Historically, our Areawide Pheromone and Sticky Trap monitoring for insects was terminated around the first of April as the produce season ended. Beginning 4 years ago however, we continued our Areawide Trapping Network throughout the summer to collect trapping data from all 15 areawide trap locations year-round.  So why is this additional trapping data useful? For several reasons: 

1) Understanding the activity of some of our key pests when produce is not grown during the summer may give us an indication of what to expect as the fall produce season begins. This may be particularly helpful for predicting moth flights and whitefly flights in August-September coinciding with early transplanting and direct seeded crops.  Another example is keeping track of corn earworm which can unexpectedly show up near the beginning of fall harvests. 
 
2) Trapping for pests during the summer has shown us that 2 of our more important produce pests are not caught in traps during the summer. We presume this is due to the absence of brassica crops and weeds for diamondback moth, and high daytime/nighttime temperatures lethal to aphids. The fact that trap catches resume in the fall supports our conclusion that these pests are absent in the summer, only to reenter the desert via winds and/or transplants in the fall. And finally, 

3) It gives me something to do in the summer other than write reports and papers. 
So, visit the Areawide Summer Trap Network if you’re curious what our key pests are up to.

In 2026 the 2007 Interim Guidelines for Lower Basin Shortages and the Coordinated Operations for both Lake Powell and Lake Mead are set to expire. The seven Colorado River Basin states and stakeholders must work together to develop the new criteria that will replace those guidelines. At present, there is a gridlock in those negotiations between the Upper and Lower Basin states and it must be resolved in 2025 to replace those guidelines expiring in 2026.

As part of the 2025 SW Ag Summit program that was conducted on Thursday, 20 February on the campus of Arizona Western College, two sessions, the morning keynote and a morning breakout session, addressed the future of the Colorado River and the next set of management plans for water allocations that will be very important for agriculture in the lower Colorado River Valley in the next decade.

We were very fortunate to have in both sessions Mr. Tom Buschatzke, Director for the Arizona Department of Water Resources, and Mr. J.B. Hamby, Commissioner for the Colorado River Board for the State of California. Mr. Bushatzke and Mr. Hamby both serve as the lead negotiators for the delegations representing Arizona and California in basin-wide negotiations on the development of the new operational guidelines for the management of the Colorado River.

In the breakout session, Mr. Bushatzke and Mr. Hamby were joined by Mr. Hank Auza, President of the Yuma County Water Users Association and Mr. Elston Grubaugh, General Manager for the Wellton-Mohawk Irrigation and Drainage District. Hank and Elston provided valuable insight on the operational plans and potential impacts on their districts that have different priority levels for Colorado River water allocations.

The discussions in both the keynote and breakout sessions were very direct, candid, and forthright. Mr. Buschatzke and Mr. Hamby both provided very thorough and informative descriptions of how the negotiation teams are structured, their function, and how the negotiations have been proceeding.

In my opening presentation of the keynote program, I described my impressions from a remote position, not being directly involved in any manner in the negotiations, that two basic schools of thought seem to have developed and appear to be dominant in the current negotiation impasse. The first apparent school of thought in the development of the new guidelines is to follow the law, specifically the Law of the River. The other school of thought is to essentially tear up the existing set of agreements, burn it all down – so to speak, and start over completely. It seems that these two schools of thought are generally held by the lower and upper basins, respectively. Tom Buschatzke offered a third possibility that could develop as a hybrid plan between the two.

Hank Auza and Elston Grubaugh provided valuable perspectives as Colorado River water users working with varying levels of legal priority for water allocations. They and their colleagues working in the various irrigation districts of the lower Colorado River Valley have a lot at stake with these negotiations and the future health of the river. Their input was also very direct, complete, and forthright. Their experience and point of view brought a lot of valuable information to these discussions for the benefit of everyone present and participating.

Collectively, both the keynote and breakout sessions dealing with the future of the Colorado River were very well delivered by Tom Buschatzke, J.B. Hamby, Hank Auza, and Elston Grubaugh. Their hard work and commitment to the good stewardship of Colorado River water resources is clear and we are very fortunate to have them each committing their time and expertise to these issues.

Last year we had many reports of downy mildew disease in onions. Seems like this year, the weather may not be as conducive to the disease, but it is still a good idea to scout the fields.

