Jul 13, 2022Insect Pest Status and Historical Losses in Desert LettuceTo contact John Palumbo go to: jpalumbo@ag.Arizona.edu
On 14 June 2022, the U.S. Senate Energy and Natural Resources Committee held hearings in Washington, D.C. to review the conditions and impacts of drought in the western U.S., including the Colorado River. The timing of these hearings was important in recognition of the fact that Lake Mead is at its lowest level ever at 28% capacity and Lake Powell is at 27%. If the current level of water use is allowed to persist any longer with the low inputs going into the Colorado River system, there is a possibility of system failure. Thus, there is a very real danger that water supply and delivery as well as hydro-electric power generation capacities could be seriously jeopardized if major changes are not made on the overall management of the Colorado River system immediately.
Bureau of Reclamation (BoR) Commissioner Camille C. Touton described the need to achieve additional reductions on Colorado River allocations. The BoR is engaging in discussions with the seven basin states that depend on the Colorado River to develop a plan for the reductions, and it needs to be done in the next 60 days. As Commission Touton described, the BoR has the authority to “act unilaterally to protect the system, and we will protect the system.” (Bureau of Reclamation, 28 June 2022)
Commissioner Touton stated that the seven basin states on the Colorado River must reduce allocations by 2 to 4 million acre-feet (maf) and that the decision regarding how to do that must be done in 60 days, mid-August 2022. She was not specific on what all that this will entail but Commissioner Touton did say that the BoR is “working with the states and tribes in having this discussion.” Thus, people in the seven basin states are working hard right now to develop proposals for consideration in addressing this immediate need. The U.S. Department of Interior has the authority and could impose cuts if the states fail to reach an agreement on their own. In the case of the Colorado River, by some estimates agriculture is responsible for nearly 80% of all Colorado River water allocations. However, with the fallowing and water transfers from ag to urban systems that have taken place in some of the Colorado River Valleys, agricultural use on the Colorado River is now ~65%. Considering states like California and Arizona are 95% and 90% urban, respectively, many urban sectors consider agricultural allocations to be the most vulnerable to reductions.
In Arizona, the full allocation of Colorado River water is 2.8 maf, which has been reduced in 2022 by the Tier One cuts associated with the Drought Contingency Plan (DCP) by 512,000 acre-feet (kaf). Agriculture is responsible for approximately 70% of total water diversions in the state and the DCP reduction is primarily being taken from the agricultural districts on the Central Arizona Project (CAP) in central Arizona, mainly Pinal County due to previous agreements and lower priority rankings of water allocations.
Based on irrigation, Arizona agriculture produces the highest yields per acre and some of the highest quality crops found anywhere in the world. Arizona also supports a huge seed industry that is important regionally, nationally, and globally. Crop production systems in Arizona support animal production systems including dairy, beef, and poultry. Arizona citizens are direct beneficiaries of these production systems. Over the past 40 years, crop production systems in Arizona and the desert Southwest have continually improved and we are now more efficient and using less water per acre to produce high yields and high-quality crops.
It is important for us to fully describe and demonstrate the good stewardship we provide for soil and water natural resources that we depend upon in the production and management of cropping systems. However, the tendency of facts being facts but perceptions often becoming people’s reality, we must recognize that it can be challenging to communicate to non-agricultural audiences the basic facts about agriculture and water use and the good stewardship being employed. For example, effectively communicating an understanding that agriculture is a process of managing living organisms; animals, and crop plants, in the field under natural environmental conditions is a challenging objective. Some people tend to think that agriculture is a factory level production process, something engineered, or managed by computer algorithms. In reality of course, irrigated agriculture is a highly sophisticated system managed daily by people in the field working with the constant changes and challenges presented to a large extent from the environment as well as markets and a plethora of other external factors.
Errant perceptions of agriculture and the management of crop production systems can be dangerous at times when we are dealing with critical resource management issues, such as water shortages. Thus, it is important for those of us working in production agriculture to communicate and demonstrate how we are serving as good stewards of the natural resources with which we work. It is good for those of us working in agricultural production systems to review the basics of how we manage water in the production of crops and the good stewardship that is employed in daily operations. Farmers and agronomists have no interest or motivation to put any more inputs into the production of a crop than is necessary.
