Summer is finally over. Brassica transplants are in the ground, and direct-seeded broccoli and lettuce plantings are now beginning.  In the past week, I’ve observed or received reports from PCAs of key insect pests beginning to show up (or not) on melon and early produce crops in the desert.   
 
Seedling pests:  Flea beetles (FB) are beginning to show up in transplanted crops like they always do, but pressure has been light so far. We haven’t seen much in our experimental plots at YAC either.  Remember, FB adults lay eggs in the soil of their favored local host plants (i.e., alfalfa, cotton, purslane, pigweed and nightshade) where larvae feed on the roots to later emerge as adults. So, keep in mind, the source of that FB infestations hitting your new stands may not just be freshly cut hay, defoliated cotton, or disked weeds. In some areas (Yuma Valley), crickets seem to be very abundant. Crickets like moisture and are often found under sprinkler pipes but can also be found in cracks in soils around fields or in drainage areas. 
 
Bagrada bug:    We’ve already had reports of bagrada bug adults on two transplanted cauliflower fields in Dome Valley. Not sure whether they arrived with the transplants or are moving from surrounding crops. However, it’s still early and they might surprise you as the season progresses.   Look for those fresh feeding signs on cotyledons and young leaves.  Experience suggests that they are most abundant after the humidity breaks.
 
Lepidopterous Larvae (worms):   Worm pressure seems to be below normal. Trap catches so far show that Cabbage looper moths are almost non-existent, and no reports on melons to date. They should pick-up as we approach October. No reports of Beet armyworm larvae on the earliest transplants yet, and areawide pheromone traps suggest that moth activity is below normal. But they will show up sooner or later, so get ready.  You have numerous insecticide alternatives at your disposal to control them.  Have had a couple of reports of Diamondback moth larvae on newly transplanted brassica crops. However, we’ve yet to capture moths on pheromone traps which suggests that adult immigration on high altitude winds associated with storms has not occurred. Remember, DBM disappear each summer and reestablish on desert crops via transplants or migrate in on monsoon/tropical storms. I strongly stress that you check your Cole crops closely this fall, particularly following storms or on plants originating from coastal CA. 
 
Whiteflies:       Area wide sticky trap captures have been about normal for early September, but whiteflies can migrate long distances on high winds. Adult numbers increased on my melon plants last week and remain high. Reports in area melons range from light to moderate numbers so far, but there is still a lot of cotton out there yet to be picked. The good news is there are several insecticide alternatives to control them in produce. 

 

Downy mildew has always been one of the major problem for PCAs and growers in the desert southwest. The symptoms observed are green to yellow angular spots on the upper surface of the leaves and fluffy growth on the lower side (See Picture). Symptoms usually start from older leaves. As disease progresses the lesion turn brown and dry up and in some occasions the disease can become systemic causing dark discoloration of vascular tissue.

Favorable condition for disease development:
The pathogen Bremia lactucae thrives in damp, cool condition, with moisture present on leaves. Spores are short-lived but dispersed efficiently by wind during moist period. Cultivated lettuce is the main host of the pathogen but it has also been reported to infect artichoke, cornflower and strawflower.

Why is downy mildew difficult to manage?
One of the main reason that hinders the disease management is the complexity of the pathogen. Bremia lactucae consists of multiple races (pathotypes), and new races continue to occur as pathogen evolves. The pathogen is one of the fastest evolving plant pathogen. And each pathotypes have developed insensitivity to fungicides to different extent.

One of the best practice is to grow resistant cultivar, but there are limitations. As the pathogen is highly variable and dynamic, resistant cultivars are not a permanent solution as the pathogen overcomes the resistance by evolving into virulent strains and isolates.

Preventative application of fungicides are effective to some extent. Reducing leaf wetness and humidity by using drip or furrow irrigation can be helpful. However, weather condition like rain during cool weather as we had in past couple of weeks is conducive to development of epidemics and we have very little control on that matter.

