Management of basil downy mildew using organic fungicides and nitrogen fertilization rate

Final Report for ONE12-152

Project Type: Partnership
Funds awarded in 2012: $6,705.00
Projected End Date: 12/31/2012
Region: Northeast
State: Connecticut
Project Leader:
Joan Allen
Assistant Cooperative Extension Educator in Residence
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Project Information

Summary:

The objective of this study is to evaluate the effectiveness of four organic products for control of basil downy mildew and compare disease severity at three levels of nitrogen fertilization combined with the fungicides.

Seven week old basil seedlings were transplanted into research plots at two Connecticut locations in early July. Monitoring for downy mildew was done weekly and control products were applied preventatively beginning August 2nd and 3rd. Disease was confirmed in the field at both locations in early August during the second week of treatments. Products were applied weekly. Treatments were applied for five weeks at Community Farm of Simsbury (CFS) and six weeks at the University of Connecticut Plant Science Research Farm (UConn). Nitrogen was applied in fish meal (8-12-12) and blood meal (12-0-0) just prior to planting at rates of 50, 90 and 120 lb/ac. Fish meal was applied equally to all plots so P and K additions would be equal and the balance of the required N was applied as blood meal for the two higher N rates. All plots received a side dress of N (blood meal) at 30 lb/ac seven weeks after planting. Disease was evaluated during the week after the final treatment at UConn and two weeks after the final treatment at CFS. The partner farmer participated in growing the basil transplants and bed preparation, planting the seedlings, applying fertilizer, mowing weeds between beds, and applying the treatments at that location.

The results varied between the two sites. This year there were no significant differences between fungicide treatments and the control at UConn. At CFS, OxiDate provided some reduction in disease severity. OxiDate reduced disease severity at both sites in 2011. At CFS, disease severity was lower at higher rates of nitrogen fertility. At UConn, disease severity was greater at the highest nitrogen application rate. These conflicting results make it impossible to conclude whether nitrogen fertility has a consistent effect on basil downy mildew severity.

The results of the 2011 (ONE11-132 Evaluation of Organic Control Products for Basil Downy Mildew, Joan Allen)and 2012 studies funded by NE SARE were presented at the 2013 Connecticut Vegetable and Fruit Growers Conference and the 2013 UConn Garden Conference. The UConn basil downy mildew factsheet that was written based on the 2011 work will be updated to include the information from 2012. The study results have been published in the American Phytopathological Society’s online publication Plant Disease Management Reports, Volume 7, 2013.

Introduction:

Basil is grown on many farms in the northeastern United States, primarily for fresh market sale. Basil downy mildew, (see images below) a new disease of basil in the US, renders the crop unmarketable as a fresh product. It is native to Europe and Africa and was first identified in the US in Florida in 2007. It has spread throughout the eastern US in field and greenhouse basil. 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 and the northeast. Basil is grown year-round in the southeastern US, providing a source of inoculum to northern locations where it doesn’t overwinter. With favorable weather, this disease can destroy a crop. Popular sweet basil varieties are among the most susceptible (Wyenandt, et al., 2010). Some research has been done on control using conventional fungicides (Raid, 2007a, 2007b, McGrath, personal communication).

There is no published research on the efficacy of products available for organic growers to control downy mildew on basil. Unpublished work shows mixed results for these products (McGrath, personal communication; Homa, et al. 2011; Allen, 2011). Organic farmers rely heavily on cultural practices to manage disease. Nitrogen fertility can impact disease severity. Studies on crops including watermelon and pearl millet have shown that high levels of nitrogen fertilization are associated with higher downy mildew disease severity (Santos, et al. 2009, Zarafi, et al., 2005.) The objective of this study is to evaluate the effectiveness of four organic products for control of basil downy mildew and compare disease severity at three levels of nitrogen fertilization combined with the fungicides. These include products containing the active ingredients Streptomyces lydicus, hydrogen dioxide, potassium bicarbonate and copper octanoate. This work will add to the knowledge on the efficacy of these control measures and the influence of nitrogen fertility on downy mildew of basil and downy mildews in general.

References

Allen, J.E. 2011. Evaluation of organic control products for basil downy mildew. Plant Disease Management Reports, Vol.12.
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.
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.
Zarafi, 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. Archives of Phytopathology and Plant Protection 38(1):11-17.

Project Objectives:

The objective of this study was to evaluate the effectiveness of four organic products for control of basil downy mildew and compare disease severity at three levels of nitrogen fertilization combined with the fungicides. These include products containing the active ingredients Streptomyces lydicus, hydrogen dioxide, potassium bicarbonate and copper octanoate. This work will add to the knowledge on the efficacy of these control measures and the influence of nitrogen fertility on downy mildews.

Three of these fungicides, S. lydicus (Actinovate), hydrogen dioxide (OxiDate) and potassium bicarbonate (Milstop) reduced disease severity during field studies in 2011. An additional treatment consisted of alternating weekly applications of OxiDate and Actinovate. Because efficacy of organic products has been variable in other studies on a variety of diseases and crops, it is of value to look at multiple season data in multiple locations and field conditions.

