Now that the desert produce season is almost completed and the spring melon season is 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 35 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 (i.e., Plinazolin). 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 essentially 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. 

The Colorado River watershed and water distribution system (Figure 1) is one of the largest in the U.S. The main channel of the Colorado River extends over 1,450 miles, covers 244,000 square miles in the drainage basin, and has the greatest elevation fall of any watershed in North America. The Colorado River supports more than 40M people, nearly 6M acres of cropland, 30 native American tribes, and provides large amounts of electrical power generation for the southwestern U.S.

Figure 1. The Colorado River watershed. Source: USGS.

The average annual flow in the Colorado River between 1906-2017 was 14.8 million acre-feet (MAF), Figure 2. The allocated water for diversion on the Colorado River has been 16.5 MAF (15 MAF in the U.S. + 1.5 MAF to Mexico). Thus, there has been a structural deficit of at least 2.0 MAF for many years. Between 2000 and 2018, the average annual flow has been ~ 12.4 MAF, which has further compounded the problem creating an overall deficit of ~ 4.0 MAF.

Figure 2. Colorado River Annual Flow, 1905-2010 with an overall average and
10-year average. Source: Bureau of Reclamation.

The foundation to the governance of the Colorado River is commonly referenced to the “Law of the River”, which is based on the Colorado River Compact of 1922 (CRC of 1922) and a collection of laws, contracts, agreements, definitions, and precedents from previous legal cases. Thus, the Law of the River is not one distinct entity but rather an amalgam of various components. A key foundational component is the CRC of 1922 which was formally negotiated among the basin states to define how much water from the Colorado River can be used by each state on an annual basis. Other agreements contribute to the aggregate Law of the River, including a 1944 Treaty, that agreed to send Colorado River water allocations to Mexico.

The CRC of 1922 was developed following a period of relatively high annual flows. Based on the records associated with the transactions leading to the signing of the CRC of 1922, the hydrologists and other scientists were providing data and interpretations to the commission that significantly influenced the CRC of 1922.

The CRC of 1922 established the operational base of Colorado River water allocation providing 15 MAF allocated among the seven basin states. Even though annual flow in the river has been less than that in most years, river managers have been able to make it work for 100 years. However, due to the annual average flow of the past 20 years being ~ 12.4 MAF, the allocation of Colorado River water based on the original CRC of 1922 has not been sustainable (Figure 2).

The Colorado River Basin is managed in a complex and multi-level legal structure that involves many stakeholders. The Colorado River watershed is divided into the Upper and Lower Basins. The Upper Basin includes the states of Wyoming, Colorado, Utah and New Mexico. The Lower Basin includes Arizona, California and Nevada. A binational treaty governs the releases to Mexico from both the Upper Basin and Lower Basin (1944 Water Treaty and Minute 319).

Due to the impacts of the recent drought, the basin states negotiated interim guidelines to deal with Colorado River water shortages and determined the reductions for each state depending on the elevation of water in Lake Mead in 2007. The reductions associated with a shortage of Colorado River water were further augmented in 2019 by the Drought Contingency Plan (DCP) among the basin states, with specific guidelines for both the upper and lower-basin states.

Within the overall structure of the Law of the River, the basin states and the Boulder Canyon Project Act water contractors must work collectively to address their water supply issues. In the Lower Basin, water supplies are administered by a federal water master, designated as the Secretary of the Interior working through the Bureau of Reclamation. In the Upper Basin, the Upper Colorado River Commission administers compliance with the 1922 Colorado River Compact. In addition, every basin also has its own unique set of laws governing the water rights that apply within those states.

The 2007 Interim Guidelines for Lower Basin Shortages and the Coordinated Operations for both Lake Powell and Lake Mead are set to expire in 2026. 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.

