Lepidopterous larvae, including beet armyworm, cabbage looper, and corn earworm are major pests of leafy vegetables grown in the desert southwest. Typically, larval populations begin infesting newly planted produce stands soon after plants emerge in early September and can remain heavy through early November under favorable weather conditions. This year is no different; populations are heavy in spots throughout the area. Fortunately for local PCAs, several insecticide alternatives are available that provide excellent residual activity on this pest. Furthermore, many of the products have different modes of action (MOA) that can be alternated throughout the growing season. Thus the rapid development of resistance by lepidopterous larvae, and in particular beet armyworm, to any of these insecticide compounds should not readily occur. However, if an insecticide compound, or products with the same MOA, are used repeatedly for Lep control in the same field, the risk of resistance increases significantly. This is particularly important with the Diamide group of insecticides (IRAC group 28) because these products can be applied as both foliar sprays and soil injections, and because there are currently six Diamide products labeled in leafy vegetables with the same MOA (Coragen, Durivo, Voliam Xpress, Voliam Flexi, Belt and Vetica). Applying these Diamide products to the soil at planting, and applying them as foliar sprays in the same field, can expose multiple generations of Lep larvae to the same MOA. That’s not a good way to use these products if you want them to remain effective for more than a couple of years. Since the Diamides, as well as the other products currently available (Radiant, Proclaim, Intrepid, Avaunt), are critical to effective management of Lep larvae in leafy vegetables, PCAs should consciously avoid the overuse of any of these compounds. The most effective way to delay the onset of resistance by BAW in leafy vegetables is to consider the recommendations provided in the guidelines recently prepared entitled Insecticide Resistance Management Guidelines for Beet Armyworm in Lettuce.

Water is the first limiting factor in desert crop production systems, followed closely by bio-available nitrogen (N).  Nitrogen fertilizer application rates for desert vegetable crops typically range from ~ 150-300 lbs. N/acre.  This variation can be due to a lot of factors, including the residual soil N levels, crop rotations, length of the production cycle for the crop, etc.  
 
Due to the critical nature of N availability for the growth of a healthy and marketable crop with good yields in a timely manner, growers are alert to preventing a N deficiency in desert vegetable crop production.  Prices for fertilizer N are always a major factor in the crop production budget for any field and that is certainly turning out to be an important issue this year with higher fertilizer N prices.
 
Figure 1 shows the average North American fertilizer price gauge pattern from 2007-2021 with a distinct surge in 2021.  This surge in fertilizer prices is reminiscent of a similar pattern in 2008 and quite an increase in relation to average prices experienced in the past five years.  More specific to N fertilizer costs, Figure 2 shows the average weekly retail anhydrous prices in the U.S. 2019-2021 with a five-year average. 
 
The primary driving force in a higher average North American fertilizer price gauge is associated with N fertilizers.  Anhydrous ammonia is a good gauge for overall N fertilizer price since so many N fertilizers utilize anhydrous ammonia in the manufacturing process.  Nitrogen fertilizer price increases are being driven by the following major factors:
 

• Anhydrous ammonia plants in Louisiana were closed in September with Hurricane Ida’s landfall.  This resulted in supply disruptions.
• Natural gas prices have been increasing in recent months.  This is important because high demand of natural gas in the production of N fertilizers and it represents a major cost in manufacturing process
• On a national level, fertilizer prices are positively correlated with corn prices.  The use of corn in ethanol production has served to tighten the relationship between corn prices and fertilizer prices.
• Similar to many other products in the U.S. and abroad, general supply chain problems and labor issues associated with the COVID-19 has had a strong impact on all industries, including the fertilizer industry.

 
Collectively, this all translates to a more costly and perhaps challenging year for nutrient management in desert vegetable production systems.  These challenges can be dealt with by consideration of the 4R approach to plant nutrient application, consisting of:
 
 1.   Right fertilizer source at the
 2.   Right rate, at the
 3.   Right time and in the
 4.   Right place
 
The 4R nutrient stewardship approach utilizes the implementation of best management practices (BMPs) that optimize the fertilizer use efficiency by the crop. The primary objective of the 4R approach and BMPs is to match nutrient supply with crop requirements and to minimize nutrient losses from fields.  With higher fertilizer prices, this can be more important in crop production management for this year.

Figure 1.  North American fertilizer prices.


Figure 2. Average weekly retail anhydrous prices. Source: Progressive Farmer, 10 November 2021.

This study was conducted at the Yuma Valley Agricultural Center. The soil was a silty clay loam (7-56-37 sand-silt-clay, pH 7.2, O.M. 0.7%). Lettuce was seeded, then sprinkler-irrigated to germinate seed on Nov 28, 2023 on double rows 12 in. apart on beds with 42 in. between bed centers.  All other water was supplied by furrow irrigation or rainfall. Treatments were replicated five times in a randomized complete block design. Each replicate plot consisted of 25 ft of bed, which contained two 25 ft rows of lettuce. Plants were thinned Jan 17, 2024  at the 3-4 leaf stage to a 12-inch spacing. Treatment beds were separated by single nontreated beds. Treatments were applied with a tractor-mounted boom sprayer that delivered 50 gal/acre at 100 psi to flat-fan nozzles spaced 12 in apart.

