Crown Rot (Phytophthora Cactorum): Strawberry Disease & Prevention Techniques

What Is Crown Rot?

Crown Rot And Its Effect On Strawberry Crops

Strawberry suffering from Crown Rot (Phytophthora Cactorum)Phytophthora Cactorum is a soil-inhabiting plant pathogen which has grown in prominence over the last 10 to 15 years.

Often confused with Anthracnose Crown Rot (both are similar, though they exhibit different symptoms, which we’ll explore in more detail below), it’s Phytophthora Cactorum that can lead to the onset of Crown Rot (also known as Vascular Collapse) in strawberry crops.

Crown Rot most often occurs in strawberries that are planted in either poorly drained or over irrigated soil, or during long periods of rain in warmer climates.

In these wet conditions, the roots and crowns of strawberry crops are infected when they come in contact with the ‘Sporangium’, which is produced when the resting spores of the disease begin to germinate. Sweet Charlie crops are the most susceptible to this disease, but it has also been recorded in both Chandler and Camarosa varieties.

The pathogen itself favours wet conditions, where it survives as a persistent, resilient resting spore which, once introduced into the soil, dirt, field or infected plants, can remain a problem for years to come if not treated effectively and in a timely manner. The primary source of infections comes via the oospores in the soil, as well as infected transplants, infected tips, or through infected water. In extremely wet conditions, for example, the disease has been known to release spores – called zoospores – into the water, which actively seek out and infect the crowns and roots of strawberry plants.

This is why the early identification and treatment of Phytophthora Cactorum is paramount to the continued health and growth of your crops.

Symptoms & Signs Phytophthora Cactorum May Be Affecting Your Strawberry Crops

As with other soil pests and diseases, the earliest signs of Phytophthora Cactorum can be found in the stunting of plants as well as the wilting of young leaves, which is most visible between flowering and harvest, as well as periods of high water need (such as hot, dry weather spells, as the fruit load increases, or after the transplants are set). These symptoms will either persevere throughout the season, or the disease will progress to a point where the foliage turns a bluish colour, before the entire plant wilts and collapses.

As the foliage changes colour, the crown also exhibits a deep, dark red discolouration, which is usually first seen in the upper part of the crown, hence the term ‘Crown Rot’. It has also been known to occur at the base or the middle of the crown, too. At this stage, taking a look at a cross-section of the crown would reveal water soaked, light brown tissue where, as the disease progresses, an extensive necrosis will begin to appear that is uniformly brown in colour and no longer just restricted to vascular tissue.

The symptoms of Crown Rot (Phytophthora Cactorum) Strawberry disease

From here, the disease spreads, causing young leaves to wilt suddenly. This wilting is often accompanied by drought like symptoms visible on the leaves, including the browning of leaf margins which moves between veins, before the leaves wilt suddenly. While they may recover, plants are usually stunted if they do. And if they don’t, then a complete collapse will usually follow within a day or two.

Below the ground, the symptoms don’t show themselves until the aboveground portions are dead. A closer look at this stage will show oospores in the root tissues, and reveal that the roots are, more often than not, black at the point that they attach to the infected crown area.

Phytophthora Cactorum Prevention & Management Techniques

Ways To Prevent & Manage Phytophthora Cactorum In Strawberry Crops

1. Choose A Site Carefully

Phytophthora Cactorum occurs in poorly drained or overly wet soil, so choose a site with adequate soil drainage to ensure that the soil won’t become waterlogged after watering or in the event of heavy rains/ This can be difficult to do, which is why it’s recommended that, whenever possible, you plant strawberry crops in raised beds, or at the very least avoid fields with a history of disease.

If circumstances dictate that you must plant in a field, rip these fields during the soil preparation process and prior to planting. This will break up any hardpans, and help to improve soil drainage for the rest of the season.

2. Use Disease Free Plants

The introduction of Phytophthora Cactorum via diseased plants can have a long-lasting impact on your ability to grow healthy strawberry crops, not to mention your bottom line as treating areas that were once healthy takes both time and money.

If you find that your crops and fields have been affected, then field treatment is likely the most economical method in most cases. Moving forward? You should implement an integrated management plan: adopt best practices to minimise the possibility of cross-contamination during plug production, and use disease free plants.

As with all disease-prone crops, you should only ever plant disease-free crops, plants and seeds. Not only will this dictate the long-term health of individual strawberry crops, but it also ensures the health and longevity of the soil you’re planting in for the seasons to come.

3. Use Common Sense Husbandry Techniques

This advice is largely self-explanatory: avoid over watering crops, and use only clean, disease-free water when you do. As discussed above, Phytophthora Cactorum spreads through the runoff of water, while waterlogged soil can both cause, and harbour, the disease.

4. Soil Fumigation & Chemical Controls

Strawberry soil services and soil fumigation products like Pic-Fume Chloropicrin and Pic Plus Chloropicrin can help to reduce inoculum, while fungicides such as Mefenoxam (Ridomil Gold) and Metalaxyl have proven to be effective in the fight against Phytophthora Cactorum when applied through drip irrigation. This is best applied soon after planting, with additional applications made throughout the season.

Images via Pacific Northwest Handbooks & NC State College of Agriculture and Life Sciences

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    PO Box 4036
    Marewa, 4143
    Napier, New Zealand

    Phone: +64 6 843 5330
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