Jul 13, 2022Insect Pest Status and Historical Losses in Desert LettuceTo contact John Palumbo go to: jpalumbo@ag.Arizona.edu
John Wesley Powell, the Civil War veteran who lost most of his right arm at the Battle of Shiloh, led his first expedition down the Green and Colorado Rivers, including the Grand Canyon in 1869. This provided the first exploration of the Colorado River basin by Americans of European descent and it began the process of understanding the nature of western territories of the United States, including Arizona (Figure 1).
The degree of aridity of this region was very strongly impressed upon Powell and he spent much of his life working to educate law and policy makers of the conditions prevalent in the western U.S. He worked diligently with lawmakers, government experts, and citizens to communicate the fact that the development of the western territories, which the nation was rapidly embarking on after the Civil War, would be limited due to the lack of water. His comments to the Montana Constitutional Convention in 1889 “All the great values of this territory have ultimately to be measured to you in acre feet” is a good example of his basic message and it has proven to be quite prophetic in our experiences of living and working in the desert Southwest in the 20th and 21st centuries.
Powell became the second director of the U.S. Geological Survey (USGS) from 1881 to 1894. In this and similar capacities, he constantly advocated for policies for the development of the arid West that were consistent with the prevailing arid conditions. As the lands in the western U.S. were being developed, the need for land “reclamation” was recognized. It was 120 years ago this week, on 17 June 1902 that Theodore Roosevelt signed the Reclamation Act and the U.S. Reclamation Service (USRS) was formed within the USGS under the Secretary of the Interior Ethan Allen Hitchcock. The new USRS was given the responsibility of studying potential water development projects in each western state with federal lands. Revenue from the sale of federal lands was the initial source of the USRS funding.
Thus began the process of the USRS in the development of about 30 western water projects between 1902 to 1907. In 1907, the Secretary of the Interior separated the USRS from the USGS and created the Bureau of Reclamation (BoR) as a distinct entity within the Department of the Interior. The Boulder Canyon (Hoover Dam) project was authorized in Congress in 1928 and funded by general funds appropriated by Congress to the BoR, and from that the development of Lake Mead began. Lake Mead is the main storage reservoir for the lower basin of the Colorado River.
In the late 19th and early 20th centuries, efforts in the western U.S. to develop lands for agriculture encountered problems with lands and soils that were found to be unsuitable for irrigation, often due to salinity, sodicity, and drainage problems. The “reclamation” of these lands became an important part of the BoR objectives and operations. All this development was dependent on the availability of water and good land and water management capacities.
During the 20th century, the BoR was responsible for some tremendously large and ambitious projects, including Boulder Dam, Grand Coulee Dam, Glen Canyon Dam, and many others. Today, the BoR operates in 17 western states with water and electrical power projects with more than 600 dams, reservoirs, powerplants, and canals. The BoR is the largest wholesaler of water in the U.S. and supports irrigation water storage and conveyance throughout the west on farmlands that produce more than 60% of the nation’s vegetables and 25% of the fruit and nut production in the country. The BoR is the second largest producer of hydroelectric power in the U.S. with 53 powerplants. The western U.S. development and population is heavily dependent on the BoR water and power works.
In Arizona and the desert Southwest, the lands and people here today have a very close relationship to the BoR for water and electrical power. All the lands along the mainstem of the Colorado River and the Central Arizona Project (CAP) are intimately connected to the BoR. Our efforts to deal with the water shortages on the entire Colorado River system are some of the greatest challenges this region and the BoR have faced since the early days of development in the 19th century.
Thus, there are many participants in the process of dealing with the current water shortage on the Colorado River system, including the U.S. Department of the Interior, the BoR, and all the basin states. An accentuating feature of the current water shortage on the Colorado River is due to the fact that for the past 22 years, the average annual flow in the Colorado River has been ~ 12.4 million acre-feet (maf) while the Colorado River water is budgeted for a total of 16.5 maf of allocations between U.S. states and Mexico.
Essentially, all of us living in the desert Southwest are in this together; including agricultural, urban, and tribal entities. All parties involved must work together to resolve this disparity between the water that the river is providing and the greater amount that is desired and allocated. The issues and general situation that we are facing has an urgency that requires immediate attention. I remain hopeful that we can meet the challenges of our time as our predecessors did in the past.
DISEASE: Center Rot of Onion
PATHOGEN: Pantoea ananatis, Pantoea agglomerans, Pantoea alli and Pantoea stewartii subsp. indologenes
HOSTS: Onion (Allium cepa L.), garlic (Allium sativum L.), shallots (Allium cepa var. aggregatum L.), leeks (Allium ampeloprasum L.), chives (Allium schoenoprasum L.).
Symptoms and signs
Center rot of onion has not been a major problem in the desert southwest but when the environment is favorable, the disease can cause up to 90% loss. Foliar symptoms (symptoms on leaves) may start with water-soaked lesions spanning the length of the leaf blade, which gradually become blighted resulting in desiccation and collapse of the tissue. Experiments have shown that the bacteria can move from leaves to the bulbs, thus protecting foliage is important to manage the disease.
