Jul 13, 2022Insect Pest Status and Historical Losses in Desert LettuceTo contact John Palumbo go to: jpalumbo@ag.Arizona.edu
In a recent edition of this newsletter on 20 April 2022, I presented a cantaloupe phenological (crop growth and development) model based on heat units accumulated after planting (HUAP, 86/55 Fo thresholds) as shown in Figure 1.
The benefits of working with and using a model like this include being able to describe and predict important stages of crop growth and development (crop phenology) and harvest dates. This can also be a good tool for improving crop management (e.g., fertilization, irrigation, harvest scheduling, pest management activities, labor and machinery management, etc.).
Included in our work with the development of this phenological model, we have also conducted nutrient uptake studies and water use studies to develop a better understanding of nutrient and water demand for desert cantaloupe production (Silvertooth, 2003; Soto et al., 2006; and Soto, 2012).
Figure 2 presents the nitrogen (N) uptake and portioning patterns for desert cantaloupes (melons), Silvertooth, 2003 and Soto et al. 2006. This data describes total N uptake for cantaloupes at ~ 140 lbs. N/acre. From this data, maximum N flux (N uptake/day) period extends from early fruit development to the netting stage.
Water use by desert cantaloupe production was also measured in these studies and patterns of water use followed the crop coefficient (Kc) patterns provided by the Arizona Meteorological Network (AZMET) and conformed to the Kc values from FAO 56 (Allen et al., 1998) and Grattan et al. (1998).
Considering N uptake and water demand patterns in relation to cantaloupe crop phenology, we can insert the overlaps as shown in Figure 1, with the red and blue lines for N and water management, respectively. Maximum N demand occurs from approximately 500 to 1,000 HUAP, which coincides with primary fruit development. Accordingly, the N application window for optimum N uptake is from approximately 300 to 800 HUAP, which is from early flowering to the netting stage of the crown fruit. The N application window is recommended in advance of the optimum N uptake period to provide for N mineralization and the plant-available forms of N for plant uptake and utilization.
Considering the N application window described in Figure 1 and a maximum seasonal uptake and demand of ~ 140 lbs. N/acre, early and split applications during this period of cantaloupe crop development can help achieve optimum utilization of fertilizer N inputs.
The period of maximum water demand extends from early fruiting stages of development through the maturation of the crown fruit, 300 to 1300 HUAP.
Considering the conditions we are experiencing these days in desert crop production with water shortages and extremely high prices of fertilizers, we have an abundance of motivation to manage our crop production systems with the highest efficiency possible. Understanding crop water and nutrient demand for each crop we are working with and using that knowledge to manage our crops most effectively, is to our benefit agronomically, economically, and environmentally.
Nitrogen is the plant nutrient required in largest amounts by most non-leguminous crops and it is important for us to manage that nutrient for a crop in a careful and deliberate manner. Water and N interactions are a critical aspect of crop growth, development, and management in any system, but particularly in an irrigated crop production system. Thus, the focus offered in this article on water and N management for desert cantaloupe production.
I encourage those who are working with spring cantaloupe production this season to test and evaluate this crop phenology model, particularly in relation to nutrient and water management under field conditions with various planting dates, varieties, and soil types. We appreciate your feedback.
Figure 1. Heat Units Accumulated After Planting (HUAP, 86/55 oF)
Figure 2. Cantaloupe (melon) N uptake and partitioning patterns. (Soto, Silvertooth, and Galadima 2006). Note: kg/ha * 0.89 = lbs/acre
Grattan, S.R., W. Bowers, A. Dong, R.L. Snyder, J.J. Carroll, and W. George. 1998. New crop coefficients estimate water use of vegetables, row crops. California Agriculture 52(1):16-21.https://doi.org/10.3733/ca.v052n01p16
Allen, R.G., L.S. Pereira, D. Raes, and M. Smith. 1998. Crop evapotranspiration - Guidelines for computing crop water requirements - FAO Irrigation and drainage paper 56. Food and Agriculture Organization of the United Nations. Rome (FAO). https://www.fao.org/3/x0490e/x0490e0b.htm
Silvertooth, J.C. 2003. Nutrient uptake in irrigated cantaloupes. Annual meeting, ASA-CSSA-SSSA, Denver, CO.
