Pest pressure in desert produce has begun to subside, but don’t become complacent. Although the local weather forecast calls for slightly below average temperatures for the next 10 days, conditions are still within the biological range of most of our fall pests. And it will soon become ideal for aphids. Below are some thoughts on the status of local pest pressure based on field sampling, trap counts and PCA reports.

Diamondback Moth (DBM): Reports of DBM on coastal transplants has quieted down a bit, but some PCAs have reported spraying more than usual for DBM on coastal transplants. So far, no reports of “uncontrollable” populations. Trials at the Yuma Ag Center are showing that standard insecticide products (Proclaim, Radiant, Exirel, Harvanta) are showing significant efficacy against DBM larvae as expected (see graph below). Of course, this is on direct-seeded cabbage and not coastal transplants. The weather should help slow down their growth and development but don’t become complacent. Populations still have the potential to get out of hand if not controlled properly, even in cooler weather. Beet Armyworm (BAW): BAW numbers are still above average in trials at YAC (1.0-1.2 larvae /plant) in untreated checks but have slowed a little. Furthermore, pheromone trap catches peaked last week and remain high areawide (see graph below). The cooler weather will slow them down, but expect light to moderate numbers for a while. Standard insecticides were effective in controlling BAW in efficacy trials at YAC this fall.

Cabbage looper (CL): CL numbers have been unusually light this fall and areawide trap catches have been historically low (see Areawide insect Trapping Network). Numbers have been significantly lower than normal in untreated plots at YAC this fall (<0.1-0.2 larvae / plant). But CL trap counts did increase in all areas last week, so keep an eye out for increased oviposition and hatches on your produce crops.

Western Flower Thrips (WFT): WFT started out strong in some locations in mid-October following winds and melon/alfalfa harvests, but have subsided considerably with cooler temps. Adult and larvae numbers are light in our insecticide efficacy trials at YAC. We did see a large population of Bean Thrips (BT) show up following the heavy winds out of the west in mid-October. Lannate and Radiant have been effectively controlling both WFT and BT in our trials. We have had our first report of INSV infected lettuce this fall, and as you can expect the infected plants were found on romaine transplants originating from the coast.

Aphids: Surprisingly, I’ve had several reports from PCAs throughout the area (Bard, Yuma Valley, Wellton and Dome) of small colonies showing up on lettuce and brassica crops. We’re also picking up small colonies at YAC. More than we typically see in Oct/Nov. Above average sticky trap catches have

shown a sharp increase in winged aphid movement in the past 3 weeks (see Areawide insect Trapping Network). This has coincided with windy conditions from the west-northwest. Most of the aphids I have seen colonizing have been green peach aphids. Weather has not been conducive for aphid population growth so far, but with the cooler temps coming you might expect to see more given the winged aphid movement we’ve been trapping. Historically, green peach aphid infestations are worse on spring

produce following above average monsoon and fall/winter rainfall. So far, it’s been pretty dry, and could be an indicator of things to come. Nevertheless, keep a close watch on aphids as we transition into our “normal” winter weather.

There are more than 100 chemical elements known to man today.  However, only 16 have been proven to be essential for plant growth.  The essential elements for plant growth are in the upper portions of the periodic table with lower atomic numbers, indicating the lighter and more volatile elements that are in higher concentrations closer to the earth’s surface and part of the rocks that commonly serve as the parent materials for soils.
 
For a nutrient to be classified as essential, certain rigid criteria must be met.  These criteria are as follows (Havlin, et al., 2014; Troeh and Thompson, 2005; Weil and Brady, 2017; Warren et al., 2017):
 

1. The element is essential if a deficiency prevents the plant from completing its vegetative or reproductive cycle.
2. The element is essential if the deficiency in question can be prevented or corrected only by supplying the element.
3. The element is essential if it is directly involved in the nutrition of the plant and is not a result of correcting some microbiological or chemical condition in the soil or culture media.

 
The essential elements and their chemical symbols are listed in Table 1.  Three of the 16 essential elements – carbon, hydrogen and oxygen – are supplied mostly by air and water.  These elements are used in relatively large amounts by plants and are non-mineral, often referred to as organic nutrients and they are supplied to plants by carbon dioxide and water. 
 
The other 13 essential elements are mineral elements and must be supplied by the soil and/or fertilizers.  Not all are required for all plants, but all have been found to be essential to some (Tisdale & Nelson).
 
 
 
Table 1.  Essential plant nutrients, chemical symbols, and sources.

Mostly from air and water (non-mineral)	Mostly from air and water (non-mineral)	From soil and/or fertilizers (mineral)	From soil and/or fertilizers (mineral)	From soil and/or fertilizers (mineral)	From soil and/or fertilizers (mineral)
Element	Symbol	Element	Symbol	Element	Symbol
Carbon	C	Nitrogen	N	Iron	Fe
Hydrogen	H	Phosphorus	P	Manganese	Mn
Oxygen	O	Potassuim	K	Zinc	Zn
		Calcium	Ca	Copper	Cu
		Magnesium Mg	Mg	Boron	B
		Sulfur	S	Molybdenum	Mo
				Cholorine	Cl

 
 
The essential plant nutrients may be grouped into three categories.  They are as follows:
 

1. Primary nutrients - nitrogen, phosphorus and potassium
2. Secondary nutrients - calcium, magnesium and sulfur
3. Micronutrients - iron, manganese, zinc, copper, boron, molybdenum, and chlorine

 
This grouping separates the elements based on relative amounts required for plant growth and is not meant to imply any element is more essential or important than another (Troeh and Thompson, 2005; Weil and Brady, 2017; Warren et al., 2017).
 
