With recent hot, dry conditions and temperatures in the 90s and above, spider mites can increase rapidly in melon fields, particularly watermelons. Under cooler conditions (~60°F), development can take over a month, but under warm conditions (~85–90°F), a generation can be completed in about a week, allowing populations to build quickly.

Natural enemies can suppress mites early, but under hot conditions—especially following broad-spectrum insecticide use—mite populations can outpace natural enemies. Watch for stippling and webbing on leaves. Consider treatment when webbing becomes evident and populations are increasing, and use selective materials whenever possible to preserve beneficials. Thorough coverage is essential for effective control.

These warm conditions may also accelerate development of other pests; although uncommon this early, whiteflies have already been reported in some melon fields and should be monitored closely.

BEE WARNING: If bees are present, follow all label precautions and avoid daytime applications. Apply insecticides at night when bees are not foraging.

For more information on spider mite management see: Spider Mites in Desert Melons

References:
Palumbo, J.C. 2025. Spider Mites on Spring Melons (2025). Vegetable IPM Updates, University of Arizona Extension, Vol. 16, No. 7, April 2, 2025.

A new active ingredient has recently been approved by EPA.

D. Victoria Reyes and Peter C. Ellsworth—Department of Entomology, University of Arizona

In November 2025, isocycloseram (IRAC Group 30) was registered by EPA. This new active ingredient expands the range of tools available to growers for insect management, supporting insecticide rotation and helping delay the development of resistance.

Isocycloseram has been registered for use in cotton under the product Vertento®, just in time for the 2026 cotton season in Arizona. This addition further expands the tools available for Lygus control in this crop.

For further information, please see the following publication: “Vertento® (isocycloseram) for Lygus Management in Arizona Cotton.”

At present, this active ingredient is also registered for use in multiple crops under different commercial products (see accompanying box). 

Justus von Liebig was a 19th century German scientist (1803-1873) who is regarded as one of founders of organic chemistry.  He is also commonly considered as the “father of agricultural chemistry and the fertilizer industry.”

Liebig developed several important analytical methods used in a broad range of applications as well as many other important contributions and developments.  Liebig was one of the great chemistry teachers of the 19th century that served as a foundation for the robust German chemical industry of the 20thand 21st centuries.

In 1840 Justus von Liebig presented a concept that is known as the “Law of the Minimum”, which was built upon a theory that had first been developed by Carl Sprengel, a German botanist (1787-1859).  The Law of the Minimum basically states that a plant’s rate and extent of growth and overall health is dependent on the amount of the scarcest of the essential nutrients that are available to the plant (Figure 1; Liebig, 1840 and van der Ploeg et al., 1999).

The Law of the Minimum has been further applied into a general model of all organisms and biological functions, including the limiting effects of other environmental factors i.e., sunlight and water in terrestrial ecosystems, as well as excesses of nutrients and other environmental factors (Bruuselma and Nigon, 2023; Davidson, 2016; and Mosaic, 2023).

An important way to consider the Law of the Minimum is that the growth of plants, or crops, is not dependent on the total amount of nutrients available, but rather by the scarcest nutrient or resource (i.e., water).  This is particularly important in relation to nutrients such as nitrogen, which is the nutrient required in largest amounts by plants, and it is the most common limiting plant nutrient.  In desert agriculture, water is commonly the first most common limiting factor in plant growth and development, closely followed by bio-available nitrogen.

The Law of the Minimum is important to understand in managing fertilizer and other agronomic inputs to a crop.  This has been demonstrated when fertilizer prices are high, particularly for nitrogen and phosphate fertilizers, and growers may be inclined to reduce or eliminate fertilizer applications.

Liebig’s Law of the Minimum is most applicable for nutrients and plant growth factors that are mobile in the soil.  This is particularly relevant for nitrogen, which is available to plants in the nitrate form (NO3--N), which is mobile in the soil.  Thus, (NO3--N) moves with soil-water. 

Accordingly, the Liebig Law of the Minimum also pertains to water in a soil-plant system.  Other growth factors or nutrients will not compensate for a deficiency in a given nutrient or plant growth factor.  Plant-available nitrate-nitrogen (NO3--N) or water are good examples, there are no substitutes.