Soto, R. O. 2012. Crop phenology and dry matter accumulation and portioning for irrigated spring cantaloupes in the desert Southwest. Ph.D. Dissertation, Department of Soil, Water and Environmental Science, University of Arizona.
Soto-Ortiz, R., J.C. Silvertooth, and A. Galadima. 2006. Nutrient uptake patterns in irrigated melons (Cucumis melo L.). Annual Meetings, ASA-CSSA-SSSA, Indianpolis, IN.
It is that time of the year! Every year, September starts with “Is it April yet?” If you did not say that, then you cannot sit with us!
This past growing season has been an interesting one. From wearing masks at 120 degree to maintaining social distancing; while producing same amount of produce, feeding same amount of people, and dealing with same amount of disease and pests. A big thank you to everyone involved in agriculture for your hard work and perseverance.
In regards to plant health, we had plenty of disease problems to deal with this year. Below is brief report of the major diseases observed in growing season 2020/2021 and the disease we should be keeping an eye on for next growing season.
We observed a lot of fields with fusarium wilt this year. We had a lot of infected watermelon fields from Winterhaven to Yuma, Wellton, and Mohawk Valley. Rain, and overwatering of fields when plants set fruits might have contributed to the disease development.
Disease management include planting clean seeds/transplants, use of resistant cultivars, crop rotation, soil fumigation, soil solarization, grafting, biological control. An integrated approach utilizing two or more methods is required for successful disease management.
Fusarium wilt of Lettuce
Though detected in a lot of fields and some new fields, the disease pressure in lettuce was relatively low. Please continue with proper management practice for next growing season. Avoid overwatering, add soil amendments/organic matter, practice crop rotation if possible.
Lettuce dieback associated virus
Lettuce dieback is a soil-borne disease caused by two closely related viruses from the family Tombusviridae Tomato Bushy Stunt Virus (TBSV) and Lettuce Necrotic Stunt Virus (LNSV) that has been reclassified as Moroccan Pepper Virus (MPV). The disease has been observed throughout the main lettuce producing areas of California and Arizona.
Sclerotinia rot (known as lettuce drop) is caused by fungi Sclerotinia sclerotiorum and Sclerotinia minor.The initial aboveground symptom is observed as wilting of outermost layer of leaves giving an impression of stress in plants. However, as infection progresses rapidly towards other leaf layers and the entire plant wilts including the head. The entire plant/planting can collapse within the matter of 2 days when the condition is favorable. Management practices include use of subsurface drip irrigation, keeping the top 5-8cm of soil on planting bed is crucial. Deep plowing, crop rotation with non-hosts like small grains and broccoli, removal of infected plant tissue from the field etc. help reduce the inoculum level. Soil fumigation is effective though may not be economical. In Florida growers flood fallow their lettuce field for 4-6 weeks in summer which has almost 100% control of S. sclerotiorum. This is something you might wan to consider doing this summer if you have had high disease pressure in your fields this growing season.
Downy mildew has been a problem for years in lettuce as well as spinach. One of the main reason that hinders the disease management is the complexity of the pathogen. Bremia lactucae (lettuce pathogen) consists of multiple races (pathotypes), and new races continue to occur as pathogen evolves. The pathogen is one of the fastest evolving plant pathogen. And each pathotypes have developed insensitivity to fungicides to different extent. Resistant cultivar, preventative application of fungicides are effective to some extent. Reducing leaf wetness and humidity by using drip or furrow irrigation can be helpful.
Impatiens necrotic spot virus (INSV)
INSV has been detected in a number in fields mostly in Tacna/Roll/Wellton area. It has been found in lower numbers in Gila Valley. If your field has been infected with INSV this growing season, be proactive next season in regards to clearing up the weeds, managing thrip population etc. If you see symptomatic plants please let me or Dr. Palumbo know.
