Recent rains favor Phytophthora crown and root rot of peppers

Soil-applied fungicides can help peppers at risk of disease.

The Great Lakes region produces a wide range of vegetables that are vulnerable to root, crown and fruit rot caused by the soilborne fungus Phytophthora capsici. This pathogen can infect both fresh market and processing plantings of all the cucurbit crops, eggplants, peppers (Photo 1) and tomatoes. This pathogen has two mating types that can come together to form long-term survival spores (oospores). These oospores may survive in soil up to 10 years or more without a susceptible crop, and both mating types that are needed for oospore production have been found in every sampled field in the region.

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Photo 1. Blighting and death of peppers caused by P. capsici.

Rainfall and warm soil temperatures favor Phytophthora. The most effective control measure that growers currently have available is to avoid planting in infested soil and limit the spread of the pathogen to clean fields. This pathogen can be found in irrigation ponds and other surface water sources which have likely led to the high number of infested acres across the major vegetable production areas of our state.

Properly constructed raised plant beds – 8 inches in height – can be helpful in limiting root and crown rot as they keep vulnerable plants from saturated soil conditions. However, raised plant beds are most readily suited for use in fresh market production. Planting tolerant pepper cultivars is an important component of a Phytophthora management strategy. Tolerant varieties can reduce costs associated with fungicide usage, transplant losses, and postharvest losses. For P. capsici, which can infect root, fruit and foliage of peppers, resistance is needed for all three symptoms (Photo 1). Fruit rot is less common for Michigan growers than root rot. Unfortunately, some fields in Michigan harbor Phytophthora isolates that are so virulent that they can overcome some of the currently available tolerant pepper isolates.

Foliar applications of preventive fungicides have been recommended with an emphasis on good coverage of the plant crown and lower stem. Michigan studies and grower reports indicated that better control was needed. Michigan State University Extension’s recommendations currently focus on the approach of applying fungicides directly to the soil either by transplant drenches or drip irrigation. These soil applications appear to be more effective in protecting the plants from crown and root rot than foliar applications alone. Unfortunately, not all fungicides include applications to the soil on their label. For example, Presidio, Ridomil Gold or Zampro can be applied via drip applications according to their labels.

Studies were conducted at the Southwest Research and Extension Center in a research plot infested with Phytophthora. Two new fungicides just released from development were applied as transplant drenches, drip applications and as later-season foliar applications. One study compared an experimental product to Presidio (fluopicolide) with each applied either as a transplant drench alone or as a transplant drench followed by foliar sprays of Presidio, Revus (mandipropamid), Kocide 3000 (copper hydroxide), or a foliar spray of the experimental product. Drench treatments were comprised of 3.5 fluid ounces of water plus the appropriate fungicide applied to the plant’s crown. Foliar sprays were directed to the plant’s stem and crown every seven days using three XR8003 nozzles per row that were calibrated to apply 50 GPA of material.

The experimental product limited plant death and protected fruit yield with a single application to the soil in this particular study (Table 1). Drenches of the experimental fungicide followed by foliar applications of Presidio/Kocide 3000 alternated with Revus/Kocide 3000 effectively limited Phytophthora. A Presidio drench followed by foliar sprays of Presidio/Kocide 3000 alternated with Revus/Kocide 3000 also limited plant death and protected the fruit yield. A one-time drench of Presidio at transplanting did not provide season-long control.

Table 1. Comparison of fungicides for Phytophthora control on ‘Red Knight’ pepper, 2012.       

Treatment* and rate/A application schedule

Death (%)

Yield

(lb/10 ft row)

8/14

8/31

9/11

Untreated control…...........................................................

17.5

 b**

32.5

 c

47.5

 b

8.0

Experimental drench at planting...........................................................................

0.0

a

0.0

a

0.0

a

15.6

Presidio 4SC 0.25 pt drench at planting..........................................................................

15.0

 b

25.0

 bc

57.5

 b

10.6

Experimental drench at planting

 Presidio 4SC 0.25 pt + Kocide 3000 46.1WDG 1 lb

 -alt- Revus 2.08SC 0.5 pt + Kocide 3000 46.1WDG 1 lb 7-day foliar spray

0.0

a

0.0

a

0.0

a

17.4

Presidio 4SC 0.25 pt drench at planting

 Experimental + Kocide 3000 46.1WDG 1 lb

 -alt- Revus 2.08SC 0.5 pt + Kocide 3000 46.1WDG 1 lb 7-day foliar spray

7.5

ab

15.0

ab

12.5

a

16.8

Presidio 4SC 0.25 pt drench at planting

 Presidio 4SC 0.25 pt + Kocide 3000 46.1WDG 1 lb

 -alt- Revus 2.08SC 0.5 pt + Kocide 3000 46.1WDG 1 lb 7-day foliar spray

0.0

a

5.0

a

10.0

a

15.3

*-alt-=alternate
**Column means with a letter in common or with no letter are not significantly different (Fisher LSD Method; P=0.05).

Another study showed that the new experimental product and Presidio/Revus were effective against Phytophthora when applied through drip irrigation (data not shown). A third pepper study looked at a new experimental fungicide (V-10208), Presidio and a newly registered fungicide called Zampro (ametoctradin/dimethomorph) applied as transplant drenches and then via drip irrigation every 14 days for the duration of the season (Figure 1). These treatments were compared to Presidio applied as a drench and then followed by foliar sprays of Presidio/Revus alternated every seven days. V-10208 was effective when applied to the soil and was comparable to Presidio (Photo 2). The 2012 field trials indicated that Presidio, Revus, Zampro, the experimental and V-10208 are very good tools against Phytophthora.

Figure 1. Plant death (%) in a pepper drench/drip trial.
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Photo 2. Left, Untreated control. Right, Experimental drench.

This material is based upon work supported by Project GREEEN GR12-020.

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

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