For the past 18 years, the UA Vegetable IPM Team has annually surveyed PCAs and growers to document insect pest activity, economic costs of insect management and insecticide usage in Arizona lettuce through interactive workshops held each spring. The results summarized following these workshops can be very useful to the lettuce industry by providing information for addressing state and federal regulatory issues, prioritize research and educational activities, and translate the PCA’s activities into economic terms for their growers.  In a recent VegIPM update (Vol 13, No.13, Jun 29), we discussed interesting trends in insecticide usage on desert lettuce based on the results of these workshops that can be downloaded from this link Insecticide Usage on Conventional and Organic Lettuce in the Desert, 202021.   Just recently we summarized the remaining data collected in the workshop surveys. Summarized over the past eighteen years (2005-2022), the survey data provides “real world” information on the pest status of key insect species, economics of insect management, and estimates of yield losses in lettuce. A quick analysis of the summary clearly shows that insect management in desert lettuce is effective, very intensive, and can be expensive.  Specifically, surveys completed by PCAs represents a large proportion of the lettuce acres grown in the Yuma, and neighboring Bard/Winterhaven growing areas.  Not surprising, the surveys showed that annually 100% of the acres are scouted for desert lettuce pests and lettuce fields are visited >4 times per week.  In terms of pest status, the Lepidoptera larvae complex (beet armyworm/ cabbage looper/corn earworm), western flower thrips, aphids and seedling, soil pests are the most economically important insects attacking desert lettuce crops based on treated acres, numbers of spray applications, and yield losses associated with each pest. In terms of yield losses, average estimated loss from any one pest never exceeded 1% in either fall or spring lettuce. Given the unpredictable insect pressure experienced each season, PCAs should be commended on their capability of keeping insect losses to such low levels over a 18-year period. However, it is important to note that this was accomplished largely by the considerable expense and time invested by PCAs in scouting for these pests, and certainly by the significant investment in insecticide and application costs used each season to prevent these key pests from causing economic damage to lettuce crops. For the 2022 season, data indicated that insect pressure was quite variable on fall lettuce, but lettuce aphid pressure during the spring was the highest we’ve observed since we started surveying in 2005.    Bottom line:  IPM in desert lettuce crops is effective, but at a cost. As my high school Economics teacher used to say:  TANSTAFL (There ain’t no such thing as a free lunch).   A copy of the complete, summarized report can be downloaded from this link:  Insect Losses and Management on Desert Lettuce:  A 15-Year Summary.

