The weather this fall is as warm and humid as I can ever remember. These conditions are no doubt one of the main reasons insect pressure continues to be heavy on our local produce crops as we approach November. Thrips and their associated scarring damage on leaves are beginning to show up on leafy vegetables throughout the desert. Their presence on these crops is not unusual in the fall and will likely remain steady until the weather breaks or we get a good winter rain. We have observed predominantly two species on lettuce this fall; the typical western flower thrips, Frankliniella occidentalis, and the bean thrips, Caliothrips fasciatus. Both are common in the fall, but bean thrips are the predominant species we’re currently seeing on lettuce at the Yuma Ag Center. It’s has also been causing significant damage to small organic lettuce in the Imperial Valley (see image below). Adult bean thrips are uniformly dark, almost black in color and their wings have two black and two white bands which can easily be distinguished with a 10-15X hand lens. Alfalfa, melons, cotton, lettuce and a number of grasses are all known host crops for the bean thrips. The good news is based on my research experience, they can easily be controlled with available insecticides such as Radiant, Lannate (methomyl), acepahate and Entrust/Success. Note: the key to preventing thrips from significantly scarring leafy vegetable plants is to prevent the larval populations from becoming established. With the temperatures we’re currently experiencing, western flower thrips larvae can complete development in about 7 days. Applying back-to-back spray applications ~ 5 days apart is an effective approach for controlling nymph populations once they become established. For more information on the identification, biology, ecology and management of thrips on desert produce please visit these links:

Insect Management: Western Flower Thrips
Thrips Management in Desert Leafy Vegetables

Soil Nitrogen
Nitrogen (N) is the essential nutrient that is required in largest amounts by plants.  Following water, N is the most limiting factor in the growth and development of non-leguminous crops. 

In most places around the world, sunlight is the first most limiting factor in terrestrial ecosystems, including crop production systems.  This is followed closely by water as a limiting factor to plant growth and biologically available N (NO3- -N) is commonly the third most limiting factor.

Nitrogen goes through many natural transformations in the soil and cycling of N can take many routes and forms. Thus, the management of N is also one of the most challenging plant nutrients to work with efficiently.

Even though N is often a limiting factor in terrestrial ecosystems and crop production systems, N is ubiquitous in the atmosphere and biosphere.  For example, 78% of the Earth’s atmosphere is made up of N gas or N2, a molecule made of two nitrogen atoms bonded together by a strong, stable, triple bond.  As a result, N gas is biologically inert.

Nitrogen is the mineral element required by plants in the greatest amount and it serves many functions in plant physiology.  Nitrogen is an integral component of amino acids, which are the building blocks for proteins.  

Proteins are present in the plant as enzymes that are responsible for metabolic reactions in the plant.  Because N is so important, plants often respond dramatically to plant-available N, which is nitrate-nitrogen (NO3- -N), (Havlin, et al. 2014; Thompson and Troeh, 2005; Warren, et al., 2017; and Weiland Brady, 2017).

Nitrogen is central to global crop production.  Many parts of the world do not have enough to achieve food and nutrition security, in other cases excess N from fertilizer leaks into the environment with damaging consequences.

Though it makes up a large portion of the air we breathe, most living organisms cannot access N in this form.  Atmospheric N must go through a natural process called “nitrogen fixation” to transform before it can be used for plant nutrition.

In both plants and humans, N is used to make amino acids, which make the proteins that construct cells, including the building blocks for DNA.  It is also essential for plant growth because it is a major component of chlorophyll, the compound by which plants use sunlight energy to produce sugars from water and carbon dioxide(photosynthesis).

The Nitrogen Cycle
The N cycle is the multi-faceted process through which N moves from the atmosphere to earth, through soils and organisms, and is released back into the atmosphere, with conversions in and out of organic and inorganic forms (Figure1).

Figure 1. The nitrogen cycle.

