Homesteaders put a lot into their crops. After all, that’s the food you need to feed your friends and family. As the cost of living increases, we all look for ways to fill the pantry on the cheap. It makes those crops that we grow extremely precious and important.
We must be careful to avoid pests and diseases or we run the risk of losing our plants. Phytophthora is one disease that could de-rail your harvest.
It’s not only destructive, but Phytophthora targets a huge range of species that you might grow. Let’s look at what you need to know.
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What is Phytophthora Blight?
Phytophthora is a genus of water molds, also known as oomycetes, that cause blight in many species. It’s commonly called pepper blight, Phytophthora blight, or Phytophthora root and crown rot. It also causes rhododendron root rot, sudden oak death, and potato late blight.
This horrendous plant pathogen lives in the soil for ten years or more, even when a host plant isn’t around. The pathogen’s zoospores travel to infect new hosts through water, on plant material, or on garden tools.
The reproductive spores are contained in puffy white to grey masses on the host plant until they are ready to open and spread.
Heavy rainfall, flooded ground, irrigation channels, saturated beds, and prolonged damp clay-based soils are prime environments for it to reproduce and travel. Once it does, it can transfer to other areas of the garden, fields, and crops.
The transfer of garden debris can also move the pathogen throughout the garden, as can planting infected vegetables or fruit or using infected compost. It can even hitch a ride on your dirty shoes or tools.
The pathogen needs warm conditions and moisture to reproduce and spread. The perfect temperature for reproduction is around 80°F, but it can tolerate a range between 75°F and 95°F. Above or below that, it won’t reproduce as readily, but it can still survive.
It is almost impossible to spot with the naked eye until it has invaded a host plant and caused symptoms. In the blink of an eye, it can sneak up on any beginner gardener or advanced farmer.
The pathogen has both male and female structures, meaning they can reproduce asexually, allowing them to rapidly colonize a garden.
Phytophthora is a formidable threat. It’s one of the most destructive diseases of vegetables and ornamentals out there. Read on to find out what to look for and what to do if it strikes.
Commonly Infected Species
The crops most at risk of this devastating disease are those in the Solanaceae, Cucurbitaceae, and Fabaceae families. These include most of the favorite crops that are go-to staples for the home grower, such as:
The primary reason such vegetables and fruits are at risk from this pathogen is that they share some genetic and physiological similarities. These similarities make them vulnerable to this specific disease.
It also impacts tons of different ornamentals, like rhododendrons,
The pathogen species tend to be plant species-specific, meaning that one pathogen species won’t attack plants in totally different genera. For example, P. cactorum attacks rhododendrons, azaleas, and orchids.
P. capsici is the species that infects cucurbits. P. cinnamomi is common in ornamentals like arborvitae, azalea, dogwood, forsythia, hemlock, holly, juniper, rhododendron, and some evergreens.
P. citricola impacts citrus plants, P. infestans causes potato blight, P. nicotianae attacks tobacco and alliums, and P. ramorum is the culprit in dozens of plant species.
Different species cause different symptoms. Some species cause root and stem rot, some focus on fruits, and some primarily appear on the leaves.
If you live in an area where this pathogen is common, and you’re growing commonly infected species, you must be aware so you can take preventative measures in the spring through fall when it’s active.
It’s most common in Zones 6-10 in areas with regular or heavy moisture.
Signs and Symptoms
Symptoms will vary depending on which species has been infected, the age of the host plant, the species of Phytophthora, and the stage of the infection.
1. Root and Stem Rot
Phytophthora causes stem and root rot. When this happens, roots and stems become soft to the touch or with water-soaked lesions at the base of the host plant. These lesions are normally visible above the soil line.
Once the roots or stem begin to rot, the foliage turns yellow and starts to wilt, even when there is water available in the soil. This is soon followed by the collapse and death of the plant.
If you dig down into the ground, you’ll find black and discolored roots. If you touch them, they’ll feel mushy and soft.
2. Fruit Rot
Fruit rot is another common symptom of Phytophthora blight. When present, lesions appear on the fruit skin. These are generally circular in shape and mushy or water-soaked. It’s most common on fruits that are in contact with the soil or have a lack of airflow.
The lesions expand quickly and the fruit may become covered in a white fluffy substance, as spores develop for further dispersal. As the disease progresses, the infected fruit collapses and rots completely.
3. Foliar Blight
When Phytophthora attacks leaves, it will cause irregular, water-soaked lesions. These will gradually expand and will cause the leaves to wilt and die. The lesions could develop a distinct dark-colored border.
