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

Seed corn maggots in spring melon plantings

By John Palumbo, UA Research Scientist and Extension Specialist

Last spring, seed corn maggots (SCM) caused problems for growers in early plantings of melons and cotton. In some instances, significant stand reductions due to larvae feeding on germinating seed required a few fields to be replanted.

Not only is this an inconvenience to the grower but replanting is expensive and can disrupt harvest schedules. Unfortunately, once maggots are found infesting the soil during stand establishment there is usually nothing that can be done.

Avoidance of the problem is the most effective way of preventing stand reductions. First, weather plays a major role in determining the damage potential for SCM to be a problem. Melon stands are more susceptible to SCM during wet, cold spring weather in which seed germination is slowed or delayed. These conditions give SCM a chance to develop in the soil and attack the seeds before they can emerge.

Another important factor is the SCM is attracted to fields with high levels of decomposing organic matter. This includes heavy plant residue remaining after harvest of the previous lettuce or cole crop, and applications of manure prior to planting. Growers are encouraged not to plant melons into fields under these conditions.

However, if growers decide to plant in these conditions, then use a preventative insecticide applied at planting to minimize the impact from SCM and give seedling stands a fighting chance.

A few alternatives are available that have shown activity against SCM and may be practical for SCM management in spring melons. Please see the publication Seed Corn Maggot Control With In-Furrow Sprays and Seed Treatments On Cantaloupes and Insecticide Alternatives for Preventative Seed Corn Maggot Control in Spring Melons.

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

Lettuce dieback

By Mike Matheron, UA Extension Plant Pathologist

Lettuce dieback disease has appeared in some romaine plantings in southeastern Imperial County, Calif. and in Yuma, Ariz. Lettuce dieback occurs in other lettuce production regions in California as well.

Initial symptoms on infected plants consist of extensive yellowing of the outermost leaves with the younger inner leaves usually remaining dark green in color. Dead spots on older leaves can develop into extensive areas of brown necrotic tissue.

As the disease progresses, plant stunting and death can occur. Rotted roots may also be present, but whether this is caused by the pathogens or is a secondary issue is unclear.

Lettuce dieback is caused by the Tomato bushy stunt virus and the closely related Lettuce necrotic stunt virus. The disease is primarily a problem on romaine lettuce, although some green leaf, red leaf and butterhead cultivars can be affected as well. To date, symptoms have not been observed in commercial plantings of crisphead lettuce.

Lettuce dieback is usually found in fields near rivers or low-lying areas that drain poorly. The viral pathogens can be dispersed by contaminated soil and water and can survive for a long period of time.

No known vectors for Tomato bushy stunt virus and Lettuce necrotic stunt virus are known. Soil fumigation or crop rotation do not reduce disease severity in subsequent plantings of susceptible lettuce varieties.

Active research is in progress to develop commercial romaine varieties that will be resistant to these two soil-borne viruses.

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

Herbicide names

By Barry Tickes, UA Area Agriculture Agent

Every herbicide has only one common name but can have several trade names. It is often difficult to identify herbicides by trade name. The chart "Herbicide Names" contains the common and trade names for 50 of the most popular herbicides used in the Arizona and southern California deserts. Common names must be approved by the American National Standards Institute (ANSI).

The company that first develops the herbicide has a proprietary use patent for that product for 17 years and it usually becomes known by that name. Almost all of the herbicides used in this region today are no longer under the original patent and are sold under various trade names.

Only four of the 50 active ingredients on the list are still under patent. It is common for the same active ingredient to be sold under different names and this may not be because they are generics.

There are often different formulations and uses for the same active ingredient sold under different trade names. This list includes only those products that contain one active ingredient and does not include the numerous premixes or products containing two or more active ingredients.

It also includes products that may not be registered for use in Arizona or California or that are available only for the turf and ornamental market. It is intended to help identify the active ingredients that are contained in the various commercial herbicides that are on the market today. There are hundreds of these and some are likely to have been missed.

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

New fumigant regulations: training and certification workshops

By Kurt Nolte, UA agriculture agent, Yuma County

The U.S. Environmental Protection Agency (EPA) has approved all soil fumigant labels, implementing the next phase of new soil fumigant mitigation measures. With these new regulations, producers using soil fumigants must abide by stronger restrictions and mitigation regulation, all of which will be noted on the pesticide label.

The soil fumigants that fall under these new EPA regulations include: chloropicrin, dazomet, 1,3-dichloropropene, iodomethane, metam sodium/potassium, methyl bromide, and methyl isothiocyanate (MITC).

One notable change is that all soil fumigants will now be classified as restricted-use pesticides (RUPs). This includes metam sodium and dazomet, which previously were not classified as RUPs. This also means that any applicator in Arizona who wishes to use soil fumigants needs to become certified before they can apply them.

Other new mitigation measures include: additional worker protection measures, written fumigant management plans, registrants’ stewardship and training programs, mandatory good agricultural practices, buffer zones and buffer posting, and emergency preparedness and response measures.

Special training workshops to address the new regulations are being organized in Arizona. Applications for 4.5 AZ/CA CEU’s have been made.

The workshop schedule includes:

Feb. 22 – Yuma – 1 a.m. to 5:30 p.m.

Feb. 23 – Buckeye – 8:00 a.m. to 12:30 p.m.

Feb. 24 – Maricopa - 8:00 a.m. to 12:30 p.m.

Feb. 25 – Willcox - 8:00 a.m. to 12:30 p.m.

Contact Nolte: (928) 726-3904 or knolte@ag.arizona.edu