Last fall, researchers from the University of California discovered pumpkin plants on the UC Research Center in Holtville that showed signs of viral infection (severe stunting, leaf yellowing, and leaf curling) associated with high populations of whiteflies. Through a series of laboratory tests, they found the plants were infested with a virus similar to Squash vein yellowing virus (SqVYV), a Bemisia whitefly transmitted ipomovirus (family Potyviridae). It is not clear where the ipomovirus originated and fortunately since the initial discovery, subsequent sampling of melons this spring has yielded no further infected plants. So why is this important? If this ipomovirus were to spread throughout the region it could pose a threat to melon production in the desert southwest, particularly on watermelons in years when whitefly populations are high during the spring. SqVYV was first identified from squash and watermelon in Florida in 2005, and had been causing serious decline of watermelon vines since 2003. To date, Florida is the most economically impacted area by SqVYV, but the virus has also been detected in Indiana and South Carolina. As noted above, whiteflies (Bemisia tabaci b-biotype) acquire SqVYV in semi-persistent manner, and appear to retain the virus for only 24 hr after leaving infested plants. In commercial watermelon production, symptoms of SqVYV vine decline are usually first noticed at or just before harvest when whitefly populations are allowed to build up. Symptoms include yellowing, scorched or brown leaves, defoliation and wilting of the vines, and a rapid collapse of mature vines. The interior of the mature fruit rind can be discolored (brown areas under the rind), rendering the fruit unmarketable. Early symptoms on watermelon include yellowing and downward curling of the new growth. Based on reports from Florida, muskmelon (Cucumis species) are not very susceptible to SqVYV. To date, the host range of SqVYV appears to be limited only to cucurbit crops and weeds. For more information on this virus visit these publications: Recommendations for Management of Whiteflies, Whitefly-transmitted viruses, and Insecticide Resistance for Production of Cucurbit Crops in Florida and A new and potentially damaging whitefly-transmitted virus of cucurbits was found this fall 2014 in Imperial County, CA. If you experience vine decline near or during watermelon harvest or observe any unusual symptoms on melons, please contact us. 

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.

We have learned a lot about viruses in the past few newsletter articles and one of the striking features of most plant viruses is that they always need a host. And the relationship between a virus and its host plant is very specific. So where do the viruses go when we do not have lettuce or melon in the field? And how do they come back at the right time to infect the crops?  (clue insect vector). The answer is weeds. A lot of the most economically important viruses are economically important viruses not just because of the losses they cause, but also because of the losses they cause in variety of plants. Viruses have small genome size that allows them to evolve faster. Viruses over time have evolved to adapt and increase their host range.
Below are some common viruses in agriculture and the number of plants they infect/overwinter. Keep in mind that there are many plants that can act as a reservoir for virus but have not been reported yet, so this is not an exclusive list. 
 
Alfalfa mosaic virus (AMV): Alfalfa, lettuce,indive, sunflower, datura, amaranth, different species of pigweed, milkweed, annual fleabane, ixeye daisy, hairy galinsoga, smallflower galinsoga, different species of mustards, common lambsquarters, hedge bindweed, field bindweed, cucurbits, different species of clover and vetch, beans, broad beans, lima beans, lupine, pea soybean, ground Ivy, healall, okra, purslane, pimpernel, black nightshade, pepper, tomato, petunia, eggplant, potato, garden pansy etc. 
 
Cucumber mosaic virus (CMV): pigweed, horseweed, oxeye daisy, coffee weed, Canada thistle, bull thistle, hairy galinsoga, Jerusalem artichoke,  prickly lettuce, wild chamomile, hawkweed, groundsel, Canada goldenrod, sowthistle, endive, sunflower, lettuce, mustard, radish, chickweed, lambs quarters, morning glory, cucurbits, common teasel, alfalfa, beans, lima beans, mung beans, geranium, ground Ivy, okra, purslane, jimsonweed, ground cherry, horsenettle, black nightshade, pepper, tomato, petunia, eggplant, potato, burning nettle, garden pansy. 
 
Lettuce mosaic virus (LMV): lettuce, bristly oxtongue, spinach. 
 
Bidens mottle potyvirus: lettuce, endive, horseweed, hairy beggarticks, virginia pepperweed, Mexican pricklepoppy. 
 
Celery mosaic virus (CeMV): Celery, giant hogweed
 
Papaya ringspot virus (PRSV): Bur cucumber, creeping cucumber, balsom pear, cucumber, cantaloupe, watermelon, summer squash, pumpkin, gourd, winter squash, butternut squash, 
 
Tomato spotted wilt virus (TSWV): Tomato, potato, pigweed, hairy beggarticks, oxeye daisy, coffeeweed, prickly lettuce, annual sowthistle, ebdive, sunflower, lettuce, shepherd’s pruse, chickweed, hedge bindweed, cantaloupe, muskmelon, bean, broad bean, mung bean, cutleaf evening primerose, broadleaf plaintain, purslane, jimsonweed, bittersweet nightshade, black night shade, pepper, tomato, petunia, eggplant, potato. 
 
Tobacco mosaic virus(TMV):  White campion, jimsonweed, pepper, tomato, tobacco. 
 
Turnip mosaic virus(TurMV):  pigweed, wild carrot, bachelo’s button, Canada thistle, hairy galinsoga, smallflower galinsoga, common catsear, pineapple weed, dandelion, endive, sunflower, lettuce, mustard, brassicae crops, corn cockle, chickweed, common lambsquarter, spinach, cucumber, alsike clover, lupine, redstem filaree, ground Ivy, okra, velvetleaf, common pokeweed, purselane, jimsonweed, black nightshade, tomato, petunia..
 
Watermelon mosaic virus (WMV) :   mustard, common lambquarters, spinach, cucumber, watermelon, cantaloupe, squash, buttercup, red clover, common vetch, alfalfa, beans, lupine, pea, henbit, common mallow, okra, common pokeweed, jimsonweed, nightshade, 
 
Zucchini yellow mosaic virus (ZYMV) : cucumber, cantaloupe, watermelon, squash, zucchini, pumpkin, gourds. 
 
 
Source: Cornell.edu

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. 14, No. 21, Oct 18, 2023           
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:            
CEW moth increased in Tacna/Roll/Dome last week, and areawide about average for mid-October.
 
Beet armyworm:          
Trap counts highest in Tacna, Wellton and Dome, but below average for October.
 
Cabbage looper:         
Cabbage looper numbers increased in Tacna/Roll/Wellton but still below average.
 
Diamondback moth:    
DBM moths are beginning to appear in traps in Yuma Valley, trending below average for early October.
 
Whitefly:                      
Adult movement increased in the past 2 weeks and above average for mid-October.
 
Thrips:                         
Thrips adult activity down over the past week, and trending below average in October.
 
Aphids:                        
Winged adults continue to be captured for the season, consistent with heavy winds from W-NW. Can expect aphid flights to increase in the coming weeks.
 
Leafminers:                  
Adult activity increased significantly in Tacna associated with maturing melons. Trending above average for mid-October.