Now that the desert produce season is almost completed and the spring melon season is beginning, now is a good time to review the insecticide chemistries commonly used in your insect management programs. This is an important consideration as you make the transition from winter produce to alfalfa, spring melons and summer cotton where many of the same insecticide products are available in all these commodities.  Sustaining long-term insecticide efficacy that provides cost-effective crop protection requires a conscious effort on the part of PCAs and growers to use insecticides responsibly.  Over the past 35 years, Agrochemical Manufacturers have developed and brought to market over 20 new classes of chemistry that are highly effective, selective, and significantly safer than their chemical predecessors. These include the neonicotinoids, spinosyns, tetramic acid derivatives and anthranilic diamides to name a few.  Most recently, we have seen new feeding disruptor products, PQZ (pyrifluquinazon) and Versys/Sefina (afidopyropen) being applied to fall melons for virus management and in winter vegetables for aphid management. Although the development of new insecticide chemistries has been a bit slow over the past few years, we’re now seeing industry beginning to develop several new experimental insecticides for desert crops. You’ll be pleased to know that several compounds are being targeted for western flower thrips (i.e., Plinazolin). Of course, at best many of these products are a few years away from registration. But this is great news as many of the older products are slowly being phased out of the marketplace. It was just a couple of years ago that flubendiamide (Belt, Vetica) was removed from the market, chlorpyrifos (Lorsban) is now essentially gone, and EPA is currently proposing label changes to the neonicotinoids which could impact their use on many important crops. Thus, it is imperative to sustain the efficacy of the newer insecticide tools currently available and Insecticide Resistance Management (IRM) is now more important than ever. 
 
The most fundamental approach to IRM is to minimize the selection of resistance by a pest to any one type of insecticide chemistry. The key to sustaining insecticide susceptibility is to avoid exposure of successive generations of an insect pest population to the same MOA. Historically, alternating, or rotating compounds with different modes of action (MOA) each time you spray has provided sustainable and effective IRM in our desert cropping systems.  When it is comes to IRM; “rotation, rotation, rotation”. In other words, never expose a generation of insects to the same MOA more than twice.  The Insecticide Resistance Action Committee (IRAC), a coordinated crop protection industry group, was formed to develop guidelines to delay or prevent resistance. Using their most recent information we have produced a brief publication which provides the latest local information on the modes of actions, routes of activity and pest spectrum for important insecticide chemistries used in desert produce and melon crops - see the attached  Insecticide Modes of Action on Desert Produce Crops. This classification list will provide you with an additional set of guidelines for the selection of insecticides that can be used in desert IPM programs. 

I want to take this opportunity to express my gratitude to the University of Arizona (UA) Vegetable Integrated Pest Management (V-IPM) Team consisting of Marco, John, Barry, Bindu, and Mark for inviting me to join the team and provide an agronomic component. This is also a good opportunity to offer some background on myself and my connection to the V-IPM realm.

I was first exposed to the concepts of IPM in crop production systems while I was an undergraduate student in agronomy at Kansas State University in the early 1970’s. Following graduation 1976, I began working as an agronomist-crop consultant in the irrigated crop production systems on the high plains of southwestern Kansas. In this capacity I was responsible for contracting 10,000-15,000 acres per year with the duty of providing useful crop production and management input to the growers on a continual basis and very importantly for protecting the crop from pests (insects, weeds, and diseases).

I learned very quickly in my first year in the field as a young agronomist-crop consultant that I could do an excellent job of assisting in the planning and management of basic agronomic inputs such as variety selection, planting management, soil fertility, tillage, rotations, etc. But if I was going to survive and do well in that job, I needed to learn how control crop pests effectively. The use of IPM practices was very new at that time and the crop consulting group I was working with were employing IPM practices in the field. The IPM approach worked best for effective pest control and gave us that capacity to protect the crop and it was the best route for economic profitability, plus we could see the environmental benefits, even the late 1970s. The farmers we worked with were somewhat dubious at first but began to see this working and readily embraced the use of IPM.

