Progress 10/01/19 to 09/30/20
Outputs
Target Audience:Leafy greens producers as well as the Pest Control Advisors that carry out management of diseases affecting these crops Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?We have started offering internships through the University of Arizona, Yuma campus. We worked with two students during this reporting period. How have the results been disseminated to communities of interest?Results from these trials have been disseminated to spinach and lettuce growers, Pest Control Advisors, and other interested communities of interest through written reports, presentations at meetings, and a Fusarium wilt of lettuce newsletter. What do you plan to do during the next reporting period to accomplish the goals?Similar studies to those reported this year will be conducted in the next growing season to confirm reported results. New trials will be added including a study on the population structure of Fusarium oxysporum f.sp. lactucae and a screen of wild-type lettuce to discover new sources of resistance. Also, testing of new crop protection products and plant varieties will occur in a continuing effort to find Integrated Disease Management Tools for these diseases.
Impacts
What was accomplished under these goals?
Fusarium wilt of lettuce trials. In 2019, lettuce Fusarium wilt research trials were conducted at two Yuma County, Arizona locations, one near Yuma and the other near Wellton. Two studies were conducted at each location; 1) evaluation of commercial lettuce varieties currently available for their relative resistance to Fusarium wilt 2) evaluation of lettuce varieties in development for their relative resistance to Fusarium wilt 3) assessment of crop protection products (conventional as well as biologically based materials) for their potential in reducing disease severity 4) evaluation of Fusarium wilt of lettuce suppression using cover crops 5) evaluation of biosolarization to suppress Fusarium wilt of lettuce. The soil at each site was a silty clay loam. Lettuce was seeded in double rows 12 inches apart on beds with 42 inches between bed centers, then sprinkler-irrigated to germinate seed on 5th and 18th of September for the Yuma and Wellton sites, respectively. Plants were thinned approximately two weeks post-planting in Yuma and Wellton, respectively, to an approximate spacing of 11 inches. Symptoms of Fusarium wilt, including stunting and chlorotic leaves, began to be observed after thinning at both locations. Disease incidence and severity was recorded at crop maturity (15 Nov in Wellton and 2 Dec in Yuma) and was determined by counting the number of plants that are dead, stunted, or chlorotic due to infection by the lettuce Fusarium wilt pathogen. Disease incidences were subjected to analysis of variance (ANOVA), then compared for significance using Fisher's Protected LSD test. Research plots at both locations were managed using customary commercial fertilization, insect management, and irrigation practices. Evaluation of commercial lettuce varieties. For the Yuma and Wellton locations, 16 iceberg varieties were planted in 300-ft-long plots, with four replicate plots per lettuce variety. Each plot contained about 300 plants in both locations. Plots were arranged in a randomized complete block design to facilitate statistical analysis of data collected. The percentage of lettuce plants of each variety rated as diseased was recorded at crop maturity. The highest percentage of healthy plants was recorded with the Blas, Midway and Meridian varieties with values ranging from 81.5-88.3% healthy. The severity of Fusarium wilt for the lowest performing group was significantly lower than that recorded for other iceberg varieties and ranged from 80-100% disease. Evaluation of pre-commercial lettuce varieties. For the Yuma and Wellton locations, 95 lettuce varieties were planted in 15-ft-long plots, with four replicate plots per lettuce variety. Each plot contained about 15 plants in both locations. Plots were arranged in a randomized complete block design to facilitate statistical analysis of data collected. The percentage of lettuce plants of each variety rated as diseased was recorded at crop maturity. These data were reported to the breeders. Assessment of crop protection product efficacy. The crop protection studies at each location were conducted in plots seeded with the iceberg varieties El Guapo and Meridian. At both locations, each treatment was applied to four 15-ft-long plots for each variety, arranged in a randomized complete block design. Six crop protection