Organic Day-neutral Strawberry Insecticide Efficacy for Tarnished Plant Bug

Article written by Will Pradel, Matthew Gullickson, Mary Rogers of the University of Minnesota.

About tarnished plant bug (TPB)

Tarnished plant bug (TPB, Ligus lineolaris) is a strawberry pest to manage for Midwest growers, especially for organic production systems. TPB feeds on developing strawberry seeds (achenes) as well as the surround parts of the young strawberry buds, flowers, and fruit. 

Their damage leads to "catfacing" deformations (apical seediness), which reduces strawberry yield and marketability. Since day-neutral strawberries continuously bear fruit throughout the season, TPB damage can be exceptionally devastating when populations are not well-managed.

University of Minnesota research trials

In the summer of 2024, an insecticide spray trial was conducted at the University of Minnesota Agricultural Experiment Station in Saint Paul, Minnesota. Three OMRI-listed insecticides were applied to organic day-neutral strawberries individually and in rotation to assess their efficacy for managing TPB.

Insecticides used:

• Pyganic 5.0 (5% pyrethrins)

• DeBug Tres (4.7% neem oil, 3% azadirachtin)

• Aza-Direct (1.2% azadirachtin)

This experiment consisted of seven treatments: 

• A high rate of Pyganic (15.6 fl oz) followed by a high rate of DeBug Tres (22 fl oz)

• A high rate of Pyganic ( 15.6 fl oz) followed by a low rate of Debug Tres (8 fl oz)

• A low rate of Pyganic (4.5 fl oz) followed by a high rate of Debug Tres (22 fl oz)

• A high rate of Pyganic (15.6 fl oz)

• A high rate of DeBug Tres (22 fl oz)

• A high rate of Aza-Direct 

• An untreated control 

Foliar insecticide applications were made weekly between July 11 and August 6, 2024. Applications were made with a CO2 backpack sprayer (1.5 ft boom; single flatfan nozzle; 35 psi; 30 gpa; 6.8 water pH). Strawberries were harvested between July 17 and August 30, 2024. 

Images: TPB damage categories in day-neutral strawberries measured in percent apical seediness. Strawberries with medium and high TPB damage were classified as unmarketable due to TPB.

Findings

• Researchers did not observe phytotoxicity or damage from any of the insecticide treatments on the strawberry plants.

• Plants treated with the Pyganic (high concentration) rotated with DeBug Tres (low concentration) or Pyganic (low concentration) rotated DeBug Tres (high concentration) had the least amount of TBP-damaged fruits. 

• TPB counts were lowest in plants treated with either Pyganic (high) or Pyganic (high) + DeBug Tres (low).

Grower recommendations

Azadirachtin, (trade name Aza-Direct) alone was previously one of the most widely-used insecticides for the management of TPB in organic day-neutral strawberries. However, the results of this study indicate that applying azadiractin and neem oil in rotation with pyrethrins, particularly a high application rate of Pyganic 5.0 followed by a low application rate of DeBug Tres, can decrease TPB pressure and fruit damage. These results support general recommendations to rotate insecticide active ingredients, not only to limit insecticide resistance, but also to increase efficacy.

Regardless of the insecticide you choose*, applications should only be made when TPB populations exceed the economic threshold. Applications should be made either in the early morning or late evening to minimize harm to pollinators, which are less active at these times. 

*The University of Minnesota Extension does not endorse any specific insecticide products or trade names. Always read and follow the pesticide label directions. The pesticide label is a legal document and must be followed when applying any pesticide product.