In the five seasons that I worked on the southern high plains in this capacity, I developed an appreciation for good programs in applied research and Extension education. As crop consultants, we appreciated the work provided by the scientist from Kansas State, Oklahoma State, Nebraska, and Colorado State Universities for developing and communicating the thresholds and control methods for the important crop pests in our region. They gave us the basic tools and we took that to the field, refined it, and made it work most effectively. It was an important partnership between the land-grant universities and our work in the crop production industry.

As a result of those experiences, I was motivated to return to graduate school in the Agronomy Department at Oklahoma State University with a major area of focus in soil-fertility and plant nutrition.

In January 1987, I interviewed, was offered, and accepted a position at the UA in Tucson, Arizona as an Extension Agronomist-Cotton (aka Cotton Specialist). Cotton production in 1987 was robust and widespread throughout southern Arizona and IPM was being introduced by UA personnel, but the cotton community was dubious, to say the least. In 1990 we were hit with horrendous pink bollworm (Pectinophora gossypiella, Saunders) infestations in cotton fields throughout the state and then whitefly populations (Bemisia tabaci Genn) rapidly increased to very damaging levels in 1991 and 1992. Working with an excellent team of UA Extension colleagues and the regional cotton industry, we were able to bring some good IPM practices, including important cultural practices, into our systems. New scientists like Drs. John Palumbo and Peter Ellsworth were hired and the IPM capacities in our UA programs significantly improved with their input and leadership.
Today, the IPM effort in Arizona is one of the very best in the country and the agricultural industry is among the most progressive as well. The V-IPM team stands out as one of the very best in this region or anywhere and I certainly appreciate the opportunity to work with this outstanding group and the vegetable crop production industry. Having some agronomic input to the V-IPM is good integration.

Last year we had a lot of watermelon fields infected with Fusarium from Winterhaven to Yuma, Wellton, and Mohawk Valley. Rain, and overwatering of fields when plants set fruits might have contributed to the disease development.

Fusarium wilt of watermelon, caused by Fusarium oxysporum f. sp. niveum, is one of the oldest described Fusarium wilt diseases and the most economically important disease of watermelon worldwide. It occurs on every continent except Antarctica and new races of the pathogen continue to impact production in many areas around the world. Long-term survival of the pathogen in the soil and the evolution of new races make management of Fusarium wilt difficult.

Symptoms of Fusarium can sometimes be confused with water deficiency, even though there is plenty of water in the field. In Yuma valley we have seen fusarium problem in some overwatered fields.

Initial symptoms often include a dull, gray green appearance of leaves that precedes a loss of turgor pressure and wilting.  Wilting is followed by a yellowing of the leaves and finally necrosis.  The wilting generally starts with the older leaves and progresses to the younger foliage. Under conditions of high inoculum density or a very susceptible host, the entire plant may wilt and die within a short time.  Affected plants that do not die are often stunted and have considerably reduced yields.  Under high inoculum pressure, seedlings may damp off as they emerge from the soil.

Initial infection of seedlings usually occurs from chlamydospores (resting structure) that have overwintered in the soil.  Chlamydospores germinate and produce infection hyphae that penetrate the root cortex, often where the lateral roots emerge.  Infection may be enhanced by wounds or damage to the roots.  The fungus colonizes the root cortex and soon invades the xylem tissue, where it produces more mycelia and microconidia.  Consequently, the fungus becomes systemic and often can be isolated from tissue well away from the roots. The vascular damage we see in the roots is the defense mechanism of the plant to impede the movement of pathogen.

Disease management include planting clean seeds/transplants, use of resistant cultivars, crop rotation, soil fumigation, soil solarization, grafting, biological control. An integrated approach utilizing two or more methods is required for successful disease management.