Farmers and agronomists are constantly striving for higher efficiencies agronomically, economically, and environmentally to conserve precious natural resources. As we have often heard “A measure of what we value is the level of energy or time we invest in taking care of it.” Arizona agriculture has invested a lot of time, energy, and money into the improvement of crop production efficiencies, and we continue to work on these improvements.
We have a good story to tell on the stewardship record of Arizona agriculture and our continued commitment to making improvements in production efficiencies. There are representatives working hard on behalf of Arizona and desert Southwest agriculture to present the case for supporting our agricultural systems and help develop plans for mitigation and response. However, given the chance to do so, we all need to be prepared to communicate the message agriculture’s good water stewardship to appropriate audiences. We all need to prepare for the changes that are coming.
Bureau of Reclamation, 28 June 2022 https://www.usbr.gov/ColoradoRiverBasin/
Botrytis rot is not considered a major problem in lettuce but it can cause significant damage/loss when the field conditions are favorable for the pathogen. Cool wet conditions are favorable for the pathogen. Symptoms include water-soaked, brownish-gray to brownish-orange, soft wet rot that occurs on the oldest leaves in contact with the soil. Old leaves are more susceptible than young leaves and the fungus can move into the healthy parts. Fuzzy gray growth can be observed in the disease area which is characteristic of the pathogen. In worse cases, the entire plant can collapse. Romaine cultivars, transplanted lettuce that are big and have leaves touching the soil are more susceptible.
The pathogen: Botrytis cinerea
Botrytis cinerea affects most vegetable and fruit crops, as well as a large number of shrubs, trees, flowers, and weeds. Outdoors Botrytis overwinters in the soil as mycelium on plant debris, and as black, hard, flat or irregular sclerotia in the soil and plant debris, or mixed with seed. The fungus is spread by anything that moves soil or plant debris, or transports sclerotia. The fungus requires free moisture (wet surfaces) for germination, and cool 60 to 77 F, damp weather with little wind for optimal infection, growth, sporulation, and spore release. Botrytis is also active at low temperatures, and can cause problems on vegetables stored for weeks or months at temperatures ranging from 32 to 50. Infection rarely occurs at temperatures above 77 F. Once infection occurs, the fungus grows over a range of 32 to 96 F.
Masses of microscopic conidia (asexual spores) are produced on the surface of colonized tissues in tiny grape-like clusters (see picture). They are carried by humid air currents, splashing water, tools, and clothing, to healthy plants where they initiate new infections. Conidia usually do not penetrate living tissue directly, but rather infect through wounds, or by first colonizing dead tissues (old flower petals, dying foliage, etc.) then growing into the living parts of the plant.
1. Buy high-quality seed of recommended varieties. Treat the seed before planting.
2. Practice clean cultivation. Plant in a light, well-drained, well-prepared, fertile seedbed at the time recommended for your area. If feasible, sterilize the seedbed soil before planting, preferably with heat. Steam all soil used for plantbeds at 180 F (81 C) for 30 minutes or 160 F (71 C) for one hour.
3. Avoid heavy soils, heavy seeding, overcrowding, poor air circulation, planting too deep, over-fertilizing (especially with nitrogen), and wet mulches.
4. Focus on healthy plant vigor. Do not over fertilize.
5. Use drop or furrow irrigation instead of sprinklers. If sprinklers have to be used, irrigate morning or early afternoon giving enough time for foliage to dry.
6. Apply recommended fungicides when conditions favor disease development. Make sure to rotate fungicide to avoid development of resistance.
As mentioned in a previous article, last month at the UC Cooperative Extension Automated Technology Field Day in Salinas, CA, several automated technologies were showcased operating in the field for the first time to a general audience. One of the “new” machines designed specifically for in-row weeding in vegetable crops was discussed previously, a second is highlighted here.
