The latest Arizona Vegetable Integrated Pest Management Update from the University of Arizona (UA) Cooperative Extension in Yuma, Ariz. released Jan. 8, 2013.

Weather and spring insect populations

By John Palumbo, UA research scientist and Extension specialist

Mark Twain once quipped that “climate is what we expect - weather is what we get.” Those of you who work in desert agriculture can relate to his sensibilities.

I remember earlier this fall the National Oceanic and Atmospheric Administration predicted that the Desert Southwest could experience a mild La Niña weather pattern this winter. NOAA subsequently altered the prediction in November and suggested that La Niña conditions were not likely to develop.

In many regards, entomologists are not much different. We can describe historical population trends for a particular pest as influenced by environmental conditions (see this report: Historical Trends in Aphid Abundance in Desert Lettuce), or explain how temperature and humidity influence insect growth and reproduction. We’re no better predicting insect outbreaks this spring than the weatherman at predicting how much it will rain next week.

Insects are poikilothermic or cold blooded. Most species are not very abundant in the cold weather we often experience during January. Yet keep in mind, some insect species actually are adapted to cooler temperatures.

Examples include aphids, seedcorn maggot, and to some extent western flower thrips.

When daytime temperatures return to the high 60s to low 70s, these pests will become active. How abundant these pests ultimately become is difficult to predict. Given our fairly mild winter, except for the last week or so, one might anticipate that insect survival during December and early January has been favorable.

I’ve been noticing quite a few whitefly adults on cole crops and lettuce plants. Does that mean they will be heavy on melon and cotton this spring and summer? You would think so, but I’ll wait until May or June to let you know for sure.

I am certain, based on historical trends and my knowledge of the biology and ecology of desert insect pests, you will experience above average insect pressure at some point this spring on some crops.

That’s my New Year’s prediction for 2013. Happy New Year’s.

Click this link to listen to John.

“Remember, when in doubt - scout.”

Contact Palumbo: (928) 782-3836 or jpalumbo@ag.arizona.edu.

Lettuce downy mildew

By Mike Matheron, UA Extension Plant Pathologist

Downy mildew has appeared since early December in several areas within the southwestern Arizona lettuce production region.

At first, one might consider this unusual as we have not received much rainfall. On the other hand, dew on plants has been common and temperatures were above normal for a good portion of December. Temperature and moisture requirements for downy mildew development were in place.

Downy mildew is best managed by having a fungicide in place before disease symptoms are apparent. Good levels of disease suppression can also be obtained by the initiation of fungicide applications at the very first sign of the disease.

However, there is a lag time between infection by the pathogen, Bremia lactucae, and the appearance of visible symptoms. This incubation period can range from three days to longer than a week; depending on the 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 UA Yuma Agricultural Center in Arizona as well as in other states have demonstrated statistically significant reduction in disease by the application of fungicides including Actigard, Aliette, Cabrio, Curzate, Forum, Presidio, Manzate, Previcur Flex, Prophyt, Ranman, Reason, Revus, and Tanos.

Several different modes of action are represented by these compounds, facilitating alternation among different chemistries for effective disease management plus pathogen resistance management.

The last few days of low relative humidity will help arrest downy mildew development. However, constant vigilance is needed as future occurrences of dew and rainfall will favor further disease expansion.

Click link to listen to Mike's Update.

Contact Matheron: (928) 726-6856 or matheron@ag.arizona.edu.

Herbicide-resistant little seed canarygrass

By Barry Tickes, UA area agriculture agent

Canarygrass resistant to some of ACCase inhibitors (Poast, Select, Fusilade and generics) was found in the Imperial Valley, Calif. about 10 years ago. An increasing number of problems with these herbicides on this weed have been reported each year.

Grass resistance to this mode of action is not uncommon in this country and worldwide. Wild oat, rye grass, brome grass, and other grasses have been documented to have developed some levels of resistance.

While many of the herbicides using this mode of action are used on broadleaf crops, some of the grass herbicides used in grain also use this mode of action to control canarygrass. These include Dakota, Discover, Achieve, Axial, and others.

It is necessary to use herbicides with a different mode of action to help avoid resistance or limit it once it has occurred. The ACCase inhibitors are the most widely used herbicides for post-emergence control of both annual and perennial grasses and this can be difficult.

There are some other effective herbicides which use a different mode of action including Osprey and Simplicity. Pre-emergence herbicides including Prowl (pendimethalin) which control grasses can also be effective.

Click link to listen to Barry's Update.

Contact Tickes: (928) 580-9902 or btickes@ag.arizona.edu.

Agronomic production workshop

Jan. 16, 2013 - registration at 7:30 a.m.
UA Yuma Ag Center, 8th Street, Yuma, Ariz. 85364
Applications for 4.5 AZ and CA CEU’s and CCA’s submitted.

Click this link to see FULL AGENDA.

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