With cauliflower and cabbage now being transplanted it’s time to be on the look-out for the elusive bagrada bug. Eleven years ago, the invasive stinkbug invaded the desert southwest, causing significant economic damage to large acreages of Cole crops. But in the past 5-6 years bagrada populations have been relatively light in our experimental plots (see graph below) and found sporadically in commercial crops. Why the drastic reduction? Not certain, but likely a combination of good insect management and a little help from mother nature. However, for the second year in a row, we found an abundance of adults and nymphs colonizing mustard and other brassica plots this past spring. Thus, you shouldn’t count them out this season; a lot will depend on how well they survived the long summer, and if there are any hitchhikers on transplants. To date, I’ve had reports from 2 local PCAs who have found single Bagrada adults on early transplanted cauliflower. In addition, bagrada bugs have been reported on cabbage transplants in the Phoenix area. No feeding signs on leaves reported is a good sign that numbers are light and may have arrived with the transplants. Similarly, I had reports during July of PCAs picking up Bagrada adults while sweeping cotton. Again, be aware of your surroundings, especially if you have a brassica crop going in the ground next to a defoliated cotton field. Experience over the past eleven years has shown us that peak adult bagrada bug abundance in the desert generally occurs on direct-seeded and transplanted brassica crops in mid-September. These peak occurrences appear to coincide with the end of the monsoon season and the much-reduced humidity. However, it’s been difficult to observe this effect lately since there has been a trend of significantly lower bagrada bug abundance since 2014, and last season was one of the lightest bagrada populations since we started tracking them in 2010. So, what should a PCA expect for this season? We’re having an active monsoon so far, and the higher humidity could play to your advantage. We can’t say for sure when they will show up and in what numbers but keep your eyes open for adults on your earliest plantings. Here are a few management tips to consider. (1) When monitoring for bagrada bugs, PCAs should look mainly for fresh feeding signs on new plant tissue, and adults later in the day when they are most active. (2) Direct-seeded and transplanted crops are susceptible to bagrada bug infestations during stand establishment and up to the 6-leaf stage. After that, bagrada rarely cause damage to head forming brassicas (ie., broccoli, cabbage, cauliflower). Leafy brassicas like kale are much more susceptible to cosmetic damage throughout the season though. (3) We recommend that control be initiated immediately if you can readily find 5% or more of plants with fresh-feeding signs. This can include chemigation or aerial applications with pyrethroids. Contact insecticides such as pyrethroids, Lannate, and Lorsban should be used once stands are lined out. Once pipe is pulled and adults continue to migrate into fields, consider alternating to dinotefuran (e.g., Scorpion) sprays. (4) Also, growers who plant NipsIt broccoli seed (clothianidin treated) should begin to closely monitor for fresh feeding damage around 14 days after emergence. More information on bagrada bug management on fall brassica crops see: Bagrada Bug Management Tips-2021.

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.

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.

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. 14, No. 22, Nov 1, 2023            

Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:            
CEW moth captures have steadily decreased over the past 2 weeks, and areawide about average for late-October.
 
Beet armyworm:         
Trap counts reached their highest levels so far this season, particularly in Tacna, Wellton and Yuma Valley, and about average for late October.
 
Cabbage looper:           
Cabbage looper numbers decreased areawide, and are still below average for this time of the year.
 
Diamondback moth:   
Sporadic DBM activity in low numbers throughout the area, trending well below average for late October.
 
Whitefly:                      
Adult movement increased in the past 2 weeks and above average for late October.
 
Thrips:                           
Thrips adult activity peaked in the last two weeks, and trending below average in October.
 
Aphids:                        
Winged adults continue to be captured for the season, consistent with heavy winds from W-NW. Aphid captures thus far have been well below average. 
 
Leafminers:                  
Adult activity decreased in most areas, and trending about average for late October.