Do Row Covers Impact Spider Mites in Strawberries?
As strawberry growers deal with cold winter weather, many are applying row covers (also called remay) to prevent injury to plants and maintain growth. The use of row covers on a short term basis to deal with periods of cold weather and prevent plant injury is somewhat unique to our strawberry growing region. In colder areas, such as New England or the midwest, row covers are typically applied for the duration of the winter. While some North Carolina growers may also use row covers for the duration of the winter, it’s also common pratice to put them on in periods of sub freezing temperature and remove them during warm weather.
Upon moving to North Carolina and beginning to work with strawberries, one of the first questions I had was what impact the use of row covers, both long and short term, would have on important arthropod pests, such as twospotted spider mites. With support from the North Carolina Strawberry Association, we conducted a multi year project to determine if row cover duration or weight had an impact on twospotted spider mites. We presented a poster summarizing the results of this work at Entomology 2013, the annual meeting of the Entomological Society of America, and at the Southeastern Strawberry Expo.
Our main findings were:
1. During cold winters, neither how long row covers were present nor row cover weight impacted twospotted spider mite severity. At both locations this trial was conducted, spider mites were not present on plants at transplant. We cannot say, based on our study, what impact row covers would have on plants infested at transplant.
2. During a warmer winter,spider mites were more severe in plots which were covered the longest, in that case, plants that were covered from December 15 through May 15. Interestingly, although mites were more severe in the plots with the longest row cover treatment, mite severity had no impact on yield at this site.
The take home message for now from these experiments is that row covers may impact mites severity, especially when used for a long time in warm areas. However, it likely remains more important to manage mite populations (if present) at transplant and in the spring before fruiting. If row covers are shared between fields, they could also move spider mites, and other pests, around to new places.
We also presented our findings on spider mite severity and biology under high tunnels over the winter in this same poster, and I’ll summarize that information in a seperate post.