Historically, our Areawide Pheromone and Sticky Trap monitoring for insects was terminated around the first of April as the produce season ended. Beginning 2 years ago however, we continued our Areawide Trapping Network throughout the summer to collect trapping data from all 16 areawide trap locations year-round.  So why is this additional trapping data useful? For several reasons. First, understanding the activity of some of our key pests when produce is not grown during the summer may give us an indication of what to expect as the fall produce season begins. This may be particularly helpful for predicting moth flights and whitefly flights in August-September coinciding with early transplanting and direct seeded crops.  Another example is keeping track of corn earworm which can unexpectedly show up near the beginning of fall harvests. Secondly, trapping for pests during the summer has shown us that 2 of our more important produce pests are not caught in traps during the summer. We presume this is due to the absence of brassica crops and weeds for diamondback moth, and high daytime/nighttime temperatures lethal to aphids. The fact that trap catches resume in the fall supports our conclusion that these pests are absent in the summer, only to reenter the desert via winds and/or transplants in the fall. And finally, it gives me something to do in the summer.  So, visit the Areawide Summer Trap Network if you’re curious what our key pests are up to. We also continue to monitor thrips activity during the summer. This involves plant sampling using a dislodgement sampling method (beat pan) to determine the relative abundance of thrips adults and larvae on alfalfa, cotton, melons, wheat, Sudan grass, and weeds.  This is being conducted to supplement our yellow sticky trap data that only indicates thrips adult flight movement an area. With this plant sampling we should be able to determine the primary host plants thrips are colonizing in the cropping season during the long hot summer. We are also trying to determine whether these crops allow for the reproduction of thrips. So far, all the crops and weeds we have sampled have shown that thrips will reproduce and complete their life cycle on them. This is important, particularly for weeds, as we are trying to determine whether INSV can be survive the summer in the absence of lettuce. It is also important because it allows us to determine potential exposure of thrips to key insecticides like Radiant and Lannate for resistance management purposes. These crops essentially serve as untreated refugia that likely sustains insecticide susceptibility and is the reason these products are still effective against thrips.  We will be conducting this work throughout the summer, as well as through next produce season. We will periodically provide updates of these thrips monitoring results throughout the summer.  As my dad used to say, “to solve the problem, you must first understand the problem”.

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 JV farms at Gila Valley. Lettuce variety ‘Guapo’ was seeded, then sprinkler-irrigated to germinate seed on September 19, 2023, on double rows 12 in. apart on beds with 42 in. between bed centers.  Rest of the irrigation 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 on October 9, 2023 at the 3-4 leaf stage to a 12-inch spacing. Treatment beds were separated by single nontreated beds. Treatments were applied by incorporating in soil before seeding or with a tractor-mounted boom sprayer that delivered 50 gal/acre at 100 psi to flat-fan nozzles spaced 12 in apart.

Month	Max	Min	Avg	Rain
September	100	71	86	0.71 in
October	93	61	77	0.00 in
November	80	51	65	0.08 in
December	71	44	57	0.82 in

 
Fusarium wilt (caused by Fusarium oxysporum f. sp. lactucae ) rating was done in the field by observing the typical symptom of lettuce wilt. Confirmation was done by cutting the cross section of roots. Disease scoring/rating was done on December 6, 2023. 
 
The data in the table illustrate the degree of disease control obtained by application of the various treatments in this trial. The disease pressure was extremely high in 2023, and most treatments showed little or no control against the disease. The treatments that showed some activity were Bexfond, Cevya, Rhyme, and Serifel. Plant vigor was normal and phytotoxicity symptoms were not observed in any treatments in this trial.

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. 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.

Leaf miners: Adult activity light in all areas, about average for this time of season