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March 2nd 2014 Vegetable IPM Updates
Insect Management
Weed Science
Pheromone/Sticky Trap Monitoring Network
Insect Management:

Seed Corn Maggots in Spring Melons

“An ounce of prevention is worth a pound of cure” so said the great American statesman Benjamin Franklin. He’ right on the money when it comes to seed corn maggots in desert melons crops. In my experience, it’s always best to prevent problems with seed corn maggots as you plan ahead for spring planting. As you likely know, seed corn maggots can cause significant stand reductions in spring melons and other large seeded crops due to larvae feeding on germinating seed, roots and stems of young seedlings. If larvae populations are high in the soil, replanting parts or all of an infested field is often necessary. Not only is this an inconvenience to the grower, but also replanting is expensive and can disrupt harvest schedules. Unfortunately, once maggots have been
soil during stand establishment, there is usually nothing you can do. Thus, 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 seed corn maggot to be a problem. Melon stands are more susceptible to seed corn maggot during wet, cool spring weather in which seed germination is slowed or delayed. These conditions give seed corn maggots a chance to develop in the soil and attack the seeds before they can emerge. But I’ve also observed seed corn maggots take down melon plants under warm dry conditions when populations were high. Secondly, our cropping system plays a key role. Melon crops following produce are the most often attacked because seed corn maggot are 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, as well as applications of manure prior to planting. Growers would be encouraged not to plant melons into fields under these conditions. However, if growers decide to plant in these conditions, then it would be wise to use a preventative insecticide applied at planting to minimize the impact from seed corn maggot and give seedlings a fighting chance. A few alternatives are available that have shown activity against seed corn maggot and may be practical for their management in spring melons. For more information visit on insecticide alternatives and Aphid Identification please visit Seed Corn Maggot on Spring Melons 2015.
Weed science
Remember, When in Doubt . . . . . “SCOUT”

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Lettuce Dieback

This disease has appeared in some romaine plantings in southeastern Imperial County, California and in Yuma, Arizona in past years. 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 not clear. 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. High salinity and plant stress will enhance lettuce dieback symptoms. The viral pathogens can be dispersed by contaminated soil and water and can survive for a long period of time. No vectors for Tomato bushy stunt virus and Lettuce necrotic stunt virus are known. Soil fumigation or crop rotation does not reduce disease severity in subsequent plantings of susceptible lettuce varieties. Active research is in progress in California to develop commercial romaine varieties that have resistance to these two soil-borne viruses.
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Weed Science:

Injury to Wheat from Herbicides Used in Lettuce

Wheat is often grown following lettuce in this region the three most commonly used herbicides in lettuce all can cause injury to wheat. Bensulide (Prefar), Benefin (Balan) and Pronimide (Kerb), inhibit root growth in many grasses and can injure wheat if much of the herbicide has remained in the soil when it is planted.

Pronamide (Kerb), moves downward with sprinkler irrigation but not with furrow irrigation. Injury to wheat was more common prior to the widespread use of sprinklers in lettuce. Lettuce that was furrow irrigated from start to finish is at greater risk from Kerb than are fields that were germinated with sprinklers. Tillage and a good flood irrigation prior to planting wheat can reduce potential injury.

Bensulide (Prefar), is safer to large seeded grasses than it is to wheat but injury can occur in rare instances. It adheres more strongly to medium and fine textures soils than pronamide and it is difficult to move with water. Tillage is the best way to reduce injury potential to wheat.

Benefin (Balan), possess the greatest risk to wheat following lettuce. It also sticks strongly to medium and fine textured soil and is difficult to move. It is a dinitroanaline (yellow) herbicide like Treflan and Prowl. These herbicides can be used safely in wheat if applied after the wheat is well established or planted well below the herbicide.

Wheat can tolerate a fair amount of injury and recover to produce normal yields.

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Area wide Insect Trapping Network

Jan 7, 2015

Results of pheromone and sticky trap catches can be viewed here.

Corn earworm: corn earworm moth activity remains very low with very few captures in the traps.

Beet armyworm: In the past two weeks, trap catches of BAW have been very low. However, BAW larvae can readily be found in the field.

Cabbage looper: Cabbage looper moths were less active in the past two weeks, but still more active than we observed this time last year.

Whitefly: Adult movement is at its lowest point of the season which is to be expected.

Thrips: Similarly, Thrips movement in very low in most areas, comparable to what we saw last fall.

Leafminers: Numbers on traps remain low across all trap locations.

Aphids: Alate (winged) activity was low over the past two weeks, similar to this time last year.

To contact John Palumbo go to:



The Vegetable IPM Updates Archive page provides links to updates from previous weeks.

The Vegetable IPM Video Archive page contains a collection of educational videos from current research work in vegetable crops by University of Arizona Researchers.


For questions or comments on any of the topics please contact Marco Pena at the Yuma Agricultural Center.
College of Agriculture, The University of Arizona, Tucson, AZ.

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