During the past 20 years, there has been an unprecedented development of insecticide chemistry that has had a major impact on how PCAs manage insects on leafy vegetables and melons. Among these were several breakthrough chemistries including the neonicotinoids, spinosyns, ketoenols and diamides. Without question these products (along with other recently registered compounds) are more effective and safer to use than compounds used prior to 1993. In 2014, several new insecticide products became available for management of the key pest found on desert crops. Sequoia (Sulfoxaflor, formerly known as Closer) is currently registered for use in leafy vegetables and melons in Arizona and should have an excellent fit for aphid and Lygus management in spring vegetables. Although it has a similar target site as the neonicotinoid chemistry, it is not considered a neonicotinoid by IRAC because of differences in how insects metabolize the toxin. Rather, it is classified as a sulfoximine and the first of the chemical class to be registered. Exirel/Verimark (Cyazypyr) was recently registered in Arizona this past fall. Cyazypyr is not a new chemistry, but rather a 2nd generation Anthanilic diamide. What sets Cyazypyr apart from the other diamides is its unique cross-spectrum activity against major chewing and sucking pests via soil systemic or foliar applications. Torac (tolfenpyrad) received a registration on leafy vegetables last spring. It is a pyrazole; a mitochondrial complex I electron transport inhibitor. In essence, it is a metabolic toxin that inhibits energy metabolism when the insect comes in contact with the compound. It has shown good thrips activity when used in combination with Radiant or Lannate, and may be an alternative to pyrethroids in tank mixtures. The last new compound, Sivanto (flupyradifurone) is anticipated to be available in early 2015. Sivanto has a similar target site as the neonicotinoid, but like Sequoia, is different from neonicotinoids and is considered a Butenolide. It has good activity against whiteflies as both a foliar spray and as a soil-applied systemic treatment. As a soil systemic in fall melons, it has shown to be very effective against adult whitefly and CYSDV suppression similar to Venom. It also has activity against aphids. More detailed information on these compounds can be found in the following publications: New Insecticides for Desert Produce and Melons. 

As reductions of agricultural water allocations in central Arizona from the Colorado River are going into place in 2022 from the Tier 1 of the Drought Contingency Plan provisions, it is important for every segment of the Arizona agricultural industry to continue to review and refine our practices associated with water management and irrigation.  
 
Seasonal conditions are a benefit to vegetable crop production and water management in the desert Southwest, both in terms of cool-season crop adaptability and the general climatic conditions that create lower environmental crop water-use demands.  For example, based on more than 30 years of Arizona Meteorological Network (AZMET) data from the Yuma, Arizona area, approximately 20% of the total annual reference evapotranspiration demand typically occurs between August and May.  
 
Reference evapotranspiration (ETo) is the collective loss of water from a field due to evaporation from the soil surface and transpiration of water vapor from the plants.  Collectively, water movement from the soil and plant systems in a field is referred to as “crop consumptive use” and it is important to understand this process in our efforts to steward our water resources most effectively.
 
The AZMET system provides both historical and real-time weather information that can be used to assist in crop water and irrigation management.  Reference evapotranspiration values can be obtained daily from AZMET for the Yuma area and applicable to most of the region in the lower Colorado River Valley.  The ETo values multiplied by an appropriate crop coefficient (K_c) can provide very good estimates on actual crop evapotranspiration (ET_c) rates, ETo * K_c = ET_c.
 
The appropriate K_c values are specific for each crop species and stage of growth.  We commonly use crop coefficient K_cvalues that are provided in the publication “Consumptive Use by Major Crops in the Desert Southwest” by Dr. Leonard Erie and his colleagues, USDA-ARS Conservation Research Report No. 29 (see attached).  Reference information for K_cvalues can be obtained in this publication for common vegetable crops grown in this region.
 
Estimating and tracking actual crop-water use can be a valuable tool in understanding crop-water demand and irrigation management.  Comparing actual crop-water demand and crop irrigation practices can be important in our efforts to understand crop management needs and field-level efficiencies.
 
Reference:
Erie, L.J., O.A French, D.A. Bucks, and K. Harris. 1981. Consumptive Use of Water by Major Crops in the Southwestern United States.  United States Department of Agriculture, Conservation Research Report No. 29.

