Tuesday, January 26

How to Manage Phytophthora Crown Rot on Southeast Louisiana Strawberries

Photo of a strawberry plant suffering from crown rot.

Baton Rouge, La. – Southern University Ag Center Agriculture and Natural Resources Agent Ahmad Robertson, Sr., along with state plant pathologists Drs. Raj Singh, Melanie Ivey and LSU Ag Center vegetable specialist Dr. Kiki Fontenot, recently visited several strawberry farms in St. Helena and Tangipahoa Parishes to assist farming operations suffering from crown, root and stem rots this winter.

The specialist provided the farmers with an action plan with control recommendations for insect and disease management.

Last year Southeast Louisiana received 12 inches of rainfall in late October. This excessive soaking after rain showers and storms can ruin a plants’ roots, which in turn affects how plants grow.  Strawberries are among the most challenging horticultural crops to grow in the South due to high levels of soil borne pathogens, such as phytophthora.

When the soil becomes saturated with water, this pathogen can produce and release zoospores, which swim through water-filled pores to infect plant tissue. Infections can occur during cool to moderate temperatures, which are typical throughout Southeast Louisiana fruit and vegetable production cycles.

Symptoms of phytophthora usually begin in the upper part of the plant's crown and spread downward. The youngest leaves wilt suddenly and often turn a bluish green color. Wilting spreads quickly throughout the plant, and complete collapse occurs within days.  When infected plants are cut open, a brown discoloration can be seen in the crown's vascular tissue or throughout the crown's tissue.

Field Management:  
The pathogen can be controlled in production fields by using soil fumigation and good cultural practices. These practices include the use of certified transplants, avoiding poorly drained soils, and preparing fields to provide good soil drainage during wet weather. 

Soil Preparation:
Good surface drainage is absolutely necessary for a successful vegetable garden. Water standing in the garden for long periods of time is fatal to the growth of vegetables. Low and wet areas can be improved by adding eight inch layers of top soil (two-three yards of topsoil per 100 square feet) to raise the garden site. Also make sure to put in drains to carry water away from the garden and plant crops on high rows.  All vegetable crops in Louisiana should be grown on raised beds at least 10 inches high. High rows encourage good drainage, especially during times of heavy rains.

Cultural Control:
Use raised beds and carefully managed drip irrigation; plant in non-infested soils that have good drainage. Soil solarization has been shown to be effective for the control of soil borne pathogens and weeds. Solarization is a method of using the natural energy of the sun to sufficiently heat the soil to temperatures high enough to kill many soil pests. To use this method, a clear plastic tarp is used to cover the soil, trapping heat beneath it. Pests that may be killed during solarization includes nematodes, plant diseases, and weeds. Most nematodes are killed when the soil temperature goes above 118 degrees.  The hottest months, June, July, and August, are the best times for solarization. Adequate moisture should be present in the soil to irrigate it, if necessary before treating. If conditions are dry it’s advisable to run some type of irrigation or soaker hose under the plastic to water the soil during the course of the treatment. The plastic tarp should be left on the area for eight weeks.

Control Management:
Commercial farmers should use fungicides, such as Ridomil Gold SL or Aliette WDG, to manage crown rots.  Begin a fungicide application at the first sign of disease and repeat applications according to the product’s directions.

Maintaining good sanitation of planting beds, inspecting plants, handling plants carefully, using crop rotation and planting resistant cultivars are great practices for disease management.

For more information, contact Ahmad Robertson, Sr. in the Tangipahoa Parish Extension Office at 985.748.9381, or in the St. Helena Parish Extension Office at 225.222.4136.


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