The rain finally showed up after almost a year.  It was significant too. The desert received over 1.25” last week and more is expected today.  And that’s not good for several reasons including the delays in disking recently harvested fields and planting spring melons. So far, I’ve seen a few cantaloupe fields planted to Yuma beds. One field had just been listed for planting with excessive produce crop residue in and on top of the beds.   The first thing I thought of was the threat of seed corn maggots on early planted melons, particularly given the colder, wet weather we’re experiencing. Seed corn maggot (SCM) is a pest that should be avoided whenever possible since control after the fact is near impossible.  SCM are always a concern in melon crops planted during late January and February, and are most prevalent under cool, wet conditions.    SCM can cause significant stand reductions in melons and other large seeded crops (e.g., cotton, corn, beans) due to the maggots feeding on germinating seed, roots and stems of young seedlings and transplants.  If larvae populations are high in the soil, replanting parts or all of an infested field is often necessary.  Not only is this an inconvenience to the grower, but replanting is expensive and can disrupt harvest schedules.  Unfortunately, once maggots have been found infesting the soil during stand establishment, there is usually nothing you can do.  Thus, avoidance of the problem is the most effective way of preventing stand reductions.  First, weather plays a major role in determining the damage potential for SCM. Melon stands are more susceptible to SCM during wet, cool spring weather in which seed germination is slowed or delayed.  These conditions (low soil temperatures, rainfall and/or excessive irrigation) give SCMs a chance to develop in the soil and attack the seeds before they can emerge. However, I’ve also observed SCMs take down direct seeded cantaloupe and transplanted watermelon stands established under warm, dry conditions when flies were abundant.  Secondly, our cropping system plays a key role.  Melon crops following produce are the most often attacked because SCM adults are attracted to freshly tilled soils with high levels of decomposing organic matter and will readily lay eggs in the soil (particularly moist soil). This includes heavy plant residue remaining after harvest of the previous lettuce or brassica crop, as well as applications of composted manure prior to planting.  Growers would be encouraged to delay planting melons into fields under these conditions.  However, if growers decide to plant in these conditions, then it would be wise to use a preventative insecticide applied at planting to minimize the impact from SCM and give seedlings a fighting chance.   A few alternatives are available that have shown activity against SCM and may be practical for their management in spring melons. For more information, visit Seed Corn Maggot in Spring Melons, 2021.  

Name That Pest

When going into the field to evaluate a crop, there are typically three fundamental points we need to take into consideration that include: 1) stage of growth, 2) general crop vigor and yield potential, and 3) anticipate the next stage of development and what we need to do in terms of field crop management.  These considerations are commonly focused on aboveground crop evaluations.  The root system is also an important part of the crop condition to evaluate but we commonly do not evaluate roots because of the difficulty in doing so.
 
Root systems and early development were described in a basic manner in a recent article on 4 September (UA Vegetable IPM Newsletter Volume 15, No. 18).  
 
The effective root zone depth is the depth of soil used by the bulk of the plant root system to explore a soil volume and obtain plant-available moisture and plant nutrients.  Effective root depth is not the same as the maximum root zone depth.  As a rule of thumb, we commonly consider that about 70% of the moisture and nutrient uptake by plant roots takes place in the top 24 inches of the root zone; about 20% from the third quarter; and about 10% from the soil in the deepest quarter of the root zone (Figure 1).  
 
The small and very fine root hairs are the most physiologically active portion of a developing root system.  It is important that plants continue to develop and generate fresh young roots and an abundance of fine root hairs to maintain water and nutrient uptake.

Figure 1.  General pattern for plant-water and nutrient uptake from the soil profile.

Root development patterns are dependent on the nature of the soil profile in the field.  Soil profiles with compaction layers, as well as rock, clay, or caliche layers can limit and alter root development and the full exploration of the soil volume that the plants are capable of (Figure 2).  So, it is good to know what the soil profile looks like in the field and understand how that will impact plant root development.

Figure 2.  Generalized soil profile with major horizons.

Leafy green vegetable crops need to develop a marketable plant in a relatively short amount of time and a strong root system is essential.  Transplants are commonly being used in vegetable crop production systems and the transition of transplants to field conditions is a major step in the production process.  The transition is primarily experienced by the plant below ground.  
 
Transplanted crops will have altered root systems due to the constraints within the rooting cone.  Further root development beyond the original cone rooting mass is important for crop success.  Thus, it is important to monitor the root system transition and the relationship to overall plant development.
 
Checking root systems is a plant destructive process since we need to literally excavate the roots from the soil and it does take time and effort.  Accordingly, it is also important to be careful of where and how we sample plants and evaluate the root systems in a field.
 
