May 5, 2021Summer Sanitation Is Important as Ever
To contact John Palumbo go to: jpalumbo@ag.Arizona.edu
Herbicide resistant weeds have received a lot of attention in recent years. It is often misunderstood. Three of the most misunderstood concepts regarding herbicide resistance are: 1- Weed tolerance and weed selection are not resistance,2- Weed resistance is not universal and does not affect every weed of a certain species from field to field or within a field and weed resistance often takes much longer than insect resistance that is more common and occurs faster.
No Herbicide controls all weeds. Those weeds that are not controlled are tolerant. They never were controlled by that particular herbicide and they are often selected for and become more prevalent over time if the same herbicide is used. Resistant weeds, on the other hand, were controlled at one time by a particular herbicide and have naturally developed a trait that stops the herbicide from working. These resistant weeds survive from generation to generation and become more prevalent over time.
Weed resistance does not occur in all weeds in a field at the same time. It can be just one plant of trillions in a field. As this plant survives the herbicide and goes to seed it becomes more widespread in the field and in other fields. We conducted a trial in Parker last year where sprangletop survived Glyphosate in one field and was killed by the same treatment down the road. If your neighbor has resistant weeds it doesn’t mean that you do too.
Lastly, insect resistance to insecticides has occurred in this region for many years and was the first exposure that many pest control advisers and growers had to pesticide resistance. The principals are the same although insects generally produce multiple generations per season and mutations that facilitate resistance occur faster than for weeds. Annual weeds often produce only one or two generations per season and resistance takes much longer.
With harvesting time getting closer to many field crops now, we are seeing higher incidence of bacterial diseases. We had few reports of bacterial spot on lettuce, cilantro, arugula, and parsley. Most times bacterial symptoms are not expected or simply ignored because we think the desert is too dry and bacterial diseases require high humidity. But as the plants grow bigger the space and aeration in between plants decreases, thus creating a humid microclimate. It is even more common on produces/herbs like cilantro, arugula, parsley etc. where the crops are grown densely, and sprinkle irrigation is used.
Initial symptoms of bacterial leaf spot are water-soaked lesions on leaves. The lesions develop into spots that are varying shades of tan or brown (see picture ‘B’ on parsley whereas advanced spots on cilantro can be black (see picture ‘A’ on cilantro). The lesions are usually limited by leaf veins and thus have an angular, square, or rectangular appearance, a typical feature of bacterial infection. Lesions tend to be relatively small about 1/8 to 1/4 inch (3–6 mm) in diameter and are visible from both the top and bottom of leaves. Under favorable conditions, free moisture from rain or sprinkler irrigation, leaf spots may coalesce and cause considerable blighting of the entire foliage.
Pseudomonas syringae pv. apii (Psa) and P. syringae pv. coriandricola (Psc). cause bacterial leaf spot on most vegetable. Pseudomonas syringae pv. apii (Psa) can cause leaf blight in celery and fennel as well. Though the problem is documented as more of a problem in cilantro and less in celery, in severe condition the disease can result in unmarketable produce in any host. The bacteria can be seedborne. However, water from rain, sprinkler irrigation, and heavy dews and fogs will splash bacteria from infected plants onto adjacent healthy foliage resulting in heavy infestation.
To manage the disease, always use tested/treated seeds, rotate crop with non-host to reduce inoculum level, switch from sprinkler to furrow irrigation to limit secondary spread, avoid excessive use of nitrogen fertilizer. If sprinkle irrigation has to be used, use light and more frequent irrigation, or irrigate in the morning or early afternoon so the plants dry off during the day. Copper spray/copper based fungicide provide limited control against the pathogens.
In next few weeks in the Clinic:
Because of the recent increase of Covid-19 related cases in Yuma, the Yuma Ag center is open only in limited capacity. Samples have to be dropped in the bench outside the main building. Please fill out the form provided when you drop samples. Our last day to take samples in the clinic for 2020 will be 18th of December. We will be using the remaining few days of the year to update the lab records, data, and prepare for 2021. Thank you for your love, support, and patience this year.
The Yuma Plant Health Clinic and Plant Pathology program wishes you safe and happy holidays!
