This study was undertaken to evaluate the efficacy of five products labeled for control of basil downy mildew and approved for organic growers. Eight week old basil seedlings were transplanted into research plots at two Connecticut locations in June 2011. Monitoring for downy mildew was done weekly and control products were applied preventatively beginning July 27th and 28th. Disease was confirmed in the field at both locations in early August. Products were applied weekly (twice weekly for OxiDate once disease was detected, at one site only). Treatments were applied for five weeks. Disease was evaluated during the week after the final treatment. The partner farmer participated in growing the basil transplants and bed preparation, planting the seedlings, mulching, weeding, applying the treatments, and disease evaluation at Community Farm of Simsbury. The results varied between the two sites. Milstop performed the best at both locations. OxiDate treated plants were also less diseased than the control plants at both sites. Actinovate, Serenade and Trilogy all resulted in significant differences from the control at one of the two sites but not the other. Results are provided in the attached table.
Basil is grown on many farms in the northeastern United States, primarily for fresh market sale. Basil downy mildew, a new disease of basil in the US, renders the crop unmarketable as a fresh product. The disease is native to Europe and Africa and was first identified in the US in Florida in 2007 and has since occurred throughout the eastern US in both field and greenhouse basil crops. Downy mildew was first observed on basil in the northeast in 2008 and was reported as severe at many farms that year (McGrath, 2009). In 2010 and 2011, basil downy mildew was confirmed at multiple locations in Connecticut. Basil is grown year-round in the southeastern US, providing a potential source of inoculum to more northern locations, where it does not overwinter. When weather is favorable, this disease may destroy an entire crop. A recent study identified resistance in some varieties from among 30 different cultivars and breeding lines. Popular sweet basil varieties were among the most susceptible (Wyenandt, et al., 2010). Some research has been done on control using conventional fungicides (Raid, 2007a, 2007b, McGrath, personal communication). Efficacy evaluation was needed for products available for control of basil downy mildew by certified organic farmers and others looking for alternatives to traditional chemicals. In Connecticut, there are currently 24 certified organic farms and 76 pledge farmers who have agreed not to use synthetic pesticides (Duesing, personal communication, Spring 2011). The objective of this study is to evaluate the effectiveness of five organic products for control of basil downy mildew. These include products containing active ingredients such as bacteria (Streptomyces lydicus, Bacillus subtilis), neem oil, hydrogen dioxide, and potassium bicarbonate. This work will add to the body of knowledge on the efficacy of these control measures for basil downy mildew and potentially other downy mildew diseases of vegetables and herbs.
McGrath, M. T. 2009. Basil downy mildew – a new disease to prepare for. http://vegetablemdonline.ppath.cornell.edu/NewsArticles/BasilDowny.html
Raid, R. N. 2007a. Evaluation of fungicides for control of downy mildew on basil, winter 2007. Plant Disease Management Reports 3:V160.
Raid, R. N. 2007b. Efficacy of four fungicides, alone and in tank mixtures with a phosphonic, for control of downy mildew on basil, winter 2007. Plant Disease Management Reports 3:V163.
Wyenandt, C. A., J. E. Simon, M. T. McGrath, and D. L. Ward. 2010. Susceptibility of basil cultivars and breeding lines to downy mildew (Peronospora belbahrii). HortScience 45(9):1416-1419.
This research project evaluated the efficacy of five organic disease control products for control of basil downy mildew in the field. Products tested included OxiDate, Milstop, Actinovate, Serenade MAX, and Trilogy. These five treatments and a control (no treatment) were applied to two species of basil. O. basilicum cultivar ‘Genovese’ (susceptible) and O. citriodorum cultivar ‘Lemon’ (less susceptible) were grown from seed from High Mowing Organic Seeds. A randomized complete block design with four replicates was used at each of two locations, Community Farm of Simsbury in Simsbury, CT(both sweet and lemon basil) and the UConn Plant Science Research Facility in Storrs, CT (sweet basil only). Blood meal was applied just prior to planting at a rate of 32 lb./acre at both sites. Eight week old transplants were placed in beds with four 6-foot rows per treatment. Planting dates were June 9 in Simsbury and June 13 in Storrs. Plants were spaced 8” apart within the rows with a between-row spacing of 18-24”. Treatment sections were separated by 4-foot strips of mulched with mulch hay. Basil seedlings were transplanted to the field in June. Preventive applications of each treatment were applied at 7-day intervals beginning in late July. Weather was favorable for disease and products were applied weekly for five weeks. The spray intervals were consistent with label recommendations. Products were applied using a CO2 backpack sprayer. The handheld boom was equipped with three Tee-Jet 11003 flat-fan nozzles adjusted to provide thorough coverage of the plant including the undersides of the leaves. The equipment was calibrated to deliver 62 gallons per acre at the rate recommended on the label. An adjuvant was added to the OxiDate, Serenade MAX and Actinovate treatments as recommended by the manufacturers. All products were applied at label-recommended rates for downy mildew. Once disease was confirmed in the field, the application of OxiDate was doubled by going over those plots twice at the request of the manufacturer representative. He also requested that we begin doing those treatments twice weekly which we were able to do at one of the two locations. Treatments and rates are shown in Table 1 (attached).
