With the desert produce season almost completed and the spring melon season beginning, now is a good time to review the insecticide chemistries commonly used in your insect management programs. This is an important consideration as you make the transition from winter produce to alfalfa, spring melons and summer cotton where many of the same insecticide products are available in all these commodities.  Sustaining long-term insecticide efficacy that provides cost-effective crop protection requires a conscious effort on the part of PCAs and growers to use insecticides responsibly.  Over the past 30 years, Agrochemical Manufacturers have developed and brought to market over 20 new classes of chemistry that are highly effective, selective, and significantly safer than their chemical predecessors. These include the neonicotinoids, spinosyns, tetramic acid derivatives and anthranilic diamides to name a few.  Most recently, we have seen new feeding disruptor products, PQZ (pyrifluquinazon) and Versys/Sefina (afidopyropen) being applied to fall melons for virus management and in winter vegetables for aphid management. Although, the development of new insecticide chemistries has been a bit slow over the past few years, we’re now seeing industry beginning to develop several new experimental insecticides for desert crops. You’ll be pleased to know that several compounds are being targeted for western flower thrips. Of course, at best many of these products are a few years away from registration. But this is great news as many of the older products are slowly being phased out of the marketplace. It was just a couple of years ago that flubendiamide (Belt, Vetica) was removed from the market, chlorpyrifos (Lorsban) is now gone, and EPA is currently proposing label changes to the neonicotinoids which could impact their use on many important crops. Thus, it is imperative to sustain the efficacy of the newer insecticide tools currently available and Insecticide Resistance Management (IRM) is now more important than ever. The most fundamental approach to IRM is to minimize the selection of resistance by a pest to any one type of insecticide chemistry. The key to sustaining insecticide susceptibility is to avoid exposure of successive generations of an insect pest population to the same MOA. Historically, alternating, or rotating compounds with different modes of action (MOA) each time you spray has provided sustainable and effective IRM in our desert cropping systems.  When it is comes to IRM; “rotation, rotation, rotation”. In other words, never expose a generation of insects to the same MOA more than twice.  The Insecticide Resistance Action Committee (IRAC), a coordinated crop protection industry group, was formed to develop guidelines to delay or prevent resistance. Using their most recent information we have produced a brief publication which provides the latest local information on the modes of actions, routes of activity and pest spectrum for important insecticide chemistries used in desert produce and melon crops - see the attached Insecticide Modes of Action on Desert Produce Crops. This classification list will provide you with an additional set of guidelines for the selection of insecticides that can be used in desert IPM programs.

This study was conducted at the JV farms at Gila Valley. Lettuce variety ‘Guapo’ was seeded, then sprinkler-irrigated to germinate seed on September 19, 2023, on double rows 12 in. apart on beds with 42 in. between bed centers.  Rest of the irrigation was supplied by furrow irrigation or rainfall. Treatments were replicated five times in a randomized complete block design. Each replicate plot consisted of 25 ft of bed, which contained two 25 ft rows of lettuce. Plants were thinned on October 9, 2023 at the 3-4 leaf stage to a 12-inch spacing. Treatment beds were separated by single nontreated beds. Treatments were applied by incorporating in soil before seeding or with a tractor-mounted boom sprayer that delivered 50 gal/acre at 100 psi to flat-fan nozzles spaced 12 in apart.

Month	Max	Min	Avg	Rain
September	100	71	86	0.71 in
October	93	61	77	0.00 in
November	80	51	65	0.08 in
December	71	44	57	0.82 in

 
Fusarium wilt (caused by Fusarium oxysporum f. sp. lactucae ) rating was done in the field by observing the typical symptom of lettuce wilt. Confirmation was done by cutting the cross section of roots. Disease scoring/rating was done on December 6, 2023. 
 
The data in the table illustrate the degree of disease control obtained by application of the various treatments in this trial. The disease pressure was extremely high in 2023, and most treatments showed little or no control against the disease. The treatments that showed some activity were Bexfond, Cevya, Rhyme, and Serifel. Plant vigor was normal and phytotoxicity symptoms were not observed in any treatments in this trial.

Due to a lack of effective selective, post-emergence herbicides, most vegetable crops are hand weeded following cultivation to remove in-row weeds.  This operation is costly and finding labor to perform the task has become increasingly difficult.  An alternative is to use automated/robotic machines for in-row weeding. These machines have been around for quite some time; the first “modern” units were commercialized in 2008. Since then, at least six companies have introduced machines and offer units for sale and/or automated weeding as a service in Yuma, AZ. 