In previous articles (Vol. 11 (13), Vol. 11 (20), Vol. 11(24)), I’ve discussed using band-steam to control  plant diseases and weeds. Band-steaming is where steam is used to heat narrow strips of soil to temperature levels sufficient to kill soilborne pathogens and weed seed (>140 °F for > 20 minutes). The concept is showing good promise. This past season, three trials were conducted examining the efficacy of using steam for disease and weed control in Yuma, AZ. In the studies, steam was applied in a 4-inch-wide by 2-inch-deep band of soil centered on the seedline using a prototype band-steam applicator (Fig.1). The band-steam applicator is principally comprised of a 35 BHP steam generator mounted on top of an elongated bed shaper. The apparatus applies steam via shank injection and from cone shaped ports on top of the bed shaper. 
Trial results were very encouraging as the prototype applicator was able to raise soil temperatures to target levels (140°F for >20 minutes) at viable travels speeds of 0.75 mph. Steam provided better than 80% weed control and significantly lowered hand weeding time by more than 2 hours per acre (Table 1). Results also showed that Fusarium colony forming units (CFU) were reduced from 2,600 in the control to 155 in the 0.75 mph and 53 in the 0.5 mph treatments, respectively (a more than 15-fold reduction). A significant difference in Fusarium wilt of lettuce disease incidence was not found, however disease infection at the field site was low (< 2%) and differences were not expected. At 0.5 mph, fuel costs were calculated to be $238/acre which was considered reasonable and consistent with the values reported by Fennimore et al. (2014).

An unexpected finding was that plants in steam treated plots appeared to be healthier and more vigorous than untreated plots (Fig. 2). This trial is still in progress and it will be interesting to see if this improved early growth translates into increases in crop yield.
In summary, early trial results are showing good promise for use of band-steam as a non-herbicidal method of pest control. We plan on conducting further trials in this multi-year study. If you are interested in evaluating the device on your farm and being part of the study please contact me. We are particularly interested in fields with a known history of Fusarium wilt of lettuce and/or Sclerotinia lettuce drop that will be planted to iceberg or romaine lettuce.
As always, if you are interested in seeing the machine operate or would like more information, please feel free to contact me.

Acknowledgements
This work is supported by Crop Protection and Pest Management grant no. 2017-70006-27273/project accession no. 1014065 from the USDA National Institute of Food and Agriculture, the Arizona Specialty Crop Block Grant Program and the Arizona Iceberg Lettuce Research Council. We greatly appreciate their support. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.
A special thank you is extended to Mellon Farms for allowing us to conduct this research on their farm.

References
Fennimore, S.A., Martin, F.N., Miller, T.C., Broome, J.C., Dorn, N. and Greene, I. 2014. Evaluation of a mobile steam applicator for soil disinfestation in California strawberry. HortScience 49(12):1542-1549.

Click link below or picture to see the band-steam and co-product applicator in action! 

 

Oxyfluorfen,(Goal and Galigan) has become a popular and effective herbicide for use on cole crops even though it was first registered in the 1980’s. Oxyfluorfen is a contact herbicide with the same mode of action as Chateau, Aim, Shark, Gramoxone, Paraquat , Sharpen and ET. They are all PPO Inhibitors that rupture cell membranes. Carfentrazone (Aim, Shark), ET and Paraquat (Gramoxone), are effective only as postemergence applications to small weeds, Sharpen and Goal are effective both preemergence and early postemergence and Chateau is used only preemergence but can cause severe crop injury if mixed with a surfactant. The only one of these that is registered for cole crops is Oxyfluorfen (Goal, GoalTender, Galigan). It does not make sense for a contact herbicide to be used on weeds that have not emerged. The way this works is that a barrier is created with the herbicide on the surface that kills the seedling weeds as they come in contact with it. It is important not to disturb this barrier or the weeds will not be affected. Oxyfluorfen (Goal) is an herbicide that defies reason in other ways as well. It normally adheres strongly to the soil and has very low water solubility. It is well known, however, that Goal can lift off of the surface and cause crop injury. When this happens, it is evaporating or going from a liquid to a gas and this is unaffected by its solubility or adsorption. It also works well when chemigated through a sprinkler system. You would think that it would wash off, but it works well with less crop injury when chemigated. Chemigation is registered for onions only but it works well with cole crops as well. It only takes half as much (4 ounces) and is safer to the crop when chemigated. It is best to apply it about 2/3 of the way through the sprinkler run to keep it in place and flush the system.

 

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

Corn earworm: CEW moth counts down in most over the last month, but increased activity in Wellton and Tacna in the past week; above average for this time of season.

Beet armyworm: Moth trap counts increased in most areas, above average for this time of the year.

Cabbage looper: Moths remain in all traps in the past 2 weeks, and average for this time of the season.

Diamondback moth: Adults decreased to all locations but still remain active in Wellton and the N. Yuma Valley. Overall, below average for January.

Whitefly: Adult movement remains low in all areas, consistent with previous years.

Thrips: Thrips adults movement decreased in past 2 weeks, overall activity below average for January.

Aphids: Winged aphids are still actively moving, but lower in most areas. About average for January.  

Leafminers: Adult activity down in most locations, below average for this time of season.