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.
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, email@example.com ) 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.
Due to a lack of effective selective, post-emergence herbicides, most vegetable crops are hand weeded following cultivation to remove in-row weeds. This operation is costly and finding labor to perform the task has become increasingly difficult. An alternative is to use automated/robotic machines for in-row weeding. These machines have been around for quite some time; the first “modern” units were commercialized in 2008. Since then, at least six companies have introduced machines and offer units for sale and/or automated weeding as a service in Yuma, AZ.
Despite these innovations and efforts, adoption of automated weeding machines has been limited. One reason for this is that weed control is only partial, and follow up hand weeding is often necessary. All commercialized automated weeders utilize metal blades that move in and out of the crop row to cultivate weeds between individual crop plants as the machine moves through the field. As such, soil disturbance is high and weeds close to crop plants cannot be effectively removed without injuring crop plants. In a two-year study (Lati et al., 2016), we found that mechanical automated weeders removed about 2/3rds of in-row weeds. The majority of uncontrolled weeds (~ 1/3rd) were observed to be within about 1” of the crop plant.
To address the lack of precision of current automated weeding machines, we developed two high speed, centimeter scale resolution sprayers to spot apply herbicides to weeds with minimal off-target spray while traveling speeds that are viable for commercial farming operations (2 mph). The first is a high precision (sub-centimeter scale resolution) sprayer designed for spot spraying cotyledon stage weeds in leaf lettuce crops. The second is a spray assembly designed for controlling in-row weeds in vegetable crops that are close to crop plants (1-cm scale resolution). We tested the device in 2019 in the laboratory and found that weed control efficacy was greater than 95% (3 species), percentage of off-target spray was less than 3% and no crop injury was observed. A link to action videos of the device in action is provided at the link below. Future work includes seeking funding, and industry partners for integrating the devices with imaging systems to develop a high precision, automated/robotic weeding machine for vegetable crops.
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.
High Speed Centimeter Scale Resolution Sprayers for Precision Weed Control – Video Link: https://www.youtube.com/watch?v=TFja9FmVjJI
To contact Mark Siemens go to: firstname.lastname@example.org
Area wide Insect Trapping Network VegIPM Update, Vol. 11, No. 21, October 14, 2020
Results of pheromone and sticky trap catches can be viewed here.
Corn earworm: Moth activity is above normal for early October ad has been steadily increasing since mid-September, particularly in Dome Valley and south Yuma Valley.
Beet armyworm: Moths remain active throughout the desert, especially in Texas Hill and Dome Valley growing areas.
Cabbage looper: Cabbage looper activity remains unusually low for early October, likely a result of unusually hot weather. Larvae just starting to show up in some fields.
Whitefly: Adult movement has been about average for this time of year. Activity highest in Wellton and Roll near fall melons.
Thrips: To date, thrips activity has been seasonably low at all trap locations; most activity found in Bard. Numbers beginning to slowly trend upward
Aphids: Aphids have been caught in only one trap thus far (Bard). Normal for this time of year. Still early, anticipate they will begin to show up in heavier numbers in mid-late October.
Leafminers: Adult activity below normal for September, but moderate numbers caught in Wellton and south Gila Valley in areas where cotton was recently harvested and disked under.