John Wesley Powell had a profound understanding of the western territories of the United States (US) and he made a strong effort to influence the geographical boundaries of territories and states that were formed in the 19^th century.  Had he been successful with those efforts, our state lines would more closely follow watershed boundaries and the nature of the negotiations for water in the west would be significantly different.
Powell was born in Mount Morris, New York in 1834.  Powell’s family moved to Ohio then Wisconsin before settling in Illinois in 1851.  From an early age he was always interested in history, literature, botany, zoology, and a broad range of natural sciences.  In 1852 he became a teacher and attended several colleges but never did receive a degree.
When the Civil War broke out in 1861, Powell enlisted in the Union Army at 27 years old, serving as a first lieutenant topographer, cartographer, and military engineer.  On 6 April 1862 at the Battle of Shiloh in Tennessee, Powell was hit with a minié ball in his right arm, and it was amputated by field surgeons at the elbow.  After recuperation, he returned to service and was promoted to the rank of Major before the end of the war (Ross, 2018 and Cope, 2019).
After the war, Powell directed much of his interested and energies to the open territories in the western U.S.  The one-armed war veteran organized his first expedition to explore the Green and Colorado Rivers that began on 24 May 1869.  The expedition was completed on 30 August 1869 when Powell and five other men climbed out of the canyon.  Powell’s second expedition on the Colorado River extended from 22 May 1871 to 7 September 1872.  The second trip offered Powell and his team an opportunity to focus on the collection of scientific data and information that included photographs, detailed maps, and observations that were later used for the development of scientific publications.
He became the second director of the United States Geological Survey (USGS) from 1881 to 1894 (Figure 1).  His experiences in the west had huge influences on Powell and he became an ardent advocate for strict water resource conservation policies for the American West’s river systems.  He saw this as particularly important at the time since most American policy makers in Washington and in the western territories did not want to accept the basic facts regarding the aridity of the west and the limitations of development due to water.
In 1869 at the Montana Constitutional Convention, Powell stated that “All the great values of this territory have ultimately to be measured to you in acre feet.”, which was not fully comprehended or incorporated into water policy.  Another good example of Powell’s prophetic opinions on the management of western water was offered in Los Angeles at the 1893 Irrigation Congress where he stated, “I tell you, gentlemen, you are piling up a heritage of conflict and litigation over water rights, for there is not sufficient water to supply these lands.” and that advice was also generally ignored.
In 1891 the USGS published its 11^th Annual Report (USGS, 1891) that contained several excellent maps.  Perhaps the most famous map from that publication is a map of the arid region of the U.S. (Figure 2) and it is commonly referred to as the John Wesley Powell Map.  This map defined the arid region of the U.S. extending west of the 100^th meridian to the Pacific Coast Range.  Working in the west today, that line is still a good demarcation opening the arid lands of the western U.S.
He resigned from his duties as the USGS Director in 1894 due to the resistance and heavy opposition to his water resource conservation efforts from western politicians.  Dealing with the water resource challenges that we have in the west today, particularly in the Colorado River basin, we can recognize the wisdom and good advice that Powell offered.  We can also see the consistency of political operators tending to ignore natural resource facts and limitations.  Some things do not change.
Now we are primarily dealing with conflicts regarding Colorado River allocations between the upper and lower basins, consisting of states defined by political boundaries and straight survey lines.  We are dealing now with many of the problems that John Wesley Powell was trying to warn people about and possibly prevent or reduce the levels of conflict.  
Thus, it is interesting to consider the Powell Map versus the state maps that we have and what those implications might have been.  We can at least appreciate his capacity to look ahead and the importance of our being able to do so today.

Figure 1.  John Wesley Powell at his desk in the
USGS office, ca. 1891.



Figure 2.  John Wesley Powell’s Map of the Arid Region of the United States,
published in the Eleventh Ann. USGS Report, Part II, PL LXIX, 1891.

References
Cope, M.  2019.  Major John Wesley Powell: 1834-1902.  Utah Geological Survey, September 2019.
Ross, J.F. 2018.  The Visionary John Wesley Powell Had a Plan for Developing the West, But Nobody Listened. Smithsonian, 3 July 2018. 
 
USGS.  1891.  Eleventh Annual Report, United States Geological Survey, 1891.

Alfalfa is a major crop grown in Yuma area as a cover crop before vegetable season. Generally expected to be a hardy and easy crop to grow, alfalfa production still can be affected by many pests and diseases. Root and crown rot in alfalfa is a common problem. The pathogen Phytopthora megasperma thrives on standing water, overwatered, and/or in soil that lacks good drainage. 
 
The above ground symptoms typically consists of plant wilting, usually occurring quite suddenly, often followed by plant death. The roots turn tan-to-brown, sometimes turning black. Sometimes orange-to-reddish streaks can be observed in rotted roots. Occasionally, the symptoms can be seen in crowns too. Infected plants succumb to death, or grow at reduced rate thus being susceptible to other pests and diseases. 
 
The causal organism survives in soil as mycelia in infected plant tissue or as thick-walled oospores. It also produces thin-walled sporangia that release motile zoospores in the presence of free water. So it is important to grow alfalfa in well drained soils. Adjust irrigation water in a way that there is no standing water for too long. If possible, install tailwater ditch to remove excess water. Plant resistant cultivars like Agate, Apollo if the problem persists in the field. Till the soil deeply to reduce wet soil pockets, level the land before planting. 
 
