The latest Arizona Vegetable Integrated Pest Management Update (Part One) from the University of Arizona (UA) Cooperative Extension in Yuma, Ariz. released Sept. 20, 2012.

Bagrada bugs are back at highest numbers ever

By John Palumbo, UA Research Scientist and Extension Specialist

Over the last several days, Bagrada bug populations have exploded throughout the low desert. The UA first observed light to moderate populations in early September on broccoli destined for research trials at the Yuma Agricultural Center (YAC).

Since we wanted to conduct Bagrada efficacy trials, we did not chemigate our first two-acre block (Aug 29 wet date). Within a week, about 75 percent of the stand was lost to the Bagrada bug and flea beetle.

Since then, we planted several more blocks of broccoli with the same intention for research trails. This week, the numbers increased significantly almost overnight and we treated the broccoli just to maintain the stands for future Bagrada research.

Based on my observations and research trials to date, the populations seen at the YAC are much high than last year, and at this time more extreme than 2010.

Numerous reports this week of heavy populations were reported in Texas Hill, Tacna, Roll, Wellton, Dome Valley, Gila Valley, and Yuma Valley; just about everywhere we grow produce.

I’m told it’s just as bad in the Imperial Valley in neighboring California.

Why are Bagrada numbers so abundant this year? I can’t say for sure. My observations are the bugs live very well under these hot growing conditions.

Here are a few things to remember:

1 - Newly emerged stands are very susceptible to Bagrada feeding, particularly with the numbers presently seen. In the past two days, I’ve observed wilted and dead seedlings in broccoli only two days post-emergence. Many of the other seedlings had feeding signs on the cotyledons.

2 - If possible, consider applying pyrethroids on new stands with aerial applications rather than by chemigation. The knockdown should be better, and the residual will depend on sprinkler irrigation schedules.

3 - Bagrada bugs are most active in the middle of the day - walking and flying. I’ve found them in the mornings at 7:00 a.m. by carefully inspecting under the cotyledons, particularly if it appears to be fed on. The adult is actually smaller than a 5-6 day-old cotyledon so look carefully. Also, wet soil and sprinklers do not appear to deter the bug from infesting fields.

As I’ve reported before, insecticides with contact activity appear to provide the most reliable control (i.e., pyrethroids, methomyl, chlorpyrifos).

We’re conducting a number of efficacy trials right now. If you would like an update on what appears to be working, just give us a call.

I’ve attached a copy of our Bagrada Bug Management Tips for the Low Desert that may assist in battles against this invasive pest.

Click this link to listen to John.

“Remember, when in doubt-scout.”

Contact Palumbo: (928) 782-3836 or [email protected].

Managing Sclerotinia Drop of lettuce with fungicides

By Mike Matheron, UA Extension Plant Pathologist

The successful management of any plant disease is achieved by focusing efforts on one or more vulnerable stages in the disease development cycle of the pathogen.

For lettuce drop caused by the fungi Sclerotinia minor and S. sclerotiorum, this point of attack centers on the fungal bodies called sclerotia. At crop maturity, sclerotia produced on infected plants will be incorporated into the soil along with crop debris as the land is prepared for the planting of the next crop.

For the Sclerotinia fungi, sclerotia serve the same purpose than seeds for plants. They allow the organism to carry over in soil in a dormant state until conditions become favorable for germination and growth.

Over the past several years of research trials, the traditional application of fungicides to the lettuce bed surface after thinning provided at best about a 50 percent to 60 percent reduction in dead plants, compared to plots without a fungicide treatment.

In a four-year comparison of fungicide efficacy when the soil contained Sclerotinia minor, the products Contans, Endura, Rovral, and Switch provided the same statistical level of disease control.

When soil contained Sclerotinia sclerotiorum, the product with the highest statistical level of disease control was Contans.

Statistically lower but equivalent disease reduction was provided by Endura, Rovral, and Switch.

The application of fungicides to the bed surface prevents germination of sclerotia at or near the soil surface, but has little effect on sclerotia deeper in the soil profile.

Ongoing research is focused on examining new chemistries and methods of application to the soil with the goal of consistently increasing the level of Sclerotinia drop control above the 50 percent to 60 percent achieved now.

Click the link to listen to Mike's Update.

Contact Matheron: (928) 726-6856 or [email protected].