A good point to begin the review of the N cycle is with biological N fixation, the process of converting biologically inert N2 gas into an organic compound or an inorganic form such as NO3- -N.  Nitrogen fixation can take place through basic routes: 1) biological fixation or 2) conversion of N2 gas to NO3--N by lightning.  The basic routes of N fixation are shown in the upper left-hand side of Figure 1.

Biological fixation occurs when naturally occurring N-fixing symbiotic and some non-symbiotic bacteria convert N2 gas from air into forms like ammonium-nitrogen (NH4+ -N) and then into nitrate-nitrogen (NO3- -N).  A very important form of biological N fixation is carried out by symbiotic bacteria that live in the root nodules of legumes converting N2 gas into ammonium (NH4+) and then nitrate (NO3-), which are commonly incorporated very quickly into organic forms.

Plants preferentially absorb nitrate -N (NO3- -N) from the soil through the root hairs and use it in their physiological systems to create the N forms they need (amino acids, proteins, enzymes, complex compounds, etc.).  Some ammonium-N (NH4+-N) can be taken up by some plants.  The preferential form of N for plant uptake and utilization is nitrate-N (NO3--N).

Organic forms of N are not taken up by the plant and incorporated into the plant physiology.

Denitrifying bacteria convert excess nitrate back into inorganic N which can be released back into the atmosphere in gaseous forms (N2O and N2).

Nitrogen fixation can also begin with lightning, the heat from which ruptures the triple bonds of atmospheric nitrogen (N2 gas), freeing its atoms to combine with oxygen and creating nitrous oxide gas (N2O), which dissolves in rain forming nitric acid (HNO3) which then can be absorbed by the soil.

Excess nitrate in the soil can be lost through leaching, the process where nutrients mobile in the soil, including nitrate-N, can pass through the soil profile and into groundwater and potentially polluting streams.

Because N is so important and plant-available forms are often limiting, plants often respond dramatically to available N.  There are no substitutes for sufficient plant-available N and management is a critical part of a crop production system.

References
Havlin, J.L., Beaton, J.D., Tisdale, S.L. and Nelson, W.L. 2014.  Soil Fertility and Fertilizers; An Introduction to Nutrient Management.  6th Edition, Prentice Hall, Upper Saddle River, NJ.

Troeh, F.R. and Thompson, L.M. (2005) Soils and Soil Fertility.  Sixth Edition, Blackwell, Ames, Iowa, 489.

Warren, J., H. Zhang, B. Arnall, J. Bushong, B. Raun, C. Penn, and J. Abit.  Oklahoma Soil Fertility Handbook. Published Apr. 2017; Id: E-1039

Weil, R.R. and Brady, N.C. (2017) The Nature and Properties of Soils.  15th Edition, Pearson, New York.

We have learned a lot about viruses in the past few newsletter articles and one of the striking features of most plant viruses is that they always need a host. And the relationship between a virus and its host plant is very specific. So where do the viruses go when we do not have lettuce or melon in the field? And how do they come back at the right time to infect the crops?  (clue insect vector). The answer is weeds. A lot of the most economically important viruses are economically important viruses not just because of the losses they cause, but also because of the losses they cause in variety of plants. Viruses have small genome size that allows them to evolve faster. Viruses over time have evolved to adapt and increase their host range.
Below are some common viruses in agriculture and the number of plants they infect/overwinter. Keep in mind that there are many plants that can act as a reservoir for virus but have not been reported yet, so this is not an exclusive list. 
 
Alfalfa mosaic virus (AMV): Alfalfa, lettuce,indive, sunflower, datura, amaranth, different species of pigweed, milkweed, annual fleabane, ixeye daisy, hairy galinsoga, smallflower galinsoga, different species of mustards, common lambsquarters, hedge bindweed, field bindweed, cucurbits, different species of clover and vetch, beans, broad beans, lima beans, lupine, pea soybean, ground Ivy, healall, okra, purslane, pimpernel, black nightshade, pepper, tomato, petunia, eggplant, potato, garden pansy etc. 
 
