Talking with a few local growers and PCAs it is clear some are still apprehensive of diamondback moth (DBM) reappearing this fall in large numbers.  In the desert, the DBM is typically considered a minor pest that occasionally builds up to damaging levels in the winter and spring. In most years, growers can easily control the pest with 1-2 well timed insecticide sprays.   But in the fall 2016, outbreaks of an invasive DBM population occurred throughout all vegetable growing regions in Arizona where it was determined that the source of the DBM originated from infested transplants grown in desert greenhouses.  We later discovered that the invasive DBM population was very resistant to the diamide insecticides (Coragen, Beseige, Belt and Vetica). The DBM infestations experienced by Arizona growers that season were not anticipated, and overall, the resistant pest caused serious economic losses in cole crops. However, the population abundance of DBM in the desert the last two seasons has been significantly lower than what was observed under widespread outbreak conditions in 2016.   We received no complaints from PCAs or growers of uncontrollable DBM infestations, crop damage or yield losses in 2017 or 2018, and PCAs reported having no difficulty controlling larvae or adults with commonly used insecticides, including the diamides.  Field inspections of transplants yielded no larvae on plants arriving from local and coastal nurseries.  Thus, we have concluded that the DBM that appeared in 2017 and 2018 were a distinctly different population than those that infested crops in the fall of 2016.  It is likely that the DBM population in 2017 and 2018 migrated concurrently onto both direct-seeded and transplanted cole crops in wind currents following September storms. Although, field trials and conducted at the Yuma Ag Center confirmed the local DBM populations were susceptible to the key insecticides (Radiant, Proclaim, pyrethroids, Verimark/Exirel) used for their management, we did find low levels of resistance to Coragen in two Yuma field populations last fall and one population from the Yuma Ag Center this past spring. We will discuss this development and its implications for management in more detail in the next IPM update (Sep 18). In an attempt to document the impact of the DBM outbreaks on Arizona cole crops the past three seasons, we conducted a two-part survey of growers and PCAs from Yuma, Maricopa and Imperial Counties in April 2019 to (1) estimate the severity of yield losses from DBM on direct-seeded and transplanted cole crops, and (2) the intensity of chemical management required to control DBM, and associated level of control provided by each insecticide product used.  To download a copy of the survey results, please go to Diamondback Moth on Desert Cole Crops: Survey Results from 2016-2018.

Name the pest that caused this damage:

Justus von Liebig was a 19th century German scientist (1803-1873) who is regarded as one of founders of organic chemistry.  He is also commonly considered as the “father of agricultural chemistry and the fertilizer industry.”

Liebig developed several important analytical methods used in a broad range of applications as well as many other important contributions and developments.  Liebig was one of the great chemistry teachers of the 19th century that served as a foundation for the robust German chemical industry of the 20thand 21st centuries.

In 1840 Justus von Liebig presented a concept that is known as the “Law of the Minimum”, which was built upon a theory that had first been developed by Carl Sprengel, a German botanist (1787-1859).  The Law of the Minimum basically states that a plant’s rate and extent of growth and overall health is dependent on the amount of the scarcest of the essential nutrients that are available to the plant (Figure 1; Liebig, 1840 and van der Ploeg et al., 1999).

The Law of the Minimum has been further applied into a general model of all organisms and biological functions, including the limiting effects of other environmental factors i.e., sunlight and water in terrestrial ecosystems, as well as excesses of nutrients and other environmental factors (Bruuselma and Nigon, 2023; Davidson, 2016; and Mosaic, 2023).

An important way to consider the Law of the Minimum is that the growth of plants, or crops, is not dependent on the total amount of nutrients available, but rather by the scarcest nutrient or resource (i.e., water).  This is particularly important in relation to nutrients such as nitrogen, which is the nutrient required in largest amounts by plants, and it is the most common limiting plant nutrient.  In desert agriculture, water is commonly the first most common limiting factor in plant growth and development, closely followed by bio-available nitrogen.