Downy mildew of onions is caused by the fungus-like Stramenopile Peronospora destructor. The pathogen produces abundant sporangia that germinate directly acting as spores. Reported hosts other than onions include shallot, leek, garlic and chives. The fungus overwinters in volunteer hosts, cull piles, and debris. Spores are wind borne. Spores of the fungus present in soil or bulbs germinate, infect roots or bulbs, and develop systemically in the plant. Spores that land on the leaf surface produce local lesions that can spread systemically to younger tissue. Infection can spread rapidly under cool (34– 82 °F), damp conditions generating new inoculum within the field. The pathogen requires cool temperatures and the presence of free moisture (rainfall, dew or overhead irrigation) to infect onion plants. Under those conditions repeated disease cycles may occur with devastating results.

Disease management:  Regular scouting of field is important toassess disease severity and apply preventative fungicides. Disease management includesuse of disease free bulbs, transplants and seed. Crop rotation with non host(small grain, corn) for at least 3 years. Destroy volunteer plants, debris andcull pile. Better soil drainage, better circulation, preventative spray canreduce disease occurrence. Always rotate fungicide from different groups toavoid resistance build up. 

Pics: https://www.omafra.gov.on.ca/IPM/english/onions/diseases/downy_mildew.html

Sources:
https://amarillo.tamu.edu/
https://barron.extension.wisc.edu/

At the 2025 Southwest Ag Summit Field Demo a couple of weeks ago, many of the latest technologies were demonstrated in the field. Most were related to pest control. Several of the technologies demonstrated are new to the Yuma, AZ area. The recent technologies presented included two types of high precision spot sprayers for weeding and applying beneficial pesticides (Fig. 1a, Fig. 1b) and an AI based lettuce thinner. Manufacturers stated the technologies will be getting even better/more versatile soon. Both precision spot sprayer companies are developing models for small lettuce so that the machines can also be used for lettuce thinning. Also new was that the AI lettuce thinner technology is being further developed so that the device can be used also be used as a weeder. Several “older” pest control technologies also seemed to garner a lot of interest. These included an implement designed for cultivating high density crops (Fig. 1d), a camera guided cultivator equipped with in-row weeding tools (Fig. 1e) and a field scale drone sprayer (Fig. 1f).

Fig. 1. Newer pest control technologies demonstrated at the 2025 Southwest Ag Summit
Field Demo included a) Ecorobotix1 Ara high precision spot sprayer, b) Verdant Robotics
Sharp Shooter, c) Niqo Robotics AI based lettuce thinner, d) Oliver high density
cultivator, e) Steketee IC Light camera guided cultivator and f) DJI Agras T50 drone
sprayer.

Thank You

In 2010 we started publishing the Arizona Vegetable IPM Updates to a small number of friends. It was embraced by the community because of contributions from Mike Matheron, John Palumbo and Barry Tickes in the Plant Pathology, Entomology and Weed Science areas. Mike, John and Barry are the original IPM dudes. 

I was honored to be part of the team editing and sending the Newsletter for almost
16 years. 


This is my last update, and I would like to thank the UA team and the agricultural community for the opportunity to work with you. 

Aphids are considered the most difficult to control insect pests in organic vegetables due to the lack of effective bioinsecticides as well as their ability to hide within plant structures. For instance, lettuce aphids normally hide in the head or heart of lettuce, making them difficult to reach by insecticide treatment or natural enemies. It is important to adopt other methods, such as nitrogen and water management, for additional aphid suppression.

As sap-sucking insects, aphids depend on the nutritional content of the sap ingested from the plant hosts for proper growth and development. Nitrogen availability is one of the most important factors in the development of aphid populations. Thus, limiting your nitrogen application to the optimum amount required for your crops is good practice for maintaining your aphid population below damaging level. Additionally, the use of slow-release (minimizing the risk of nutrient deficiency or excess) nitrogen fertilizer can be beneficial for aphid control. On the other hand, excess of nitrogen will make your crops a superfood for aphids. This accelerates the growth, development, and reproduction of the pests, reduces their generation time, and results in an increase in the number of generations and density during the cropping season. Excess of nitrogen particularly affects aphids on host crops such as lettuce, wheat, and sorghum. In some situations, high nitrogen levels in plant tissue can decrease resistance and increase susceptibility to aphids’ attacks. Applying the optimum amount of nitrogen fertilizer can tremendously help to manage aphids. In addition to pest management, effective fertilizer usage can also result in economic and environmental benefits.

Selected References:
1- Altieri, M. A., C. I. Nicholls, and M. A. Fritz. Manage insects on your farm: a guide to ecology strategies. SARE. https://www.sare.org/resources/manage-insects-on-your-farm/

2- Aqueel, M. A., and S. R. Leather. 2011. Effect of nitrogen fertilizer on the growth and survival of Rhopalosiphum padi (L.) and Sitobion avenae (F.) (Homoptera: Aphididae) on different wheat cultivars. Crop Protection. 30:216-221.