Cucumber mosaic virus (CMV): pigweed, horseweed, oxeye daisy, coffee weed, Canada thistle, bull thistle, hairy galinsoga, Jerusalem artichoke,  prickly lettuce, wild chamomile, hawkweed, groundsel, Canada goldenrod, sowthistle, endive, sunflower, lettuce, mustard, radish, chickweed, lambs quarters, morning glory, cucurbits, common teasel, alfalfa, beans, lima beans, mung beans, geranium, ground Ivy, okra, purslane, jimsonweed, ground cherry, horsenettle, black nightshade, pepper, tomato, petunia, eggplant, potato, burning nettle, garden pansy. 
 
Lettuce mosaic virus (LMV): lettuce, bristly oxtongue, spinach. 
 
Bidens mottle potyvirus: lettuce, endive, horseweed, hairy beggarticks, virginia pepperweed, Mexican pricklepoppy. 
 
Celery mosaic virus (CeMV): Celery, giant hogweed
 
Papaya ringspot virus (PRSV): Bur cucumber, creeping cucumber, balsom pear, cucumber, cantaloupe, watermelon, summer squash, pumpkin, gourd, winter squash, butternut squash, 
 
Tomato spotted wilt virus (TSWV): Tomato, potato, pigweed, hairy beggarticks, oxeye daisy, coffeeweed, prickly lettuce, annual sowthistle, ebdive, sunflower, lettuce, shepherd’s pruse, chickweed, hedge bindweed, cantaloupe, muskmelon, bean, broad bean, mung bean, cutleaf evening primerose, broadleaf plaintain, purslane, jimsonweed, bittersweet nightshade, black night shade, pepper, tomato, petunia, eggplant, potato. 
 
Tobacco mosaic virus(TMV):  White campion, jimsonweed, pepper, tomato, tobacco. 
 
Turnip mosaic virus(TurMV):  pigweed, wild carrot, bachelo’s button, Canada thistle, hairy galinsoga, smallflower galinsoga, common catsear, pineapple weed, dandelion, endive, sunflower, lettuce, mustard, brassicae crops, corn cockle, chickweed, common lambsquarter, spinach, cucumber, alsike clover, lupine, redstem filaree, ground Ivy, okra, velvetleaf, common pokeweed, purselane, jimsonweed, black nightshade, tomato, petunia..
 
Watermelon mosaic virus (WMV) :   mustard, common lambquarters, spinach, cucumber, watermelon, cantaloupe, squash, buttercup, red clover, common vetch, alfalfa, beans, lupine, pea, henbit, common mallow, okra, common pokeweed, jimsonweed, nightshade, 
 
Zucchini yellow mosaic virus (ZYMV) : cucumber, cantaloupe, watermelon, squash, zucchini, pumpkin, gourds. 
 
 
Source: Cornell.edu

Plans are firming up for The Desert Difference: A Showcase of AgTech Opportunities for Growing in the Desert. The two-day event will be held November 13-14th in Yuma, AZ. The first day will be a Field Day, the second will be a standard conference with keynote speakers, breakout sessions and trade booths. Details of the event and Conference Day (Day 2) activities can be found here.

The focus of this article is the Field Day which will be held Wednesday, November 13th at the Yuma Agricultural Center. Registration begins at 7:00 am and the program starts at 7:30 am (agenda below). As with our previous AgTech Field Days, the educational workshop will feature 12 of the latest automated and robotic technologies for pest control and improved vegetable production being demonstrated in the field.

This year, we’ve added a twist we think you’ll like. We’ve asked people demonstrating equipment to treat one of their plots two weeks prior to the event. This way, attendees can “see” the end result of the treatment – how well an automated weeding machine technology actually controlled weeds, for example. A second set of plots, immediately adjacent to the pre-treated plots, will be used for a live demonstration of the equipment used.

As mentioned in previous articles, we would love to showcase as many innovations as possible. All live demo slots have been filled, however there are still openings for static displays. If you are interested in being added to the program, please let me know and we will do our best to try and accommodate you. It’s an open invitation - private companies, university and government researchers are all welcome.

