Like last winter, lettuce aphids, Nasonovia ribisnigri, (aka., red aphid) have already been found colonizing lettuce fields in several locations throughout the Yuma area. In the desert, we typically associate lettuce aphid with the warm growing conditions in February and March. However, lettuce aphids have been found during January the past two seasons.   With the above average temperatures, we’ve experienced this winter, its not surprising they are showing up early.  I’ve had reports and identified lettuce aphids appearing from head lettuce and leaf lettuce in Bard and Yuma Valley. We’ve picked them up this week in head lettuce at the Yuma Ag Center.  Previous experience has taught us that daytime high temperatures in the 70-80's are ideal for population growth.  Given their widespread incidence, they likely came into the desert on one of the multiple flights of winged aphids we’ve reported from sticky traps this winter. Nonetheless, they are here and PCAs should be prepared to battle them, particularly with the above-average temperatures we’re experiencing.

A few things to remember about lettuce aphids relative to the other aphids we commonly see. First, the immature nymphs are small and have a red appearance, whereas the apterous (wing-less) adults are typically a large brown colored aphid with dark bands running across the abdomen (see images below).  Second, among the crops we grow locally, lettuce aphids are only found on the lettuce types (Lactuca spp.). Lettuce aphids prefer to colonize the terminal growth, and can often be found in heads or hearts, whereas green peach aphids are often found on the frame leaves in high numbers before moving into the heads. Sampling should be focused in the terminal growth of young plants, and in the heads and hearts of older plants. Third, they can reproduce prolifically, producing many more alates (winged) adults than other species, which can quickly lead to widespread abundance in a field and dispersal throughout a growing area.  Finally, as the saying goes "he who hesitates is lost". If lettuce aphids are found on your lettuce, it is recommended that you respond quickly with an insecticide treatment.  The product of choice is Movento at 5 oz/ac. Because of its systemic activity, Movento will reach aphids in the protected terminal growth.  Be sure to include a penetrating adjuvant for best results at a rate of at least 0.25% v/v.  It normally requires 7-10 days of activity before significant reduction in the infestation is observed. Sequoia and Sivanto are good rotational products if coverage of terminal areas can be attained. For more information on lettuce aphid please refer to Lettuce Aphid on Spring Produce-2021. 

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.

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.

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. 

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.