3- Bal, R., M. Groshok, and Y. Jama. 2024. Effects of nitrogen and potassium-based fertilizers on green peach aphid and abundance and arugula condition and growth. The Scientist. 6:1. https://journals.mcmaster.ca/iScientist/article/view/2931

4- Sinha, R., B. Singh, P. K. Rai, A. Kumar, S. Jamwal, and B. K. Sinha. 2018. Soil fertility management and its impact on mustard aphid, Lipaphis erysimi (Kaltenbach) (Hemiptera: Aphididae). Cogent Food & Agriculture. 4: 145094.

5- Xia, C., W. Xue, Z. Li, J. Shi, G. Yu, and Y. Zhang. 2023. Presenting the Secrets: exploring endogenous defense mechanisms in chrysanthemums against aphids. Horticulturae. 9: 937. https://doi.org/10.3390/horticulturae9080937

Supplying the optimum amount of water to your crop is also very important for effective pest control. Water availability around plant roots increases nitrogen absorption. Additionally, with high water availability, there is an increase in phloem pressure, making food more accessible to sap-sucking insect pests. Supplying the required amount of water using appropriate irrigation methods and irrigation scheduling can be beneficial for pest management. Although these practices will not completely prevent infestation of aphids, they can surely play a role in reducing the density of aphid populations on your crops.

In the February 5, 2025 issue of the Arizona Vegetable IPM Newsletter, the potential benefits of biostimulants in lettuce production were highlighted. These naturally derived substances like seaweed extracts, microbial inoculants, and humic acids are known to improve soil health, enhance crop growth rates, and boost both yield and yield quality in lettuce farming. However, a critical question arises: Is the biostimulant safe for my organic and/or conventional lettuce farming?

Safety is paramount, especially for leafy greens like lettuce that go directly from the field to the consumer’s plate or bowl. Consumers expect high-quality produce that is not only nutritious but also free from harmful residues. This concern drives the need for a careful evaluation of any new agricultural input.

Biostimulants could offer several potential promising benefits for lettuce production by enhancing various aspects of plant and soil health. They improve soil health by increasing microbial diversity and boosting organic matter content, which leads to better soil structure and improved water retention. Additionally, biostimulants promote enhanced crop growth by stimulating root development and nutrient uptake, resulting in more vigorous and resilient plants.

When considering biostimulants, growers should be mindful of both the source and composition of the products used. Biostimulants come in two main forms: microbial, which contain beneficial bacteria or fungi such as Bacillus spp. or mycorrhizae, and non-microbial, which are derived from organic sources like seaweed extracts, humic acids, or amino acids. Along with these benefits, it is crucial to manage potential contaminant risks. For instance, microbial biostimulants may carry pathogens that pose food safety risks, while certain formulations might contain trace levels of heavy metals or residues that exceed safe limits. To ensure the safety of lettuce, growers can adopt proper application methods and timing: applying biostimulants to the soil generally carries a lower risk, as soil microbes help break down contaminants, whereas foliar applications done too close to harvest could leave undesirable residues on edible leaves. By carefully selecting products and adhering to these guidelines, growers can harness the benefits of biostimulants while maintaining the safety and quality of their lettuce crops.

To further assess biostimulant safety, growers should check for certifications such as an OMRI listing or third-party organic approval and adhere to Good Agricultural Practices (GAPs) by applying biostimulants at safe intervals before harvest.

Take-Home Message: For optimal safety and effectiveness, consider applying biostimulants using subsurface drip irrigation instead of foliar spraying, and avoid applications close to harvest. When possible, opt for non-microbial formulations to further minimize any risks.

Results of pheromone and sticky trap catches can be viewed here.
Area wide Insect Trapping Network   VegIPM Update, Vol. 15, No. 15, July 24, 2024

Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:             
CEW moth counts increased in Roll and Yuma Valley; about average to previous years.
 
Beet armyworm:          
BAW moth counts increase in Tacna and Wellton; comparable to previous summers.
 
Cabbage looper::          
Cabbage looper numbers are low consistent with previous years and higher temperatures.
 
Diamondback moth:      
DBM moths were not caught in any trap; average for this time of the year.
 
Whitefly:                      
Adult movement continues to increase consistent with disking of late melon fields and volunteers.
 
Thrips:                          
Thrips adult activity continues to decline, comparable to mid-summer.
 
Aphids:                        
Aphid movement is absent and consistent with what we typically see during the summer.
 
Leafminers:                  
Adult activity about average for early July.