Strawberries and Fungicides

Published: January 1, 2013

Strawberries offer potential as a profitable crop for Missouri farmers. However, strawberry disease management is often a problem because of environmental conditions favorable for disease development, cultivars that are in many cases disease-susceptible, and the presence of diseases at many production sites. Strawberry disease management programs have often focused on intensive fungicide applications. More recently the emphasis has become more integrated, incorporating disease resistance, cultural practices, and biological control, along with the fungicide use, but at lesser amounts.

Strawberry IPM requires a thorough knowledge of disease biology. For a complete discussion of strawberry diseases note the publications in the reference list, particularly the Compendium of Strawberry Diseases, for details. For this article I'll use gray mold, a common and sometimes severe disease in Missouri, as a case study. This disease is caused by the fungus Botrytis cinerea, and it attacks strawberry fruit, calyxes, and flowers. Botrytis fruit rot usually begins as a small lesion at the blossom end of the fruit, or where a berry is touching another infected berry. The infected portion is firm and brown while the berry is still green, but it expands and softens as the fruit ripens. A powdery gray mass of spores covers infected berries if the weather remains humid and/or air circulation is poor. Under typical Missouri conditions gray mold can destroy 50% or more of a strawberry crop.

Typical symptoms of gray mold rot on strawberry fruit.

How do we manage gray mold in Missouri? Unfortunately the common strawberry cultivars are not resistant to gray mold (or most other economically significant diseases). This fungus has a wide host range and can survive on plant debris in the soil; thusHow do we manage gray mold in Missouri? Unfortunately the common strawberry cultivars are not resistant to gray mold (or most other economically significant diseases). This fungus has a wide host range and can survive on plant debris in the soil; thus disease inoculum is present in or around most strawberry fields. Moist conditions and temperatures between 40°F and 80°F promote it and are expected each year. Biological control of gray mold is not considered practical for in field production, but some research looks promising. Cultural practices to focus on are:

• promoting good air movement among the plants (adequate plant spacing, narrow row width, raised beds, weed control, fertilizing after fruit harvest)
• irrigation by drip instead of overhead sprinklers.

Use of fungicides is highly encouraged if one wants to harvest a high percentage of fruit produced. The fruit will hold better as well. Reduced fungicide use is possible. As an example, in the past a typical gray mold fungicide program emphasized 6 applications from bloom through harvest. More recently research has demonstrated that most initial gray mold infections take place during bloom, and that 2 or 3 applications during the bloom period give adequate gray mold control for the season. A very simple home garden recommendation may suffice for many small growers- a spray of Captan at these times:

early in spring when new growth starts (a week or two after mulch removal);
• when plants begin to bloom;
• at full bloom.

Sources for more information:

• Midwest Commercial Small Fruit and Grape Spray Guide (MU Bulletin MX377)
• Midwest Small Fruit Pest Management Handbook (OSU Bulletin 861)
• Midwest Strawberry Production Guide (OSU Bulletin 926)
• Compendium of Strawberry Diseases (1998, APS Press)
• Production Guide for Organic Strawberries (NYS IPM Publication No. 226)