At the Southwest Ag Summit (SWAG) Feb. 17-19, my project stood in full bloom as a trailer of sweet alyssum. The scent caught attention of conference attendees, and people quickly realized this was more than just a pretty trailer.

The trailer represents a project I’ve been developing, supported by the Arizona Department of Agriculture Specialty Crop Block Grant Program, to explore a bigger question for desert vegetable production:

Can off-field habitat open the door to new tactics in vegetable IPM encouraging us to think beyond traditional in-field control?

This work builds on traditional trap cropping concepts but modernizes them through mobile trap crop trailers planted with sweet Alyssum (Alyssum maritimum). Unlike fixed trap crops, the trailers can be repositioned as field conditions shift, making them adaptable to real-world vegetable production systems.

At its core, this project examines the potential to use natural insect movement as part of a broader IPM approach:

Attract → Aggregate → Eliminate.

By positioning flowering habitat outside production fields, we aim to influence insect movement and aggregation. If pests are drawn into a managed zone, that area can function as a pest sink, concentrating populations where they can be intentionally and effectively eliminated.

At SWAG, I used the trailer display to emphasize a broader principle:

IPM is a strategy.
Individual actions are tactics.

Habitat manipulation, monitoring, thresholds, and selective chemistries are not competing tactics. When layered intentionally, they reinforce one another.

In systems where insecticide options are limited, redirecting pest pressure into a managed off-field zone may strengthen the effectiveness of available control tactics. Research is ongoing to evaluate how these mobile habitat trailers influence pest pressure and beneficial insects in nearby crops.

Figure 1. Mobile sweet alyssum trailer displayed at SWAG, illustrating the use of off-field habitat as an IPM tactic.


Figure 2. Project poster displayed at SWAG illustrating key principles of IPM.

Crops need to be monitored during all stages of growth to best manage water and nutrient inputs.  Taking crop condition into account and adjusting nutrient and water management accordingly is critical in achieving the optimum management of a crop and the best use of an irrigation system and fertilization program.  This is often referred to as a “feedback” system of crop management (Silvertooth, 2001).  This concept and approach to crop management can perhaps be most useful with an irrigated crop production system.  Irrigated chile (Capsicum annuum L.) production in the desert Southwest is a good example and it demonstrates the benefits in crop management when coupled with a fundamental understanding of crop phenology (growth and development). 

Increased efficiency is an important objective for developing sustainable chile crop production systems.  Efficiency can be defined in economic (return on the investment), agronomic (crop system response), or environmental (impact on environmental quality) terms.  Each of these concepts of efficiency can be successfully addressed simultaneously, which requires good management and attention to the changes that take place over the growth cycle of a crop.

When monitoring any crop in a production system there are several factors that are very important to consider including: 1) stage of growth, 2) crop vigor, and 3) yield potential.  A feedback system of management can be useful in adjusting critical crop inputs such as water and fertilizer inputs (particularly N) in response to actual crop conditions.  For example, in the case of irrigated chile, if the crop is experiencing poor vigor and symptoms of stress, it would be very important to identify the source of the stress and make an effort to address or correct it.  This could relate to several issues such as pest infestations (insects, weeds, or diseases), water stress, salinity stress, nutrient deficiency, etc.  If for example a crop is experiencing poor vigor due to water stress, the application of additional N will not be effectively utilized by the crop until the water stress situation is adequately addressed.  Alternatively, if a chile crop is experiencing very high vigor and excessive vegetative growth (often accompanied by a poor fruit load), a more conservative approach with N inputs would be warranted and at the same time it would be important not to impose a water stress per se.

Thus, monitoring a chile crop production system and having a gauge on basic factors such as stage of growth and the plant relationships to water and nutrient requirements are essential in realizing optimum efficiency regarding irrigation and fertilization inputs.  Flexibility in management is required to better respond to the crop and production conditions that can change quite rapidly during a production season and will vary from season to season.  Accordingly, managers need to be flexible in managing the system in response to the appropriate queues to realize the full potential from a crop production system.  This type of agronomic system efficiency is important for both short- and long-term sustainability.

