Temperatures are still warm and worm pressure remains steady in most growing areas.   Here at the Ag Center, beet armyworm pressure is about average for early October, and still troublesome on new stands. Cabbage looper eggs are beginning to now show up. Pheromone trap counts for armyworm and loopers remain below average in most areas. However, diamondback moth larvae are present on broccoli and transplants at the Ag Center.  I’ve had several PCA reports of diamondback pressure in transplanted brassica crops in Wellton and Roll, and in the Yuma Valley. Trap catches have begun to increase also. So far, all insecticide products we’ve tested are providing good Lep control and no complaints from the field.  
 
Fortunately for local PCAs, several insecticide alternatives are available that provide excellent residual activity on Lep pests.   Perhaps equally important, many of the products have unique modes of action (MOA) that can be alternated throughout the growing season. This is important because the most fundamental way to reduce the risk of insecticide resistance is to eliminate exposure of multiple generations of Leps to the same MOA.   By using a different MOA on each subsequent spray application, you can minimize the risk of resistance by Lep larvae to these insecticide compounds. In contrast, repeatedly applying insecticide products with the same MOA for Lep control in the same area will significantly increase the risk of resistance.  This is particularly important with the Diamide group of insecticides (IRAC group 28). These products can be applied as both foliar sprays and soil systemic treatments, and currently 7 Diamide products are labeled for use in leafy vegetables - all with the same MOA (Coragen, Durivo, Besiege, Minecto Pro, Verimark, Exirel and Harvanta).  To avoid confusion among the Diamides, the IRAC group number (28) is placed on each label, adjacent to the product name.  Furthermore, applying a Diamide product (i.e., Coragen/Verimark) to the soil at planting or as a tray drench, and then subsequently applying Diamide foliar sprays (i.e., Harvanta/Besiege) on the same field is not a good idea as it can expose multiple generations of Leps to the same MOA.  For example, under ideal weather conditions, one could potentially expose 5-6 generations of BAW or DBM to the same MOA given the residual efficacy of the diamides.  That’s not a good way to use these products if you want them to remain effective.   Since the Diamides, as well as the other key products currently available (e.g., Radiant, Proclaim, Intrepid, Avaunt, Bts), are critical to effective management of Leps 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 Leps in leafy vegetables is to consider the recommendations provided in the guidelines entitled Insecticide Resistance Management for Beet Armyworm, Cabbage Looper and Diamondback Moth in Desert Produce Crops.

Throughout the desert Southwest and across the nation, we have continued to experience high prices for fertilizers used in crop production agriculture.  Accordingly, there are a lot of concerns and many anecdotes being passed around in an effort to understand the causes.   Following a review of the current situation, the conditions that have created these high fertilizer prices, and the prospects for the future; there are many factors involved.
 
What we are experiencing is illustrated nicely in Figure 1, which describes the pattern of anhydrous ammonia (NH₃) costs since September 2008.  A very similar story is told in review of the costs for urea (46-0-0), diammonium phosphate (DAP, 18-46-0), and most other fertilizer materials.  The high price trends we are now seeing began in September 2020.
 
Fertilizer prices also experienced a rapid increase in 2008 when nitrogen (N) fertilizer prices increased 32%, phosphate 93%, and potash 100%.  Prices then dropped to pre-2007 levels by the end of 2009 and in review the surge was primarily due to high global and national demand and low inventories.  The conditions we are now experiencing differ from the 2008 situation.
 
To better understand this current rise in fertilizer prices it is important to recognize that fertilizer is a global commodity and 44% of all fertilizer materials are exported to a different country. Thus, fertilizer production and prices are affected by other countries demanding fertilizer and the transportation rates to get the fertilizer to the final destination are all important factors.
 
The U.S. is the third-largest producer of fertilizers globally, and we require the importation of N, phosphorus (P), and potassium (K) to fully meet domestic demand.   The U.S. fertilizer dealers and producers pay the price defined by the global market and that include the costs for the base fertilizer, other fertilizer materials, and the transportation requirements.
 
Anhydrous ammonia (NH₃) provides a good example of the U.S. production in relation to the rest of the world.  In 2020 NH₃ was produced at 36 domestic plants and shipped around the country by pipeline, rail, barge, and truck. As of 2018, U.S. ranked second with 11.6% of global in NH₃ production. China at 24.6% led in global NH₃ production and India was ranked third with 11.3%.
 
For phosphate fertilizer production, the U.S. ranked 2nd with 9.9% of global production, led by China at 37.7%, and India with 9.8%.
 
