May 5, 2021Summer Sanitation Is Important as Ever
To contact John Palumbo go to: jpalumbo@ag.Arizona.edu
Clovers can be very difficult to control weeds here, but it is also a major crop and common ornamental. Clovers can survive under poor growing conditions and are not controlled with glyphosate and seem to get worse every year. There are more than 50 types and 300 species of clover and they can be easily misidentified. They are all in the legume (Fabracea) family and can use a bacterium (rhizobium) in the soil to convert nitrogen in the atmosphere to a form that they and other plants can use for fertilizer. There are only 4 or 5 clover species that are agricultural pests here. The ones we get the most questions on are white and yellow sweet clover. These are in the Melilotus family. White sweet clover (Melilotus albus) is tall for a clover and can get 3 to 5 foot in height. The leaves are thinner than most clovers and this difficult to control weed lives at least 2 years and sometimes longer. Glyphosate and most of the contact herbicides do not control it. The plant growth regulator herbicides work best. Yellow sweet clover (Melilotus officinalis) is less common here. The flowers are yellow, and it is not as tall and vegetative as white sweet clover. Yellow is more common at higher elevations. California burclover (Medicago polymorpha) and Black medic (Medicago lupina) are in the same genus as alfalfa and are more of a problem in landscapes, parks and golf courses than in agricultural fields here. They do not grow upright and spread below the crop or turf. The true clovers are in the Trifolium genus and include white and strawberry clover. These creep along the ground and root at the nodes of the stem. These are more of a urban landscape weed and not considered an agricultural problem. Creeping woodsorrel or Oxyalis looks like a clover but it is not related. It is a turf weed that spreads rapidly along the ground and can live for several years. Preemergent herbicides are effective against all these clovers before they become established. The postemergence herbicides that are most effective in controlling these clovers are the plant growth regulators. Contact herbicides and glyphosate are generally ineffective.
It is about that time of the year/growing season when you start seeing bacterial diseases. With the rain we got last week and as plants get more vegetative growth bacterial issues become more prevalent. Cilantro and parsley are two crops grown in desert southwest that often suffer from bacterial leaf spots. Most times, the disease incidence is also high because of sprinkler irrigation used in these cropS. On both crops, 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 parsley and cilantro. 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 are likely seedborne in both crops. 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. Copper spray/copper based fungicide provide limited control against the pathogens.
Vol. 12, Issue 7, Published 4/7/2021
Over the last several years, there has been a tremendous amount of research activity towards the development of autonomous agriculture vehicles. A quick internet search will reveal over 50 companies or university research groups working in this space. A question I get often from groups developing such platforms is “What is a good agricultural application for our lightweight “robot”?”. It’s a great question, and for Arizona vegetable production, it’s also one that I’m not sure I have a satisfying answer for.
The calls I get regarding autonomous robots are mostly related to automated weeding applications. Automated weeding machines are commercially available, but their adoption has been limited not because of labor costs for tractor operation, rather it is the lack of the development of a functional and cost-effective means for identifying and removing weeds.
For decades, researchers have been attempting to develop sensing systems that are able to reliably detect weeds. Techniques such as 2-D and 3-D color imaging, x-rays, hyperspectral sensing and artificial intelligence have been tried (Slaughter, 2014; Bender et al., 2020). The best performing systems provide about 96% accuracy, meaning that 4% of the crops plants are identified as weeds and would be destroyed by the weeder. For high value vegetable crops like lettuce with gross revenues of roughly $10,000 per acre, killing 4% of the crop equates to $400 per acre of losses. Economically, this does not make sense as hand weeding labor costs are typically $300 per acre or less. The other main issue is that current automated weeding technologies are not highly precise and provide only partial control. Our studies with these types of machines have shown that these systems remove only about 1/3rd of the in-row weeds (Lati, et al., 2016) and a follow up hand weeding operation is often necessary. To be highly cost effective, elimination of the hand weeding step is needed.
In short, my recommendation to research groups asking about applications for autonomous robots is that their time and technical skills would best be served developing reliable crop/weed differentiation systems and a technique to remove a very high percentage of weeds.
Bender, A., Whelan, B. & Sukkarieh, S. 2020. A high‐resolution, multimodal data set for agricultural robotics: A Ladybird's‐eye view of Brassica. J. Field Robotics. 37(1): 73-96.
Lati, R.N, Siemens, M.C., Rachuy, J.S. & Fennimore, S.A. (2016). Intrarow Weed Removal in Broccoli and Transplanted Lettuce with an Intelligent Cultivator. Weed Technology, 30(3), 655-663.
Slaughter, D.C. The biological engineer: Sensing the difference between crops and weeds. Autonomous robotic weed control systems: A review. Computers and Electronics in Agriculture 61(2008): 63-78.
The Yuma County Leaf Wetness Network remains in place for the 2018/19 vegetable season. Growers and PCAs may access information generated by the network by entering the following internet address: http://220.127.116.11:460
Upon entering the address above, you will be transferred to internet page that provides a series of tabs at the top of the page. Simply click on the tabs to access the information of interest.
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.