Month	Max Temp (°F)	Min Temp (°F)	Average Temp (°F)	Rainfall
November	80	51	65	0.08 in
December	71	44	57	0.82 in
January	68	42	54	1.14 in
February	73	47	59	0.50 in

 
Powdery mildew (caused by Golovinomyces cichoracearum) efficacy trial treatments were made on February 15,2024, February 23, 2024, March 4, 2024, and March 12, 2024and .Disease was first seen on February  26,2024. Disease rating was done on March 15, 2024.   Disease severity was determined  by rating 10 plants within each of the four replicate plots per treatment using the following rating system: 0 = no powdery mildew present; 0.5 = one to a few very small powdery mildew colonies on bottom leaves; 1 = powdery mildew present on bottom leaves of plant; 2 = powdery mildew present on bottom leaves and lower wrapper leaves; 3 = powdery mildew present on bottom leaves and all wrapper leaves; 4 = powdery mildew present on bottom leaves, wrapper leaves, and cap leaf; 5 = powdery mildew present on entire plant. These ratings were transformed to percentage of leaves infected values before being statistically analyzed. Yield loss due to rejected lettuce heads would likely begin to occur on plants with a powdery mildew rating above 2.0 (percentage of leaves infected value of 40).         
The data in the table illustrate the degree of disease control obtained by application of the various treatments in this trial. Most treatments significantly reduced the final severity of powdery mildew compared to nontreated plants. The most effective fungicides were Rhyme, Merivon, Quintec, Cevya, Luna Sensation, Luna Experience, and Elisys. 

For those interested in autonomous ag field robots, Future Farming (Misset Publisher, BV, Doetinchem, Netherlands) put together an informative video that features 16 commercially available units. A wide range of robots are highlighted – tool carriers, planters that geo-reference seed placement, several weeding machines and even a rock picker. The short, 3 minute 20 second video is interesting and a quick way to get up to date on these technologies. 

It will be interesting to see what the future holds and whether these types of machines will become adopted in Arizona vegetable production. When discussing the high cost of automated weeding and other “smart” machines with a grower, he stated that the tractor driver was the cheapest part of the system. It’s a good point and one that’s hard to argue with.
Click here or on the image to see Commercial Autonomous Ag Robot video.

Some of the oldest and most effective broadleaf herbicides are the growth regulators. These include 2,4-D (Several names 2,4-DB (Butyrac, Butoxone), MCPA (Rhomene Rhonox, Chiptox, Battleship & others), Dicamba (Clarity, Banvel), Clorpyrolid ( Stinger), Triclopyr (Garlon, others), and many products containing 2 or more of these.Their principle use in this region are on grain, bermudagrass, alfalfa,cole crops and sugarbeets. Their utility is very limited in this region, however, because of their volatility and potential to move and cause injury to sensitive crops. Volatility is very different than spray drift. Spray drift is the airborne movement of the herbicide to non-target sites. It is often related to physical conditions like wind speed, nozzle type and pressure, application technique and other factors. Volatility, on the other hand, involves movement after the herbicide has evaporated into the air as a gas. It is affected not only by physical conditions but more importantly by characteristics of the herbicide including chemical properties of the active ingredient, especially vapor pressure, and formulation type. All of the growth regulators have high vapor pressure and are volatile. These herbicides can be formulated differently and formulation can significantly affect volatility. The amine formulations are much less volatile than the ester formulations of all of these products. The amount of product used can vary with formulation and there is generally more volatilization potential with higher use rates. The type of salt used with the amine formulations are also influential. Formulations of dicamba that use sodium salt ( Distinct, Celebrity Plus and Northstar) or diglycolamine salt (Clarity) are less volatile, for instance, than formulations using the DMA salt used in Banvel. The volatility of all of these growth regulators is always higher during the hot summer temperatures. Their use is restricted in some counties in California between March 15 and October 15. Questions come up every year at this time about how long after application these products can volatilize and how far they will move. You can find information that claims everything from that they are safe after drying to that they can volatilize 60 days after application. Many of us have seen them not move at all at times and move a mile or 2 at others. This is likely because volatility is affected by so many factors. It will always be difficult to predict. A sample list of the vapor pressures (mm/Hg) of herbicides that are used here follows. Vapor pressures very significantly by formulation and measurement technique and are affected by many factors. This list can give you a general idea of how potentially volatile an herbicide can be. The higher the vapor pressure the more potentially volatile it is. How volatile it becomes will depend upon temperature, humidity, wind, rate, adjuvants used and other factors. 

HerbicideVapor pressure(mm of Hg)

Prowl1.2 x 10-5

Treflan1.5 x 10-2

Glyphosate1.8 x 10-7

Goal2.0 x 10-7

Clethodim2.6 x 10 -9

Dicamba3.4 x 10 -5

2,4-D ester3.9 x 10-7

Eptam4.5

Area wide Insect Trapping Network   VegIPM Update, Vol. 13, No. 15, Jul 13, 2022
Results of pheromone and sticky trap catches can be viewed here.
 THE MOST RECENT RESULTS
Corn earworm:            
CEW moth counts increased slightly in the past 2 weeks and remains higher than the previous 2 summers.
 
Beet armyworm:         
Trap counts stay active in some locations (Yuma Dome Valley and Tacna) but lower than last summer
 
Cabbage looper:          
Cabbage looper numbers remain low consistent with the lack of activity this fall compared to last season.
 
Diamondback moth:      
DBM moths were not caught in any trap in the past 2 weeks; average for this time of the year.
 
Whitefly:                     
Adult movement continuing to increase, particularly in Gila, Yuma and Dome Valleys consistent with melon harvest.
 
Thrips:                         
Thrips adults decreasing in most locations, and trending comparable to previous years.
 
Aphids:                       
Aphid movement is absent consistent with what we typically see in the summer. 
 
Leafminers:                  
Adult activity has highest in Wellton and Dome Valley, and above average for early July.