Phytophthora: Not Just a Bean Disease

Mention the word “Phytophthora” and many readers will think of damping off in soybean fields. They think of massive seedling death due to fungal infection. However, this disease is not only a scourge in grain production. Phytophthora can present a serious threat in peppers, tomatoes, and eggplants. In our area, it is well known for sometimes causing devastating losses in pumpkins.

The water-loving fungus responsible for causing this disease is not the same species that plagues soybean fields, but it is related. Beans are attacked by Phytophthora sojae, while pumpkins are attacked by Phytophthora capsici. The names may be different, but the lifecycles of both fungi are similar. Phytophthora fungi can infect plants throughout the growing season killing seedling plants, causing crown collapse in more mature plants, forming leaf and/or stem lesions, and infecting fruit both pre- and post-harvest.

Phytophthora capsici persists in the soil and/or within debris as thick walled spores, termed oospores, that tend to be very hardy. Oospores are the “offspring” of “mating” by strands of fungal hair (mycelia). Given warm, wet conditions – oospores produce “bag-like” structures called sporangia (singular “sporangium”). Eventually, zoospores (swimming spores that actually have “tails” – correctly named “flagella”) are produced. Given time and wet conditions, these swimming spores come into contact with and eventually enter the plant. Additional sporangia are produced from this infection, and those sporangia release additional zoospores. The fungus itself may be observed as a white mold growing on plant tissue.

Symptoms of infection vary. Small dark lesions may develop in proximity and a few inches above the soil line as plants are eventually killed by the “damping off” version of this disease. Crown rot may eventually produce dark brown lesions that girdle the stem, killing everything above. Leaf symptoms may eventually cause foliage to brown. Fruit can become covered with white, moldy lesions. Lesions often start on the portion of the fruit in contact with the soil, but they can also appear in proximity to the fruit stem. Yield losses may approach 100 percent in some cases.

Phytophthora management in beans and Phytophthora management in pumpkins have some similarities. However, there is one significant difference between management in pumpkins and management in beans.

In beans, the use of resistant varieties is widespread. Soybean growers are familiar with resistant traits such as Rps1k, Rps1c, and Rps1a, and they often use these traits in the field. Unfortunately, resistance has not proven to be an option in pumpkin production. Instead, pumpkin growers rely upon a host of cultural and chemical management techniques.

On the cultural side, growers are encouraged to rotate pumpkin production from field to field to reduce the chances of encountering Phytophthora blight. They are also encouraged to stay away from fields that were previously in other Phytophthora host crops (peppers, tomatoes, etc.).

Growers also try to encourage a less-favorable environment for the disease by planting the crop where water does not tend to stand. In a similar fashion, growers are also encouraged to maintain good drainage. Both practices eliminate water from the Phytophthora-equation making it difficult for zoopsores to reach healthy plant tissue. Minimizing the spread of this disease is also important. The University of Illinois discourages growers from working fields when wet, encourages growers to clean equipment – when possible – before moving from field to field, and emphasizes that diseased fruit/plant material should be removed from the field as soon as possible.

Growers are encouraged to harvest ripe fruit as soon as possible to reduce any potential exposure to the fungus and/or time for the disease to develop post-infection. Chemical recommendations typically revolve around the use of mefenoxam (an RNA inhibiting seed treatment) and mixtures of dimethomorph (a post-emergence, sterol-inhibiting fungicide) and copper compounds. The former provides a few weeks of protection following emergence.

Leave a Reply

Fungicides Stories

Soybean field
FungicidesValent Launches New Seed Protection Fungicide For Soybeans
July 16, 2014
The INTEGO SUITE System contains the first new, novel seed protection fungicide chemistry registered in 30 years by the EPA for protection against Pythium and Phytophthora. Read More
FungicidesNew Players May Make Pest Headlines In Corn, Soybean
April 1, 2014
The usual insects and diseases took a bit of a break in 2013, but other culprits surfaced — and could return. Read More
Frog eye leaf spot on soybean
FungicidesMake The Case For Fungicides In 2014
February 3, 2014
New products are looking good, but will growers bite with lower crop prices? Read More
FungicidesMANA Introduces Custodia Premix Fungicide For Row Crops
January 14, 2014
New fungicide for corn, soybeans, and wheat contains the two most complementary systemic active ingredients available today in an optimized ratio to deliver both preventive and curative disease control. Read More