Fig.1. Technologies for controlling weeds “pre-treating” plots two weeks prior to the AgTech Field Day. Weed control efficacy of the pre-treated plots along with the technology being operated in the field will be shown at the event.


Fig. 2. Field Day agenda (Day 1) for The Desert Difference: A Show case of AgTech Opportunities for Growing in the Desert event. More information about the event and Conference Day activities (Day 2) can be found here.

 

In the August 21, 2024 update we mentioned our plans to do a demonstrative trial at the Yuma agricultural center. This experiment was established on 10/2 and planted on 10/14. Sprinklers started on10/15. A stand evaluation was done on 10/28 and Phytotoxicity and Goosefoot and Lambs quarter weed control evaluated yesterday. The treatments suggested by some of the people in the industry, where:

Treflan (trifluralin) Applied at 1.5pt/A pre-emergent on the flat ground incorporated mechanically by disking approximately at 4” depth, then make the beds and plant the crop to germinate with sprinkler irrigation. The same method was utilized for Prowl herbicide at the rate of 1 pint product per acre. Also Prowl non-incorporated was included, Devrinol2XL at 1 pt/A, Prefar at 6qt/A as well as a high rate of Goal (oxifuorfen)preemergence to evaluate and document phytotoxicity levels.

As mentioned, we have collected weed control data, which we plan to include in future updates.

Would you like to see how this treatments look? Some of the observations, even though expected are very interesting, such as the fact that 16 floz of Goal Tender preemergence didn’t allow goosefoot germination but similarly broccoli didn’t emerge.

Come to the NW corner of the Ag Center (you can’t miss it) and look at the plots and see the difference between Prowl mechanically incorporated and non-incorporated, compare it with Prefar and Devrinol. We put some very clear signs as you can see in the picture above. The experimental plots are 14x60ft so they are large enough to illustrate what would happen in a farm.

We thank you for your suggestions ...please come and let us know what you think!

Preliminary results from a field trial that is being conducted at the Yuma Agricultural Center experimental farm to evaluate seven bioinsecticides against whiteflies in broccoli demonstrate that M-Pede (Potassium salts of fatty acids aka insecticidal soap), BotaniGard 22WP (Beauveria bassiana Strain GHA), Pyganic (Pyrethrins), Surround (Kaolin clay), and Venerate (Burkholderiaspp. Strain A396) may favor measurable control of the pest. These insecticides exhibited a reduction in whitefly adults and nymphs density relative to the nontreated control (Figure 1). The trial is ongoing, and more data will be collected to assess the efficacy of these insecticides further. Potassium salts of fatty acids are produced by adding potassium hydroxide to fatty acids found in animal fats and in plant oils. Pyrethrins is a mixture of six active compounds extracted from Chrysanthemum cinerariifolium plants. Beauveria bassiana is a naturally occurring entomopathogenic fungus. Burkholderia spp. strain A396 is a naturally occurring entomopathogenic bacteria. Kaolin clay is a soft, white, naturally occurring clay mineral.

Figure 1. Means whitefly adults (A), small whitefly nymphs (B), large whitefly nymphs (C),
and total whitefly nymphs (D) as affected by bioinsecticide applications. Bars with the
same letters are not statistically significant.

Area wide Insect Trapping Network   VegIPM Update, Vol. 15, No. 20, Oct 2, 2024
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:             
CEW moth counts low in most traps; below average for this early produce season. 
 
Beet armyworm:         
Trap counts decreasing in most areas, and below average for late September
 
Cabbage looper:          
Cabbage looper trap counts low in all locations, typical for mid-late September.
 
Diamondback moth:   
Adult activity beginning to pick up in Dome Valley.  Overall, typical of late September with minimal monsson activity.
 
Whitefly:                       
Adult movement most active in Dome Valley; overall below average for mid September
 
Thrips:                          
Thrips adult movement light; overall activity typical for September. 
 
Aphids:                        
Aphid movement absent so far; anticipate activity to pick up when winds beginning blowing from N-NW. 
 
Leafminers:                  
Adult activity light in all areas, about average for this time of season.