Crop species can vary significantly in their patterns of root development, and it is important to know what is “normal” when evaluating crops in the field.  An excellent reference for vegetable crop root system development is a 1927 publication by Dr. John E. Weaver and William E. Bruner from the University of Nebraska (Root Development of Vegetable Crops).  This publication can be found at the following link:
 
https://soilandhealth.org/wp-content/uploads/01aglibrary/010137veg.roots/010137toc.html
 
A few basic examples from the Weaver and Bruner publication are provided in the following figures (Figures 3-10).

Figure 3.  Cauliflower, 3 weeks after transplanting


Figure 4.  Cabbage roots, 55 days after transplanting.


Figure 5.  Cabbage roots, 75 days after transplanting.


Figure 6.  Pepper roots, 24 days.


Figure 7.  Pepper roots, 45 days (6 weeks).


Figure 8.  Pepper roots, mature.


Figure 9.  Lettuce roots, 3 weeks.  The roots on the right were grown in compact
soil, the roots on the left were grown in loose/open soil.


Figure 10.  Lettuce roots, 60 days.

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.

Last week, we initiated our first on-farm demonstration of soil steaming of the season with our self-propelled steam applicator. The machine is designed to inject steam into the soil and raise soil temperatures to levels sufficient to kill weed seed and soilborne pathogens (140°F for > 20 minutes). After the soil cools (< ½ day), the crop is planted into the disinfested soil.
In this trial, we are examining the viability of soil steaming for controlling weeds in organic carrot at the field scale level (plot size > ½ ac). The machine performed well in that it was able to reach target soil temperatures at reasonable travel speeds (> 0.4 mph), provide uniform temperature distribution across the bed and form nicely shaped beds suitable for subsequent planting. Stay tuned for reports of weed control efficacy, crop yield and overall profitability as compared to the grower standard. 
We are seeking collaborators to conduct similar field-scale trials/demos in Yuma, AZ. The primary objectives are to assess the viability of soil steaming at the field-scale level and obtain grower feedback on the device’s commercial potential. The machine can be adjusted to work with most bed configurations including narrow (40”, 42”) and wide (80”, 84”) beds, and is suitable for use in conventional or organic crops (soil steaming is organically compliant). To date, the device has been successfully trialed in iceberg lettuce, romaine lettuce, baby leaf spinach and carrot crops.
If you are interested in an on-farm demo of soil steaming, please let me know. I’d be happy to work with you.

Fig. 1. On-farm demonstration of a self-propelled steam applicator for weed and
disease control

Acknowledgements

This project is sponsored and funded in part by the Arizona Specialty Crop Block Grant Program and the Propane Education and Research Council (PERC). We greatly appreciate their support.

According to some authors "the human brain can process images up to 60,000 times faster than words"¹. So, I decided to share images of some of the onion herbicide tests we did at the Yuma Ag Center last season hoping you find them interesting as the season progresses. As you know the products tested could respond differently under different environments. Also some of these trials are done searching for new alternatives, therefore products are not registered.

 

1. https://www.linkedin.com/pulse/why-pictures-speak-louder-than-words-laura-nicole-brown#:~:text=According%20to%20Krista%20Neher%2C%20the,that%20really%20captures%20your%20attention.

Included below is a list of organic insecticides that you can consider for your organic IPM programs. Although there are few alternative organic insecticide options, it is important to rotate when possible. Like conventional insecticides, continuous exposure to the same biopesticides may pose some risk of further reducing their efficacy and leading to the development of resistance. 

A good organic insecticide rotation practice is to alternate selective organic insecticides with broad-spectrum organic insecticides. The use of selective organic insecticides favors the increase of beneficial arthropod populations which may help to keep the pest population in check and delay repeated application of insecticides. When the population of lepidopteran pests is low, spraying Bt-based insecticides first and pyrethrin or Spinosad-based products thereafter is a good strategy. Proper insecticide rotation is important because it can help reduce insecticide application frequency, resulting in reduced crop production costs. 

 Tank-mixing can help improve the efficacy of some organic insecticides against some target pests. Tank-mixing a Bt insecticide with pyrethrin, such as Xentari + Pyganic or Dipel + Pyganic, can be an effective combination for controlling lepidopteran larvae. Additionally, combining Pyganic and a neem-based insecticide like Aza-Direct can be a favorable combination for small lepidopteran larvae. Tank-mixing Entrust (spinosad) and M-Pede can help suppress flea beetles and bagrada bugs.

 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.