Jul 13, 2022Insect Pest Status and Historical Losses in Desert LettuceTo contact John Palumbo go to: jpalumbo@ag.Arizona.edu
Cantaloupes (Cucumis melo L.) or “melons” are one of the important spring and fall vegetable crops of Arizona and the desert Southwest. Technically, “true” cantaloupes are rough, warty fruit, primarily grown in Europe. On a production scale, cantaloupes are not grown commercially in the United States. However, in the United States “cantaloupe” has become a general name of all netted, musk-scented melons (Simmone et al., 1998 and Soto, 2012).
Cantaloupes in the U.S. are divided into eastern and western types. The eastern type is characterized by round-shaped fruits, usually about five to seven pounds, sutured (sutures are the green lines that divide the rind into several sections), with variable levels of netting (netting is the network of cork-like marks that cover the rind), and large seed cavities. The western type is characterized by oval-shaped fruits of three to four pounds, sutureless, and a coarsely netted rind (Simmone et al., 1998 and Soto, 2012).
According to the United States Department of Agriculture (USDA) National Agricultural Statistical Services (NASS), the harvested Arizona cantaloupe acreage from 1992 to 2021 has ranged from 13,200 to 23,300 acres with an estimated production value ranging from $38 million to $82.5M. There were 19,300 acres of Arizona cantaloupes in 2021 (USDA, 2021). Most of the Arizona cantaloupe production takes place in Yuma, Maricopa, and Pinal Counties. Among the nine states with recorded cantaloupe production, Arizona commonly ranks second to California in acres and total production. (USDA, 2021 and Murphree, 2015).
Being able to accurately describe and predict important stages of crop growth and development (crop phenology) and harvest dates is important for improving crop management (e.g. fertilization, irrigation, harvest scheduling, pest management activities, labor and machinery management, etc.). Since plants operate on “thermal time”, they have no regard for calendars or time as we commonly measure it. So, we find it is best to monitor and predict plant development based on the actual thermal conditions in the plant’s environment. Various forms of temperature measurements and units commonly referred to as heat units (HU), growing degree units (GDU), or growing degree days (GDD) have been utilized in numerous studies to predict phenological events for many crop plants (Baker and Reddy, 2001 and Soto, 2012).
Boswell (1929) first documented the concept of heat summations relative to vegetable crop production in 1929. Thereafter, HU accumulation techniques have been successfully applied to numerous vegetable production systems like cantaloupe (Baker et al., 2001).
The use of HU accumulations has been shown to be an efficient technique for modeling and predicting growth stages in crops (such as cantaloupes) as compared with the traditional days after planting (DAP) method, since variations among seasons and locations can be better normalized using heat units accumulated after planting (HUAP) calculations rather than DAP.
For more than 35 years we have had the benefit of excellent weather data collection in Arizona from the Arizona Meteorological Network (AZMET), which was first developed and directed by Dr. Paul Brown. For warm season crops, such as cantaloupes, we have been working HUs with both upper and lower temperature thresholds (86/55 oF), as first described by Baskerville and Emin (1969) and shown in Figure 1 (Brown, 1989). We have successfully developed crop phenology models using HUs with 86/55 oF thresholds for other common warm season crops in the desert Southwest, such as cotton (Silvertooth, 2001) and New Mexico type chiles (Silvertooth et al., 2010).
Baker et al., (2001) developed a muskmelon phenology model that could be run with easily obtainable weather station data and used by growers to quantify phenological development and aid in projecting harvest dates. The average model accuracy in predicting harvest dates ranged between 1 to 3 days for the data set used to construct the model. Also, after the evaluation of the performance of two GDD models to predict commercial harvest dates in 30 commercial melon fields in California, Hartz (2001) found that the two models were useful in predicting the date of harvest initiation. The standard deviation for the prediction of harvest date from emergence date represented between 2-3 days of normal growing-degree-day accumulation.
Beginning in 2000, we began working in Arizona to develop and test a phenology model for desert cantaloupe production. Following data collection from many spring cantaloupe fields, primarily in the Yuma area, we were able to develop and test the basic cantaloupe phenology model shown in Figure 2 (Silvertooth, 2003; Soto et al., 2006; and Soto, 2012).
I encourage those who are working with spring cantaloupe production this season to test and evaluate this crop phenology model in the field under various planting dates, varieties, and conditions. We appreciate your feedback.
Figure 1. Graphical depiction of heat unit computation using the single sine
curve procedure. A sine curve is fit through the daily maximum and minimum
temperatures to recreate the daily temperature cycle. The upper and lower
temperature thresholds for growth and development are then superimposed
on the figure. Mathematical integration is then used to measure the area
bounded by the sine cure and the two temperature thresholds (grey area). (Brown, 1989)
Figure 2. Heat Units Accumulated After Planting (HUAP, 86/55 oF)
Baker, J.T., and V.R. Reddy. 2001. Temperature effects on phenological development and yield of muskmelon. Annals of Botany. 87:605-613.
Baskerville, G.L., and P. Emin. 1969. Rapid estimation of heat accumulation from maximum and minimum temperatures. Ecology 50:514-517.
Boswell, V. R. 1929. Factors influencing yield and quality of peas. Maryland Agric. Exp. Sta. Bull. 306.
Brown, P. W. 1989. Heat units. Ariz. Coop. Ext. Bull. 8915. Univ. of Arizona, Tucson, AZ.
Hartz, T.K. 2001. Development and testing of a growing degree day model to predict melon harvest time. California Melon Research Board. 2001. Annual Report.
Murphree, J. 2015. Fun Statistics about Arizona Agriculture’s Melons and Sweet Corn. Arizona Farm Bureau https://www.azfb.org/Article/FunStatistics-about-Arizona-Agricultures-Melons-and-Sweet-Corn
Silvertooth, J.C. 2001. Following cotton development over the fruiting cycle. University of Arizona Cooperative Extension Bulletin No. AZ 1206.
Silvertooth, J.C. 2003. Nutrient uptake in irrigated cantaloupes. Annual meeting, ASA-CSSA-SSSA, Denver, CO.
Silvertooth, J.C., P.W. Brown, and S. Walker. 2010. Crop Growth and Development for Irrigated Chile (Capsicum annuum). University of Arizona Cooperative Extension Bulletin No. AZ 1529
Simonne, A., E. Simonne, R. Boozer, and J. Pitts. 1998. A matter of taste: Consumer preferences studies identify favorite small melon varieties. Highlights of Agricultural Research. 45(2):7-9.
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.
USDA Stats: 2021 State of Agriculture Overview.
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.
Interested in the latest ag technologies? FIRA USA and a number of other entities are organizing a 3-day event October 18-20 in Freson, CA focused on autonomous ag robotics and technologies. The event includes keynote speakers, break out sessions, a trade show and in-field demos of harvesting, weeding, thinning, and planting robots. The emphasis is on specialty crops so it should be very interesting program. For more information, click here.