Jan 24, 2024Avoid Seed Corn Maggots in Spring Melons (2024)To contact John Palumbo go to: jpalumbo@ag.Arizona.edu
I recognize alfalfa is not a vegetable crop per se, but I also recognize that alfalfa has become an emblematic crop for desert agriculture, particularly in the water resource arena. In recent weeks alfalfa production in Arizona has come under intense scrutiny and criticism by state leaders. The Arizona Attorney General has been quoted as stating that alfalfa production in Arizona is “stupid” and leases of state land being used for alfalfa production are being considered for cancelation (Fischer, 4 October 2023). This is a point of concern for Arizona agriculture and the possible regulatory implications regarding what crops should be irrigated and grown. Alfalfa is an important crop, and it is grown in Arizona for good reasons, some of which are described in this article.
Merits of Alfalfa Production in the Desert Southwest
Alfalfa is a major crop in Arizona, the desert Southwest, and most parts of the United States. Alfalfa has been planted to the largest acreage of any crop in Arizona for several years with about 260,000 acres being grown in 2023 (USDA, 2023 and Table 1).
Alfalfa is an extremely important crop due to its rich nutritional value as feed for animals, particularly cattle, horses, and sheep. In Arizona and the desert Southwest alfalfa has high value as nutritious feed for dairy and beef cattle. Most fresh dairy products are sold within about 300 miles of their point of origin.
Arizona’s population of 7.3 million people has a high demand for fresh dairy products. Arizona has 90% of the population living in urban areas. Over 6 million people in Arizona reside in Maricopa, Pinal, and Pima counties in the central and southern part of the state (82% of Arizona’s population). It is not surprising that there is a high concentration of dairies in central Arizona and alfalfa is grown near the dairies to provide a local source of high-quality forage.
Alfalfa is often demonized as a very poor crop choice in Arizona and the desert, usually by people outside of agriculture who are probably well-intentioned but not well-informed. These attitudes and opinions serve to remind us of Dwight D. Eisenhower’s statement at Bradley University in September 1956 when he said, “You know, farming looks mighty easy when your plow is a pencil, and you’re a thousand miles from the corn field.”
People who criticize and complain about alfalfa production in Arizona should consider their needs for fresh dairy products. If they are drinking milk, eating ice cream, yogurt, and butter they are consuming alfalfa as secondary consumers after the dairy cattle have rendered fresh milk from a healthy diet including alfalfa. Thus, Arizonans are the direct beneficiaries of local alfalfa production.
In the case of alfalfa, it is in fact an excellent crop for Arizona and the desert Southwest and a favorite among agronomists (crop and soil scientists), farmers, and farm managers (Putnam, 2015; Mostafa, 2015; and Yost, 2020). Alfalfa is an important crop in the desert Southwest and it provides important contributions to crop production system efficiency agronomically, economically, and environmentally. Several good reasons for growing alfalfa in the desert are summarized in the following points:
Figure 1. Alfalfa rooting depth compared to several other common
crops. Source: Backyard Gardening Blog
Alfalfa production supports other food products, primarily dairy and meat. Reductions in alfalfa acres will in turn require a greater reliance on food from non-local sources, including those imported from abroad. This will likely increase food prices and extend the supply chain.
This point was illustrated in the following written testimony provided by the Family Farm Alliance to the U.S. House of Representatives Subcommittee on Water, Wildlife and Fisheries in March 2023 (U.S. House of Representatives Natural Resources Committee, 2023):
"The Western U.S. is a critical part of what has long been a proud national agricultural powerhouse, where our country consistently has run an agricultural trade surplus. But in 2019, for the first time in more than 50 years, the U.S. agriculture system ran an agricultural trade deficit, importing more than it exported. The USDA forecasts the U.S. will again run a deficit in 2023 for the third time since 2019. This growing deficit is driven primarily by our dependence on imported Mexican fruits and vegetables (Politico Pro DataPoint). Increased reliance on foreign food has never been, and should never be a policy our Nation has intentionally embraced."
Agri-Environmental Scheme of Agriculture
It is interesting to note that alfalfa is recognized as an important crop in what is often referred to as “sustainable agriculture” or “regenerative agriculture” that emphasizes the use of natural systems for enhancing soil health and plant community ecology.
Alfalfa has been a popular a crop rotation component in Europe, and encouraged globally, as an element of the Agri-Environmental Scheme (AES), which is intended to reduce the impacts of “commercial” agriculture intensification on the environment (Gonzalez del Portillo, et al. 2022).