The Law of the Minimum is important to understand in managing fertilizer and other agronomic inputs to a crop.  This has been demonstrated when fertilizer prices are high, particularly for nitrogen and phosphate fertilizers, and growers may be inclined to reduce or eliminate fertilizer applications.

Liebig’s Law of the Minimum is most applicable for nutrients and plant growth factors that are mobile in the soil.  This is particularly relevant for nitrogen, which is available to plants in the nitrate form (NO3--N), which is mobile in the soil.  Thus, (NO3--N) moves with soil-water. 

Accordingly, the Liebig Law of the Minimum also pertains to water in a soil-plant system.  Other growth factors or nutrients will not compensate for a deficiency in a given nutrient or plant growth factor.  Plant-available nitrate-nitrogen (NO3--N) or water are good examples, there are no substitutes.

The Liebig Law of the Minimum is an important concept in soil fertility and plant nutrition and overall agronomic crop management in an irrigated production system.

Figure 1.  Graphic illustration of the Law of the Minimum with shortest stave in
the barrel representing the most limiting nutrient in the soil-plant system.

References:
Bruulsema, T, and Nigon, L.L. Crops & Soils Magazine, November–December 2023 American Society of Agronomy.  pp.  54-59.

Davidson, D. 2016.  Nutrient Management Magazine.https://www.no-tillfarmer.com/articles/5648-no-till-notes-how-to-plan-your-summer-fertility-program?v=preview

Liebig, J. 1840.  Die organische Chemie in ihrer Anwendung auf Agri- Sprengel, C. 1831. Chemie fu¨ r Landwirthe, Forstma¨nner und Cameralisten (Chemistry for agronomists, foresters, and agricultural econo-cultur und Physiologie (Organic chemistry in its applications to agri-culture and physiology). Friedrich Vieweg und Sohn Publ. Co., mists). Volume 1. Vandenhoeck und Ruprecht Publ. Co., Go¨ ttingen, Germany. Braunschweig, Germany.

Mosaic.  2023.  How Law of the Minimum Impacts Crops' Nutrient Use. In: No-Till Farmer. https://www.notillfarmer.com/articles/12637-how-law-of-the-minimum-impacts-crops-nutrient-use

Vander Ploeg, A.R;   Böhm, W.; and M. B. Kirkham.  1999.  On the Origin of the Theory of Mineral Nutrition of Plants and the Law of the Minimum. Soil Sci. Soc. Am. J. 63:1055–1062.

Bacterial leaf spot is caused by the bacterium, Pseudomonas syringae pv. Aptata. Hosts of the pathogen include Table beet, Sugar beet, Spinach, Swiss chard, Snap bean, Dry bean, Cantaloupe, Pumpkin, Squash, Lettuce, and Pepper.
 
Significance
Bacterial leaf spot is most commonly found affecting table beet at early stages of growth. This may be because younger plants are more susceptible. It may also be related to the prevalence of cool, wet conditions at the beginning of the cropping season. These conditions are most conducive to infection and disease development. The disease may affect green leaf area in developing seedlings and in severe cases can lead to plant death. Diseased leaves will lead to weakened seedlings which may affect transplant success. Bacterial leaf spot does not directly affect root quality.

Figure 1. Bacterial leaf spot caused by Pseudomonas syringae pv. aptata of
table beet: (left) Small focus of the disease, and (right) 2-6 true leaf stage of
plants affected by the epidemic.

Symptoms
Bacterial leaf spot symptoms are irregular in shape and black to brown in color. The spots may occur across the leaf surface but have a tendency to occur on the leaf edges. Lesions are water-soaked not often accompanied by chlorosis (yellowing). Lesions may initially be small (up to ¼ inch in diameter) but if conditions are conducive may rapidly expand and coalesce but do not cross major veins. The leaf is usually puckered and deformed around the lesions, especially if they occur on the margins (Fig. 2). When the disease is severe, the affected the tissue may also tear giving the appearance of abiotic damage such as hail.

Figure 2. Symptoms of bacterial leaf spot on table beet (cv. Merlin). Note the
black color of the lesions and puckering and deformation of the leaves around
the symptoms.