This week in Clinic
If you haven’t submitted your entry for Melon powdery mildew fungicide trial for this spring please send it to Dr. Bindu Poudel-Ward (email@example.com)
Herbicide resistant Palmer amaranth is becoming increasingly problematic in Arizona cotton production. Cultivation is an effective way to control the pest, but standard cultivators do not remove in-row weeds. Finger weeders are an in-row weeding tool made from flexible rubber. Pairs are centered on the seed row and overlapped slightly to remove in-row weeds. In a two-year study, Dotray et al. (2021) evaluated the use of finger weeders for controlling in-row weeds in cotton at the Texas A&M research station in Lubbock, TX. In the study, a cultivator configuration developed by organic cotton grower Carl Pepper, Lubbock, TX was utilized. The device uses 34” wide, shallow pitched sweeps followed by finger weeders mounted on a spring-loaded arm (40” row spacing) (Fig. 1).
In the trials, use of finger weeders was compared to standard tillage, and an XtendFlex system where multiple herbicides were applied throughout the growing season (trifluralin – preplant incorporated; prometryn – preemergence; dicamba, S-metolachlor, glyphosate – early postemergence; dicamba, dimethenamid, and glyphosate second post emergence application). Six cultivations and two spray applications were made each year as dictated by weed pressure. Weed counts were recorded following cultivation and/or herbicide application on the dates indicated in Table 1. Hand weeding operations were performed twice during the season to control weed escapes.
The results were very promising. Control of Palmer amaranth with finger weeders was as good as chemical control using the XtendFlex system and significantly better than standard tillage. The authors also reported 95% in-row weed control when Palmer amaranth was ≤ 3 inches, and about 50% when plants were 3-4 inches tall. Crop injury due to cultivation was minimal, even in seedling cotton (1-3 leaf).
Some observations that are key to making the setup successful are that: 1) sweep blades are oriented such that the end of the sweep is pointed towards the crop row rather than away from it. This facilitates fracturing of soil toward the crop row making it easier for the finger weeders to loosen in-row soil and at a deeper depth, and 2) small diameter (9”) finger weeders made from relatively firm, yet flexible rubber are used and oriented at a steep angle. This configuration promotes soil penetration and loosening in firm soil.
A video of the device canhere or by clicking on the image below.
Dotray, P.A., Keeling, J.W., & Russell, K.R. 2021. Precision cultivation with finger weeder systems. Project No. 20-190 Final Report. Cary, N.C: Cotton Inc.
hanks are extended to Peter Dotray, Wayne Keeling and Kyle Russell, Texas A&M University for sharing their project findings. Credit and thanks are also extended to Kyle R. Russell, Texas A&M University, for recording and sharing images and video.
Project funding provided by Cotton Inc. Their support is greatly appreciated.
Table 1. Palmer amaranth population at various dates throughout the growing season following cultivation and/or spray application in 2020 and 2021.
Fig. 1. Cultivator configuration used in Texas A&M studies investigating the use of finger weeders and wide sweeps to control in-row and between-row weeds in cotton. Cultivator design and setup credit: Carl Pepper, Lubbock, TX.
Fig. 2. Video of finger weeders and wide sweeps operating in seedling cotton to control in-row and between-row Palmer Amaranth. Video credit: Kyle R. Russel, Texas A&M University. Cultivator design and setup credit: Carl Pepper, Lubbock, TX. Click here to see the video.
Last Thursday April 28, 2022 the EPA issued a notice of intent to suspend (NOITS) DCPA, which when effective, will prevent the sale, distribution, and use of the technical-grade product containing the pesticide dimethyl tetrachloroterephthalate (DCPA).
Please see all details of the NOITS by clicking the following link:
Dacthal was first registered in 1958 and we are constantly adjusting it to our changing cultural practices. Recently some evaluations were done of Dacthal’s safety to iceberg lettuce applied Pre and Post-Transplanting. The product showed promising results. It is a mitotic inhibitor and kills germinating weeds by stopping cell division. This mode of action is similar to preemergence herbicides such as Prowl, Kerb, Balan, Trifluralin and others but its chemistry and how it moves in the soil differs. Dacthal is absorbed by both shoots and roots of germinating seedlings although most of the activity is from shoot absorption. When absorbed by the shoots, it will move upward into the plant. It is not absorbed by foliage and can be safely applied over the crop. Dacthal adheres strongly to soil particles. The best time to apply Dacthal is when the soil is moist but not saturated.
We are also including in this update the statement from registrant AMVAC Corporation for more information regarding notice of intent to suspend DCPA: https://www.amvac.com/news/amvac-regulatory-issues-statement-regarding-dachtal-dcpa.