The bacteria can overseason to infect onions in a number of different ways. Like many bacterial pathogens, P. ananatis can be seed-borne with infested seed serving as a survival mechanism as well as a means of dissemination. It has been demonstrated that P. ananatis can be both naturally seed-borne and seed-transmitted in onion. The significance of the bacterium's ability to colonize seed is uncertain, as most onion seed production sites are located in arid climates but extremely important to understand to manage the disease.
Although P. ananatis can be seedborne, the proposed primary mode of transmission is by two insect vectors. Two species of thrips, tobacco thrips (Frankliniella fusca (Hinds)) and onion thrips (Thrips tabaci), have the ability to transiently acquire and transmit P. ananatis and P. agglomerans . The bacterium can persist in a non-circulative manner in the gut of thrips for 128 h, allowing the vector to infect plants over an extended period of time.
P. ananatis can survive epiphytically and endophytically on a wide range of hosts. These alternative hosts can serve as a source of inoculum in fields where susceptible crops are grown. In Georgia alone, 25 weed species, including carpetweed (Mollugo verticillata), common ragweed (Ambrosia artemisiifolia), crabgrass (Digitaria sanguinalis), common cocklebur (Xanthium pensylvanicum), curly dock (Rumex crispus), Florida pusley (Richardia scabra), sicklepod (Cassia obtusifolia), stinkweed (Thlaspi arvense), Texas panicum (Panicum texanum), vaseygrass (Paspalum urvillei), wild radish (Brassica spp.), yellow nutsedge (Cyperus esculentus) and other multiple crop plants were found to harbor P. ananatis populations asymptomatically.
Pic Credit: Colton Tew
Onion cultivars resistant to Pantoea sp. are not commercially available. Use of certified onion seeds is encouraged to avoid introduction of Pantoea sp. inoculum in the production field. Planting early maturing or mid-maturing onion varieties are often recommended for growers. Late maturing varieties provide a larger window for infection and a potential epidemic to occur, which are favored by thrips pressure, hot and humid conditions, and lack of effective bactericides. Overhead irrigation should be avoided as it promotes bacterial spread compared with sub-surface or drip-irrigation. Controlling thrips population can be an effective management strategy to reduce center rot incidence as these vectors play an important role in bacterial transmission.
Center rot management in onion fields relies heavily on copper applications mixed with an ethylenebisdithiocarbamate fungicide (EBDC), such as mancozeb, which growers may apply weekly as a protectant. In addition, researchers found P. ananatis strains to be copper-tolerant indicating overuse and potential risk of insensitivity to this chemistry. Repeated applications of copper sprays during susceptible growth stages can be effective only to a limited extent and does not offer a robust solution to the problem. Perhaps the inefficacy of these sprays could be due to thrips preference to colonize certain parts of the onion plant, e.g. the basal meristems (neck region).
The implementation of successful weed management strategies are important in reducing P. ananatis inoculum in the field. By reducing weeds, growers can potentially reduce initial inoculum.
Based on last week’s weather, it’s officially summer in my book. Things seem to be slowing down, so I thought I’d change pace this week and take the opportunity to ask you, the readers of this newsletter, if there are any ag automation/mechanization topics you would be interested in hearing more about. I am happy to do some research and share the findings in future articles. Drop me a line at firstname.lastname@example.org or feel free to call me at 928.782.5869. I’d love to hear from you.
Fig. 1. Futuristic farming. (Image credits: Emery Reddy, Seattle, WA.)
Overreliance in glyphosate could increase the risk of reduced efficacy of this herbicide. Some the weeds difficult to control with glyphosate in our area are: Hairy fleabane (Coniza bonariensis), Horseweed (Coniza canadiensis), White sweet clover (Melilotus albus). Pig weed (Amaranthus palmeri), and Cheeseweed (Malva parviflora). We are conducting experiments in the Yuma area to identify effective herbicide control options for Hairy fleabane. Some research done in Australia has shown that Fleabane cannot be controlled with a single herbicide treatment even with knockdown herbicides such as paraquat + diquat, and researchers suggest the need of combinations of different modes of action to achieve control effectively1. In one fleabane evaluation started May 6, 2022, we included the following treatments: 1. Embed Extra 2pt/A+5%NIS 2. Rely 82 floz+5%NIS 3. Chateau+ Treevix+MSO (12oz+1oz/A+1%)
We noticed treatments including Glufosinate (Rely) showed best burndown activity, but regrowth was observed in two weeks (13-14 plants per ft2). So, a second application was performed on three weeks after first on the Rely plots.
The grower and PCA informs us that Sulfenacil (Sharpen) has worked effectively for them with sequential applications. Additionally, we are evaluating Suppress and Clopyralid in the same location.
You are always welcomed to send your comments, suggestions to the IPM Team. Let us know what you are doing and your findings. We know there is a researcher in every grower and PCA and your input is greatly appreciated.