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.
We talked a bit about INSV in last newsletter and the importance of the virus in produce industry.
Impatiens necrotic spot virus, also known as INSV is a tospovirus closely related to Tomato spotted wilt virus. Infected plants usually have leaves with brown to dark brown necrotic areas. Sometimes the symptoms may be confused with “chemical burn”. As necrosis progresses the leaf browns or die out. Plants infected in early stage may become stunted and die or become unmarketable.
As visual diagnosis of the virus is confusing and could even be misleading at times, it is very important to confirm a symptomatology via clinical diagnosis.
The good news is there are tools available for quick and easy diagnosis of INSV. You can order the immunostrips from Agdia (https://orders.agdia.com/agdia-immunostrip-for-insv-isk-20501)
The immunostrips cost anywhere from $5-20 depending on how much you buy. They perform better when they stay refrigerated until just before use.
Immunostrips are quick and easy tool to use. The kit comes with a buffer bag and immunostrip.
3. Let it sit for a minute and Insert the inmmunostrip on the side of the mesh bag in the tissue blended solution. You will see the plant sap going up in the immunostrip.
4. Results: 2 bands means positive and one band means negative!
One band means that the positive control worked which means the system worked. Sometimes you see no bands at all. This means the system did not work and you have to repeat the test.
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.
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://22.214.171.124:460
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.
Beet armyworm: Moth counts remain very low consistent with seasonal temperatures, but below average for this point in the season.
Cabbage looper: Slight increase in activity, but moth counts remain unusually low for late January.
Whitefly: Dult movement is at seasonal low consistent with temperatures and lack of melons or cotton.
Thrips: Activity remains lower than normal for this point late January. Increased movement noted in Roll/Tacna.
Aphids: Seasonal aphid counts peaked during the past 2 weeks, suggesting movement with recent winter storms and lack of desert vegetation. Counts were particularly high in North Yuma and Gila Valleys, and Bard. Above average for this time of year.
Leafminers: Adult activity remains light in most trap locations. Trap counts increasing slightly in the South Gila Valley.