To optimize N management for a chile crop it is important to make fertilizer N applications in the “Nitrogen Application Window” (NAW) described in Figure 1 which provides a baseline for chile growth and development as a function of heat units accumulated after planting (HUAP, 86/55 F thresholds; Brown, 1989; Baskerville and Emin, 1969).   Chile crop phenology as a function of HUAP is described in Extension Bulletin AZ1529 (Silvertooth et al., 2010).  The NAW is positioned just prior to the period peak N demand by the chile crop during the phase of growth when N demand is rapidly increasing after the crowning stage of development.  Nitrogen applications made in this manner in advance of the N demand period increases the probability of fertilizer N uptake and recovery by the plant.  Thus, the NAW extends from the crowning stage to just past peak bloom (~1200 – 2300 HUAP).  

Chile crop water demand also increases quite rapidly during this same period of growth with maximum chile crop water demand occurring from early bloom until the completion of development of the primary pod set (~1600 – 2500 HUAP).  For green chile this peak water demand will extend up to the time of crop harvest.  For red chile, peak water demand declines as the crop transitions from ~ 50% green and 50% red chile on the plants, or the stage that is commonly referred to as the maximum “chocolate chile” stage.

For both water and N management it is important to monitor crop growth and development as well crop condition including vigor, fruit load, etc.  Water stress should be avoided during these stages of growth and N management needs to be flexible in response to changes in crop condition during these peak periods of demand.  Crop monitoring and flexibility are key elements to management for optimum crop production efficiency.

Nitrogen application rates will vary depending on other factors such as residual soil N levels, N concentrations in the irrigation water, previous N fertilizer applications, cropping history for the field and residual crop residues, as well as the current condition of the crop or field in question.  Nutrient uptake studies have shown that approximately 180 lbs. N/acre is the maximum amount of total N required by green and red chile crops for optimum yields.  Actual total fertilizer N amounts needed by an irrigated chile crop usually equate to a total of 100 – 150 lbs. N/acre for the entire season.  However, as previously stated, this rate can vary tremendously depending on actual crop and soil conditions.

Nitrogen management for irrigated chile should be directed to provide the total fertilizer N for a crop within the NAW with split applications toward a maximum target of approximately 100 – 150 lbs. N/acre.  Late season N fertilizer applications can delay crop maturity and harvest.  Crop and soil monitoring in-season is critical to allow appropriate adjustments in N fertilizer applications to best match in-season conditions in the field optimize this important facet of chile crop management.

Figure 1.  Nitrogen (N) application window and maximum water demand period
for New Mexico type chiles in the desert Southwest of the U.S.

References
Baskerville, G.L. and P. Emin.  1969.  Rapid estimation of heat accumulation from maximum and minimum temperatures.  Ecology 50:514-517.
Brown, P. W.  1989.  Heat units.  Bull.  8915, Univ. of Arizona Cooperative Extension, College of Ag., Tucson, AZ.
Silvertooth, J.C. 2001.  Feedback requirements for nitrogen in irrigated cotton.  AZ1201, University of Arizona Cooperative Extension Bulletin.
Silvertooth, J.C., P.W. Brown, and S. Walker.  2010. Crop Growth and Development for Irrigated Chile (Capsicum annuum).  AZ 1529, University of Arizona Cooperative Extension, College of Agriculture and Life Science, Tucson, AZ.

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 

For those of you interested in the latest thoughts on ag technology, you might want to check out the keynote address given by John Deere¹ at CES 2023 earlier this week. The presentation can be found on YouTube at: https://youtu.be/1kjZMHZl538. As you might expect, there is a fair amount of company self-promotion, but it is interesting to hear their view on the current state and future of agricultural technologies. A couple of key takeaways for me were that telematics and computer vision systems will play key roles in the future and that increased precision will continue to be a focus.

[1] Reference to a product or company is for specific information only and does not endorse or recommend that product or company to the exclusion of others that may be suitable.

The IPM team frequently receives questions from our friend PCAs in Yuma regarding possible injury with herbicide combinations. A recent inquiry was about the addition of Prowl (pendimethalin) to Prefar herbicide preplant.
We found in our archives an evaluation that was done in 2002 by Barry Tickes from Arizona Cooperative Extension that addressing this question. The evaluation was located on 8^th Street and the Levee in Yuma CO and included the following treatments: Dacthal at 10 and 12lb, Prefar at 6qt alone and with the addition of 0.5pt Prowl. All treatments were applied in 20 gallon/A spray volume as a 50% band on 42-inch beds. The plot size for this experiment was 600 ft. x 8 beds. Immediate incorporation was done with sprinkler irrigation. The results reported are in the following table:

As can be seen the addition of 0.5pt of pendimethalin to 6qt of bensulide produced 20% stunting in this case. 

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.