Nitrogen fertility management can be implemented along with other practices to reduce the susceptibility of the plants to disease when research shows a correlation between application rate and disease severity. In this study, results at the two plot locations were conflicting so conclusions could not be drawn on a relationship between nitrogen fertility and severity of basil downy mildew.

Cooperators

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Research

Materials and methods:

This project evaluated the efficacy of five fungicide treatments for control of basil downy mildew in combination with three different nitrogen (N) fertilization rates under field conditions. Plots were located at two sites in Connecticut, the UConn Plant Science Research Farm in Storrs and Community Farm of Simsbury (CFS) located in Simsbury. The two farms are approximately 40 miles apart. Soil tests were done prior to planting at both locations. A randomized complete block design was used with three replicates.

Seeds of sweet basil cultivar ‘Genovese’ were sown seven weeks prior to planting in a high tunnel on May 16. Seven week old transplants were set in plots on July 4 at CFS and July 5 at UConn. At CFS plants were placed into beds with black plastic mulch and drip irrigation using a bed-making tractor implement. Plots consisted of two ten foot rows containing 9 plants each with a between plant spacing of 9” and a between row spacing of 12”. Between plot spacing was six feet and weeds between plots were mown. At the UConn Farm, plot layout was the same as at CFS. Organic mulch (mulch hay) was used instead of black plastic and applied one week after planting.
There were two fertilizer applications, first just prior to planting (fish meal (8-12-12) on all plots plus blood meal (12-0-0) for the additional N at the two higher rates) and a second application of blood meal as a side dress to all plots seven weeks later. Nitrogen rates tested were 80, 120 and 150 lbs/acre. Initial amendments supplied 50, 90 and 120 lb N/acre followed by the side dress of blood meal at the rate of 30 lbs N/acre applied seven weeks later.

Preventive applications of the fungicide treatments began on August 2 at CFS and August 3 at UConn. Disease was confirmed at CFS on August 9 and at UConn on August 10. Incidence was high at CFS at nearly 100% and low at UConn at less than 25% overall. By the following week, during which wet weather favorable to disease occurred, disease developed to a high incidence level in all plots at both locations. Treatments were applied at seven day intervals at rates recommended on the product label as described in Table 1. Applications were made 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 product label. A surfactant, Yucca Ag-Aide, was added to the Actinovate, OxiDate, and Cueva as recommended by the manufacturer. Products, active ingredients and application rates are shown in Table 1 (attached).

Research results and discussion:

The project overall has gone as planned. The first activity after purchasing necessary supplies and materials was to grow the basil transplants. Bed preparation and planting went well. At CFS, a bed maker was used to create raised beds using drip irrigation and black plastic mulch. At UConn, beds were in the ground and mulched with hay. The seedlings had a nearly 100% survival rate and thrived in the field. Applications of control treatments commenced just prior to disease detection in the field as planned. Five weekly applications were applied at CFS and six at UConn.

For the treatment alternating OxiDate and Actinovate, OxiDate was used during the first week and the products were alternated every other week thereafter. Disease incidence was nearly 100% in the field at CFS by the second week of treatments. Disease was detected the same week at UConn but incidence was less than 30%. Disease was evaluated at UConn one week after the final sprays and two weeks after at CFS. The results of the trial showed no significant differences between fungicide treatments and the control at UConn and only OxiDate reduced disease severity at CFS this year. The only change from the original plans was the omission of foliar nitrogen testing at the close of the experiment due to poor plant condition. Detailed results and statistical analyses are contained in the pdf file of the report published in Plant Disease Management Reports in the Publications/Outreach section of this final report.

Research conclusions:

This research project did not lend itself to quantitative measurement of direct outcomes or impacts. The immediate result is knowledge gained and shared with growers. Information gained as a result of this work may help both organic and conventional growers of basil reduce losses to downy mildew, a highly destructive disease. Some of the products tested can be used in both greenhouse and field settings, increasing the impact and value of the information. In addition, the products tested are options available to home gardeners who learned about the work at the 2013 UConn Garden Conference in March. The audience at the 2013 Connecticut Vegetable and Fruit Growers Conference included extension personnel in addition to growers.

Participation Summary

Education & Outreach Activities and Participation Summary

Participation Summary

Education/outreach description:

In January 2013, the results of both this and last year’s work were presented at the Connecticut Vegetable and Fruit Growers Conference in a Power Point presentation. The number of growers attending was approximately 150. The content of this presentation was presented by another speaker at the 2013 UConn Garden Conference attended by approximately 275 people. Another presentation will be given at the Business and Extension meeting during the 2013 annual meeting of the Northeast Division of the American Phytopathological Society. A report of the results has been published in the Plant Disease Management Reports, Volume 7, an online peer-reviewed publication of the American Phytopathological Society. The UConn Vegetable IPM fact sheet written in 2011 has been updated to reflect the results of the 2012 study.

Project Outcomes

Assessment of Project Approach and Areas of Further Study:

Areas needing additional study

It would be of value to repeat the evaluation of disease severity at different levels on nitrogen fertilization. High nitrogen fertility has been linked to higher disease severity in downy mildew diseases of other crops and understanding whether this also applies to basil downy mildew would add to the tools growers could use to reduce the use of chemicals and improve the efficacy of chemicals used.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.