This is the second in a series of articles discussing technological advances being made by manufacturers of automated thinning and weeding machines. This is a fast-moving space and innovations are entering the marketplace constantly. One of these on the near-term horizon is a robotic thinner/weeder being developed by Tensorfield Agriculture, San Francisco, CA that uses hot vegetable oil to kill weeds. The idea is to spray a “micro-dose” of hot oil (320 °F) onto the targeted plant/weed with high levels of precision. Why vegetable oil and not water or steam? Sufficient levels of heat from any source will rupture cell membranes and kill plants, but the advantage of vegetable oils is that they adhere to plant surfaces better than water and can be raised to much higher temperatures before boiling. Soybean oil for example, has a boiling point of 450 °F which is much higher than that of water at 212 °F. Consequently, vegetables oils transfer more heat faster than hot water and kill plants more effectively. A limitation of steam is the difficulty in concentrating the heat energy onto the target plant.
The concept of using hot vegetable oil to control weeds with an automated machine is not new and has some merit. Vegetable oil degrades naturally in the soil and thus can be used in commercial and organic crop production. Researchers at UC Davis developed and tested a prototype, hot oil based micro-dosing sprayer for automated weeding in tomato crops (Giles et al. 2005, Zhang et al., 2012). They found the technique effective at controlling weeds (>90%), but computing speeds were too slow for the integrated automated weeding machine to be commercially viable at the time.
Tensorfield Agriculture is rejuvenating the idea using modern computers, artificial intelligence and automation. The company has built a micro-dosing sprayer that delivers heated oil to target weeds at the 1/2” scale level of precision (Fig. 1). The sprayer assembly is mounted on an autonomous, robotic platform (Fig 2 - please note that the robotic platform depicted is a first-generation design developed for testing and debugging purposes and that a commercial style unit is forthcoming). Computer imaging and artificial intelligence are used to detect crop plants and weeds. The company will be testing and debugging the system this winter in California with carrot, spinach and romaine crops. The aim is to have prototype commercial systems available for the spring of 2021.
Some of you may have visited Tensorfield Agriculture’s booth or seen their technical breakout-session presentation at the 2020 Southwest Ag Summit in Yuma, AZ. They have an interest in working in the Yuma area and with the University of Arizona. It will be interesting to see how this technology progresses over the winter and how killing weeds with heated vegetable oil may benefit weed management systems.
As I mentioned, automated thinning and weeding technologies are advancing at a very rapid pace. If you know of a new technology that would be of interest and appropriate for this publication, please feel free to contact me.
 Reference to a product or company is for specific information only and does not endorse or recommend that product or company to the exclusion of others that may be suitable.
Fig. 1. Custom built sprayer modules for delivering high temperature vegetable oil (350 °F) to kill weeds organically. The units are designed for precision weed control (1/2” scale of resolution) by Tensorfield Agriculture, San Francisco, CA (Photo credit – Tensorfield Agriculture).
Fig. 2. Autonomous robot for thinning and weeding using heated vegetable oil. The unit is a first-generation prototype designed for testing and debugging purposes by Tensorfield Agriculture, San Francisco, CA (Photo credit – Tensorfield Agriculture).
Giles, D.K., Lanini, W.T. & Slaughter, D.C. 2005. Precision weed control for organic and conventional specialty crops. In Buy California Crop Block Grant Program Final Report. Sacramento, Calif.: California Department of Food and Agriculture.
Zhang, Y., Staab, E.S., Slaughter, D.C., Giles, D.K. & Downey, D. Automated weed control in organic row crops using hyperspectral species identification and thermal micro-dosing. Crop Protection 41: 96-105.
Results of pheromone and sticky trap catches can be viewed HERE.
Results of pheromone and sticky trap catches can be viewed HERE.
Corn earworm: CEW moth activity increased a bit in the past 2 weeks but remains well below average for late spring.
Beet armyworm: Moth counts increased slightly, but remain very low consistent with seasonal temperatures, and below average for this point in the season.
Cabbage looper: Significant increase in activity in Dome Valley, Gila Valley and Tacna, but moth counts remain unusually low for this time of year, as they have all season.
Whitefly: No adult movement recorded across all locations and overall low numbers consistent with temperatures.
Thrips: Thrips adult movement beginning to pick up considerably, particularly in Yuma and Dome Valleys. Movement is below average for late March.
Aphids: Seasonal aphid counts down considerably compared with the Feb and Jan. Counts highest in Bard and Gila Valley. Below average movement for this time of year. Majority of species found on traps were green peach aphid.
Leafminers: Adult activity up slightly in some locations, but well below average for late season.