducted by Rohm & Haas was with head lettuce.

The EPA now regards leaf and head lettuce in different crop classifications requiring separate studies. Leaf lettuce is a major market for Kerb. Dow AgroSciences has completed most of the required tests. Some additional tests that were not previously required are still being conducted.

It takes several months from the submission of the required information until registration is approved. Full registration for leaf lettuce is expected to be re-established in 2012.

If you need more information, consider attending an upcoming Dow AgroSciences meeting. The dates and locations can be obtained with this link: http://ag.arizona.edu/crops/counties/all/events.html#all.

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

2010 summer vegetable prices holding strong

By Kurt Nolte, UA agriculture agent, Yuma County

As desert preparations continue for the upcoming winter vegetable season, a quick check on summer (June, July, and August) produce prices (FOB, Los Angeles) mostly ranged from strong to moderately strong and very steady.

Iceberg prices (wrapped 24s) topped the $20/carton range during an extended period in June and again in July, and have averaged well over $16 per carton during the entire summer.

The June-July average for Romaine (24s) has hovered around the $11.50 range and recently topped $14/carton last week.

After starting the summer at $19/carton (bunched, 14s), broccoli prices have held steady at or around the $11/carton range during June and July and into the first week of August.

To date, lower and fluctuating prices, typically seen during a production season, have been a rarity during the summer of 2010.

For a detailed look at the summer vegetable prices for iceberg, romaine, and broccoli, go to this link: http://extension.arizona.edu/sites/extension.arizona.edu/files/resourcefile/resource/marcop/2010%20Summer%20Vegetable%20Prices%20081110c.pdf.

Contact Nolte: (928) 726-3904 or [email protected].

Upcoming meeting

Preseason Vegetable Workshop, Aug. 31, 2010:

Yuma County Cooperative Extension Auditorium, 2200 W. 28th Street, Suite 102, Yuma, Ariz. from 7:00 a.m. to noon. Applications for 4 AZ/CA PCA and CCA hours have been made. For more information, contact Kurt Nolte at (928) 726-3904.