The Liebig Law of the Minimum is an important concept in soil fertility and plant nutrition and overall agronomic crop management in an irrigated production system.

Figure 1.  Graphic illustration of the Law of the Minimum with shortest stave in
the barrel representing the most limiting nutrient in the soil-plant system.

References:
Bruulsema, T, and Nigon, L.L. Crops & Soils Magazine, November–December 2023 American Society of Agronomy.  pp.  54-59.

Davidson, D. 2016.  Nutrient Management Magazine.https://www.no-tillfarmer.com/articles/5648-no-till-notes-how-to-plan-your-summer-fertility-program?v=preview

Liebig, J. 1840.  Die organische Chemie in ihrer Anwendung auf Agri- Sprengel, C. 1831. Chemie fu¨ r Landwirthe, Forstma¨nner und Cameralisten (Chemistry for agronomists, foresters, and agricultural econo-cultur und Physiologie (Organic chemistry in its applications to agri-culture and physiology). Friedrich Vieweg und Sohn Publ. Co., mists). Volume 1. Vandenhoeck und Ruprecht Publ. Co., Go¨ ttingen, Germany. Braunschweig, Germany.

Mosaic.  2023.  How Law of the Minimum Impacts Crops' Nutrient Use. In: No-Till Farmer. https://www.notillfarmer.com/articles/12637-how-law-of-the-minimum-impacts-crops-nutrient-use

Vander Ploeg, A.R;   Böhm, W.; and M. B. Kirkham.  1999.  On the Origin of the Theory of Mineral Nutrition of Plants and the Law of the Minimum. Soil Sci. Soc. Am. J. 63:1055–1062.

We have recently seen an increase in celery samples coming into the clinic presenting with symptoms including elongated necrotic pitting with significant horizontal cracking on the inner stalks and sometimes total breakdown of the young tissues (petiole and leaf) within the heart. In these same samples, the outer stalks and leaves appear healthy and unaffected.  

At first glance, these symptoms resemble several known issues in celery, including black heart caused by calcium deficiency, black streak caused by boron deficiency, cucumber mosaic virus (CMV), and lygus feeding injury. Field observations have consistently shown low-to-absent lygus populations despite widespread incidence of severely affected celery, making insect damage an unlikely primary cause. CMV can also cause sunken, buff-colored lesions on the stalks but typically presents with additional foliar symptoms including leaf cupping and discoloration. Also, CMV doesn’t discriminate between young and old tissues, and despite testing every sample the YPHC has received thus far we have failed to detect the presence of the virus in any of the samples.  

Furthermore, I have had the chance to walk two severely affected fields in-person, from which I found two consistent observations. First, these symptoms are observed uniformly throughout large sections or the entirety of the field, a distribution pattern which is atypical of a sudden outbreak of a biotic pathogen or insect pest. Second, hosts from different plantings showed uniform severity, which indicates the issue arose at the same time across celery in the area. These two observations suggest that an abiotic culprit rather than a biotic pest is to blame for this sudden eruption of host symptoms.

So with lygus and CMV being unlikely causes and consistently negative cultures for any other bacterial or fungal causes, the last two options that fit the symptoms of these samples are both abiotic in nature. Black heart is a physiological disorder most frequently associated with calcium deficiency. The internal hearts of celery with black heart experience significant breakdown of all tissues due to insufficient calcium transport, similar to what can be observed on tomatoes with blossom end rot. Black streak, similarly, is also a physiological disorder, however, it is most often associated with boron deficiency. Black streak typically presents as elongated, sunken lesions along petioles and stems with significant crosswise cracking along the petioles. However, development of brown areas and die back in black streak cases has also been reported. 

Figure 1. Early blackheart symptoms


Figure 2. Late blackheart symptoms + secondary colonization


Figure 3. Black streak of celery

Both disorders can arise from inadequate fertilization of either calcium or boron or when rapid growth outpaces the plant’s ability to uptake enough of these nutrients from the soil. Both conditions have been linked to several causal environmental factors, but they commonly develop into severe losses when celery is grown in elevated temperatures above 90°F.  