For the mining and processing of potash (K₂O) deposits, Canada is the global leader with 31.9% of global production, followed by Belarus with 16.5%, and Russia with 16.1%.  The U.S. produces 0.8% of global potash and ranks 11th in the production of the global supply
 
Thus, the U.S. is not the sole or dominant player in the global fertilizer industry or market.  In point of fact, the U.S. share in terms of global use has dropped from 25% in 1961 to 10% in 2018.
 
Another major factor to consider are the energy requirements for the production and transport of fertilizer materials.  Fertilizer production facilities require a large amount of energy to convert the raw chemical materials into their applicable farm-use state. This is very important in terms of N fertilizers.  
 
There are two basic methods of fixing atmospheric diatomic N gas (N₂), which is biologically inert and represents 78% of the earth’s atmosphere.  The first, is the natural and miraculous process of biological N fixation which converts inert N₂gas from the atmosphere into ammonium-N (NH₄).  The second is the industrial process, which is also amazing, where anhydrous ammonia is produced by the Haber-Bosch process and atmospheric N₂ is combined with hydrogen (H) to synthesize the ammonia (NH₃).  This reaction is not thermodynamically favorable under natural conditions and huge amounts of energy with high temperatures and pressure are required to accomplish the process. In the Haber-Bosch process, natural gas is the H source and it also the energy source for further N fertilizer synthesis. 
 
Energy costs account for 70% to 90% of the fertilizer production variable costs in the synthesis process. For example, 33 million metric British thermal units (MMBtu) per material ton of NH₃ are required to make the conversion in the Haber-Bosch process.  Natural gas prices have risen dramatically over the past year, especially in Europe where more than a 300% increase has been experienced since March 2021.  This has forced many European Union N plants to close.
 
The aforementioned factors are dominating the increase in fertilizer prices that we are now experiencing.  There are also other important factors including supply chain disruptions, trade duties, and geopolitics.  These latter factors tend to get a lot of attention in the agricultural communities and the media often exacerbates that impression.  But we see from this basic review, that there are many factors at play, and we can also better understand why fertilizer prices are not likely to come down soon.
 
Reference:
 
Myers, S. and N. Nigh.  2021. Too Many to Count: Factors Driving Fertilizer Prices Higher and Higher.  Farm Bureau. https://www.fb.org/market-intel/too-many-to-count-factors-driving-fertilizer-prices-higher-and-higher

Figure 1.  Pattern of anhydrous ammonia (NH₃) costs since September 2008.  


Figure 2.  Pattern of U.S. share in the global nutrient market since 1961.

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%). Variety: Deluxe (HMX2595) was seeded, then sprinkler-irrigated to germinate seed on March 20, 2024on 84 inches 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. 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. 

Spray treatments were done on 05-21-2024, 05-31-2024, 06-07-2024 and 06-14-24. Powdery mildew was first seen on 06-05-24. Please see excel file for additional details.  

Disease severity of powdery mildew (caused by Sphaerotheca fuliginea and S. fusca) severity was determined 6-17-2024 by rating 10 plants within each of the four replicate plots per treatment using the following rating system: 0 = no powdery mildew present; 1 = one to two mildew colonies on leaves  ;2 = powdery mildew present on one quarter of leaves; 3 = powdery mildew present on half of the leaves; 4 = powdery mildew present on more than half of leaf surface area ; 5 = powdery mildew present on entire leaf. These ratings were transformed to percentage of leaves infected values before being statistically analyzed.

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. Quintec, Merivon, Tesaris, Luna Sensation, and V6M-5-14 V gave the best disease control. Phytotoxicity symptoms were not noted for any treatments in this trial.

ANR Webinar 10/17 click link for details.

Vol. 13, Issue 2, Published 1/26/2022

Public health and environmental concerns about the use of herbicides in addition to the rise in the number of herbicide resistant weeds has led to increased interest in non-chemical methods for weed control. Steam application is one technique that is gaining popularity as an alternative to applying glyphosate and other herbicides in public areas such as parks and school yards. Steam kills weeds by heating plant tissue to levels sufficient to rupture plant cell walls. As you might imagine, the method is energy intensive and slow. To kill even small weeds, exposure to superheated steam for several seconds (2-4) is required (Upadhyaya et al. 1983).
 
Steam is also used to control weeds in commercial agriculture. There are several manufactures of equipment designed for use in orchards, vineyards and even row crops (Fig. 1-2) (M.M. S.r.l., Modena, Italy; WeedTechnics, Terry Hills, NSW, Australia). These types of machines are equipped with high powered steam generators (200 HP) that convert water to steam at a rate of about 170 gal/hr. Recommended travel speeds are 1-2 mph depending on weed species and density. For orchards and vineyards, steam is typically applied in bands using steam hoods mounted on arms that extend to the crop row (Fig 2).

