Pheromone/Sticky Trap Monitoring Network
Fall Pest Pressure on Desert Vegetable Crops
As is typical this time of the year, the weather has finally broken and it feels
like “winter” has arrived in the desert. With cooler temperatures, you can expect
a steady decline in insect abundance until temperatures begin to warm up again.
Last fall, I felt that the insect pressure on produce and melons crops in the Yuma
was as heavy as I’d seen in many years. This year it didn’t seem quite as heavy,
but I’ve heard many PCAs complain of heavy insect pressure, particularly during
November which was unusually warm. A quick look at both recent and historic data
on pest abundance recorded from our research plots here in the Yuma area suggests
that insect pressure this fall was a little lighter than last year, but still heavier
as compared to previous years. First, whitefly adult numbers on fall melons and
produce were extremely high in August, but monsoon rainfall in early September appeared
to suppress their numbers for a couple of weeks thereafter. Much like last fall
however, untreated melons plots on the Ag Center wilted and died rapidly as a direct
result of heavy whitefly infestations. Sticky trap captures of whiteflies near cantaloupe
fields from Wellton to Texas Hill, were lower than last fall, but were still higher
than the previous four years. However, numbers of adults caught on traps in the
Roll/Tacna area were higher in late-August this fall than we’ve ever recorded. Similarly,
CYSDV incidence at harvest in cantaloupe fields in these areas was very high this
fall. In all cases, high traps catches were found in melon fields in near proximity
to cotton fields. Based on counts from untreated lettuce at the Yuma Ag Center,
beet armyworm and cabbage looper population abundance this fall was slightly lower
than last fall. However, worm pressure the past two years was higher than we’ve
seen the previous 5 years. Populations began infesting plots in early September,
and remained steady throughout October and into early November. Egg deposition and
larval development has only recently declined significantly. Corn earworm numbers
were lower than what we observed last year, but could still easily be found in untreated
plots. Finally, Bagrada bug infestations were abundant in untreated broccoli plots
at YAC for the 4th consecutive year. As expected, low-moderate population appeared
in early September, but increased steadily through September and peaking in early
October. Overall, the peak numbers observed were not as high as either 2010 or 2012,
but much higher than in 2011. The infestation levels in our untreated broccoli plots
this year remained at damaging levels throughout October and into mid-November.
This is the first year we have seen Bagrada bugs this abundant in November. In contrast,
similar to last fall, western flower thrips population numbers have been relatively
low, but unlike last fall, we’ve been picking up winged green peach aphids and colonies
on sticky traps and in untreated lettuce plots since early November. How these aphid
and thrips numbers will translate into potential population pressure in January
and February is unknown, but you should anticipate their abundance as usual. I’m
often asked why we see such differences in insect pest numbers each year. It’s obviously
a very complex question, and I don’t have a good answer. The bottom line; insect
abundance and outbreaks are dictated by many abiotic, biotic and crop management
factors within our cropping system. Moreover, it’s nearly impossible to consider
all the factors necessary to draw a reliable conclusion. Nonetheless, graphics showing
these recent trends in Whitefly, CYSDV, Lep Larvae and Bagrada abundance can be
Pest Abundance on Desert Produce and Melon Cops in 2013
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Lettuce Downy Mildew
The storm that passed through Arizona last week deposited a significant amount of
rainfall in the region, ranging from 2/3 of an inch at the Yuma Valley Agricultural
Center to about 2.5 inches in the North Gila Valley. This moisture plus dew on lettuce
in the days following the rain increases chances for development of downy mildew.
This disease is best managed by having a fungicide in place before disease symptoms
become apparent. Good levels of downy mildew control can also be obtained by starting
fungicide applications at the very first sign of the disease; however, there is
a lag time between infection by the pathogen (Bremia lactucae) and appearance of
visible symptoms. This incubation period can range from 3 days to longer than a
week, depending on temperature, relative humidity, and lettuce variety susceptibility
to the pathogen. By the time lettuce downy mildew lesions are observed, many more
are likely present but have not matured to a sufficient extent to be visible. Fungicide
evaluation trials conducted at the Yuma Agricultural Center in Arizona as well as
in other states have demonstrated statistically significant reduction in disease
by application of fungicides such as Actigard, Aliette, Cabrio, Curzate, Dithane,
Forum, Presidio, Manzate, Previcur Flex, Prophyt, Ranman, Reason, Revus, and Tanos.
Several different modes of action are represented by these compounds, thus facilitating
alternation among different chemistries for effective disease management as well
as pathogen resistance management.
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Cole Crops and The Dinitroaniline (yellow) Herbicides
Two of the dinitoanaline herbicides, Pendimethalin (Prowl) and Trifluralin (Treflan),
are registered for use on cole crops in Arizona. They are generally safe to use
but must be properly incorporated or injury can occur.
These herbicides are used preemergence and work the same way to kill weeds. They
stop cell division in in the roots and shoots of developing seedlings. They move
very little in the plant and work only on the roots and shoots that contact them.
Growth is stopped at the point of contact. The symptoms that can be seen are a lack
of root development and swollen or brittle stems if much of the herbicide is concentrated
at or near the soil surface.
Both of these herbicides are generally safe to cole crops if they are mixed into
the soil prior to planting or transplanting the crop. Prowl incorporates adequately
with overhead sprinkler water although Trifluralin must be mechanically incorporated.
If too much herbicide is at the surface the stems of the crop can become brittle,
swollen and break off.
Pesticide Diagnostic Laboratory
We have established a laboratory at the Yuma Agriculture Center to help growers
and Pest Control Advisers determine the levels of certain pesticides in their fields.
Our focus has been upon herbicides in lettuce and other leafy vegetables but we
have expanded our efforts and can now run several other products as well. We want
to use this season to build a database and verify our procedures. We are running
samples free of charge this season and our turnaround time is normally one day or
less. We need one pound of soil or 20 grams (a small baggy) of plant material as
a composite sample taken separately from affected (showing symptoms) and unaffected
(no symptoms) areas across each field. Soil should be collected from the top 2 inches.
Samples should be put in paper bags and labeled as “affected” or “not affected”
with the location, crop, your name and phone number, date and the pesticides you
want to check for. Please call either myself (928-580-9902) Marco Pena (928-782-5871)
or Octavio Lopez (928-919-8736) to let us know you are bringing them or have questions.
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Areawide Insect Trapping Network
Results of pheromone and sticky trap catches can be viewed
Corn earworm/Tobacco budworm:
Flight activity has declined significantly
in all growing areas, and no moths have been captured in any of the traps since
Flight activity was down significantly in all areas during
the past 2 weeks. Numbers caught in the highest trap were averaging only 4.3 adults
Overall, sticky traps show that adult movement is almost negligible
consistent with cooler weather and the melon and cotton harvest coming to a close.
Numbers remain low in most trap locations and are highest in the
Roll area. Numbers on untreated lettuce at YAC are moderate and increasing.
Winged aphids catches are beginning to increase in all areas consistent
Winged aphids catches are beginning to increase in all areas consistent
with the winds and cooler weather. Alate green peach aphids are beginning to show
up on traps.
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.
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