Despite these innovations and efforts, adoption of automated weeding machines has been limited. One reason for this is that weed control is only partial, and follow up hand weeding is often necessary. All commercialized automated weeders utilize metal blades that move in and out of the crop row to cultivate weeds between individual crop plants as the machine moves through the field. As such, soil disturbance is high and weeds close to crop plants cannot be effectively removed without injuring crop plants. In a two-year study (Lati et al., 2016), we found that mechanical automated weeders removed about 2/3rds of in-row weeds.  The majority of uncontrolled weeds (~ 1/3rd) were observed to be within about 1” of the crop plant. 

To address the lack of precision of current automated weeding machines, we developed two high speed, centimeter scale resolution sprayers to spot apply herbicides to weeds with minimal off-target spray while traveling speeds that are viable for commercial farming operations (2 mph). The first is a high precision (sub-centimeter scale resolution) sprayer designed for spot spraying cotyledon stage weeds in leaf lettuce crops. The second is a spray assembly designed for controlling in-row weeds in vegetable crops that are close to crop plants (1-cm scale resolution). We tested the device in 2019 in the laboratory and found that weed control efficacy was greater than 95% (3 species), percentage of off-target spray was less than 3% and no crop injury was observed. A link to action videos of the device in action is provided at the link below. Future work includes seeking funding, and industry partners for integrating the devices with imaging systems to develop a high precision, automated/robotic weeding machine for vegetable crops.

Cited reference:

Lati, R.N, Siemens, M.C., Rachuy, J.S. & Fennimore, S.A. (2016). Intrarow Weed Removal in Broccoli and Transplanted Lettuce with an Intelligent Cultivator. Weed Technology, 30(3), 655-663.

High Speed Centimeter Scale Resolution Sprayers for Precision Weed Control – Video Link: https://www.youtube.com/watch?v=TFja9FmVjJI

To contact Mark Siemens go to: siemens@cals.arizona.edu

It is surprising that some pretty common weeds are on the “Arizona List of Prohibited Noxious Weeds” The Arizona Department of Agriculture (AZDA) has an officially adopted list of noxious weeds. Southern Sandbur and Wild Mustard are among several other weeds that appear as Class A Prohibited Weeds. Class A are categorized as” a species of plant that is not known to exist or of limited distribution in the State and is a high priority pest for quarantine, control, or mitigation.”  There are 18 other weed species on this list. Class B Prohibited Weeds include Sahara Mustard, Black Mustard, Halogeton and Bull Thistle. These and 19 others are those categorized as a species of plant that is known to occur, but of limited distribution in the State and may be a high priority pest for quarantine, control, or mitigation if a significant threat to a crop, commodity, or habitat is known to exist.  Class C Prohibited Weeds include Field bindweed, Morningglory, Puncturevine and Saltcedar.  These are categorized as a species of plant that is widespread but may be recommended for active control based on risk assessment. There are 11 other species on this list. You can find the complete list here: https://agriculture.az.gov/pestspest-control/agriculture-pests/noxious-weeds

In addition to state regulations, many local communities establish weed control districts that raise funds to help control or eradicate particularly harmful weeds. Weed seeds are commonly heavily regulated by states. The Yuma County Pure Seed Association started many years ago and was the precursor to the Arizona Crop Improvement Association.

Area wide Insect Trapping Network   VegIPM Update, Vol. 15, No. 21, Oct 16, 2024

Results of pheromone and sticky trap catches can be viewed here.

Corn earworm: CEW moth counts increased in most traps; about average for early October.

Beet armyworm: Trap counts increased in most areas last week, and about average for early October.

Cabbage looper: Cabbage looper trap counts still most locations, below average for this time of the season.

Diamondback moth: Adult activity increasing, particularly in the Yuma and Dome Valleys.  Above average for this time of season.

Whitefly: Adult movement increasing Tacna, Dome Valley and Yuma Valley; overall about average for early October.

Thrips: Thrips adult movement picking up in all areas, overall activity above average.

Aphids: Winged aphids beginning to show up the north Yuma and Gila Valleys; about average for early October.

Leaf miners: Adult activity light in all areas, about average for this time of season