It’s unfortunately a very great season to be a plant pathologist…

We have confirmed the first sample of Fusarium wilt on lettuce submitted to the Yuma Plant Health Clinic from Yuma County. The stunted seedlings looked like any other typical case of damping-off at the seedling stage. When plated on culture media, subsequently confirmed Fusarium colonies grew abundantly from the declining plant tissues. If you’re not already on guard and scouting, this is a warning that Fusarium is active in Yuma County.

Adding on to this early alert, we’ve received a surge of submissions of young brassicas to the clinic. Several severely wilted and declining plants from around Yuma County have cultured positive for Pythium, likely as an opportunistic invader coming in on the back of all the early-season rain that brought stress to seeds and young transplants. Growers may want to consider oomycides, but only if the seedling disease is first confirmed to be Pythium. Remember, many seedling diseases caused by true fungi are indistinguishable from those caused by Pythium.

If you have any concerns regarding the health of your plants/crops please consider submitting samples to the Yuma Plant Health Clinic for diagnostic service or booking a field visit with me:

Chris Detranaltes
Cooperative Extension – Yuma County
Email: cdetranaltes@arizona.edu
Cell: 602-689-7328
6425 W 8th St Yuma, Arizona 85364 – Room 109

Weed escapes are easy to spot in vegetable fields at harvest time. Some growers have these weeds pulled, bagged and removed by hand from the field because they are unsightly and to reduce seedbank loads. This can be a costly operation. An alternative solution might be to use high voltage electricity to kill these weeds. The idea of using electricity to “zap” weeds is not new. Machines for agriculture applications were developed decades ago and commercially available in the late 1970’s. Although the devices worked, they were not widely adopted due in part to the availability of low cost and efficacious herbicides.

Because of environmental concerns, herbicide resistant weed issues and increased organic production, non-chemical, high voltage weed control technology is seeing a resurgence. There are now five companies, three established within the last four years, offering or developing machines for commercial agriculture. Although configurations differ, all machines operate using the same principles. To explain, consider the example of the machine shown in Fig. 1. The unit comprises high voltage electrodes (8-15 kV) positioned above the crop canopy, an electric generator and a soil engaging coulter connected to ground. During operation, when an electrode touches a weed protruding above the canopy, current flows through the plant back to the generator via the ground contacting coulter. Current flow combined with electrical resistance in the plant causes rapid heating and plant fluids to vaporize. This ruptures cell walls and kills the plant. Although there are few recent reports in the literature, prior research on dated machines showed that the technique can provide better than 98% weed control in moderate weed densities (15,000 weeds/acre) at travel speeds of 2 mph (Diprose & Benson, 1984).

Modern approaches that utilize high voltage electricity in combination with smart machines to spot treat weeds are being developed. The idea is to use camera imagery and artificial intelligence to locate weeds and high voltage electricity to kill them. One such machine being developed by the MASCOR Institute¹ and the Zasso Group is an autonomous robot equipped with cameras, on-board computers and robotic arms (Fig. 2). As the machine moves through the field, high voltage electrodes mounted on the movable, computer controlled robotic arms zap weeds. Another unit is being developed by Stekettee and RootWave. It is tractor pulled and designed to travel at 3 mph. Stekettee’s machine vision system identifies the weeds and RootWave’s high voltage electric technology shocks the weed with a pulsed 5 kV charge. Power is supplied by a generator connected to the tractor’s PTO. Both systems are in late stages of development with field tests conducted in 2020.

These systems appear promising and if they prove to be effective and economical, may be something to look for in the future.

¹Reference to a product or company is for specific information only and does not endorse or recommend that product or company to the exclusion of others that may be suitable.

The off-target movement of Dicamba and 2,4-D that was applied to resistant cotton and soybeans in the Midwest and south has been in the news for the last few years. It has exploded recently with the cancellation of these uses by a Federal court and the EPA. There have

not been serious problems with these herbicides here in Arizona. The focus of this article is to explain why not.

