- Additional Plants: herbs
- Pest Management: biological control, biorational pesticides, cultural control
- Production Systems: organic agriculture
Sweet basil is the most widely grown culinary herb in the eastern United States. Basil downy mildew, a disease that renders the crop unmarketable (fresh market), has been widespread and often severe throughout the northeast since 2008. There is limited research evaluating the efficacy of organic control products for this disease. Organic growers rely heavily on cultural practices for disease control. Fungicides are used to supplement cultural practices when disease pressure is high or when plant quality is a priority as in fresh market basil. The proposed study will evaluate five fungicide treatments for control of basil downy mildew: Milstop, Cueva, Actinovate, OxiDate, and an Actinovate/Oxidate rotation. These products were chosen because of strong performance in my 2011 project ‘Evaluation of Organic Control Products for Basil Downy Mildew’ with the exception of the new addition Cueva. Cueva will be included this year to add a copper formulation. The product development manager (Brett Highland, Certis USA) has stated that there is a potential for herbs to be added to the product label in the future. Disease caused by numerous pathogens has been shown to be affected by nitrogen fertility. This project will evaluate the effect of nitrogen fertilization rate alone and in combination with the fungicides on basil downy mildew severity. This will provide valuable information in the management of this important disease for both organic and conventional growers.
Project objectives from proposal:
Integrated pest management programs with an emphasis on cultural practices are used for disease control by organic growers and those trying to reduce the use of chemical pesticides. Little research has been done on the efficacy of organic products available for control of basil downy mildew. The proposed study will evaluate five fungicide treatments for control of basil downy mildew: Milstop, Cueva, Actinovate, OxiDate, and an Actinovate/Oxidate rotation.
A number of pathogens have been shown to cause greater or lesser disease on their host plants in relation to nitrogen fertility. On pearl millet, sugarcane, watermelon and cucumber, research has shown that incidence and severity of downy mildew were higher as nitrogen fertilization rate increased (Vitung 1997, Vietnam 1997, Zafari et al 2005, dos Santos et al 2009). Soil fertility management may be a tool for use in IPM programs to reduce incidence and severity of downy mildew diseases of plants including basil.
The proposed study will include three levels of nitrogen (N) fertilization. The New England Vegetable Management Guide recommends an application rate of 115-130 lbs/acre for basil. The rates that will be applied for this study are 80 lbs/ac (low), 120 lbs/ac (recommended), and 150 lbs/ac (high). Each N rate will be applied with each of the fungicide treatments to evaluate the combined effects of the two management practices.
This would be the first study to look at the effect of nitrogen fertility on incidence and severity of basil downy mildew and the first to evaluate N fertilization rate in combination with fungicide treatments.
This proposed study will continue recently completed research. In the summer of 2011, five organic control products were evaluated at two locations for basil downy mildew control (Allen, 2011). The products included Actinovate, Serenade MAX, Trilogy, Milstop, and OxiDate.
Results are shown in Table 1.
In the 2011 study, the following disease rating scale was used: 0 = no symptoms or sporulation, 1 = symptoms and 0-10% of the leaves on the plant with sporulation, 2 = 10-50% of the leaves with sporulation, and 3 = >50% of the leaves with sporulation. The analysis shows the likelihood of plants in a treatment to receive a higher rating than the control. Milstop and OxiDate were significantly different from the control at both locations and will be included in the study for 2012. When ratings were combined (0 and 1 vs. 2 and 3) to reflect disease severity relating to marketability (0 & 1 marketable, 2 & 3 unmarketable), only Milstop, OxiDate and Actinovate were significantly different from the control, and all at only one location (CFS). Actinovate will be included for re-evaluation in 2012. At the request of the Technical Services Manager (Vijay Kumar Choppakatla) for BioSafe Systems, manufacturer of OxiDate, a treatment of OxiDate in rotation with Actinovate will be tested.
Table 2 lists the fungicide treatments to be evaluated in 2012.
Allen, J.E. 2011. Evaluation of organic control products for basil downy mildew. Unpublished.
dos Santos, G.R., M.D. de Castro Neto, H.S.M. de Almeida, L.N. Ramos, R.A. Sarmento, S. de O Lima, and E.A.L. Erasmo. 2009. Effect of nitrogen doses on disease severity and watermelon yield. Horticultura Brasileira 27:330-334.
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.
Vietnam, N.T.P. 1997. Nitrogen and phosphorus effect on cucumber yield. Paper presented at ARC Training, Kesetsart University, Kampheengsaen, Nakhan, Pathom, Thailand.
Vitung, A. 1997. Effect of nitrogen fertilization on sugarcane downy mildew infection. Abstract, ARD completed research.
Wyenandt, C. A., J. E Simon, M. T. McGrath, D. L. Ward. 2010. Susceptibility of basil cultivars and breeding lines to downy mildew (Peronospora belbahrii). Hort Sci ence 45(9):1416-1419.
Zafari, A.B., A.M. Emechebe, A.D. Akpa, and O. Alabi. 2005. Effect of fertilizer levels on grain yield, incidence and severity of downy mildew in pearl millet. Arch. Phytopathology and Plant Protection 38(1):11-17.