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October 16, 2019 Vegetable IPM Updates
Insect Management
Weed Science
Plant Diagnostics

Insect Management:

Don’t Forget about Resistance Management

Don’t be fooled by the cool weather; it may slow insect activity down a bit, but they will still be moving around until it gets really chilly in December. So be vigilant in your scouting, especially with harvest approaching. Lepidopterous larvae, (beet armyworm, cabbage looper, corn earworm and diamondback moth, and known collectively as “worms”) are typically the most important pests of fall produce in the desert southwest. And this was a typical year; heavy worm pressure in early September and remaining consistently abundant thus far. Fortunately for local PCAs, several insecticide alternatives are available that provide excellent residual activity on these pests. Perhaps equally important, many of the products have unique modes of action (MOA) that can be alternated throughout the growing season. This is important because the most fundamental way to reduce the risk of insecticide resistance is to eliminate exposure of multiple generations of Leps to the same MOA. By using a different MOA on each subsequent spray application, you can minimize the risk of re sistance by Lep larvae to these insecticide compounds. In contrast, repeatedly applying insecticide products with the same MOA for Lep control in the same area will significantly increase the risk of resistance. This is particularly important with the Diamide group of insecticides (IRAC group 28). These products can be applied as both foliar sprays and soil systemic treatments, and currently 7 Diamide products are for use labeled in leafy vegetables - all with the same MOA (Coragen, Durivo, Besiege, Minecto Pro, Verimark, Exirel and Harvanta). To avoid confusion among the Diamides, the IRAC group number (28) is placed on each label, adjacent to the product name. This is very helpful in avoiding repeated use of the same MOA. A complete list of all registered compounds and their MOA can be found at the IRAC MOA Classification Scheme. Furthermore, applying a Diamide product (i.e., Coragen/Verimark) to the soil at planting or as a tray drench, and then subsequently applying Diamide foliar sprays (i.e., Harvanta/Besiege) on the same field can expose multiple generations of Leps to the same MOA. For example, under ideal weather conditions, one could potentially expose 5-6 generations of diamondback moths to the same MOA given the residual efficacy of the diamides. 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 key products currently available (e.g., Radiant, Proclaim, Intrepid, Avaunt), are critical to effective management of Leps 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 Leps in leafy vegetables is to consider the recommendations provided in the guidelines entitled Insecticide Resistance Management for Lepidopterous Larvae in Desert Produce Crops.
Name that Pest


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

video link

To contact John Palumbo go

Downy Mildew

We are approaching that time in the desert vegetable production season when downy mildew can become a concern. Development of downy mildew on crops such as lettuce, spinach, onions, broccoli, cauliflower, and cabbage is strongly regulated by the presence and duration of free moisture on plant leaves. This moisture can be supplied by rainfall, dew, and sprinkler irrigation. Optimal management of downy mildew is achieved by having a fungicide in place before disease symptoms become apparent. Less than optimal control will occur when fungicide applications are not started until downy mildew symptoms are visible on plants. This is because there is a lag time between infection by the microscopic pathogens that cause downy mildew on these crops and the appearance of visible symptoms. This incubation period can range from 10 or more days, depending on temperature, relative humidity, and plant susceptibility to the pathogen. By the time downy mildew lesions are observed, numerous additional infection sites are developing but have not yet grown sufficiently to become 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, Orondis, 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 for pathogen resistance management. The publication entitled “Biology and Management of Downy Mildew of Lettuce” provides additional information on the biology and management of the disease on this crop and is available at the following website


video link

To contact Mike Matheron go to:
Weed Science:

The Harmful Effects of Cultivation on Weed Control

Cultivation is probably the most commonly used method of weed control used here. In addition to immediate gratification, it can eliminate many small weeds. Newly cultivated fields look healthier and are free of weeds. The gratification of cultivation can be short-lived. In the long term, cultivation may be more harmful than good for weed control and soil health.

Most weed seeds are very small and have difficulty making it to the surface alive. Cultivation helps bring small seeds to the surface where they can grow.

Cultivation is also an ideal method to spread and plant many weeds like Bermuda grass and Nutsedge. It also propagates established purslane and other weeds that re-root at the nodes.

Cultivation will uproot and dry out many small weeds but if it is done too close to the crop it can damage roots.

Rarely is cultivation used alone. It is often used in combination with and to incorporate herbicides. Many preemergent herbicides work by creating a chemical barrier at the surface. Cultivation can disrupt this barrier and reduce herbicide efficacy. It not only dilutes the herbicide but breaks up the soil structure so that herbicides, fertilizers and organic matter can leach below the region where they are needed


To contact Barry Tickes go to:
Biometeorology in IPM:

Leaf Wetness Update

The Yuma County Leaf Wetness Network remains in place for the 2018/19 vegetable season. Growers and PCAs may access information generated by the network by entering the following internet address:

Upon entering the address above, you will be transferred to internet page that provides a series of tabs at the top of the page. Simply click on the tabs to access the information of interest.

To contact Paul Brown go to:
Plant Diagnostics:

The Pieces in The Puzzles: Damping Off of Field Cole Crops

The last couple of weeks we have been getting many calls and samples of cabbage, cauliflower, and broccoli plants wilting. The incidence has been higher on Imperial valley. The lower leaves turn yellow and the whole plants wilt. In all the samples we have observed so far, the plants seem to have black fungal growth in the crown (see picture), which might confuse the PCAs as black leg disease. However, when those spores were observed under the microscope, we identified it as Alternaria spp.

Upon surface sterilization and isolating pathogen under selective media, we isolated Rhizoctonia from each sample. Alternaria is a facultative parasite, meaning it can live on both living and dead plant tissue. So Alternaria in this particular situation is a secondary opportunist pathogen taking advantage of the weak plants and Rhizoctonia and possibly other damping off fungi are the main culprit.

Damping off is a common problem on overwatered fields and fields with low drainage (thus more of an issue in Imperial Valley). Overwatering, high salts from over fertilizing and cool soil temperatures are all associated with damping off. Damping off pathogens are divided into two main groups. The “true fungi” that include Rhizoctonia, Fusarium, Thielaviopsis genera. And the second group are oomycetes that include Pythium and Phytopthora.

Water management is crucial for disease management. Avoiding wet feet, watering the plants early in the day leaving enough time for the soil to dry up, use of soil amendments to improve soil health and soil aggregate can be beneficial. Ridomil, Endura, Fontelis will help, but the key is to not create the environment not conducible for pathogen.


This Week in the Clinic
Everyone stop what you are doing and go check out your very own Yuma Plant Pathology website.
And do send us your feedbacks please!

What is happening in HEMP nation?
The U.S. Department of Agriculture (USDA) released long awaited draft hemp production regulations, produced under direction of the 2018 Farm Bill. Under Secretaries Greg Ibach and Bill Northey held a briefing, featuring a message from Secretary Perdue, regarding details of the Hemp Production Interim Rule.

USDA also released a new page for hemp producers detailing programs available for farmers.

For information about University of Arizona Hemp Program Visit:
Contact: Dr. Bindu Poudel
Robert Masson (


Real IPM

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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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