Strawberry clipper is considered to be a major pest on matted-row strawberries in the northern U.S. and Canada. This pest is thought to be so threatening that even a single clipped bud indicates the potential for serious and rapid damage. Conventional wisdom states that fields should be treated for clipper during warm weather if they have a history of clipper damage—even if fields have not been scouted. Thresholds (fi ve clipped buds per meter) are based on the assumption that one clipped bud is equivalent to the loss of one average-sized berry. However, our data show no correlation between clipper damage and yield in field surveys, and our artificial clipping studies have found that strawberry plants have the ability to compensate for flower bud loss by increasing allocation to other fruits. For example, in plots of cv. Jewel, no significant difference was found in total yields between plots with no flower bud removal and plots with all primary flower buds removed (an average of 100 clipped buds per meter)—so long as the clipping happened early in the season. An increase in the size of secondary and tertiary fruit balanced the reduced fruit numbers. Similar trends were found with Kent. The ability to compensate for early flower bud loss also was assessed in a separate study with 10 strawberry cultivars. These studies suggest that our current threshold for clipper may be nearly two orders of magnitude too low, and that clipper may not be a true economic pest of strawberry.
Marvin P. Pritts and Greg English-Loeb
Marvin Pritts, Mary Jo Kelly and Greg English-Loeb
The strawberry bud weevil (Anthonomus signatus Say; clipper) is considered to be a serious early-season pest in perennial matted row strawberry (Fragaria ×ananassa Duchesne) plantings in North America. Adult females damage flower buds in early spring by depositing an egg in the bud, then clipping the bud from the pedicel. Action thresholds are low (two clipped buds/meter of row) because pest managers and growers have assumed that one clipped flower bud results in the loss of one average-sized fruit. Fields with a history of clipper damage are often treated with insecticides during the first period of warm weather that coincides with inflorescence development, without scouting for clipped buds or evaluating damage. We examined 12 strawberry cultivars and found that most can compensate for a significant amount of flower bud loss, provided that the loss occurs early in the development of the inflorescence. A new threshold is proposed in which the potential loss of fruit per inflorescence is considered, along with the total number of severely damaged inflorescences. We believe that in most circumstances and with most cultivars, clipper injury will remain below the damage threshold.