Why is field pansy a problem in strawberries?

Field violets, or field pansies, are problem weeds for strawberry growers. Rob Grohs, a weed technician at the University of Guelph in Simcoe, provided some information on why this weed can be such a problem.

Why is field pansy a problem in strawberries? Field pansy is a winter annual weed. This means that it is one of a class of plants which germinates in the late summer or fall, over winters as a seedling or small plant, then continues growth in the spring. Winter annuals cannot withstand hot weather, and generally set seed and die as summer weather begins. Winter annuals are problem weeds for strawberry growers for several reasons. First, the lack of fall or spring tillage in strawberries means that the growth of winter annuals is not disturbed. Second, winter mulch provides protection for these weeds, and increases winter survival. And third, renovation does not affect winter annual weeds, as they have usually produced seed and died by the time renovation is performed. Renovation does disturb summer annual weeds (weeds which germinate in the spring and die in the fall), so winter annual weeds tend to become dominant in strawberries

Biology: Field pansy flowers from April to October. The flowers can be cross-pollinated by insects but are self-fertile and largely autogamous. Each seed capsule contains around 75 seeds and a plant may produce 1,500 to 2,500 seeds. An isolated plant growing in favourable conditions can produce many more seeds but in competition with a cereal crop seed production is much lower. Plants can be found in fruit for 7 months of the year.

Persistence and Spread: Seed longevity in soil is at least 4 years. Seeds broadcast onto the soil surface, then ploughed to 20 cm and followed over a 6-year period of cropping with winter or spring wheat had a mean annual decline rate of 48% and an estimated time to 95% loss of 4-6 years.

In dry conditions some mature seed capsules split open explosively and disperse the seeds over 2 m from the parent. Other seeds remain in the capsules even after soil cultivation leading to small but dense patches of seedlings emerging in unison.

Up to 55% of seeds remain on the plant at cereal harvest and many are collected up with the cereal straw. The seeds are dispersed when the straw is used as mulch or for animal bedding.

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