Historically, worms (Lepidopterous larvae; -beet armyworm, cabbage looper and corn earworm) are the most important pests of desert pruduce during September and October. So, it is no surprise that worms are everywhere particularly in Dome Valley where heavy beet armyworm pressure has been reported over the past week or so. Many PCAs have reported that armyworm have been infesting lettuce as early as 8 days after wet date, which seems quicker than usual. Corn earworm larvae have also been reported in a few fields. Here at the Yuma Ag Center, one can easily find newly new egg masses and neonate beet armyworm larvae on 10 day old lettuce and broccoli stands. Cabbage loopers are beginning to show up and their populations will likely increase. Remember, temperatures drive larval development and adult moth activity, particularly when night time temps remain high (in the mid-70s or higher). The moths are nocturnal and will actively oviposit when evenings are warm and winds are light. With shorter days coming, the moths have more time to lay eggs at night. As long as the average temperature remains around 80-85°F, worms should be active at damaging levels. Those ideal conditions are consistent with the weather forecast for the next 10 days (daytime highs in the low 100’s and nighttime lows in the mid 70’s). Fortunately, there are a number of very effective insecticides that can be applied as stand-alone foliar products that provide effective residual control of both of these lepidopterous species. Radiant, Proclaim, Intrepid, Avaunt and any one of the Diamide products (Belt, Coragen, Exirell, Vetica, and Voliam Xpress) can provide good knockdown and extended residual control of armyworms and loopers. Addition of a pyrethroid often enhances knockdown of corn earworm and cabbage looper for many of the products. Of course, residual control will often depend on the rate applied. In general, the higher the rate, the longer the residual. But this will also depend on plant size at time of application and how fast the plant is growing. Before selecting a product for worm control, be conscious of products (chemistries) previously used on the crop. Avoid using products with the same mode of action more than twice on any given field. More information on the insecticides available for effective control of beet armyworm and cabbage looper can be found in this document: Lepidopterous Larvae Management in Desert Produce Crops, 2015.

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%). Spinach ‘Revere’ was seeded, then sprinkler-irrigated to germinate seed Jan 18, 2024 on beds with 84 in. between bed centers and containing 30 lines of seed per bed.  All irrigation water was supplied by sprinkler irrigation.  Treatments were replicated four times in a randomized complete block design.  Replicate plots consisted of 15 ft lengths of bed separated by 3 ft lengths of nontreated bed.  Treatments were applied with a CO₂backpack sprayer that delivered 50 gal/acre at 40 psi to flat-fan nozzles. 
 

Month	Max	Min	Average	Rainfall
January	68	42	54	1.14 in
February	73	47	59	0.50 in
March	77	50	63	0.31 in

 
Downy mildew (caused by Peronospora farinosa f. sp. spinaciae) was first observed in plots on Feb 19  and final reading was taken on February 26, 2024. Spray date for each treatments are listed in excel file with the results.   Disease severity was recorded by determining the percentage of infected leaves present within three 1-ft² areas within each of the four replicate plots per treatment.  The number of spinach leaves in a 1-ft² area of bed was approximately 144. 

The data (found in the accompanying Excel file) illustrate the degree of disease reduction obtained by applications of the various tested fungicides. Products that  provided effective control against the disease include Orondis ultra, Thrive 4 M, Fungout, Cevya, Eject and Zampro. No phytotoxicity was observed in any of the treatments in this trial.

In 2018, University of Arizona Cooperative Extension, Yuma Agricultural Center and the Yuma Center of Excellence for Desert Agriculture hosted an Automated Thinning and Weeding Technologies Field Day. The event featured twelve equipment vendors and university researchers showcasing and demoing the latest automated ag technologies in the field. Company representatives were on hand to discuss the technologies and answer questions. Since then, there has been a tremendous amount of innovation and development in these technologies. Several start-up companies have introduced new machinery into the marketplace and the older technologies have advanced greatly. We haven’t set a firm date yet but are planning for mid-October. The event is open to all companies and researchers that would like to show their automated thinning and/or weeding technology. If you are interested in demoing your equipment or know someone that is, please contact me. Stay tuned! 

Fig. 1. Highlight video of 1^st Automated Thinning and Weeding Technologies Field Demo (2018).