Vision Robotics1 (https://www.visionrobotics.com/) demoed an innovative mechanical in-row weeding machine (Fig. 1). As with most other automated weeding machines currently on the market, in-row weeds are controlled with knife blades that cycle in and out of the crop row. Each knife blade however is controlled independently by an electric motor rather than in coupled pairs. Another feature is that the imaging system calculates a prescribed path for the blades to follow based on a contour of the crop plant and a user defined offset distance from the contour (Fig. 2) Because electric motors are used, blade position can be continuously and precisely controlled, thus facilitating close cultivation.
In the demo, the prototype seemed to work pretty well, but the run was short, and it was difficult to fully evaluate its performance. The video they shared of their imaging system with path planning and blade movement operating in real time impressed and showed good promise (Fig. 2). The innovation was recently patented, and the company is planning commercial units for interested customers.
Developments such as these are worth investigating as our and other researchers’ studies have shown that automated in-row weeding machines control about 50-66% of the in-row weeds, and the majority of uncontrolled weeds were observed to be close to the crop plant (Lati et al., 2016; Mosqueda et al., 2021).
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.
Mosqueda, E., Smith, R. & Fennimore, S. 2021. 2020 Evaluations of automated weeders in lettuce production. ANR Blogs. Davis, Calif.: University of California Davis. Available at: https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=45566.
A special thank you to Tony Koselka, Vision Robotics Inc., for uploading the videos referenced in this article.
 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. Prototype in-row weeding machine developed by Vision Robotics1 demonstration at UCCE Automated Technologies Field Day. Clear here or on the image to view the machine in action.
Fig. 2. Plant contour and cultivating blade path planning of prototype in-row weeding machine developed by Vision Robotics1. A contour of the crop plant is traced (left) and a prescribed path a user defined distance from this contour (right) is determined for the blade tips to follow. Clear here or on the image to view the system in action.
What is the “seed bank”? It’s the reserve of viable seeds present in your soil surface or mixed with your soil at different depths. There are also other vegetative propagules that can contribute to increase your weed infestations such as tubers, solons etc.
How can we reduce our seedbank? When we fallow the fields during the summer preemergence herbicides can be applied with good results because weeds geminate after irrigations or rain.
The chart here shows that summer weeds germinate starting February-March and peak germination is in June and in some cases, they continue germinating until October.
Preemergence herbicides are often used for fallow weed control only when at least 30 -45 days or longer are available1. We must take into consideration most preemergence herbicides last about 3 months depending on soil conditions. Others like Eptam may last only like 3-4 weeks because of volatility2.
Also contact herbicides like Paraquat (Gramoxone, Firestorm), Carfentrazone (Aim, Shark), Pyraflufen (ET), Pelargonic Acid (Scythe) and others are used. These products act quick and leave little or no residual but must be applied when weeds are not too large. The systemic used most frequently is still Glyphosate. It has no residual and is broad spectrum herbicide. Another product registered for fallow use is Oxifluorfen (Goal, Galigan).
Another method used for lowering the seed bank in the summer is “Solarization”. Transparent polyethylene is effective for heating the soil. It is sufficient 4-6 weeks for satisfactory control of most weeds. Some weeds are very sensitive to solar heating of the soil. Sweet clover because of hard seeds and Nutsedge because of the tubers are hard to kill with solarization. Also, Bermuda because of the rhizomes is not easy to control.
Another method is water to germinate and kill weeds mechanically or with herbicides. Some weeds like Common purslane have succulent stems and can survive after cultivation. They could re-root from the nodes and produce seeds. Therefore, carefully monitor plants to uproot them small. Tillage has a negative effect on perennials such as nutsedge and Bermuda. By repeat irrigating and disking we really are spreading them instead of killing them.
WEED DYNAMICS AS INFLUENCED BY SOIL SOLARIZATION - A REVIEW R.H. Patel, Jagruti Shroff, Soumyadeep Dutta and T.G. Meisheri, Anand Agricultural University, S A College of Agriculture, Anand - 388 110, India