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March 2nd 2014 Vegetable IPM Updates
Insect Management
Weed Science
Insect Management:

Insect Pests during Stand Establishment on Fall Crops

Desert growers have begun planting fall melons and transplanting cole crops, while direct seeding of produce crops is just a couple of week away. Accordingly, PCAs and growers will soon be faced with a number of important insect management issues. As crops begin to emerge, they can expect to encounter a number of insect pests that have the potential to cause serious economic losses to crop stands. These include flea beetles, crickets (sometimes grasshoppers), darkling and rove beetles, and saltmarsh caterpillars (‘woolly worms’). These insects all have chewing mouthparts and most are capable of consuming large amounts of leaf tissue in a short period of time. Seedling crops at the cotyledon stage are most susceptible; these pests can devour entire cotyledons or outright kill small seedlings. If left unprotected, larger seedling plants (1-2 leaf stage) can sustain significant feeding damage on the terminal growing points or newly emerged leaves. Not only can this feeding stunt plant growth, but can result in lack of stand uniformity and ultimately, maturity at harvest. Host crop sources of flea beetle, cricket and "woolly worm" infestations include numerous summer crops (e.g., sudan grass, cotton and alfalfa) and weeds (e.g., purslane). We are currently noticing high numbers of flea beetles and crickets at the Yuma Ag Center on sudan grass and weeds. Salt caterpillars have not been detected, but are known to disperse from alfalfa and pima cotton. Experience indicates that melon fields planted adjacent to these crops/weedy areas are at a high risk from these seedling pests, particularly flea beetles. As summer crops are harvested or terminated during 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 sprinkler chemigation (i.e., pyrethroids) or foliar sprays (i.e., methomyl, neonicotinoids) that can cost-effectively minimize their abundance and damage to emerging produce and melon crops. Additionally, seed treatments are available for lettuce and cole crops that will protect stands from flea beetles. For more information on insect pests of leafy vegetables and melons at stand establishment please see Insect Management on Desert Produce and Melons: Pests at Stand Establishment.



Name the insect pest that caused the damage to this cantaloupe leaf. - Looper Damage

Remember, When in Doubt . . . . . “SCOUT”

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Plant Pathogen Survival in the Desert

As the seemingly endless days of summer heat in the desert persist, at least we can seek refuge in air-conditioned vehicles or buildings. Also, we can obtain food from any number of sources at any time. Not so for plant pathogens, which must survive both high temperatures and lack of food by employing other tactics. A few plant pathogens can thrive at temperatures common in the desert during the summer and cause disease on plants growing at that time; however, most others cannot function at temperatures much above 90°F. To survive inhospitable temperatures or lack of a host on which to feed, fungal pathogens often produce thick-walled durable spores or other structures that allow the organisms to survive hostile environments in a dormant state. The visible dark-colored sclerotia produced by the lettuce Sclerotinia pathogens are examples of such structures. Much smaller sclerotia and thick-walled spores facilitate long-term survival of the soil-borne pathogens Rhizoctonia and Fusarium, respectively. On the other hand, most bacterial plant pathogens do not have recognized survival structures, but can subsist for some time in a reduced metabolic state on, in, or near living or dead plant tissue. Virus pathogens also cannot make resistant structures, so survival usually occurs in vectors or living plants including weeds or cultivated crops that do not express disease symptoms, but serve as sources of virus to visiting insect vectors. Finally, nematode survival stages can include eggs and certain larval forms. Many of the cultural disease management methods used are effective because they disrupt the normal survival capacity of these plant pathogens.

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Weed Science:

Weeds to Be on the Lookout For

Despite the development of new herbicides and other control techniques, weeds are as much of a problem today as they have ever been. Those that can be controlled diminish over time while those that are difficult to control become more widespread. New weed species are constantly being introduced. Some of these become established and others never do for a variety of reasons including cropping patterns, climatic conditions, registered herbicides , management practices and other conditions. There are a few species that have become established in other regions around Yuma but have never become widespread here. Some that you should be on the lookout for are:

Common Groundsel (Senecio vulgaris)
This is a winter annual that is has been established in the surrounding states for many years. It first started to appear in La Paz County,Az. about 15 years ago and is now widespread there and in the Imperial valley. It is mostly in alfalfa but also present in many other crops. It is in the composite or sunflower family but is more difficult to control than most other weeds in this family. Oxyfluorfen will control small groundsel in cole crops but it is difficult to control selectively pre or postemergence in lettuce. It is best if you can germinate and kill it prior to planting.

Hairy Fleabane (Conyza bonariences)
This is classified as a summer annual but it can be found year round in the low desert. It is often confused with horseweed or marestail (Conyza canadensis). It has appeared in La Paz county in the Parker Valley, but has not known to be established in Yuma County. This weed is more gray green and hairy than the horseweed that has been in Yuma for many years. Fleabane characteristically branches from the base more than horseweed. Both can be difficult to control. Glyphosate resistant fleabane is becoming more widespread across the country. The horseweed that has been in Yuma for a long time still appears to be controllable with glyphosate.

Hood Canarygrass (Phalaris paradoxa)
This is similar to the littleseed canarygrass (Phalaris minor), that has been here for many years. The seedlings are different and it can be misidentified when it first emerges. The leaves are broader than littleseed and do not bleed when broken at the stem. Hood canarygrass was first identified last year in the south Gila Valley. We had not recognized it previously in Yuma County. The seed head looks similar but is different. The spikelets have a characteristic hook on them compared to littleseed which is smooth. Hood Canarygrass is difficult to control postemergence with clethodim (Select) or sethoxydim (Poast). Neither of these was effective last season.

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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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