The Agri-Environmental Scheme (AES) offers the following attributes of alfalfa which are consistent with our basic agronomic understanding for many decades:
• Alfalfa also may help reduce the impacts of climate change due to canopy cover of the soil for a longer period than any other crop, alfalfa is envisioned as a leading option for soil carbon sequestration, also known as “regenerative agriculture,” especially with the need to decrease carbon emissions and introduce the carbon credits initiative.
• Alfalfa is a rich habitat for wildlife allowing for a diversity of local niches and preserving many endangered species from different animal families.
• Alfalfa fields are important contributors to the biodiversity of agricultural systems by functioning as insectaries for beneficial insects, many of which are pollinators or natural enemies that play important roles in the low desert agroecosystem.
• Beneficial insects move from alfalfa fields into other crops, where they play crucial roles in pollination and biological control.
• These roles reduce the reliance on synthetic insecticides, which if used incorrectly could have negative impacts on human, animal, and environmental health.
• Western alfalfa production, due primarily to irrigation and the vigorous plants that grown, provides a rich habitat for insects, which enhances the crop ecology.
• The year-round insectary characteristic allows alfalfa to play an important role in insecticide resistance management by serving as a refuge, i.e., aphids and whiteflies.
Arizona Crop Acreages 2022
Seasonal Water Use (inches)
Total Acres (2022)
*Seasonal water use estimates from Erie, et al. 1981 unless otherwise noted.
**Norton and Silvertooth, 2001
Del Portillo, D.G, B. Arroyo & M.B. Morales (2022) The adequacy of alfalfa crops as an agri-environmental scheme: A review of agronomic benefits and effects on biodiversity. Journal for Nature Conservation 69(2):126253.
Erie, L.J., O.A French, D.A. Bucks, and K. Harris. 1981. Consumptive Use of Water by Major Crops in the Southwestern United States. United States Department of Agriculture, Conservation Research Report No. 29.
Fischer, H. 4 October 2023. Arizona cancels a lease for farm that exports alfalfa to Middle East. Tucson Daily Star.
Norton, E.R. and J.C. Silvertooth. 2001. Evaluation of a drip vs. furrow irrigated cotton production system. Cotton, A College of Agriculture Report Series P-125, University of Arizona, Tucson, AZ. p. 126-132.
Mostafa, A.M. 2015. The Benefits of Alfalfa to the Southwest Ecosystem. Arizona Agriculture.
Putnam, D. 2015. Why alfalfa is the best crop to have in a drought. University of California- Davis. Alfalfa and Forage News.
U.S. House of Representatives Committee on Natural Resources; The Water, Wildlife and Fisheries Subcommittee. Farm Family Alliance written testimony, March 2023.
USDA. 2022. State Agriculture – Arizona.
USDA. 2023. News Release: NASS, 30 June 2023 Arizona crop report.
USDA. 2023. October 2023 Pacific Region crop production report.
Yost, M., N. Allen, E. Creech, D. Putnam, J. Gale & G. Shewmaker. 2020. Ten Reasons Why Alfalfa is Highly Suitable for the West. Utah State University Extension.
Bacterial leaf spot is caused by the bacterium, Pseudomonas syringae pv. Aptata. Hosts of the pathogen include Table beet, Sugar beet, Spinach, Swiss chard, Snap bean, Dry bean, Cantaloupe, Pumpkin, Squash, Lettuce, and Pepper.
Bacterial leaf spot is most commonly found affecting table beet at early stages of growth. This may be because younger plants are more susceptible. It may also be related to the prevalence of cool, wet conditions at the beginning of the cropping season. These conditions are most conducive to infection and disease development. The disease may affect green leaf area in developing seedlings and in severe cases can lead to plant death. Diseased leaves will lead to weakened seedlings which may affect transplant success. Bacterial leaf spot does not directly affect root quality.
Figure 1. Bacterial leaf spot caused by Pseudomonas syringae pv. aptata of
table beet: (left) Small focus of the disease, and (right) 2-6 true leaf stage of
plants affected by the epidemic.
Bacterial leaf spot symptoms are irregular in shape and black to brown in color. The spots may occur across the leaf surface but have a tendency to occur on the leaf edges. Lesions are water-soaked not often accompanied by chlorosis (yellowing). Lesions may initially be small (up to ¼ inch in diameter) but if conditions are conducive may rapidly expand and coalesce but do not cross major veins. The leaf is usually puckered and deformed around the lesions, especially if they occur on the margins (Fig. 2). When the disease is severe, the affected the tissue may also tear giving the appearance of abiotic damage such as hail.
