Phytophthora in pepper production: How to minimize the losses

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.  

Phytophthora is a problem this year for pepper and cucurbit growers. The heavy rains experienced in some areas of the state are certain to cause a rapid increase in disease in fields that were showing early symptoms.

Fungicide trial

Research conducted at Michigan State University has identified fungicides that can be used to limit plant loss and fruit infection of peppers. At one time, the standard systemic fungicide mefenoxam (Ridomil Gold, Ultra Flourish) was very effective in protecting the plants and fruit from infection. However, the repeated use of this fungicide and the genetic adaptation capability of P. capsici resulted in resistant populations of the pathogen in many Michigan vegetable fields. In these cases, using Ridomil Gold or Ultra Flourish does not offer any control and alternative fungicides should be used (Table 1). Recent registrations of Acrobat (dimethomorph), and Tanos 50DF (famoxadone + cymoxanil) give growers alternatives to Ridomil Gold or Ultra Flourish and are helpful as rotational products for growers interested in using Ridomil Gold or Ultra Flourish.

Table 1. Products available for Phytophthora capsici control in peppers.

Product Active ingredient(s)
Ridomil Gold/Ultra Flourish mefenoxam
Ridomil Gold Copper mefenoxam/copper hydroxide
ProPhyt/Phostrol phosphorous acid equivalents
Kocide, Champ/Cuprofix Disperss copper hydroxide/copper sulfate
Manex maneb
Tanos famoxadone + cymoxanil
Acrobat/Forum dimethomorph

During the summer of 2005 a study was conducted at a grower cooperator’s farm in Oceana County with a history of P. capsici. Plots were established in raised beds that were covered with plastic mulch and drip irrigation. A single drip tape was installed under the black plastic mulch and was used to apply soil-applied products. Treatments applied at planting were made via injection into the drip tape. Irrigation occurred for approximately 45 minutes during the injection period and created a 12 in. wide treatment band surrounding the transplants. Foliar applications started 14 days after planting and were applied with a CO 2 backpack sprayer calibrated to deliver 50 GPA using three XR8003 nozzles. Foliar treatments were applied eight times on a 7-day spray schedule. Information on average plant loss and yields for the plot are presented in Table 2.

Table 2. Efficacy of fungicides for Phytophthora crown, root, and fruit rot of peppers.

Treatment and application technique Plant loss
(%)
Yield
(lb/40 ft)
Untreated 42.1 19.2
Ridomil Gold 4SL 1 pt drip applied
Ridomil Gold Copper 65WP 2.5 lb foliar application
5.4 53.1
ProPhyt 4.2SC 2.5 pt drip applied
Ridomil Gold Copper 65WP 2.5 lb foliar
14.6 43.2
Ridomil Gold 4SL 1 pt + ProPhyt 4.2SC 2.5 pt drip applied
Ridomil Gold Copper 65WP 2.5 lb foliar
10.8 44.9
Ridomil Gold 4SL 1 pt drip applied
Ridomil Gold Copper 65WP 2.5 lb + ProPhyt 4.2SC 6 pt foliar
14.3 36.8
Ridomil Gold 4SL 1 pt + ProPhyt 4.2SC 2.5 pt drip applied
Ridomil Gold Copper 65WP 2.5 lb + ProPhyt 4.2SC 6 pt foliar
10.7 43.5
ProPhyt 4.2SC 2.5 pt drip applied
ProPhyt 4.2SC 6 pt foliar
13.1 43.8
Ridomil Gold 4SL 1 pt + ProPhyt 4.2SC 2.5 pt drip applied
A12946 2.08SC 5.5 fl oz foliar
11.3 42.0
Ridomil Gold 4SL 1 pt drip applied
Tanos 50DF 10 oz + Kocide 2000 54DF 1.5 lb
alternate with Manex 4FL 2 qt + Kocide 2000 54DF 1.5 lb foliar
13.6 40.9

The untreated plots had higher plant and yield loss compared to the chemical treatments. Because of variability within the plot, here were no significant differences among the different chemical programs tested. All treatment programs were helpful in limiting P. capsici although no program completely prevented plant loss. The mefenoxam based-treatments seemed to be effective as these fungicides have not been used frequently at this site and the P. capsici is still sensitive to this product in this area.

Dr. Hausbeck’s work is funded in part by MSU‘s AgBioResearch.

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