Bacterial leaf spot symptoms may be confused with other fungal foliar diseases (e.g. Cercospora and Phoma leaf spots; see complementary fact sheets for these diseases) and insect damage (e.g. thrips). Bacterial leaf spot lesions do not have black pin-head, fungal structures across the lesions as found in Cercospora leaf spot. Phoma leaf spot lesions also have small, black structures within the lesions but found in rings and usually accompanied by an ooze of spores.
Disease Cycle
Figure 3. Schematic diagram of the potential sources of Pseudomonas syringae pv. aptata inoculum which may contribute to Bacterial leaf spot epidemics in table beet.
P. syringae pv. aptata may be introduced to the table beet crop through several ways (Fig. 3). P. syringae pv. aptata is seedborne and infested seed is a common means of pathogen introduction into table beet fields. The pathogen can also be present in the infested crop residues from the previous season as well as the alternative hosts. Alternative crop hosts include typical Chenopods (e.g. spinach, sugar beet, and Swiss chard) but also other non-related species including beans, cucurbits, and lettuce. Cool temperatures between 45-60°F and wet conditions typical of those that occur in early spring in upstate New York are conducive for pathogen infection and disease development. These conditions are similar to those that predispose table beet also to Phoma leaf spot. The pathogen can spread within the field through infested seed and irrigation water.
Disease Management
One of the most critical factors to achieve management of bacterial leaf spot is the use of certified seeds (Fig. 4). Other factors that will also contribute to reducing the initial inoculum and hence risk of disease include: (i) tillage to bury plant residues to promote breakdown, (ii) rotation between host crop species of at least three years; and (iii) drip or furrow irrigation to avoid dispersal of the pathogen through water splash. Currently, little is known of differences in cultivar susceptibility to bacterial leaf spot. Anectodal reports have described severe epidemics in cvs. Merlin, Boro, and Pablo.

Figure 4. Complementary practices towards the management of Bacterial leaf spot of table beet.
In-season control. If bacterial leaf spot is severe, applications of copper-based products should be considered to prevent disease spread. There are a range of conventional and OMRI-listed copper-based products available, including: Cueva (copper octanoate; FRAC M1), Badge X2 (copper oxychloride + copper hydroxide; FRAC M1), and Kocide 3000-O (copper hydroxide; FRAC M1). Remember to check the label for rates, re-entry intervals, and pre-harvest intervals applicable to your state and crop. Avoid applying copper-based products on transplants before hardening off, and in high temperatures due to the risk of phytotoxicity.
 
Source: 
https://www.vegetables.cornell.edu/pest-management/disease-factsheets/bacterial-leaf-spot-of-table-beet/

Vegetable season is well underway and early planted vegetable crops are already about one month old. Many fields have or soon will need to be cultivated. As such, I thought it would be timely to “repost” this video on “new” technologies for cultivating weeds - 1) a camera-guided side-shift hitch and 2) finger weeders, an in-row weeding tool (Fig. 1). The video shows the device operating in seedling corn, but it will work similarly in other crops such as broccoli or cauliflower.

We have found the devices work well. Trials conducted in cotton over 3 years showed that use of camera-guidance improved weed control by more than 30% and finger weeders removed about 45% of the in-row weeds. Weed control using the two technologies together simultaneously was roughly 90% for broadleaf weeds and about 85% for all weed species including grasses.

If you are interested in trying these technologies, please contact me. We still have the equipment and I’d be happy to work with you.

Fig. 1. Technologies for precision cultivation and in-row weeding include a) a
camera-guided side-shift hitch attached to a cultivator and b) in-row weeding
tools (finger weeders).



Watch the Video Below

There are more than 50 broadleaf and grass weeds in this area that are common and have been here for a long time.  It would be great to have an herbicide that will control all of them, be safe to the crop and be gone the next day after harvest.

Obviously, we are a long way from achieving this. What we have done instead is select for the weeds that escape our weed control practices. Anything that shifts the advantage to the crop instead of the weeds will help. Our practices include the use of herbicides, mechanical techniques and hand hoeing. Good weed control can be achieved using all three but may not be economical.