With black streak, greenhouse studies demonstrated that susceptibility was not uniform over time and that the highest susceptibility in celery is observed during the rapid growth phase, about 4-7 weeks after transplanting (Ngouajio 2012). During this period of rapid growth and development boron demand may not be met when the growth of aboveground tissue is further stimulated by hot weather.

When celery is affected by blackheart, it often develops the most severe symptoms as plants approach maturity. This disorder is more frequently associated with rapid fluctuations in soil moisture from drought to flood conditions, excessive fertilization or soil fertility levels of nitrogen and potassium, and high soil salinity.

Of the cases submitted to the YPHC so far, both have been occurring at roughly equal frequencies. 

Sources and further reading:
Ngouajio, M.. “Hot weather requires careful management of celery to avoid black streak disorder”. Michigan State University Extension. 2010. URL: https://www.canr.msu.edu/news/hot_weather_requires_careful_management_of_celery_to_avoid_black_streak_dis

Guan, W.. “Picture of the week: Blackheart of celery”. Purdue University Extension Plant and Pest Diagnostic Lab. 2022. URL: https://ag.purdue.edu/department/btny/ppdl/potw-deptfolder/2022/blackheart-of-celery.html

If you have any concerns regarding the health of your plants/crops please consider submitting samples to the Yuma Plant Health Clinic for diagnostic service or booking a field visit with me:

Christopher Detranaltes, Ph.D. Cooperative Extension – Yuma County Email: cdetranaltes@arizona.edu
Cell: 602-689-7328
6425 W 8th St Yuma, Arizona 85364 – Room 109 

Interested in staying up to date on the latest robotic ag technologies? The International Forum for Agricultural Robotics, FIRA, hosts two annual conferences focusing on robotics and autonomous farming solutions, one in Europe and one in the USA. They recently uploaded recordings of sessions from the 2024 World FIRA, held in Toulouse, France to YouTube. The site also contains playlists of themed breakout sessions from previous European and USA events (over 400 videos total). Highlights include panel discussions with growers and company executives, robot demos, and inno’pitches from startup companies. Most of the content, particularly from the USA events, is high quality and worth viewing. 
Check it out by clicking here or on the image below.

We did some trials at the University of Arizona Yuma Agricultural Center in broccoli to evaluate and compare Napropamide (Devrinol) liquid formulation 2XT versus the Dry formulation DF-XT. 
This product inhibits the production of fatty acids in plants, which is crucial for plant development. It affects primarily the meristematic cells which are in growing points of the stems and roots. We saw activity especially on seedling development that we show in some pictures at the end of the article. 
Some growers expressed their concern on the safety of different levels of incorporation with sprinkler irrigation. Therefore, we established a test in which we applied the product as a broadcast application after planting. Then we used different levels of incorporation in some sections using 12, 24 and 36 hours of sprinkler irrigation. No difference was observed with the incorporation level in our trial. We observed temporary phytotoxicity from 4-10%. The data was obtained from visual evaluations. Also, a 0.5 to 1” height reduction was exhibited when compared to untreated plots. 
It is common that growers and PCAs make management decisions on herbicide applications in different crops knowing that some injury is expected. Such is the case for alfalfa, wheat, spinach, lettuce and in this case broccoli. Frequently slight stunting it is not noticed because commercial fields don’t have untreated areas for comparison.
We talked to PCA’s and growers at the SW Ag Summit and asked for their experience with napropamide this past season. Some noticed the broccoli exhibited similar levels of phyto, which they considered economically tolerable. 
We noticed that good soil prep was important for before the application of the product and avoiding direct contact of the seed with the product for best results.
On weed control we noticed good activity on nettleleaf goosefoot and lambsquarter. 
At the 45day we collected data counting SMALL and LARGE weeds and at the 60 day evaluation we noticed most of the SMALL goosefoot and lambsquarter in the high rate of napropamide plots stayed small (pic. below).