products were evaluated at both trial sites. Four of these products were tested at several rates. Treatments were applied with a CO2 backpack sprayer that delivered 50/gal per acre at 40 psi to flat-fan nozzles. Treatments were applied in a 4-inch band over each seed line. The first application of products was made right after seeding and before the germination sprinkler irrigation. Each plot contained about 180 plants in both locations. No treatment significantly reduced the severity of lettuce Fusarium wilt compared to nontreated plants in both trials. Evaluation of cover crops. Nine cover crops were planted on March 6th and incorporated May 7th in a growers' field in Yuma. These crops were: canola, broccoli, mustard seed blend, single variety mustard, sudan grass, alfalfa, sesbania, hemp and radish. Three iceberg lettuce varieties were planted on September 24th, Desert Eagle, Tamarack and El Guapo. Disease incidence data will be collected during the next reporting period. Biosolarization pilot project. The objective of this trial was to perform a pilot study in 2019 to determine the feasibility of implementing a full-scale Soil Biosolarization (SBS) trial in Yuma. The elements evaluated included the use of Sudan grass as a carbon source and the irrigation method. This pilot study was conducted in August of 2019 with the help of a grower-cooperator. The trial was designed as a demonstration plot trial meaning that large plots were used with a single plot per treatment. Sudan grass was used as carbon sources for SBS at three and six tons per acre rates. Dry Sudan grass was applied to the plot and was incorporated into the soil. Plastic was applied to the beds and sprinkler irrigation was used to saturate the beds. Lettuce was planted on Septembe 18, disease incidence was recorded on Dec 2nd. No significant reduction in disease severity was recorded for this trial likely because we were not able to maintain water saturation and thus, anaerobic conditions. A trial was conducted in August 2020 implementing lessons learned. Treatments included beds with plastic and flooded beds with and without an external labile carbon source. On September 24th three lettuce varieties were planted on these plots and evaluations will take place in December 2020. Downy mildew of lettuce. Genetic variation has led to the development of new races of downy mildew (Bremia lactucae) and plant breeding programs need to keep in pace. To this end, lettuce samples with downy mildew were collected throughout Yuma and sent to Richard Michelmore at the University of California, Davis. These samples are part of a study to determine the genetic diversity of Bremia lactucae and to help appropriately screen lettuce varieties for resistance to new races. Downy mildew of spinach. Peronospora farinosa f. sp. spinaciae is an important pathogen of spinach. In February 2020 we assisted with a field day of spinach varieties grown in the presence of downy mildew to demonstrate levels of plant resistance to the current races in Yuma. This field day was in cooperation with Jim Correll from the University of Arkansas.
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Progress 10/01/18 to 09/30/19
Outputs
Target Audience:Spinach and lettuce producers as well as the Pest Control Advisors that carry out management of diseases affecting these crops Changes/Problems:A lettuce downy mildew fungicide evaluation trial was also established during this reporting period; however, no disease developed. Mike Matheron, the original Project Director from Plant Sciences retired on January 1, 2020. Stephanie Slinski from the Yuma Center of Excellence for Desert Agriculture replaced him as the new Project Director on January 6, 2020. What opportunities for training and professional development has the project provided?
Nothing Reported
How have the results been disseminated to communities of interest?Results from these trials have been disseminated to spinach and lettuce growers, Pest Control Advisors, and other interested communities of interest through written reports, presentations at clientele meetings, and University of Arizona Vegetable IPM newsletter articles. What do you plan to do during the next reporting period to accomplish the goals?Similar studies to those reported this year will be conducted in the next growing season to confirm reported results. Also, testing of new crop protection products and plant varieties will occur in a continuing effort to find Integrated Disease Management Tools for these diseases.
Impacts
What was accomplished under these goals?