Damping-Off
This disease commonly affects seeds and young transplants and is caused by the soil-borne fungi such as Pythium, Fusarium, Rhizoctonia etc. Infected seeds decay in the soil. Seedlings and young transplants will “damp-off” or rot at the soil line, before they eventually collapse and die. 
The fungus, Rhizoctonia solani, causes wirestem. Stems of plants become constricted and brittle at the soil line. The plant becomes stunted and may rot at the soil line. This disease is more severe on fall cole crops when the soil is warm. We have seen lot of this problem in the fields last year. Make sure you get certified disease free seedlings. 

Prevention & Treatment: Cultural controls include planting on raised beds and providing good drainage. In greenhouse where transplants are grown, use new potting soil and new or thoroughly cleaned and disinfested containers and trays. Wash used containers with soapy water to remove all traces of old soil mix, and then briefly submerse containers in a 10% bleach solution. Allow to dry before planting in containers. Both in greenhouse and fields: avoid overwatering and wet feet in plants/seedlings. 

k Rot
Black rot is another common disease we observed in the fields last growing season. Black rot is caused by a bacterium, Xanthomonas campestris pathovar campestris, and can affect all vegetables in the crucifer family. Above-ground parts of the plant are primarily affected, and symptoms may vary depending on the type of plant, age of the plant and the environmental conditions. In general, yellow, V-shaped lesions appear along the tips of the leaves with the point of the V directed toward a vein. When lesions enlarge, wilted tissue expands toward the base of the leaves. Veins turn black or brown. Infection may spread into the stems. Cutting into the stems often reveals a black-brown discoloration with a yellowish slime present. Symptoms on cauliflower may appear as numerous black or brown specks, black veins and discolored curds.

Prevention & Treatment: With no effective curative measures available, preventative measures are very important. The bacteria survive the winter on plant debris and on weeds, such as wild mustard and Shepherd’s purse. It also can survive in and on seeds from infected plants. It can remain alive on plant residue buried in the soil for up to two years. The disease is easily spread by splashing water, wind, insects and garden tools. High temperatures and humidity favor development of the disease.
Use certified disease-free seed and transplants. If source of the seeds is unknown, or infested seedlots must be used, treat seed with hot water to eradicate pathogenic bacteria. Cabbage, broccoli, and Brussels sprouts can be treated at 122 °F for 25 minutes, while seeds of cauliflower, kale, turnip, and rutabaga are treated for 15 minutes. However, this treatment may reduce the viability of seed.
Choose varieties tolerant to black rot.  Do not plant cole crops where black rot has occurred in the past two to three years. Select well-drained sites with good air circulation. 
 
 
Downy Mildew
This disease is caused by the fungus Peronospora parasitica and can attack both seedlings and mature vegetable plants. Infected plants develop a gray mold on the lower leaf surface. The upper leaf surface of infected plants first turns yellow and then may turn brown or necrotic. Leaves wither and die. Symptoms differ from powdery mildew in that the downy mildew fungus grows only on the lower surface of the leaf. Development of the disease is favored by moist conditions.

Article source: https://hgic.clemson.edu/

Time flies. It’s the first week of February already and that means it is farm equipment/ag trade show season. Upcoming regional events include the WorldAg Expo, Tulare, CA, February 11-13, the Southwest Ag Summit, Yuma, AZ, February 18-20, and AgroBaja, Mexicali, Mexico, March 6-9.  If you are interested in the latest ag tech and farm machinery, all are outstanding events and well worth attending. For more information, click on the links or images below.

SourhWest Ag Summit
World Ag Expo
Agro Baja

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.

Organic lettuce is a high-demand crop for organic nitrogen sources. Lettuce requires a substantial amount of nitrogen to support its growth, particularly during the heading stage when most nitrogen uptake occurs. This demand is driven by its rapid growth rate and the production of large leaf biomass. The organic iceberg lettuce production system is gaining importance both locally and nationally due to the growing demand for healthy, hygienic, and safe food, along with the need for long-term sustainability (McGrady et al, 1991; Koide & Bache, 2021).