It’s September and planting season is underway. When planting lettuce, uniform seed spacing is critical for efficient, economical crop thinning. Seedlings spaced too close together, commonly referred to as “doubles”, are difficult and time consuming to remove by hand. Automated thinning machines which intermittently deliver an herbicidal solution to thin excessive plants often consider doubles as a single plant. In such instances, both seedlings are left in the field (Fig. 1). This results in increased labor costs during the subsequent hand weeding operation where weeds and doubles are removed. 

Several years ago, we conducted trials examining the influence of planter travel speed on seed spacing uniformity (Siemens and Gayler, 2016). In the study, a Stanhay 785 Singulaire vacuum planter was tested at travel speeds of 1.0, 1.5, 2.0 and 2.5 mph on shaped beds at the Yuma Agricultural Center. The results showed that the percentage of “difficult to thin” spacings, defined as doubles and seeds spaced less than 1 1/8” apart, increased from about 5% to 10% as speed increased from 1.0 mph to 2.5 mph (Fig. 2) . Similarly, the percentage of seeds “precisely placed” within 0.5” of the target location (i.e., 2.0 ± 0.5”) decreased from 70% to less than 45%, and the percentage of skips increased from 7% to 30%. Variability of seed spacing uniformity as measured by the coefficient of variation (COV) of seed spacings also increased. In short, planter travel speed had a significant effect on seed spacing uniformity and doubles - the higher the speed, the poorer the performance.

You may be asking what is the reason for the phenomenon observed? A logical explanation is that seeds are traveling at the speed of the planter when they are released and tend to “bounce and roll” in the direction of travel when they hit the soil surface. Thus, the higher the travel speed, the further seeds bounce and roll resulting in increased seed spacing variability. Other factors such as bed condition (i.e., cloddy vs well tilled) can also affect the amount of bounce and roll and cause poor seed placement and closely spaced seedlings that are difficult to thin (Fig. 3).

If you would like more information on how to accurately assess and analyze planter performance or are interested in conducting trials to determine how planter speed is affecting the percentage of doubles in your field conditions, please feel free to contact me.

References
Siemens, M.C., & Gayler, R.R. (2016). Improving seed spacing uniformity of precision vegetable planters. Appl. Eng. Agric., 32(5), 579-587.

Fig. 1. Lettuce seedlings intermittingly sprayed with an herbicidal solution by
automated thinning machine for purpose of thinning excess seedlings. Examples
of closely spaced seedlings, “doubles”, that are not sprayed and must be
subsequently thinned by hand (circled).


Fig. 2. Seeding performance of a vegetable planter sowing lettuce when
operated at four travel speeds.


Fig. 3. Poor seed spacing uniformity, possibly due to cloddy soil
conditions causing excessive seed bounce and roll.

An increasingly diverse number of minor acreage specialty crops are grown in this region every year. Managing some of these crops can be difficult without local experience. It is helpful to at least know what botanical family they belong to because crops in the same family often have similar growth habits, pest problems and fertility requirements. There are almost no pesticides registered for some of these crops because of the limited acreage, but response to pesticides is often, but not always, similar to that of other crops in the same family. Knowing the family they are in can often give you an idea of what to expect. Kerb, for instance, is generally safe to crops in the Composite family (Lettuce, artichokes, radicchio) but is harmful to crops in the brassica family (Broccoli, cabbage, bok choy). The following chart lists crops by botanical family. 

Crop Families

 Areawide Insect Trapping Network   VegIPM Update, Vol. 15, No. 16, Aug 7, 2024
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:            
CEW moth counts decreased areawide; about average to previous years.
 
Beet armyworm:        
BAW moth counts decreased; 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 decrease, average for this time of the year.
 
Thrips:                          
Thrips adult activity continues to decline, average for early August.
 
Aphids:                       
Aphid movement is absent and consistent with what we typically see during the summer.
 
Leafminers:                   
Adult activity declining and below average for early August.