It looks like we dodged a bullet from Hurricane Hilary; about ½ inch of rain and 50 mph wind gusts on Sunday. But time will tell if she delivered any unwelcomed guests.  Insects are notorious for hitching a ride on the winds associated with the remnants of hurricanes and tropical storms originating off the coast of Baja Mexico. As the storms dissipate upon arriving in the desert, they tend to “release” the flying pests onto our fall crops.  The Diamondback Moth (DBM) is a good example. Following the DBM outbreaks during the 2016-2017 season, we established over 50 pheromone traps from Texas Hill to San Luis to monitor year-round DBM activity over a three-year period.  The most important thing we learned from that study was that trap catches during the summer months in all three years showed that DBM were non-existent in the desert during July and August due to the unavailability of suitable brassica host plants. In essence, the populations become “extinct” during this two-month window when Cole crops and brassica weeds are absent. Thus, DBM disappear in the summer, only to reappear in the fall on transplanted and direct-seeded cauliflower, cabbage and broccoli.  Of course, we know from firsthand experience that DBM will come into the desert from transplants produced in CA coastal growing areas where DBM are active year-round. However, we also observed that sharp increases in areawide moth trap captures in October occurred following the remnants of Hurricane Rosa (Sep 30), and in again 2019 following remnants of Hurricane Lorena (Sept 24). Shortly thereafter, PCAs began reporting DBM larvae appearing on seedling stands and newly transplanted crops throughout Yuma. This strongly supports our contention that these DBM populations migrated into the area on these storms.  In contrast, in the fall of 2020, monsoon activity was negligible in Yuma and no tropical storms/hurricanes were reported in the region.  Accordingly, we only observed significant DBM activity adult in traps adjacent to transplanted cauliflower and cabbage fields in mid-September further suggesting that transplants certainly play an important role in annual reinfestation of fall Cole crops in the absence of wind events. But DBM is not the only insect pest that migrates into the desert from storms. 

Other lepidopterous pests are known to migrate from Mexico. Remember the cabbage budworm, that unusual pest that showed up in the desert in late September infesting the terminals and stems of transplanted cauliflower and direct-seeded broccoli. It is a rare pest and had never been reported on desert crops before. Because the cabbage budworm is of tropical origin, it was likely no coincidence that budworm larvae began to appear in the desert following heavy monsoon storms and the remnants of hurricane Kay in early September. The high humidity in the desert last fall season likely made the pest feel right at home. 

Bottom line:   DBM are like a box of chocolates: “You never know what you’re going to get”.  Do not become complacent.  Because DBM populations disappear from the desert each summer and reappear on fall crops from outside sources (see graph below), we never really know where they originate from, when they will show up, how abundant fall populations will be, or how susceptible to insecticides they are. So be vigilant in scouting and follow IPM guidelines for DBM management.  For more information see:

• Impact of Diamondback Moth on Desert Cole Crops, 2016-2021
• Cabbage Budworm in Desert Cole Crops
• 2023 Guidelines for Diamondback Moth Management in Desert Cole Crops

 

With the planting of every crop there is a time of anticipation as we wait and watch for germination, seedling emergence, and the development of a good stand of plants to start the crop season.  Successful seedling establishment is the first critical step for the production of any crop and it determines the foundation for either the success or failure of the future harvest. So, it is worthy to review some fundamentals associated with the process of seed germination and seedling establishment.
 
Most crops produced worldwide begin with the planting of a seed and management to sufficiently establish a satisfactory population of new plants in the field. Good seed germination and establishment is an essential and critical first step in the production of a good crop. Most crop seeds are desiccation tolerant while dormant and as a result can be stored and transported while preserving their ability to grow.  Seeds carry the full genetic complement of the crop and serve as the genetic delivery mechanism for a crop production system. Farmers require seeds that will provide for a reliable and successful establishment of a crop.  
 
An interesting aspect of seed germination and establishment is that seeds generally represent the condition of highest degree of resistance to extreme environmental conditions, while seedlings are most sucseptible.  Viable seeds are dormant living organisms that contain living, embryonic tissue that is essential for germination.  All fully developed seeds contain an embryo and a reserve supply of carbohydrates and nutrients to carryout germination and establishment and the full “package” is contained within a seed coat. 
 
Seeds are stimulated to “wake up” and start the germination process when soil moisture and temperature conditions are appropriate for them to grow.  The three cardinal points of vital activity for germination are: 1) a minimum temperature, below which no activity occurs, 2) an optimum temperature at which the highest germination  occurs, and 3) a maximum temperature above which no germination takes place.  
 