2019 Downy Mildew of Spinach Fungicide Trial. This study was conducted at the Yuma Valley Agricultural Center. The soil was a silty clay loam (7-56-37 sand-silt-clay, pH 7.2, O.M. 0.7%). Spinach 'Lanzarote' was seeded, then sprinkler-irrigated to germinate seed Jan 14, 2019 on beds with 84 in. between bed centers and containing 30 lines of seed per bed. All irrigation water was supplied by sprinkler irrigation. Treatments were replicated five times in a randomized complete block design. Replicate plots consisted of 15 ft lengths of bed separated by 3 ft lengths of nontreated bed. Treatments were applied with a CO2 backpack sprayer that delivered 50 gal/acre at 40 psi to flat-fan nozzles. Torac was first applied Feb 11, whereas all other treatments were first applied Feb 6. Subsequent applications of all treatments, including Torac, were made Feb 18, 25, and 28. Downy mildew (caused by Peronospora farinosa f. sp. spinaciae) was first observed in plots on Feb 11, the same date Torac was first applied and 5 days after the first application of all other treatments.. Disease severity was recorded Mar 11 by determining the percentage of infected leaves present within three 1-ft2 areas within each of the five replicate plots per treatment. The number of spinach leaves in a 1-ft2 area of bed was approximately 300. Two treatments, Torac as well as Orondis alternated with Zampro, provided exceptional disease control with no evidence of downy mildew. These treatments would be useful for growers of baby-leaf spinach, where tolerance for downy mildew is very low. On the other hand, 76 to 87% of spinach leaves in plots treated with GWN-10320 or GWN-10474 showed symptoms of downy mildew infection. In comparison, 90% of leaves in nontreated plots were infected with downy mildew. Fusarium wilt of lettuce trials. In 2018, lettuce Fusarium wilt research trials were conducted at two Yuma County, Arizona locations, one near Yuma and the other near Wellton. Two studies were conducted at each location; 1) evaluation of lettuce varieties currently available or in development for their relative resistance to Fusarium wilt, and 2) assessment of crop protection products (conventional as well as biologically based materials) for their potential in reducing disease severity. The soil at each site was a silty clay loam. Lettuce was seeded in double rows 12 inches apart on beds with 42 inches between bed centers, then sprinkler-irrigated to germinate seed on 14 and 24 Sep for the Yuma and Wellton sites, respectively. Plants were thinned 14 and 24 Oct in Yuma and Wellton, respectively, to an approximate spacing of 11 inches. Symptoms of Fusarium wilt, including stunting and chlorotic leaves, began to be observed after thinning at both locations. Disease severity was recorded at crop maturity on 3 and 17 Dec for Yuma and Wellton trials, respectively, by counting the number of lettuce plants in each test plot that were dead, chlorotic, or stunted. Disease severity data were subjected to analysis of variance (ANOVA), then compared for significance using Fisher's Protected LSD test. Research plots at both locations were managed using customary commercial fertilization, insect management, and irrigation practices. Evaluation of lettuce varieties. For the Yuma and Wellton locations, respectively, 16 (12 crisphead, 4 romaine) and 19 lettuce varieties (14 crisphead, 5 romaine) were planted in 75-ft-long plots, with four replicate plots per lettuce variety. Each plot contained about 180 plants in both locations. Plots were arranged in a randomized complete block design to facilitate statistical analysis of data collected. The percentage of lettuce plants of each variety rated as diseased was recorded at crop maturity. The lowest percentage of diseased plants was recorded with the romaine varieties Del Sol, Duquesne, PX1337, PX497 and Valley Heart, with values ranging from 0 to 4.3% in both trials, and the four crisphead varieties Meridian, Oracle, 16C648 and 16C650, with values ranging from 2.6 to 5.3 in at least one of the two field trials. The severity of Fusarium wilt for these romaine and specific crisphead varieties was significantly lower than that recorded for other crisphead varieties, which ranged from 16.0 to 100%. Considering the 10 crisphead varieties present in both trials, the severity of Fusarium wilt at the Wellton site (60.9%) was significantly higher than at the Yuma site (35.3%). Assessment of crop protection product efficacy. The crop protection studies at each location were conducted in plots seeded with the crisphead variety Raider. At both locations, each treatment was applied to four 75-ft-long plots, arranged in a randomized complete block design. At the Yuma and Wellton locations, 10 and four treatments were evaluated, respectively. Treatments were applied with a CO2 backpack sprayer that delivered 50/gal per acre at 40 psi to flat-fan nozzles. Treatments were applied in a 4-inch band over each seed line. The first application of products was made right after seeding and before the germination sprinkler irrigation. Each plot contained about 180 plants in both locations. Treatments containing Experimental #1 and Experimental #2 significantly reduced the severity of lettuce Fusarium wilt compared to nontreated plants in both trials. Two seed treatments with the lettuce variety Raider also were evaluated at both trial locations. These treatments, Optimum and Optimum Plus, did not significantly reduce the final severity of Fusarium wilt compared to nontreated seed.