In arid regions like Yuma, AZ, where annual precipitation is often less than 3 inches, long periods of drought and frequent heat waves create challenging conditions for soil health. Limited rainfall restricts natural moisture replenishment, leading to soil dehydration and reduced microbial activity. Prolonged drought intensifies soil compaction and salinity buildup, while extreme heat accelerates organic matter decomposition, further depleting essential nutrients. These factors collectively hinder soil fertility, making it more difficult to sustain productive organic lettuce farming without strategic soil health management practices.

Therefore, many questions arise about whether combining fertilizers with biostimulants may improve soil health, particularly soil water retention while also enhancing crop growth, development, and yield. Several studies indicate that the combination of biostimulants with organic fertilizers has a positive effect on soil structure and mitigates stress and crop yield (Rodgers et al., 2020 Li et al., 2021; Zhang et al., 2021). They enhance soil physical properties and boost crop productivity in multiple ways. The potential of biostimulant to align with sustainability policies offers promising prospects for the future of agriculture. Given the environmental challenges associated with current fertilization practices, there is a pressing need to prioritize research that optimizes plant-microbe interactions to establish more sustainable agricultural systems. Biostimulants can positively influence a plant’s response to stress and adverse environmental conditions, promoting growth by enhancing germination, root development, and the plant's ability to access water and minerals.

Thus, investigating the magnitude of the potential impacts of coupled organic fertilizer and biostimulant on soil properties (i.e., soil water retention), lettuce crop growth development and yield for local or regional conditions can result in more effective, relevant, and practical information that can aid users in making management decisions. To address the identified knowledge gaps, preliminary field experiments were conducted during the Fall 2024 growing season at the Valley Research Center, University of Arizona Yuma Agricultural Center. These experiments aimed to establish foundational data to support this proposal.

The field (Figure 1) was planted on October 29th, 2024, and the pre-sprinkler irrigation strategy was utilized to ensure germination which was noticed on November 06, 2024. On December 5, when the lettuce was about 1 inch tall, the first application of 2 quarts/acre biostimulant (FBS Organics® Zicron®) was applied via the subsurface irrigation system. A second application of 1 gallon/acre was applied on January 9, 2025.

To quantify changes in soil water retention, three types of high-tech sensors (Figure 2) were installed after crop emergence to continuously monitor soil moisture levels, along with other key parameters. Additionally, plant height (Figure 3) measurements have been taken to assess the impact of biostimulants combined with organic fertilizers on crop growth and development. Finally, yield differences will be evaluated after harvest to determine the overall effectiveness of these treatments (Figure 4). Stay tuned for the results and conclusions after harvesting.

Figure 1. Satellite image view of the organic research field in the Valley Research
Center at the University of Arizona, Yuma Agricultural Center, Yuma, Arizona.


Figure 2. Nitrate-N sensor and soil moisture sensor from AquaSpy and soil
moisture and salinity sensors from Sentek were installed between two healthy
plants in the organic lettuce production field at the Valley Research Center at the
University of Arizona, Yuma Agricultural Center, Yuma, Arizona.

Figure 3. Plant height measurements in the field at the Valley Research Center at
the University of Arizona, Yuma Agricultural Center, Yuma, Arizona


Figure 4. Lettuce few weeks before harvesting in the field at the Valley Research
Center at the University of Arizona, Yuma Agricultural Center, Yuma, Arizona.

 

Area wide Insect Trapping Network  VegIPM Update, Vol. 14, No.5, Mar 8, 2023
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:           
CEW moth counts remain low at all trap locations and average for this time of year. 
 
Beet armyworm:         
Trap counts increased over the past 2 weeks; average compared to previous years.
 
Cabbage looper:           
Cabbage looper counts decreased slightly in most traps and below average for this time of season.
 
Diamondback moth:   
DBM moths remained low in most areas. Well below average for this time of the year.
 
Whitefly:                      
Adult movement was negligible and typical for this time of year. 
 
Thrips:                           
Thrips adult counts increased slightly in some areas the past 2 weeks. Currently, well below average compared with previous years.
 
Aphids:                      
Aphid movement decreased in most locations, and average activity for late-February.
 
Leafminers:                  
Adult activity down in most locations, and below average for late-February.