All seeds need correct moisture and temperature environments (Table 1) to initiate internal biochemical processes associated with the initation of germination. Soil-water content generally needs to be at least approximately 50–75%  of field capacity. A fine-textured seedbed and good seed-to-soil contact are very imporant for optimal germination. 
 
Good soil aeration that facilites good gas exchange between the germinating embryo and the soil environment is very important. Seeds respire just like any other living organism. Germinating seeds need oxygen and they produce carbon dioxide (CO₂). The CO₂ needs to be able to diffuse away from the seed and if the soil is compacted or saturated, aeration is inhibited and the CO₂  respiration will not be able to dissipate to the atmosphere, and as a result the seeds can suffocate in the soil. 
 
There are three major steps in the initial process of seed germination.  These include: 1) imbition, 2) interim or lag phase, and 3) radicle and root emergence.  
 
In the imbibition process seeds rapidly absorb water through the hilum of the seed and the seed coat will then swell and soften.  
 
In the interim or lag phase the seeds internal biochemical and physiological system goes into action.  Cells begin respire with this physiological activity and the seed begins to metaboloize its storehouse of energy and nutrient reserves to manufacture proteins other essential metabolites.
 
The radicle is the very first element of the rooting system that is developed and it is the first thing to emerge from the seed.  In the field, we often refer to the radicle as the first “stinger” root that is developed.  In the field, it is good to dig into the seedbed and examine early seedling development and look for healthy radicles, with clean, white, and turgid tissue.  
 
In the process of radicle and root emergence, the cells of these tissues start to elongate and divide, the seed continues to imbibe water, and then it begins to extend out and away from the seed into the soil.  These early root tissues, specifically the fresh root hairs become quickly capable of water and nutrient uptake.  The young root tissues are very sensitive to the soil environment, particularly the soil solution.  It is in this stage for example when seedlings are often very sensitive to salinity in the soil solution and disease infections.  
 
When the radicle begins absorbing water from the soil solution, the seedling gains the capacity to extend a shoot from the seed towards the soil surface for emergence.  In dicotyledonous (dicot) plants (generally referred to as broadleaf plants) the two seed leaves are extended above the soil for emergence.  The section below the shoot and the cotyledons is referred to as the “hypocotyl” and the section of the shoot above the cotyledons is the “epicotyl”, Figure 1. 
 
There are two basic methods of emergence for plants.  In most dicot plants, a hook is formed in the section of shoot below the cotyledons which serves to pull the cotyledons and the growing point of the new plant up through the soil.  Upon the reaching the soil surface, the hook will straighten and pull the cotyledons (seed leaves) and shoot tip into the air.  For the farmer or agronomist in the field, that is a good sight to see. This method of emergence is called “epigeous or epigeal germination”.  Examples of epigeal germination are cotton, sunflower, castor, and bean (common bean), Figure 1.
 
In other plants a process of “hypogeous or hypogeal germination” takes place.  In hypogeous germination, the hypocotyl remains short and the cotyledons do not emerge from the seed and remain underground.  Instead, the radicle and epicotyl axis will elongate and extend out of the seed coat. The epicotyl grows up through the soil and emerges above the soil surface and forms a epicotyl or “plumule” for the first leaf, Figure 2a and b.
 
All monocotyledons plants such as maize, rice, wheat, and coconut show hypogeal germination. It is also interesting to note that some dicot plants show hypogeal germination such as groundnut, gram, and peas.
 
In general, plants with epigeal germination, most dicot or broadleaf plants, are more sensitive to soil crusting and environmental inhibitions to emergence.  So it is good to know what type of germination and emergence characteristics are natural for a given crop species and to track seedling development in the field accordingly.
 
As we begin any new crop season in the field and plant the seeds, it is good to review the basic process of seed germination and establishment.  We can easily take all of this for granted until something goes wrong and we have problems in the field with emergence.  After planting, it is good to monitor in-field seedling conditions and progression of growth and development, both above and below ground, and provide good management that supports the young plants as they get established and start their growing cycle.

Table 1.  Soil temperature (^oF) for crop germination.  Adapted from Kemble and Musgrove (2006).