Publications
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Progress 10/01/17 to 09/30/18
Outputs
Target Audience:Lettuce and spinach producers as well as the Pest Control Advisors that carry out management of diseases affecting these crops. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?
Nothing Reported
How have the results been disseminated to communities of interest?Results from these trials have been disseminated to lettuce and spinach growers, Pest Control Advisors, and other interested communities of interest through written reports, presentations at clientele meetings, and University of Arizona Vegetable IPM newsletter articles. What do you plan to do during the next reporting period to accomplish the goals?Similar studies to those reported this year will be conducted in the next growing season to confirm reported results and examine new crop protection products and varieties in a continuing effort to find Integrated Disease Management Tools for downy mildew of lettuce and spinach as well as Fusarium wilt of lettuce.
Impacts
What was accomplished under these goals?
2017-2018 Downy Mildew of Lettuce Fungicide Trial. This study was conducted at the Yuma Valley Agricultural Center. The soil was a silty clay loam (7-56-37 sand-silt-clay, pH 7.2, O.M. 0.7%). Lettuce varieties Bubba, Domingos 67, Gabilan, Havasu, Navajo, Salute, and SV773560 were seeded, then sprinkler-irrigated to germinate seed on Nov 16, 2017 on beds with 84 in. between bed centers, with each bed containing six rows of lettuce. Sprinkler irrigation was used to germinate seed and grow the crop to maturity. Treatments were replicated five times in a randomized complete block design. Each replicate consisted of a 25 ft length of row on beds containing six rows of lettuce. Plants were thinned Dec 21, 2017 at the 3-4 leaf stage to an approximate 12-inch spacing. Treatments were applied with a tractor-mounted boom sprayer that delivered 50 gal/acre at 100 psi to flat-fan nozzles spaced 12 in. apart. Foliar applications of treatments were applied 20 and 27 Feb and 7 Mar, depending on the treatment. Downy mildew (caused by Bremia lactucae) was first observed in plots on Feb 26, six days after the first application of products. Disease severity was determined Mar 16, 19, and 20 by recording the number of downy mildew lesions on 10 lettuce plants arbitrarily selected within each treatment plot. Statistical analysis of disease severity among the nontreated lettuce varieties revealed no significant differences; therefore, fungicide treatment data for all seven lettuce varieties were combined before final statistical analysis. All treatments significantly reduced the final severity of downy mildew compared to nontreated plants. The two best treatments, V-10365 alternated with Zampro and Revus+Orondis Ultra alternated with Zampro, reduced the number of downy mildew lesions by over 50% compared to nontreated plants. Phytotoxicity symptoms were not noted for any treatments. 2018 Downy Mildew of Spinach Fungicide Trial. This study was conducted at the Yuma Valley Agricultural Center. The soil was a silty clay loam (7-56-37 sand-silt-clay, pH 7.2, O.M. 0.7%). Spinach 'Lanzarote' was seeded, then sprinkler-irrigated to germinate seed Jan 16, 2018 on beds with 84 in. between bed centers and containing 18 lines of seed per bed. All irrigation water was supplied by sprinkler irrigation. Treatments were replicated four times in a randomized complete block design. Replicate plots consisted of 15 ft lengths of bed separated by 3 ft lengths of nontreated bed. Treatments were applied with a CO2 backpack sprayer that delivered 50 gal/acre at 40 psi to flat-fan nozzles. Application date for at emergence treatments was Jan 25 and other foliar treatments were applied Jan 31, Feb 6, 19, and 27, depending on the treatment. Downy mildew (caused by Peronospora farinosa f. sp. spinaciae) was first observed in plots on Feb 20, almost 3 weeks after the first foliar application of products. Disease severity was recorded Mar 8 by determining the percentage of infected leaves present within three 1-ft2 areas within each of the four replicate plots per treatment. The number