Feb 10, 2021Lettuce Aphids Showing Up Early Again
To contact John Palumbo go to: jpalumbo@ag.Arizona.edu
Malva (malva parviflora) is one of the oldest and most pervasive weeds that that we deal with here. It is also known as little mallow or cheeseweed and is in the same family as cotton, okra and hibiscus. It is often classified as a winter annual but survives all year in this region. It has a deep taproot and can grow in compacted clay or sand and in freezing conditions and high temperatures It provides a refuge for insects and diseases that can damage several crops.
Malva is easy to identify both as a seedling and mature plant. The seedlings are distinctively heart shaped and the mature plant is broad and palm shaped. It is very vegetative and can grow to 6 ft.
The deep tap root of this weed makes it difficult to cut out after it is established. Its response to herbicides id somewhat unusual. It is very sensitive to contact herbicides that do not move into the plant. These include Goal, Sharpen Gramoxone , Rely,Aim and others. However, it is not sensitive to systemic herbicides like 2,4-D and Glyphosate. It reproduces from seed and can be controlled preemergence with many of the same preemergence herbicides used in cotton like Prowl or Treflan. The seed pods are wheel shaped which is where the name cheeseweed comes from. Each seed pod contains 10 to 12 seeds
Lettuce dieback is a soil-borne disease caused by two closely related viruses from the family Tombusviridae Tomato Bushy Stunt Virus (TBSV) and Lettuce Necrotic Stunt Virus (LNSV) that has been reclassified as Moroccan Pepper Virus (MPV). The disease has been observed throughout the main lettuce producing areas of California and Arizona.
Since December in 2019, we received some samples that looked like lettuce dieback disease. The samples came positive for a new virus tentatively named as Lettuce dieback associated virus. We have been seeing symptoms in resistant cultivars (with Tvr1 gene) which suggests that the new virus is involved in the symptomology.
Little is known about the virus as of now, as it is still a work in progress. What we know so far, is that the virus is soilborne, and has been found to have more correlation with the dieback disease more than Tomato bushy stunt virus.
Dr. William Wintermantel (pictured above, firstname.lastname@example.org ) has been working on the virus and has developed protocol for virus testing.
Dr. Wintermantel has also shared the protocol with Trical Diagnostics so if you want rapid molecular diagnosis please contact Steve Koike (SKoike@trical.com).
If you have plants showing symptoms of Tomato bushy stunt virus, please bring the samples to Yuma Plant Health Clinic for diagnosis.
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.