Time to Think About Sampling Spider Mites in Strawberries
While it is still cool outside, February is the time of year when North Carolina strawberry growers should begin preparing to monitor twospotted spider mites, the most frequent and often most damaging arthropod pest of southeastern strawberries.
When should I start monitoring twospotted spider mites?
Twospotted spider mite activity is affected by both temperature and day length. A portion of the population becomes reproductively inactive during winter when day length is shorter, and twospotted spider mites are inactive at temperatures lower than 50°F. Mite sampling should begin in February or March when daily high temperatures are consistantly above 50°F.
How often should I monitor twospotted spider mites?
Under ideal conditions (68°F and dry), twospotted spider mites can complete a generation in as little as week. Therefore, we recommend that growers monitor spider mites weekly in order to keep trap of potentially rapidly growing populations.
How should I montitor twospotted spider mites?
We recommend that growers collect 10 leaflets (one lobe of a leaf) per acre and observe the number of mobile mites on this sample. Mites can be observed on individual leaves with a 10x or 20x hand lens, or all the leaves in a sample can be combined onto a single glass plate using a mite brush and observed under a microsope, as described in our latest Specialty Crop IPM video:
How do I know when my mite populations are too high?
Twospotted spider mite feeding most significantly effects yield in strawberries when it occurs prefruiting, so the treatment threashold for mite populations early in the season is 5 mobile mites/leaflet. When plants are fruiting and growing rapidly, they can handle higher mite populations, so we recommend treating post fruiting only if mobile mites per leaflet exceed 15. Practically, what this means, is that for your 10 leaflet per acre sample, you have reached threshold prefruiting if you have observed 50 mobile mites, and you have reached threshold post fruiting if you have observed 150 mobile mites. Be careful not to confuse mobile pest mites (twospotted spider mites) with beneficial predatory mites.
What should I do if my mite populations exceed the treatment threshold?
If mite populations exceed the treatment threshold based on plant growth stage, management is justified. Both conventional and organic management recommendations are available from the Southern Region Small Fruit Consortium Strawberry IPM Guide and the NC Agricultural Chemicals Manual.