Hope you are all enjoying the summer so far and keeping busy. Although, we’re about 2 months away from the Fall produce season, it’s never too early to begin thinking of IPM strategies you will be using to battle key insects next season. This includes keeping track of their typical activity during June, July, and August. Below is a short discussion detailing individual pests. 
 
Aphids:    The major aphid species that are important in produce crops each spring include green peach aphid, foxglove aphid and lettuce aphid.  These species are considered cool season pests and are biologically most active during the winter and spring when temperature average around (55-65 F). We do not find them on summer crops as the high temperatures prohibit their activity. They essentially become extinct each summer only to reappear in the fall to infest crops in Oct-Dec migrating into the desert via N-NW winds that occur after the monsoons.
 
Diamondback Moth (DBM):  Another key pest that disappears each summer but for a different reason than for aphids. The host range of DBM is limited to only brassica crop and plants. Although brassica weeds are common during the winter, they occur during the summer due to high temperatures and dry conditions. Thus, like aphids, DBM populations from the previous spring season become “extinct” during the summer when brassica crops and weeds are absent. They reappear each fall migrating in on high winds associated with tropical storms from Mexico, or arrive into the region on infested brassica transplants from California.
 
Whiteflies:       A resident pest that occurs year-round in the desert. As a warm season pest, whiteflies are most abundant on fall produce crops, and seldom a problem during the winter and spring. Peak abundance occurs during the summer months on cotton, and again in September and October on fall brassica, leafy vegetables and fall melons.  Thus, it is important to control whiteflies in cotton prior to defoliation to prevent large migrations onto fall produce crops. In addition, whiteflies can be found on several weeds such as purslane, goosefoot, ground cherry, and sunflowers. Sanitation in and around fields being prepped for fall plantings is important. Preventatively, growers should consider applying soil, system insecticides such as imidacloprid or Verimark to Fall produce crops.

Beet Armyworm (BAW):  A warm-season pest that occurs year-round in the desert. They tend to reach peak abundance twice a year. Generally, the most important peak is in September and October when weather is ideal for their development, flight activity and oviposition. A second peak occurs in late spring. Activity is generally light during the summer, occurring primarily in alfalfa crops. Although BAW is known to migrate in from the south via monsoon and tropical storms, resident populations annually occur in alfalfa during the summer. Thus, to minimize BAW in fall produce crops, thorough management of BAW can potentially minimize their movement onto Fall produce crops.  Weeds are also a source of BAW (purslane, goosefoot, sunflower and Russian thistle) so sanitation in and around fields is important.
 
Western Flower Thrips (WFT):  Also a resident pest that can be found in the desert year round. WFT is most abundant on lettuce in the late spring, but peaks in abundance on alfalfa, melons and cotton is May and June. During the late summer numbers drop dramatically where thrips can be found on melons and alfalfa and weeds like goosefoot and purslane. WFT slowly move into lettuce again in early fall and are least abundant during the winter.  Sanitation of weeds during the summer can help reduce thrips abundance moving into the fall crops and weeds.
 
For more information see:   Keeping Track of Major Produce Pests During the Summer

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.

 

Interested in the latest developments in automated weeding machines and ag tech? There are a couple of opportunities at the upcoming 2025Southwest Ag Summit to stay up to date. One is the “Ag Tech: Innovations in Weed Control and Vegetable Crop Production Technologies” breakout session where university experts and cutting-edge innovators will provide updates on the latest advances in AI high precision smart spot sprayers and soil steaming for pest control (agenda below). The session will be held Thursday, February 20^th from 1:30-3:30 pm at Arizona Western College (AWC) in Yuma, AZ.

The other is the Southwest Ag Summit Field Demo on Wednesday, February19^th, where several of these technologies and other state-of-the-art automated weeders will be demonstrated operating in the field. The Field Demos will also be held at AWC. Breakfast will be served at 7:00 am and demonstrations begin at 8:00 am.

For more information about the Southwest Ag Summit, visit https://yumafreshveg.com/southwest-ag-summit/.

 

In the August 21, 2024 update we mentioned our plans to do a demonstrative trial at the Yuma agricultural center. This experiment was established on 10/2 and planted on 10/14. Sprinklers started on10/15. A stand evaluation was done on 10/28 and Phytotoxicity and Goosefoot and Lambs quarter weed control evaluated yesterday. The treatments suggested by some of the people in the industry, where:

Treflan (trifluralin) Applied at 1.5pt/A pre-emergent on the flat ground incorporated mechanically by disking approximately at 4” depth, then make the beds and plant the crop to germinate with sprinkler irrigation. The same method was utilized for Prowl herbicide at the rate of 1 pint product per acre. Also Prowl non-incorporated was included, Devrinol2XL at 1 pt/A, Prefar at 6qt/A as well as a high rate of Goal (oxifuorfen)preemergence to evaluate and document phytotoxicity levels.

As mentioned, we have collected weed control data, which we plan to include in future updates.

Would you like to see how this treatments look? Some of the observations, even though expected are very interesting, such as the fact that 16 floz of Goal Tender preemergence didn’t allow goosefoot germination but similarly broccoli didn’t emerge.

Come to the NW corner of the Ag Center (you can’t miss it) and look at the plots and see the difference between Prowl mechanically incorporated and non-incorporated, compare it with Prefar and Devrinol. We put some very clear signs as you can see in the picture above. The experimental plots are 14x60ft so they are large enough to illustrate what would happen in a farm.

We thank you for your suggestions ...please come and let us know what you think!

Western Flower thrips is among the most economically important insect pests that infests desert lettuce. Bean thrips started to become a major pest of fall lettuce in the desert over the last decade. Our objective is to determine alternative organic insecticides that can be used as part of an IPM program targeting these pests in leafy vegetable crops.

This fall, at the YAC experimental farm, we evaluated 10 organic insecticides frothier efficacy in suppressing western flower thrips and bean thrips in organic head lettuce. M-Pede, Pyganic, and Aza-Direct were evaluated with Oroboost included in one treatment and Orbit DL included in the other treatment. Thus, we evaluated these aforementioned insecticides in two different treatment entries. The purpose was to understand the performance of these insecticides with Orbit DL or Oroboost as adjuvant. The remaining insecticide treatments had only Oroboost as adjuvant. Both Oroboost and Orbit DL are OMRI approved organic adjuvants.

We expected that several of these bioinsecticides would exhibit some measurable level of thrips suppression. However, our data showed that only Entrust exhibited measurable reduction in immature thrips, western flower thrips, and bean thrips numbers (Fig. 1-3). Gargoil and Pyganic with the Orbit as adjuvant exhibited a slight reduction in western flower thrips adults (Fig. 2). We will continue to evaluate these organic insecticides against the thrips to gather more research-based evidence which will allow us to draw more accurate conclusions and make relevant recommendations.

Figure 1. Mean thrips nymph/plant as affected by organic insecticide application.
DAT=Day After Treatment.


Figure 2. Mean western flower thrips adult/plant as affected by organic insecticide
application. DAT=Day After Treatment.


Figure 3. Mean bean thrips adult/plant as affected by organic insecticide application.
DAT=Day After Treatment.

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.

 Areawide Insect Trapping Network   VegIPM Update, Vol. 15, No. 16, Aug 7, 2024
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:            
CEW moth counts decreased areawide; about average to previous years.
 
Beet armyworm:        
BAW moth counts decreased; 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 decrease, average for this time of the year.
 
Thrips:                          
Thrips adult activity continues to decline, average for early August.
 
Aphids:                       
Aphid movement is absent and consistent with what we typically see during the summer.
 
Leafminers:                   
Adult activity declining and below average for early August.