Despite being organically compliant and indifferent to herbicide resistant weeds, use of steam for post emergence weed control in commercial agriculture has seen limited adoption. A major limitation is that steam provides only partial weed control. Large, susceptible weeds die back, but tend to regrow 3-4 weeks after application and follow up applications are required. Further, some weed species are tolerant to steam when applied at reasonable travel speeds and rates. Abdulridha et al. (2019) investigated the use of steam for weed management in citrus. At travel speeds of 1 mph, goatweed and sedges were controlled (>72%), but Florida pusley and guinea grass were not (< 36%). Other researchers reached similar conclusions; although steam treatment is effective on small weeds (2 true leaves or smaller), control of large weeds is highly dependent on weed species with mortality rates ranging from 100% to 0% (Merfield et al. 2017).

Except for some very specific circumstances, use of steam for post emergence weed control is probably best left to urban areas where cost and time required for application are not as critical as they are in commercial agriculture.

References
Abdulridha, J.J., Kanissery, R.G., McAvoy, C.E. & Ampatzidis, Y.G. Evaluation of steam application for weed management in citrus. Appl. Eng. in Agric.,35(5): 805-814.

Merfield, C.N., Hampton, J.G. & Wratten, S.D. 2017. Efficacy of heat for weed control varies with heat source, tractor speed, weed species and size. New Zealand J. Agric. Res., 60(4): 437-448.

Upadhyaya, M.K., Polster, D.F. and Klassen, M.J. 1993. Weed control by superheated steam. WSSA Abstracts, 33, 115. 

Fig. 1. Applying steam post emergent weed control. (Photo credits: Weedtechnics).


Fig. 2. Applying steam to organically control weeds in a vineyard. (Photo credits: M.M. S.r.l).

The purpose of the survey is to provide information to help you make weed management decisions and will include weed species, location, and infestation level monitored monthly. Twenty four points have been marked for sampling. They are distributed from San Luis to Texas Hill and includes the Yuma Mesa. A three to five acre radius will be surveyed around each point and will be reported on an aerial photograph of the county. A separate map will be provided for each species. We know that we can’t find every weed out there across the county and will make an interactive map so that you can include infestations that we have missed. Just send the Arizona Vegetable IPM Team an image of the weed species and the GPS location from your phone and we will add it to the map. Our email is AZVegIPM-Team@email.arizona.edu or contact Marco Pena at marcop@ag.arizona.edu.

It is well known that weeds can be reservoirs for insect pests such as western flower thrips sweetpotato whitefly and for insect-transmitted viruses like Cucurbit Yellow Stunting Disease Virus (CYSDV) or Inpatiens Necrotic Spot Virus (INSV). It is our hope that the survey data aids in identifying concentrations of the weeds that could serve as hosts and are possible sources of infection.

The scale used on this survey for the infestation level on each weed is color coded as follows:

Color Code	Infestation Level	Plants / acre
White	ND: Not Detected	0
Blue	P: Present	1-3 pl/ac
Yellow	L: Low	4-50 pl/ac
Orange	M: Medium	51-200 pl/a
Red	H: High	Above 200 pl/ac

We are reporting a couple of the most abundant weeds in this update. Additional Yuma county weed maps will be uploaded to the site vegetableipmupdate.arizona.edu in the Weed Science Updates  Spatial Distribution of weeds in Yuma County.

The next image contains the location of our 24 sampling points:

Figure 1. Location of areas surveyed


Figure 2. Nettle leaf goosefoot increased in most sampling locations in the Yuma County


Figure 3. Purslane distribution

Results of pheromone and sticky trap catches can be viewed here.
Area wide Insect Trapping Network   VegIPM Update, Vol. 15, No. 15, July 24, 2024

Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:             
CEW moth counts increased in Roll and Yuma Valley; about average to previous years.
 
Beet armyworm:          
BAW moth counts increase in Tacna and Wellton; comparable to previous summers.
 
Cabbage looper::          
Cabbage looper numbers are low consistent with previous years and higher temperatures.
 
Diamondback moth:      
DBM moths were not caught in any trap; average for this time of the year.
 
Whitefly:                      
Adult movement continues to increase consistent with disking of late melon fields and volunteers.
 
Thrips:                          
Thrips adult activity continues to decline, comparable to mid-summer.
 
Aphids:                        
Aphid movement is absent and consistent with what we typically see during the summer.
 
Leafminers:                  
Adult activity about average for early July.