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

Clothianidin Seed Treatment for Bagrada Control

Since the bagrada bug became established in the desert in 2010, growers and PCAs quickly found that preventing excessive feeding damage on newly-established crops is critical to economic broccoli production. Local surveys have estimated that the invasive stink bug annually infests more than 80% of the acreage in Arizona and southern California, resulting on average in more than 10% stand losses and plant injury to direct-seeded broccoli crops. The potential for the pest to cause significant crop losses coupled with the lack of biological control alternatives has left little alternative but to control outbreak populations with foliar applied insecticides. Furthermore, because bagrada bug can quickly cause significant feeding damage to seedling plants, effective insecticide treatments applied in the field need to be quick acting. Currently, vegetable growers in Arizona and California rely heavily on frequent applications of pyrethroid insecticides to control adult infestations on seedling cole crops. Given the magnitude of pyrethroid usage historically applied to desert vegetable crops, alternative insecticides will be needed to protect desert cole crops from bagrada bugs and conserve the pyrethroid chemistry. Among the newer classes of chemistry, foliar-applied neonicotinoids such as Venom/Scorpion have been shown to effectively control bagrada bug adults, but at-planting, soil systemic applications of neonicotinoids such as Admire Pro, Belay and Venom do not prevent bagrada bug from damaging seedling broccoli plants. However, in other parts of the world neonicotinoid seed treatments have been shown to provide protection against bagrada bug. For example, in India, field trials showed that planting mustard seeds treated with imidacloprid resulted in significantly lower plant damage due to bagrada bug. Recently, Valent U.S.A. registered clothianidin as a seed treatment on broccoli under the name of Nipsit®. Based on our research, this technology provides another tool for broccoli growers to use in their annual battle against bagrada bugs in the desert. The results of field trials conducted at the Yuma Ag Center from 2012-2014 that evaluated the effectiveness of Nipsit (clothianidin) seed treatments for preventing bagrada bug feeding damage and yield loss in broccoli can be found in Evaluation of Clothianidin Seed Treatments for Bagrada Bug Control in Broccoli.


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

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Summer Preplant Soil Flooding as a Management Tool for Sclerotinia Lettuce drop

We are now in the hottest part of the year in the desert southwest region of Arizona, with respective average high and low temperatures of 108 and 83°F. Lettuce disease management is probably the last thing on a Pest Control Advisor’s or grower’s mind at this time. However, this is the perfect time to perform preplant soil flooding in fields that had high levels of Sclerotinia drop this past season. How can a soil flooding treatment in the summer help manage a disease that will not be a problem for several more months in a yet to be planted lettuce crop? The two fungi that cause lettuce drop, Sclerotinia minor and Sclerotinia sclerotiorum, carry over in fields between crops of lettuce as small black structures called sclerotia. These fungal propagules function like seeds, remaining dormant until they germinate in cool moist soil and infect lettuce plants. Many sclerotia decay naturally over time; however, sufficient numbers can remain in a field after one or more years to cause lettuce drop when a planting is established. If virtually all sclerotia in a field could be destroyed, then this field would no longer be a source of the Sclerotinia lettuce drop pathogens. This is where summer preplant soil flooding comes in. Past research conducted at The University of Arizona Yuma Agricultural Center demonstrated that a 3-week period of flooding in the summer destroyed virtually all sclerotia of S. minor and S. sclerotiorum present in soil. Some growers in the Yuma area have used this soil treatment technique to successfully manage Sclerotinia lettuce drop in fields chronically affected by this disease.

Flooding for Disease Control
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Weed Science:

Burning Wheat Stubble

It is necessary to remove wheat stubble from harvested fields. Although windrowing and baling wheat straw has become increasingly popular, burning stubble to remove it is still a common practice. The burning of wheat fields is a controversial practice and various reasons are sometimes given for doing it. Weed and disease control are sometimes cited as reasons for burning wheat fields. Although burning has some value in controlling these pests, it is not enough to significantly affect either. Some annual weed seeds that are within the top quarter inch are killed. It has little effect on most of the others. Wheat is not one of the weedier crops grown in this region and there are commonly not a lot of weeds left in the field at harvest. Some weed seeds with hard seed coats actually germinate better after being burned. The most common reason for burning wheat fields after harvest is to economically and quickly remove stubble from the field to prepare for the next crop.
Burning Wheat Stubble

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Question to the IPM Team:
Some residenSome residents from the Foothills in Yuma Arizona contacted the Vegetable IPM for identification of the following weed invading their yards. This weed is called Skeleton Weed or Flat Crown Buckwheat: Eriogonum deflexum from the polygonaceae family.
Leaves: Round to kidney shaped. Flowers: White with a branched inflorescence.
Common in the Sonoran desert and Mexico in young stages may look very different than mature plants and therefore its identification can become difficult.
Photographed at the Telegraph Pass Yuma, AZ

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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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