In humid conditions, white cottony growths can appear on the underside of the leaves.
4. Seedling Damping Off
Phytophthora can cause damping off in seeds and young seedlings, resulting in failure to germinate properly or quick death at emergence.
Seedlings may fail to develop correctly and thrive. They often wilt, as their roots are unable to uptake water from the soil. You’ll also see discolored stems at the soil line, leading to complete seedling collapse and death.
Prevention and Management
The best option in the case of Phytophthora is to try to prevent it in the first place.
Denying the pathogens the favorable conditions they need to strike and multiply can help manage potential outbreaks and re-infections.
1. Site Planning and Soil Preparation
Choose planting locations that are well-draining and with a history free from Phytophthora infestations. If you’ve had Phytophthora in the past ten years, choose resistant species. Ginkgo, birch, rose, willow, dahlia, aster, mint, fern, trillium, geranium, impatiens, and sweet potato are all resistant.
Be mindful of planting in low areas of the garden, like the bottom of slopes, where water may not drain away promptly. Good drainage is vital in preventing the spores from developing and reproducing.
It is also advisable to test the drainage in your growing area. Heavy clay soils are more likely to pool water. Consider utilizing raised beds or amend the soil at least two feet deep with well-rotted compost or manure.
Make sure any soil additions to your property come from a reliable source so as not to transfer the disease from an infected garden.
2. Crop Care
With all crops susceptible to Phytophthora, proper care is a vital step in prevention and management.
For crops that have a tendency to fall over due to fruit weight or trail along the ground, they should be supported through staking or grown on a trellis. This improves air circulation and reduces the chances of infection.
Thinning plants can also help improve air circulation, as can planting with good spacing.
Any sick or failing seedlings should not be planted out. If in doubt dig it up and throw it out.
3. Crop Rotation
Developing a crop rotation plan each season is an advantage in all aspects of growing your own food. Crop rotation helps you avoid all kinds of pests and diseases, not just Phytophthora.
Alternate the planting of susceptible crops with non-host plants. You should plant susceptible plant in the area only once every five years. Doing this assists with breaking the disease cycle.
Select plants that have been developed to resist or tolerate this disease. Some bell pepper varieties, for example, have been hybridized to withstand P. capsici. Be sure to read the label to see which diseases the plant can resist.
4. Irrigation Management
You should always water at the ground level and not on the foliage of the plant. Wet foliage encourages disease and splashing water assists with the spread of the pathogens. Instead, use drip line irrigation or, if hand watering, water at soil level.
Optimize irrigation practices to avoid water logging and maintain well-drained soil conditions. Regularly add good-quality organic compost or mature compost to gardens to assist with nutrients and drainage.
Incorporating good organic matter, fertilizer, and compost into the soil will help to improve the structure, consistency, and microbial diversity. This enhances the resilience of the plants.
Avoid overwatering or constant wick methods in the greenhouse and cold frame growing. Too much water promotes this disease’s development.
Don’t put numerous plants in one area. Instead, opt for smaller trays spread out on shelves. Promptly dispose of any sick plants.
Use clean, fresh rainwater or well water. Avoid water from canals if Phytophthora is a known problem in your area.
5. Garden Hygiene
You absolutely must practice good garden hygiene. It’s imperative not only for this disease but also for many others.
Use clean tools, equipment, and footwear when working in the garden to prevent the introduction or spread of spores.
Avoid disposing of contaminated water or garden debris in other areas of the garden. If this disease is suspected, carefully remove all affected plants and soil.
Treating Phytophthora
Early detection can make all the difference in stopping this disease. At the first sign of trouble, take immediate action. If Phytophthora arrives, all hope isn’t lost. Fungicides can usually help stop the disease in its tracks. They can also be used as a preventative.
In addition to the plants themselves, make sure the surrounding vegetation and soil is also treated. This is especially important if your growing space is small and plants are relatively close to one another, such as in an urban backyard.
Always read the instructions on any treatments and apply them in accordance with the manufacturer’s recommendations. Some cases may require frequent applications to ensure protection.
Copper fungicide can be effective, especially as a preventative or when applied at the first sign of problems. Buy a 16-ounce concentrate at Amazon.
A product that contains Bacillus amyloliquefaciens strain D747 is also effective. Monterey Disease Control contains this powerful bacteria and can be found at Amazon, as well.
Or, look for a product like Mycostop, which contains the beneficial bacteria Streptomyces Strain K61.
Rotate fungicides with other prevention and management methods to avoid fungicide resistance developing.