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%). Spinach ‘Revere’ was seeded, then sprinkler-irrigated to germinate seed Jan 18, 2024 on beds with 84 in. between bed centers and containing 30 lines of seed per bed.  All irrigation water was supplied by sprinkler irrigation.  Treatments were replicated four times in a randomized complete block design.  Replicate plots consisted of 15 ft lengths of bed separated by 3 ft lengths of nontreated bed.  Treatments were applied with a CO₂backpack sprayer that delivered 50 gal/acre at 40 psi to flat-fan nozzles. 
 

Month	Max	Min	Average	Rainfall
January	68	42	54	1.14 in
February	73	47	59	0.50 in
March	77	50	63	0.31 in

 
Downy mildew (caused by Peronospora farinosa f. sp. spinaciae) was first observed in plots on Feb 19  and final reading was taken on February 26, 2024. Spray date for each treatments are listed in excel file with the results.   Disease severity was recorded by determining the percentage of infected leaves present within three 1-ft² areas within each of the four replicate plots per treatment.  The number of spinach leaves in a 1-ft² area of bed was approximately 144. 

The data (found in the accompanying Excel file) illustrate the degree of disease reduction obtained by applications of the various tested fungicides. Products that  provided effective control against the disease include Orondis ultra, Thrive 4 M, Fungout, Cevya, Eject and Zampro. No phytotoxicity was observed in any of the treatments in this trial.

Automated thinning machines were first commercialized in 2012, almost a decade ago. Since then, the machines have improved tremendously, and automated thinning has become the standard practice in the Yuma area. As such, I was a bit surprised to see numerous fields this year with sub-optimal thinning performance. Many fields had numerous amounts of excess seedlings that should have been thinned and needed to be removed during the follow-up hand weeding/double removal operation (Fig. 1). There were also some fields where the machine was apparently not readily detecting seedlings, resulting in long sections of plants being killed and a poor final stand (Fig. 2).

Automated thinning machines can and do perform very well when set-up and calibrated correctly. However, field conditions such as lighting, levels of crop residue, weed pressure or soil type (color) change throughout the day and affect the way the machine chooses which plants to selectively thin.

As such, it may be beneficial to establish a protocol where automated thinning machine settings are checked at regular intervals throughout the day to ensure the unit is performing optimally. Doing so may help lower follow-up hand weeding/double removal costs and minimize the number of unnecessary skips in the field.

Fig. 1. Labor crew removing excess lettuce seedlings and weeds after machine thinning.


Fig. 2. Poor final stand establishment following machine thinning, possibly due to incorrect machine calibration.

Preemergence herbicides can be very effective in the low deserts where weeds germinate with every irrigation or rainfall. It is essential, however, that they be at the right place in the soil at the right time. The right place is in the soil around the weed seeds and the right time is when they are germinating. Only fumigants kill seeds. For most other herbicides, the seed must germinate and are then killed. When weed seeds germinate is dependent on a great number of interdependent variables.  These include weed species, soil type, moisture, soil temperature, condition of the seed, depth, organic matter and many other variables. Many seeds have biochemical mechanisms that allow them to germinate at different times. Some may germinate in a few hours and some may not germinate for several years. If they all germinated at the same time, they would be easier to control. The methods used to predict when weed seeds will germinate vary from very sophisticated numeric equations to Farmers Almanac type lore involving things like the thickness of gopher fur, the cuticle thickness of plants or the condition of bird feathers. Some methods will give you a precise day while others will give you just a general idea. In general, as the precision goes up, the accuracy goes down. Regardless of what technique you use, now is the best time to apply preemergence herbicides for the control of annual weeds. It is better to be a month early than a day late.We have conducted trials to determine how long it takes various weed species to germinate after receiving moisture. Results will vary depending on several factors and from field to field and year to year. Results are summarized below for individual species and by month. An average of all species is also included.
   Hours to Germination

NG = No germination

Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm::            
CEW moth counts continuing to increase in areas, and about average for late-September
 
Beet armyworm:         
Trap counts increased in most locations, bet well below average for mid- September.
 
Cabbage looper:          
Cabbage looper activity slowly increasing, particularly in  Dome Valley and Wellton. About average for this time of season.
 
Diamondback moth:     
DBM moths starting to become active in a few areas (Dome and Wellton); below average for this time of the year.
 
Whitefly:                      
Adult movement increased in the past week, but below average for this time of year. 
 
Thrips:                          
Thrips adults increased markedly in many locations (Tacna, Dome, Yuma Valley), and higher than previous years.
 
Aphids:                        
Aphid movement is absent and consistent with what we typically see during September. 
 
Leafminers:                   
Adult activity up in a few locations (Yuma Valley), below average for September.