Does mulch help manage pests in organic day-neutral strawberries?

 Article written by Will Pradel, Undergraduate Research Assistant, Matthew Gullickson, Post-doctoral Associate, and Mary Rogers, Associate Professor of Organic Horticulture at the University of Minnesota

Organic day-neutral strawberries are gaining interest in Minnesota because they allow growers to harvest fruit well beyond the traditional June-bearing season. However, extended harvest also means extended pest pressure, which can make it difficult for new and transitioning growers to maintain fruit quality.

Tarnished plant bug and western flower thrips are two of the most challenging pests of day-neutral strawberries in Minnesota, especially in organic systems. Mulches come in different colors and coatings, and their reflective properties can influence insect movement and habitat preferences. A two-year study in Minnesota and Wisconsin evaluated whether different mulch types could help reduce insect damage and improve marketable yield in organic day-neutral strawberry production.

Researchers compared four mulch types:

• Black plastic

• White on black plastic (commonly used by growers)

• Reflective (metallic) plastic

• Biodegradable paper mulch

• 

Far left and far right: white-on-black plastic; left: paper mulch; center: reflective plastic; right: black plastic.

What did this study find for growers?

Marketable yield and insect damage

Across both years, black plastic mulch produced the highest proportion of marketable fruit, followed closely by reflective plastic mulch.

White-on-black plastic and paper mulch produced a lower proportion of marketable fruit.

In the paper mulch plots, fruit quality was reduced in part because the mulch broke down during the season. Torn and deteriorating paper allowed soil and paper fibers to stick to berries, making fruit unmarketable.

Image: Paper mulch after a damaging weather event. 

Tarnished plant bug (TPB)

• Reflective plastic had the lowest amount of fruit damage caused by TPB.

• White-on-black plastic had the highest amount of fruit damage caused by TPB.

Although reflective mulch did not reduce TPB numbers, it was associated with less TPB-damaged fruit.

Strawberries with TPB damage

Image: Strawberries showing classic "catface" due to tarnished plant bug damage. Photo by Eric Burkness.

Western flower thrips (WFT)

• Reflective plastic consistently had the fewest thrips.

• White-on-black plastic had the most thrips.

• Black plastic and paper mulch were intermediate.

When fruit damage from thrips (bronzing) was evaluated:

• Black plastic had the most bronzed fruit.

• Damage levels among the other mulch types were similar.

It is important to note that bronzing caused by thrips can be difficult to visually separate from discoloration caused by heat and solar radiation, which may explain the higher levels of bronzing seen in the black plastic treatments.

Image: Varying levels of bronzing due to western flower thrip damage. Photo by H.A. Smith, University of Florida

What should growers consider?

Based on two years of data from Minnesota and Wisconsin:

Growers should consider using black or reflective plastic mulches to reduce insect-related losses while maintaining high marketable yield.

• Black plastic provided the highest overall marketable yield.
• Reflective plastic provided the lowest thrips pressure and the lowest TPB damage.
• White-on-black plastic, the current standard for many growers, consistently performed worse for insect damage and marketable yield in this study.
• Paper mulch broke down quickly, required more weed management, and increased the risk of dirty and unmarketable fruit.

Interested in learning more about day-neutral strawberry production? Check out the UMN Extension day-neutral strawberry farming webpages for more information.