Primary Non-Mineral Nutrients: Carbon, Hydrogen and Oxygen
Carbon is the backbone of all organic molecules in the plant and is the basic building block for growth.  After absorption of carbon dioxide (CO₂) by the leaves of the plant, carbon is transformed into carbohydrates by combining with hydrogen and oxygen through the process of photosynthesis.
 
Metabolic processes within the plant transform carbohydrates into amino acids and proteins and other essential components.
 
The essentiality of all mineral nutrients is associated with their use in structural plant components and/or physiological and biochemical reactions associated with essential processes in plant growth and development.  Plants cannot complete the life cycle if they are deficient in an essential nutrient.
 
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.

Widely accepted definition of a living organism “A living organism has a cellular structure and is manifest by growth through metabolism, reproduction, and the power of adaptation to the environment through changes that originate internally”. Viruses are not cellular and do not metabolise, but they reproduce and adapt. 
 
A virus is a set of one or more nucleic acid template molecules, normally incased in a protective coats of protein or lipoprotein and is able to organize its own replication but only within a suitable host cells. Record of plant viruses do not go as far as human viruses, but plant viruses have caused considerable loss in agriculture system. 
 
 
One of the most common virus we see in agriculture system in todays world is Cucumber mosaic virus(CMV). CMV belongs to family Bromoviridae. The genome size of cucumber mosaic virus (see pic) is about 8000 to 9000 nucletotide bases (1 base=1 letter of AGTC). The genome size of Covid19 Coronivirus is about 30,000 bases and the genome size of human DNA is 6.4 billion bases. 
 
CMV has a very wide host range and is transmitted by aphids in nonpersistent manner (stylet borne). This means that the aphids acquire the virus particle in their stylet within seconds of feeding in infected plants, hop on to next plant and start feeding on next plant. The virus is transmitted to the next plant immediately. 
 
Next is incubation period. Viruses cause systemic infection. It can take anywhere from few days to few weeks from initial entry of the virus to symptom exhibition in your plants. The severity of symptoms varies depending on many factors. The age of plant (infection stage), the general plant vigor (health), varietal susceptibility, conducive environment (viruses express better in colder weather than hot weather), a plant that has already been infected with other viruses (preesisting condition) are to name a few.

1. Attachment – the virus attaches itself to the outside of a  new plant cell 
2. Penetration – the protein pushes the nucleic acid strand into the plant cell
3. Replication – the viruses’ nucleic acid uses the plant cell DNA to make many new nucleic acid strands and protein sheathes
4. Assembly – the nucleic acid and protein assembly into millions of new virus copies
5. Release – the viruses leave the cell – at this stage the cell is normally dead and bursts releasing the viruses
6. Transmission – the viruses move using a vector to new cells to infect.

When you see the symptoms in your plants, the first thing you have to understand is virus infection is systemic. The best you can do to manage the virus is to limit the transmission (flatten the curve). Some viruses need a vector for transmission like insects and nematodes. Some viruses are mechanically transmitted from one infected plant to another. Washing field tools between plants/field whenever possible limits the transmission of virus. Soap, bleach, and disinfectants reduce transmission by protein denaturalization of the virus.

Interested in more information about mechanical weed control in vegetable crops? Check out this seminar given by Sam Hitchcock Tilton, Lakeshore Technical College. Topics covered include weed ecology, systems-based strategies for weed control, new and emerging machines on the market, individual tools and implements and best-use strategies for cultivating equipment. Although the target audience is small-scale vegetable growers, Sam gives many practical tips and insights that are applicable to large-scale vegetable farms. Even if you’re very knowledgeable about mechanical cultivation, this entertaining seminar is a good refresher on the basics of integrated weed management and one I think you’ll find interesting and informative.

 

Fig. 1. Sam Hitchcock Tilton presenting seminar entitled “Mechanical Weed
Control and Weed Ecology in Vegetable Production”. Click the video above to view a recording of the presentation. (Photo credits: Practical Farmers of Iowa,
Ames, IA).

Wanted to share the following weed germination calendars now that the season has begun. Some summer weeds withstand part of the winter and some winter annuals the summer, so these charts are general guidelines. We hope this helps for making management decisions in your operation.

As the intense heat of the Yuma summer finally fades, cooler days bring the promise of lush fields which set the stage for a vibrant growing season. However, the cooler weather also signals the arrival of seasonal pests, ready to take advantage of your organic fields. These pests tend to have an especially strong appetite for organic crops, making it essential to stay vigilant. Thus, it is important to implement appropriate IPM techniques to combat these insect pests effectively. It is crucial to plant resistant varieties, scout regularly, ensure your crops are healthy, diversify your crops, use physical/mechanical control, enhance biological control, or apply biopesticides when necessary. 

Remember, some IPM tactics may be unsuitable in some situations because IPM is not a one-size-fits-all. Therefore, an IPM program should be planned on a case-by-case basis. 

Results of recent pheromone and sticky trap catches can be viewed here.
 
Corn earworm:           
CEW moth counts decreased in the past 2 weeks and about average for this time of summer.
 
Beet armyworm:         
Trap counts stay active in some locations (Yuma Valley and Wellton) but about average for July.
 
Cabbage looper:          
Cabbage looper numbers remain low consistent with the lack of activity this fall compared to last season.
 
Diamondback moth:       
DBM moths were not caught in any trap in the past 2 weeks; average for this time of the year.
 
Whitefly:                       
Adult movement continuing to increase, particularly in Gila and Yuma Valleys consistent with melon harvest.
 
Thrips:                           
Thrips adults decreasing in most locations, and trending comparable to previous years.
 
Aphids:                        
Aphid movement is absent consistent with what we typically see in the summer. 
 
Leafminers:                  
Adult activity has highest in Yuma and Dome Valley, and above average for early July.