Integrated pest management (IPM) involves the utilization of a combination of several tactics for the effective management of pests. This concept was developed by entomologists and is currently adopted by pest managers to target many kinds of pests, including insects, weeds, and pathogens. Most IMP tactics fit well in both conventional and organic crop production. It is not uncommon that most pest management techniques that are approved for organic crop production are not very effective as a stand-alone tactic. Therefore, it is essential to use a combination of pest management techniques that will complement each other to control the pests adequately. This is like a many little hammers approach, where each of the management tactics is a little hammer hammering on the pests. When planning your IPM programs targeting pests in organic crop production, it is important to consider planting resistant/tolerant varieties, scouting regularly, implementing economic thresholds (when possible), practicing cultural control, physical/mechanical control, and biological control, and applying biopesticides when necessary. 

• Resistant varieties: Resistant varieties are crucial for effective IPM in organic crop production. When available, the use of resistant varieties should be the first line of defense against pests. Resistant varieties help save on production costs and mitigate environmental impacts associated with insecticides and their applications. 

• Cultural control: Cultural control includes cropping systems (trap cropping and push-pull), planting date (early planting or late planting), crop rotation, and growing of crop varieties with early maturity traits. Implementing trap cropping and/or push-pull systems can cause the diversion of insect pests. Early or late planting, crop rotation, and variety with early maturity traits can favor the avoidance of damaging insect pest pressures. 

• Scouting: Proper and timely scouting helps determine the levels of pest infestations, allowing the pest manager to trigger control action in a timely fashion. Scouting also helps to prevent unnecessary insecticide applications. 

• Economic thresholds: The economic threshold determines the pest or injury level at which control action should be taken. The economic threshold works side by side with scouting. This helps to determine when a management action should be triggered, allowing a reduction of unnecessary insecticide utilization, which will consequently help in delaying or mitigating resistance. 

• Physical/mechanical control: This method includes establishing physical barriers, plowing, and sanitation (elimination of volunteer crops and other potential hosts). Plowing can help to bury soil insect pests deep into the ground, directly kill them, and expose soil insects to adverse weather conditions, birds, and other predators, which will adversely impact these pest populations. 

• Biological control: This method involves using insect pests’ natural enemies, including predators such as spiders, lady beetles, syrphid fly larvae, big-eyed bugs, pirate bugs, lacewing larvae, and parasitoids such as parasitic wasps and flies. 

• Biopesticides: Biopesticides are based on botanical extracts, entomopathogenic fungi, entomopathogenic bacteria, or entomopathogenic viruses that have adverse effects on insect pests. Entrust, Bt, Pyganic, AZA-Neem, M-Pede, Celite, and Venerate are commonly used insecticides for insect pest control in organic crops grown in Arizona. 

The implementation of IPM permits to manage pests economically while preserving the environment and reducing negative impacts on human health. In other words, IPM aims at managing pests in an economically viable, socially acceptable, and environmentally safe manner. It is important to note that all the IPM tactics are not always viable in all situations (IPM is not a one-size-fits-all). Therefore, the management techniques choice for an IPM program should be done on a case-by-case basis. 

VegIPM Update Vol. 17, Num. 5

March 4, 2026

Results of pheromone and sticky trap catches below!!

Corn earworm:  CEW moth activity seen in some areas, but numbers have been low; About average for this time of season.

Beet armyworm: BAW numbers decreased across most locations since last collection. Above average  for this time of the season. Historically BAW numbers peak in March/April.

Cabbage looper:  Cabbage  looper moth activity decreased across most sites since last collection, but  remains higher than average for late-February. Historically cabbage looper moth  numbers peak in March/April. 

Diamondback moth: Adult activity remains steady across most locations. About average for this time of the year. 

Whitefly: Adult activity remains low across all locations, about average for this time of year.  

Thrips:  Thrips adult activity remains steady across locations, about average for this time of year. Expect numbers to continue increasing as temperatures warm up.

Aphids:  Winged aphid numbers decreased at most sites since last collection; below average for this time of the year.

Leafminers: Adult leafminer activity remains steady, high numbers seen in Yuma Valley, about average for this time of the season.