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.
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.
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.