of spinach leaves in a 1-ft2 area of bed was approximately 300. In nontreated plots, 82% of leaves were infected with downy mildew at harvest time. Several different treatments provided a statistically significant reduction in disease compared to nontreated plots; however, the following four treatments provided exceptional disease control with no evidence of downy mildew: 1) Ridomil Gold + Quadris, Actigard, A-21591, Actigard, Revus; 2) Ridomil Gold + Quadris, Actigard, A-21591, Revus; 3) Actigard, Orondis Gold + Ridomil Gold, Revus, Zampro; 4) Orondis Gold + Ridomil Gold. These treatments would be useful for growers of baby-leaf spinach, where tolerance for downy mildew is very low. Fusarium Wilt of Lettuce Trials. In 2017, two lettuce Fusarium wilt research trials were conducted in a grower's field near Yuma, AZ. The objectives of these trials were 1) to evaluate lettuce cultivars currently available or in development for their relative resistance to Fusarium wilt, and 2) to examine crop protection products (conventional as well as biologically based materials) for their potential in reducing disease severity. The soil at this site was a silty clay loam. Lettuce was seeded 11 Sep in double rows 12 inches apart on beds with 42-inch centers, then sprinkler-irrigation was initiated 13 Sep to germinate seed. Plants were thinned 9 Oct to an approximate spacing of 11 inches. Initial symptoms of Fusarium wilt, including stunting and chlorotic leaves, were first observed on some plants at thinning. Disease severity was determined at crop maturity (10 Nov) by recording the percentage of lettuce plants in each test plot that were dead, chlorotic, or stunted due to infection by Fusarium oxysporum f. sp. lactucae. Disease severity data were subjected to statistical analysis to determine significant differences in severity of Fusarium wilt among lettuce cultivars or crop protection products. Research plots were managed using customary commercial fertilization, insect management, and irrigation practices. Evaluation of lettuce cultivars. Thirty crisphead lettuce cultivars, either commercially available or in development, were planted in 70-ft-long plots, with four replicate plots per lettuce cultivar. Each plot contained about 150 plants. Plots were arranged in a randomized complete block design to facilitate statistical analysis of data collected. The percentage of lettuce plants of each cultivar that were dead or diseased was recorded at plant maturity. The percentage of plants affected by Fusarium wilt ranged from a low of 7% for Oracle to a high of almost 47% for the cultivar 1221. In addition to Oracle, the cultivars Icepalace, Icecastle, and LS5528 sustained less than 10% losses due to Fusarium wilt. Further evaluation of promising cultivars is planned for future field evaluation studies to confirm results from this trial. It should be noted that Oracle was among the least diseased of crisphead cultivars in two field trials conducted in 2016 as well. Assessment of crop protection product efficacy. The crop protection study was conducted primarily with the crisphead cultivar Raider. Also examined was the effect of treating seed of cultivars 1221 and Meridian with Manzate. Each treatment was applied to or seed treated with products were planted in four 70-ft-long plots in a randomized complete block design. Six different treatments were applied to beds seeded to Raider. Treatments applied to beds were in a 4-inch band over each seed line using a CO2 backpack sprayer that delivered 50/gal per acre at 40 p.s.i. to flat-fan nozzles. First application of products was made after seeding and before the germination sprinkler irrigation. Each plot contained about 150 lettuce plants. Disease severity was assessed at crop maturity. Tested crop protection products included Rhyme, A-19649B + Actigard, Actigard, Promax, Natural Guard, and Expulso. None of the treatments applied to plots or applied to seed before planting significantly reduced the percentage of lettuce plants affected by Fusarium wilt compared with plants in nontreated plots or those originating from nontreated seed.
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