Some Videos to Check Out
IRM Guidelines for Beet Armyworm in Lettuce
The beet armyworm (BAW) is the most common lepidopterous pest infesting lettuce
throughout the desert southwest where larvae are most prevalent from August through
November. Historically, PCAs have been able to effectively control this pest using
available insecticides. Because many of the products have different modes of action
(MOA) that can be alternated throughout the growing season, the rapid development
of resistance by BAW to any of these insecticide compounds should not readily occur.
In fact, resistance by BAW to insecticides has not been recorded in nearly 20 years
in the desert as a result of the judicious usage of these insecticide chemistries.
However, if an insecticide compound, or products with the same MOA, are used repeatedly
for worm control in the same field, the risk of resistance increases significantly.
This is particularly important with the Diamide group of insecticides (IRAC group
28) which can be applied as both foliar sprays and soil injections. With the recent
registration of cyantraniliprole (Exirel and Verimark), PCAs now have eight different
diamides insecticide products within the diamide chemistry (IRAC group 28) to choose
from for worm control. Foliar uses include Coragen, Voliam Xpress, Voliam Flexi,
Exirel, Belt and Vetica; Soil uses include Coragen, Durivo and Verimark. Applying
these Diamide products to the soil at planting, and then following with foliar sprays
of Dimades in the same field, can expose multiple generations of Lep larvae to the
same MOA. This places increased selection pressure on populations. That’s not a
good way to use these products if you want them to remain effective for more than
a couple of years. Since the Diamides, as well as the other products currently available
(Radiant, Proclaim, Intrepid, Avaunt), are critical to effective management of worms
in leafy vegetables, PCAs should consciously avoid the overuse of any of these compounds.
The most effective way to delay the onset of resistance by BAW in leafy vegetables
is to consider the recommendations provided in the guidelines recently prepared
Insecticide Resistance Management Guidelines for Beet Armyworm in Lettuce
BAW Egg Mass and Neonates
Remember, When in Doubt . . . . . “Call Barry Tickes”
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Plant Pathogen Survival in the Desert
As the seemingly unending days of summer heat in the desert persist, we can seek
refuge in air-conditioned vehicles or buildings and can obtain food from any number
of sources at any time. Not so for plant pathogens, which must survive 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
will allow the organisms to survive hostile environments in a dormant state. The
visible dark-colored sclerotia produced by the lettuce Sclerotinia pathogens
are 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, 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. These plants
can include 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 that we employ are effective because they disrupt the normal survival capacity
of these plant pathogens.
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Common Purslane (Portulaca oleracea
) is at the same time one of the most troublesome
weeds in vegetable crops and one of the most nutritious leafy vegetables. It is
very widespread in the desert southwest but is also on the list of Arizona Prohibited
Noxious Weeds which means that it is prohibited from entry into the state. Common
Purslane is eaten in Mexico (Verdolaga), Europe and Asia and contains more omega
3 fatty acids than any other leafy vegetable. It also contains vitamins A, B and
C and dietary minerals.
Common Purslane is often lumped together with Horse Purslane although the two are
in different families. Common Purslane is in the Portulaca family while Horse Purslane
is in the Trianthema or Carpetweed family.
In lettuce, Purslane is often controlled during ground preparation where it is geminated
and killed with chemicals or tillage. Timing is important with both of these techniques.
Purslane grows rapidly and one plant can produce thousands of seeds. These seeds
can germinate in 12 hours after receiving moisture in August and September. They
can also germinate in January and February but will take 3-7 days to germinate at
that time. The stems are very succulent and unless they are completely killed and
desiccated they can reroot at the nodes. Tillage that does not completely desiccate
the plants can spread rather than eliminate this weed.
Herbicides used to kill this weed during ground preparation include both contact
(Gramoxone, Aim and ET) and systemic (glyphosate) herbicides. Results can range
from 0 to 100% depending upon weed size, rate and adjuvant used at the time of application.
The contact herbicides can produce almost 100% control when the Purslane is less
than 2 inches in diameter and less than 50% control when larger than this. This
is especially the case with Aim where control can drop from excellent to poor in
3 - 5 days.
Purslane has a thick waxy cuticle and an adjuvant is needed with all of these herbicides
to help penetrate into the leaves and stems. A non-ionic surfactant will help the
herbicide spread and stick while crop oil concentrates help break up this waxy layer.
Time of day when applied can also be important. During the morning hours leaf pores
are open, new growth is occurring and the plant is more sensitive to herbicides
than during the middle of the day when the plant is conserving water and energy.
There is a wide range of rates used with Aim, Gramoxone and glyphosate to control
Purslane during ground preparation. Normal rates vary from 0.5 to 2.0 oz. with Aim,
1.5 to 4.0 pt. with Gramoxone and 1.0 pt. to 2.0 qts. with glyphosate when used
alone or in combination. All of these herbicides only work on emerged weeds and
people often wait until they are sure most of the weeds have emerged to avoid making
multiple applications. As a result, there can be a wide range of weed sizes at the
time of application. Rates should target the largest weeds. It is less costly to
choose a higher initial rate than to have to make additional applications.
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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.
document located at: http://cals.arizona.edu/crops/vegatables/advisories/advisories.html
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