Trending Articles

Green Valley Ag facility
Retail FacilitiesGreen Valley Ag Adopts A.J. Sackett’s Precision Fertilizer Blending® Technology At New Facility
July 8, 2014
Sackett's Precision Fertilizer Blending® Technology is making huge strides around the world. Green Valley Ag adopts the technology at its new facility to support its advancing agronomic needs. Read More
Retail FacilitiesWaconia Manufacturing Builds Facility Designed For Speed, Efficiency
July 7, 2014
To make its new hub facility more efficient, Cooperative Elevator enlisted the aid of Waconia Manufacturing. Read More
EquipmentSummer Show Preview 2014: Superior Sprayers Take The Field
July 3, 2014
In this final installment of our coverage of the major categories of Big IRON that retailers can expect to test-drive at this summer’s events, here is a look at 19 sprayers. Read More
Scouting a soybean patch at Green Valley Ag.
EmployeesCropLife Compensation Survey: Battling Talent Drain
July 2, 2014
Retailers too often lose employees to companies outside of agriculture, while recruiting efforts are most often limited to competitors and other ag-focused organizations. Read More
HerbicidesDow AgroSciences Introduces SureStart II Herbicide
June 16, 2014
The enhanced formulation has improved viscosity and increased stability under heat and controls more than 60 high-anxiety grasses and broadleaf weeds found in corn fields. Read More
HerbicidesBASF Investing $270 Million To Expand U.S. Herbicide Production
June 11, 2014
BASF has invested more than $270 million to expand herbicide production capacities in the U.S., including more than 20 new products to be launched over next two years. Read More

Latest News

StewardshipMonsanto Joins Panel Of Innovators To Advance Research …
July 30, 2014
Monsanto Co. and The Climate Corp., its division, recently joined a roundtable of experts at the White House to share ideas and research approaches to help the world’s farmers manage and adapt to the impact of climate change on the global food supply. Read More
Crop InputsSoybean Checkoff Produces Big ROI
July 30, 2014
Under the soy checkoff program, all U.S. soybean farmers contribute a small percentage of their gross soybean sales for research and marketing projects that maximize their profit potential. Read More
CropLife 100Learfield Sports, CHS Agree To Football-Centric, Colleg…
July 30, 2014
CHS Inc. will embark on a highly integrated collegiate sports sponsorship platform with 24 Division I universities in 19 states designed to reach the farmer-owned cooperative's rural owners and customers. Read More
LegislationUSDA Implements Key Farm Bill Crop Insurance Provision
July 30, 2014
The new Supplemental Coverage Option, available through the federal crop insurance program and set to begin with the 2015 crop year, is designed to help protect producers from yield and market volatility. Read More
CropLife 100Wilbur-Ellis Forms New Organizational Structure For Its…
July 30, 2014
The new structure will provide more responsive internal support and will allow regional vice presidents and area managers to spend more time with customers, on talent development and on operational excellence across branches. Read More
Palmer pigweed in cotton
HerbicidesNew Training Modules On Herbicide Resistance Now Availa…
July 30, 2014
The Weed Science Society of America has announced the availability of three new education modules on herbicide resistance in weeds. Read More
HerbicidesWillowood To Market Glufosinate
July 28, 2014
Willowood USA recently announced that Federal EPA has approved its technical registration for glufosinate. Read More
InsecticidesHow To Scout For Corn Earworms In Corn
July 28, 2014
In her weekly report, University of Missouri Agronomy Specialist Jill Scheidt discusses what to look for when scouting for corn earworm. Read More
Crop InputsDuPont Pioneer, Weyerhaeuser Enter Technology License A…
July 28, 2014
The agreement brings together agricultural and forestry know-how to sustainably improve crop productivity for corn growers around the world. Read More
EquipmentAGCO Launches Global iPad App
July 28, 2014
The free AGCO Global iPad App can be downloaded from the Apple iTunes Store and features the full family of RoGator self-propelled sprayers and TerraGator high-floatation spreaders. Read More
Eric SfiligojYuma Centennial Ag Supply Earns 2014 National Environme…
July 28, 2014
Colorado-based ag retailer receives top trophy in 24th annual DuPont Crop Protection/CropLife ceremony. Read More
CropLife 100Pinnacle Forms Alliance With Wildlife Managment, Seed O…
July 25, 2014
The strategic alliance will provide Tecomate with key wildlife products, processing facilities, distribution centers and sales through Pinnacle’s ever-growing retail network. Read More
ManagementFranken Presses White House On RFS Support
July 25, 2014
Al Franken and a group of Senate democrats recently met with senior White House official John Podesta to urge the administration to change its position on an EPA proposal. Read More
ManagementASA, FarmLink To Launch ‘Operation Benchmark̵…
July 25, 2014
The American Soybean Association (ASA) and FarmLink are teaming up to help farmers close the $11 billion gap between what they harvested in 2013 and what they could harvest annually. Read More
StewardshipNorthey: Farmers Commit $1.4 Million to Try New Water Q…
July 25, 2014
The practices that are eligible for funding include cover crops, no-till or strip till and using a nitrification inhibitor when applying fall fertilizer. Read More
Precision AgFarmers Learn How Changing World Will Impact Iowa
July 24, 2014
Technology and understanding global consumer demand for Iowa farm products brought hundreds of farmers and agribusiness leaders to Ames recently for the annual Iowa Farm Bureau Federation Economic Summit. Read More
HerbicidesPurdue: Late Season Weeds May Require Manual Removal
July 24, 2014
Hand-rouging and pulling late season weeds by hand may be the best way to remove them, more so than using a herbicide, a Purdue Extension weed scientist says. Read More
Soybean Field
InsecticidesTransform WG, Closer SC Insecticides Receive R&D 10…
July 23, 2014
Dow AgroSciences has received the award from R&D Magazine for Transform WG insecticide and Closer SC insecticide with Isoclast active. Read More