Weed selection due to herbicide availability was evident a few years ago when leaf lettuce was removed from the Kerb label in 2009. It is well known that Kerb, Prefar and Balan were the standard herbicides used in lettuce for the last 60years. Kerb will control the grasses and most of the broadleaves consistently including many that are not controlled by the other two products such as shepherds purse, london rocket and wild mustard. The longer that Kerb was unavailable the more prevalent some weeds would become. On January 12, 2016, the EPA label for Kerb was reinstated for leaf lettuce bringing back the tool to the industry1.

Prefar will control grass consistently, purslane and pigweed most of the time, lambs quarters and goosefoot some of the time. Balan will control grass consistently and many of the small-seeded broadleaves some of the time.

The postemergence grass herbicides were registered about 30 years ago but for broadleaf weeds there has not been a new registration in half a century.

Reference:
1.    Retrieved from the www on Oct 14, 2024 https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=21270#:~:text=On%20January%2012%2C%202016%20the%20Federal%20EPA,55%20day%20prior%20to%20harvest%20(Table%201).

2.    https://cales.arizona.edu/crop/vegetables/advisories/more/weed122.html

Calvin’s lab conducted an experiment this fall to evaluate bioinsecticides that can help to control pale striped flea beetles inorganic crops. The experiment was conducted at the Yuma Agricultural Center experimental farm. Four insecticides and insecticide mixes, including Biolink (insect& bird repellent), Biolink + Pyganic, Pyganic, and M-Pede + Entrust, were evaluated along with a nontreated check. Insecticide treatments were applied using chemigation through sprinklers during the last 40 minutes of germination water. Each treatment was applied to a strip of 10 beds of cabbage, and each strip was divided into 4 subsections representing 4 replications. Precautions were taken to avoid cross-contamination across treatments. Because there was a stand issue, stand count data was not considered for evaluation. The treatments were compared using the percentage of damaged plant data. This data was collected by inspecting 20 plants per subsection. We also inspected each of these 20 plants and their immediate surroundings for the presence of flea beetle adults. While we observed a lot of flea beetle damage, we only saw one flea beetle throughout the experiment. The assessment was made on the 4thand the 7th day after application (DAA).

At 4 DAA, all insecticide-treated strips showed a comparable reduction in injured plants. However, only Biolink, Biolink +Pyganic, and M-Pede + Entrust exhibited a level of injured plants that was significantly lower than that of the non-treated control. At 7 DAA, only Biolink showed injured plant incidence that was significantly lower than that of the non-treated control. However, Biolink + Pyganic, and M-Pede + Entrust were comparable to the Biolink alone treatment (Figure 1). The data suggests that the evaluated bioinsecticides and bioinsecticide mixes can be used alternatively when targeting pale striped flea beetles in brassica seedlings. However, an additional application after 4 DAA would be necessary for better protection of the crop.

Figure 1a. Brassica plant with flea beetle feeding injury


Figure 1b. Adult pale striped flea beetle.


Figure 2. Means percentage of cabbage plants damaged by flea beetles. Bars
with the same capital letter or lowercase letter are not statistically different. IBR
= Biolink (insect & bird repellent).

Area wide Insect Trapping Network   VegIPM Update, Vol. 15, No. 21, Oct 16, 2024

Results of pheromone and sticky trap catches can be viewed here.

Corn earworm: CEW moth counts increased in most traps; about average for early October.

Beet armyworm: Trap counts increased in most areas last week, and about average for early October.

Cabbage looper: Cabbage looper trap counts still most locations, below average for this time of the season.

Diamondback moth: Adult activity increasing, particularly in the Yuma and Dome Valleys.  Above average for this time of season.

Whitefly: Adult movement increasing Tacna, Dome Valley and Yuma Valley; overall about average for early October.

Thrips: Thrips adult movement picking up in all areas, overall activity above average.

Aphids: Winged aphids beginning to show up the north Yuma and Gila Valleys; about average for early October.