 

It is much easier to kill weeds when there is no crop in the field and now is a good time to reduce the weed seed bank of weeds in fallow fields. It is an especially valuable time to reduce the population of perennial weeds, like nutsedge, that will continue to get worse every year until the field is almost unfarmable for many crops. Weed seeds are buried at variable depths in the soil, some have hard seed coats and there are other variables that cause them to germinate over a long period of time. If they all came up at the same time they would be much easier to control. It takes time, therefore, to repeatedly irrigate, germinate and kill weeds with either tillage or herbicides. We have conducted trials that indicate that in most years summer annual weeds begin to germinate in February, reach a peak in June but continue to germinate into October. Perennial weeds often have to be actively growing to be adequately controlled and now is a good time to get started. 
 Tillage Repeated germination and tillage of small annual weeds can be very effective at reducing the weed seed bank. It can also spread weeds in some situations. Proper timing of tillage to kill weeds can be important with some species. Succulent weeds like purslane can survive for several days after cultivation or hoeing. They can reroot at the nodes and continue to grow if they are allowed to get too big before they are uprooted. Growers sometimes allow early emerging weeds to get fairly big in an effort to germinate as many seeds as possible. Incorporating big weeds can temporarily build up large amounts of organic matter into the soil and have a negative effect on some preemergent herbicides used in vegetables. Many of the root and shoot inhibitor herbicides like Trifluaralin, Pendimethalin, Benefin, DCPA and others can bind to organic matter and be less available to kill weeds.
Tillage has the opposite effect on perennial weeds such as nutsedge and bermudagrass than it has on annual weeds. These weeds are spread vegetatively and repeatedly irrigating and tilling them will spread rather than kill them.
 Herbicides Both contact and systemic herbicides are used during fallow periods to control weeds. The contact herbicides include Paraquat (Gramoxone, Firestorm), Carfentrazone (Aim, Shark), Pyraflufen (ET), Pelegonic Acid (Scythe) and others. Some of the advantages of these are that they are quick and have no soil residual allowing crops to be planted soon after application. Disadvantages are that they are effective primarily only on small weeds. The highest labelled rates of Paraquat is effective, however, on some big weeds.
The most commonly used systemic herbicide for fallow ground is Glyphosate. Timing is especially important when using glyphosate to control perennial weeds. Glyphosate moves both up and down from the foliage through plants. More of it moves down into the reproductive parts of perennial weeds late in the season. Late season applications will work better on perennial weeds.  It is broad spectrum and has no soil residual except on very course soils. Many of the systemic herbicides registered for fallow use, such as Oxyfluorfen (Goal, Galigen) or EPTC (Eptam) require at least 90 days before planting many vegetable crops. If done correctly, Eptam can be very effective in controlling nutsedge during summer fallow. It is sensitive to use for fallow weed control and application procedure is important. Eptam is extremely volatile and can be leached or evaporated when it contacts water. It works best when incorporated into dry soil to create a chemical tarp in the top 2 to 6 inches. The best technique is to irrigate and cultivate or spray the weeds with glyphosate when dry. One half gallon of Eptam should the be incorporated into the dry surface and left smooth. Avoid getting the field wet. The longer it can be left the better. Preferably at least 30 days. Longer if possible. Some people have chemigated the Eptam on and had fair control. I am surprised that this works but higher rates than 0.5 gallon have been used which my offset much of what is lost in the water. A couple good irrigations will be necessary to remove the residual Eptam when it get warmer and before planting vegetables 
Only the fumigants kill weed seeds. These include Chloropicrin, Methyl Bromide, Metam Sodium, Dazomet, Telone and others. Most preemergent herbicides only work after the seed has germinated. Preemergent herbicides are often used for fallow weed control only when at least 30 -45 days or longer are available. Fumigants are expensive, can be difficult to use and are often used for disease or nematode control with the added benefit of controlling weeds.
Soil solarization and flooding have become increasingly popular in recent years as techniques to control pests during summer fallow. Few regions are as well suited for these techniques as the low desert. They are used primarily to control diseases but have the benefit of controlling some summer annual weeds as well.

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.

Leaf miners: Adult activity light in all areas, about average for this time of season