Crop	Minimum oF	Optimal Range oF	Optimum oF	Maximum oF
Beet	40	50–85	85	85
Cabbage	40	45–95	85	100
Cauliflower	40	45–85	80	100
Celery	40	60–70	70	85
Chard	40	50–85	85	95
Cucumber	60	60–95	95	105
Eggplant	60	75–90	85	95
Lettuce	35	40–80	75	85
Melons	60	75–95	90	100
Onion	35	50–95	75	95
Parsley	40	50–85	75	90
Pepper	60	65–95	85	95
Pumpkin	60	70–90	90	100
Spinach	35	45–75	70	85
Squash	60	70–95	95	100
Tomato	50	70–95	85	95

 

Figure 1.  Seed germination and plant establishment for a plant with epigeal
germination and emergence, which is common with most dicot or broadleaf
plants.

Figure 2a.  Examples and comparison of epigeal and hypogeal germination.



Figure 2b. Examples and comparison of epigeal and hypogeal germination.

References
 
Kemble, J., and M. Musgrove.  2006.  Soil Temperature Conditions for Vegetable Seed Germination. Alabama Cooperative Extension. 

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.

Over the last several years, Dr. Steve Fennimore, Extension Specialist - Weed Science, UC Davis and I have been collaborating on investigating the use of band-steam for controlling in-row weeds and soilborne pathogens. Band-steam is where, prior to planting, steam is injected in narrow bands, centered on the seedline to raise soil temperatures to levels sufficient to kill weed seed and soilborne pathogens (>140 °F for > 20 minutes). After the soil cools (<1 day), the crop is planted into the strips of disinfested soil.

This spring, we completed fabrication of a second-generation prototype band-steam applicator that is simpler in design and easier to operate than our first prototype. Steve has been demonstrating the device to growers on their farms in the Salinas valley this summer (Fig. 1). Similar to Yuma trials, application of band-steam is being found to provide very good weed control in the treated band (Fig. 2). Stay tuned for reports of full trial results including hand weeding labor savings, control of Sclerotinia lettuce drop and crop yield in future articles.

The band-steam machine will be back in Yuma in a couple of weeks! If you are interested in testing the device on your farm, please contact me. I’d be happy to work with you.

Acknowledgements
This work is supported by the Crop Production and Pest Management grant no. 2021-70006-35761 /project accession no. 1027435 from USDA-NIFA. We greatly appreciate their support. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

Fig. 1. On-farm demonstration of a prototype band-steam applicator in Salinas,
CA. The machine injects steam into the bed in narrow beds centered on the
seedline prior to planting for control of weeds and soilborne pathogens. (Photo
credits: Steve Fennimore, UC Davis)


Fig. 2. Weed control with band steaming in lettuce. Steam was applied
in a 4-inch band centered on the two seedlines marked by the red
arrows. The weeds outside of the treated band are in areas that were
not steamed, but can be cultivated out easily because they are not
close to the crop seedline. Trials conducted by Steve Fennimore, UC
Davis, in 2022 in Salinas, CA. (Photo and caption credits: Steve
Fennimore, UC Davis).

In the year 2000 Weed scientist and Area Agriculture Agent Barry Tickes from the University of Arizona Yuma Agricultural Center conducted many evaluations to determine the best application method for Pronamide Herbicide (Kerb) in lettuce. His studies revealed that in the low desert the product was losing significant efficacy because it was applied right after planting and before starting sprinkler irrigation. Pronamide is very soluble in water and was often leached below weed seeds prior to their germination.The goal of these projects was to delay the application of the product to have it available at the right time for weed germination. To do this Tickes stopped the sprinkler irrigation at different timings before weed germination and sprayed plots with a CO2 experimental backpack in the mud. 
He demonstrated that Kerb applications should be delayed from 1 to 6 days after starting sprinklers depending on the time of the season. Delayed applications at the time were done with aerial applications, but after the terrorist’s attacks 21 years ago all air traffic was suspended. Then PCAs asked if the product could be chemigated (applied through the sprinkler irrigation). To answer this question Tickes conducted several trials in Yuma. 
Surprisingly the results revealed that the product performed better chemigated than applied by air. Today most of the Kerb in Arizona is chemigated and applied in delayed applications, also the method is extensively used in California. 
It all started with a little trial in a Yuma Experiment Station that demonstrated delayed applications work. Then 9/11created the circumstances that forced the industry to take that course. If you would like to review the original data from this research please visit: Timing Kerb Applications in Lettuce and Evaluation of Kerb Applied by Sprinkler Irrigation to Lettuce both by Barry Tickes.

Timing Kerb Applications in Lettuce

Area wide Insect Trapping Network   VegIPM Update, Vol. 15, No. 17, Aug 21, 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 are up in south Yuma valley and Dome valley; about average for August

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 August.
 
Aphids:                       
Aphid movement is absent and consistent with what we typically see during the summer.
 
Leafminers:                  
Adult activity declining and average for August.