Infection of plants was by naturally occurring inoculum. Plants were monitored weekly to document the date of the onset of infection in the study plots and disease was confirmed in early August in both locations. Disease incidence was measured by estimating the percentage of plants in each treatment that showed signs of downy mildew (sporulation). Disease severity was evaluated using a scale from 0-3 as follows: 0 = no symptoms or sporulation present, 1 = symptoms with 0-10% of leaf area with sporulation, 2 = 10-50% leaf area with sporulation, and 3 = greater than 50% of leaf area with sporulation. Plants in the center two rows of each treatment were rated. Treatments were done for five weeks. Tropical storm Irene knocked the plants over in many plots after the fifth treatment week and the experiment was ended. Disease incidence and severity were evaluated the following week. Statistical analysis of the results was done using the SAS 9.2 Ordinal Logistic Analysis program.
Downy mildew was confirmed at the UConn plots on 9 August and at Community Farm of Simsbury on 11 August during the third week of treatments. Weather for disease development was favorable with regular rain events at both locations and moderate summer temperatures. Results varied between the two sites. Some treatments were significantly different from the control at both sites and others at only one of the sites. Data were analyzed using the individual ratings and also by combining the 0 and 1 ratings and the 2 and 3 ratings to reflect the quality of the basil for fresh market sale. The two products that had the most consistent control were Milstop (Active ingredient potassium bicarbonate) and OxiDate (Active ingredient hydrogen dioxide). Phytotoxicity was not observed. The detailed results and statistical analysis are shown in Table 1 (attached in Materials and Methods section).
Impacts of Results/Outcomes
This project did not include a verification plan. The findings have been shared with various audiences as described in the Publications and Outreach section below. This work gives basil growers knowledge that can be used in preventing downy mildew with products approved for organic systems. When products have a proven track record in the field, they can be selected over other products that have unknown efficacy, therefore reducing the risk of spending time and money on a product that will be ineffective and the resulting loss of yield. This information is useful to extension personnel that need to make reliable research-backed recommendations to the growers and farmers they work with.
Education & Outreach Activities and Participation Summary
This work has been published in Plant Disease Management Reports (American Phytopathological Association), Crop Talk (University of Connecticut Newsletter for Commercial Vegetable and Fruit Growers) (attached), Capital District Growing Trends (Cornell University Cooperative Extension of Albany County Newsletter), and a fact sheet (attached) for the University of Connecticut Vegetable IPM website (to be posted in fall 2012). In addition, power point presentations were made to share this work at a fall 2011 meeting of the University of Connecticut IPM staff and at the 2011 Extension and Industry portion of the annual meeting of the Northeast Division of the American Phytopathological Society (NEDAPS) at Rutgers University in October 2011. There were approximately 12 people at the UConn IPM meeting and approximately 40 people at the NED APS meeting at Rutgers.
I have heard from one greenhouse grower from Vermont who has used the results from my work in selecting products for basil downy mildew control. They grow about 5000 basil plants per year and lost the entire crop last year. This year they have been using two products either alternating weeks or together and one of them is Milstop, the product that performed best in my study. The grower stated I am really grateful for your work in this area – it was quite a financial loss for us to have to dispose of most of a year’s worth of basil. Other interest was expressed by an extension educator in New York State who wrote to inquire about reprinting my article in the Cornell publication describe above in another newsletter the Hudson Valley Horticulture e-newsletter.
Biological and biorational fungicides tend to be less consistent in their field performance than their synthetic chemical counterparts. This may be due to their modes of action, residual activity, environmental sensitivity or other factors. Because of this, repeat studies are important to confirm results achieved. Organic growers use a variety of cultural control methods to reduce pest and disease problems. Field tests using organic fungicides in combination with practical cultural control practices would provide additional valuable information on the most effective combination of tools. One factor that has been shown in other studies to affect downy mildew severity in other crops is nitrogen fertility. My 2012 NE SARE Partnership project will evaluate some of the same products in combination with different levels of nitrogen fertility.