If diagnosis is confusing, bring the samples to the Yuma Plant Health Clinic for proper diagnosis. Make sure to bring healthy looking plants, sick plant, plants in between etc. Remember, there is no such thing as too much plant tissue when it comes to submitting samples to the clinic!

We are in the process of organizing The Desert Difference: A Showcase of AgTech Opportunities for Growing in the Desert. The two-day event will be held November 13-14^th in Yuma, AZ. The first day will be a Field Day, the second will be a standard conference with keynote speakers and breakout sessions. Details of the conference will be coming soon. The focus of this article is the Field Day. As with our previous AgTech Field Days, the workshop will feature the latest ag technologies being demonstrated in the field. I’ve been reaching out to multiple companies but am sure I’m not aware of all the cutting-edge technologies out there. We would like to showcase as many innovative ag technologies as possible, so please contact me if you are interested in demoing your equipment or know someone that is. It’s an open invitation - private companies, and university and government researchers are all welcome!

Fig. 1. Previous University of Arizona AgTech Field Days.

This inquiry has been brought to us for different herbicides; How much time does this product require to safely plant lettuce? 
Of course, this depends on many variables such as the management done in the crop before lettuce, texture, water applied, rate, climatic conditions presented, and many other factors. 
The following table published in this Newsletter by Barry Tickes can serve as a general guideline to base Integrated Pest Management decisions and program our strategies. It’s always recommended to check the label for the product used in previous crops.

Aphids are sap-sucking insects that 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 herbivore populations. Excessive application of nitrogen fertilizer to crops is likely to increase insect pests feeding preference and consumption resulting in the survival, growth, and reproduction of the pests. This particularly affects aphids where excessive nitrogen application to host crops such as lettuce, wheat, sorghum, etc. may boost their populations by enhancing their growth and development, thus reducing their generation time, resulting in an increase in the number of generations and density during the cropping season. 

Report from a study conducted on Arugula shown that excessive supply of nitrogen increased green peach aphid density. In some situations, high nitrogen levels in plant tissue can decrease resistance and increase susceptibility to aphids’ attacks. Given that, adequate management of fertilizer like nitrogen can tremendously help to manage aphids which are difficult to control pests specifically in organic lettuce production. In addition to pest management, effective fertilizer usage can also result in economic and environmental benefits. 

Like fertilizer management, water management is also very important for effective pest control. Water availability around plant roots affects the rate at which nutrients are 

absorbed by the plants. Thus, an increase in water availability will increase nitrogen uptake which can affect the population dynamic of aphids. 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 this practice is not likely to completely prevent infestation of aphids, it can surely play a role in reducing the density of aphid populations on crops. 

Figure 1. Aphid selection of host plants: (a) The migrating aphid’s choice of landing on a particular plant depends on receiving the plant-reflected wavelengths (between about 500 nm and 600 nm); upon landing, antennal receptors detect the plant surface volatiles for initial assessment. (b) After making contact with the plant surface, the aphid briefly and tentatively pierces the epidermis using its stylet (<1 min) and ingests a small quantity of plant sap for further evaluation by a gustatory organ in the epipharyngeal area. (c) If the initial assessment is favorable, the aphid penetrates the epidermis to pierce the mesophyll and parenchyma tissues and briefly ingests more sap from vacuoles for additional evaluation and to determine the appropriateness of further ingestion (<1 min). (d) Upon identifying the host plant, the 

aphid pierces the epidermis of the leaf and passes through the intercellular air spaces of the mesophyll cells using its stylet to reach the sieve tube element in plant phloem, releasing salivary enzymes to protect the mouthparts and prevent plant tissue repair, enabling continuous sap consumption. If ingestion in the sieve tube exceeds 10 min, the host plant is deemed suitable (Xia et al. 2023). 

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 

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.