Figure 2. Symptoms of bacterial leaf spot on table beet (cv. Merlin). Note the
black color of the lesions and puckering and deformation of the leaves around
Bacterial leaf spot symptoms may be confused with other fungal foliar diseases (e.g. Cercospora and Phoma leaf spots; see complementary fact sheets for these diseases) and insect damage (e.g. thrips). Bacterial leaf spot lesions do not have black pin-head, fungal structures across the lesions as found in Cercospora leaf spot. Phoma leaf spot lesions also have small, black structures within the lesions but found in rings and usually accompanied by an ooze of spores.
Figure 3. Schematic diagram of the potential sources of Pseudomonas syringae pv. aptata inoculum which may contribute to Bacterial leaf spot epidemics in table beet.
P. syringae pv. aptata may be introduced to the table beet crop through several ways (Fig. 3). P. syringae pv. aptata is seedborne and infested seed is a common means of pathogen introduction into table beet fields. The pathogen can also be present in the infested crop residues from the previous season as well as the alternative hosts. Alternative crop hosts include typical Chenopods (e.g. spinach, sugar beet, and Swiss chard) but also other non-related species including beans, cucurbits, and lettuce. Cool temperatures between 45-60°F and wet conditions typical of those that occur in early spring in upstate New York are conducive for pathogen infection and disease development. These conditions are similar to those that predispose table beet also to Phoma leaf spot. The pathogen can spread within the field through infested seed and irrigation water.
One of the most critical factors to achieve management of bacterial leaf spot is the use of certified seeds (Fig. 4). Other factors that will also contribute to reducing the initial inoculum and hence risk of disease include: (i) tillage to bury plant residues to promote breakdown, (ii) rotation between host crop species of at least three years; and (iii) drip or furrow irrigation to avoid dispersal of the pathogen through water splash. Currently, little is known of differences in cultivar susceptibility to bacterial leaf spot. Anectodal reports have described severe epidemics in cvs. Merlin, Boro, and Pablo.
Figure 4. Complementary practices towards the management of Bacterial leaf spot of table beet.
In-season control. If bacterial leaf spot is severe, applications of copper-based products should be considered to prevent disease spread. There are a range of conventional and OMRI-listed copper-based products available, including: Cueva (copper octanoate; FRAC M1), Badge X2 (copper oxychloride + copper hydroxide; FRAC M1), and Kocide 3000-O (copper hydroxide; FRAC M1). Remember to check the label for rates, re-entry intervals, and pre-harvest intervals applicable to your state and crop. Avoid applying copper-based products on transplants before hardening off, and in high temperatures due to the risk of phytotoxicity.
Presentation given at 2021 ASABE Annual International Meeting on the development and evaluation of a novel, band steam applicator for controlling soilborne pathogens and weeds in lettuce. Band-steam is where steam is used to heat narrow strips of soil to levels sufficient to kill soilborne pathogens and weeds (140 °F for 20 minutes). Development of a band-steam applicator that applies steam in 4" wide by 2" deep band centered on the seedline is presented. Two trials investigating the use of band-steam for controlling Sclerotinia lettuce drop and weeds in lettuce were conducted. Trial results were promising. Highlights included finding that treatment with steam provided better than 85% weed control, and the unexpected result that crop yields were improved by more than 24%. Energy requirements were high and treatment costs were more than $650/acre. Band-steam may be a viable technique for controlling soilborne pests in high value vegetable crops such as lettuce if the significant yield increases found in this study can be realized.
To watch presentation click: A Novel Band-Steam Applicator
During this time of the year, we visit fields and constantly receive plant samples with symptoms of what could be herbicide, disease, or insect injury. Our Plant Pathologist Dr. Bindu Poudel-Ward analyzes them for pathogens, Dr. John Palumbo checks for insect damage, and we also examine for possible herbicide injury.
As we all know IPM involves an interdisciplinary effort to identify and prevent problems we encounter in our industry.
Kerb, Balan, and Prefar are the major herbicides we have used in lettuce production in Arizona for the last 50 years. These herbicides work by inhibiting root growth in small weeds and under some specific conditions can injure lettuce.
Symptoms of injury could include stunting, leaf margin chlorosis, malformation of the cotyledons and first true leaves, inhibition of main root and lateral roots. Diagnostics sometimes can be challenging because some of the symptoms can also be produced by other factors such as the soil salinity, water management problems, environmental stress or cold, diseases, possible drift from chemical thinning operations and other factors.
It is common that growers send soil or tissue samples to laboratories to compare herbicide concentrations from a healthy section of the field with the affected injured area. If the concentration of the compound in question is significantly different between “healthy” and “bad” samples this could be an indication of herbicide injury. Most laboratories use gas chromatographs (GC) and liquid chromatographs (HPLC) for analysis. Standard extraction and detection methods are costly but accurate and precise3.
The following links will take you to publications that (1) could help you identify some of the symptoms of common lettuce herbicide injury and (2) interpret results reported by laboratories.