The Problem
Much of the cotton, corn and soybeans grown in the U.S. was Glyphosate resistant for several years. The number of Glyphosate resistant weeds have increased every year and new concerns about the effect of Glyphosate on human health and environmental safety have arisen. In response to this problem, new varieties of cotton, corn and soybeans have been developed that are resistant to a couple of old but highly effective herbicides, Dicamba and 2,4-D. These herbicides have high vapor pressures and can volatilize after application. They change from a liquid or solid to a gas after application and can move, sometimes long distances, in the air. Any herbicide can drift onto sensitive crops during application and cause injury. This is different than volatilization. New formulations of 2,4-D and Dicamba have been developed, however, that have significantly lower volatility. Studies have shown that while the potential is lower that it still can occur.  Volatilization of both Dicamba and 2,4-D have caused widespread problems to field crops, trees, parks, school yards, landscapes… to cause “Silent Spring “type conditions in the Midwest and south.  Volatility problems occasionally occur but widespread and serious problems have not been encountered in Arizona.

Environmental Conditions
The extreme conditions that exist during the summer in the low deserts of Arizona all contribute to herbicide volatility. High temperature, low humidity and the occurrence of temperature inversions have always made it difficult to use volatile herbicides here. Growers and Pest Control Advisers have learned to be cautious when using these products. They are rarely used after daytime temperatures go much above 90 degrees.

Acreage and Crop Diversity
Crops are grown in Arizona on a smaller scale and more intensively than they are in the Midwest and south. This is especially true in the southwestern counties. The acreage of cotton in 2019, for instance, was 173,000 acres in Arizona,4,350,000 in Texas,1,305,000 in Georgia,550,000 in Oklahoma and 497,000 in Alabama. This smaller scale allows Arizona growers to practice more careful management. Sprayers are cleaned more carefully or dedicated to spraying only volatile products. Fields and surrounding area are checked more frequently. In high acreage states, tens of thousands of acres can be treated at the same time with the same products. The amount of herbicide in the environment at those times is very high.  In Arizona not only are crops grown on a smaller scale, but they are more diversified. It is not uncommon to see 3 ,4 or more different crops being grown at the same time on a 20 acre block. When fields are sprayed it is done very carefully.

Newer formulations and Varieties
New formulations of both Dicamba and 2,4-D have been developed that are much less volatile than the old formulations. Although some of these are promoted as non-volatile, they can still move. Some studies have shown that they are 30 to 50% more stable. It will be variable and dependent on many factors. It is important to choose those cotton varieties that have been developed to tolerate Dicamba or 2,4-D. According to Randy Norton, U of Az. Cotton Specialist, upwards of 60% of the cotton varieties being grown in Arizona this year are Dicamba resistant. Randy states that these varieties were selected for their yield and lint quality more so than their resistance to Dicamba.

This time of year, John would often highlight Lepidopteran pests in the field and remind us of the importance of rotating insecticide modes of action. With worm pressure present in local crops, it’s a good time to revisit resistance management practices and ensure we’re protecting the effectiveness of these tools for seasons to come. For detailed guidelines, see Insecticide Resistance Management for Beet Armyworm, Cabbage Looper, and Diamondback Moth in Desert Produce Crops .

VegIPM Update Vol. 16, Num. 20

Oct. 1, 2025

Results of pheromone and sticky trap catches below!!

Corn earworm:  CEW moth counts declined across all traps from last collection; average for this time of year.

Beet armyworm: BAW moth increased over the last two weeks; below average for this early produce season.

Cabbage looper: Cabbage looper counts increased in the last two collections; below average for mid-late September.

Diamondback moth: a few DBM moths were caught in the traps; consistent with previous years.

Whitefly:  Adult movement decreased in most locations over the last two weeks, about average for this time of year.

Thrips: Thrips adult activity increased over the last two collections, typical for late September.

Aphids: Aphid movement absent so far; anticipate activity to pick up when winds begin blowing from N-NW.

Leafminers: Adult activity increased over the last two weeks, about average for this time of year.