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Wednesday, July 24, 2013

End of harvest concerns in blueberries

As blueberry harvest nears the end in North Carolina, a few important insect related issues require some attention.

Spotted wing drosophila in processing fruit
Rainfall makes SWD management more challenging, a
s growers have discovered in the last two months.  As we move into the end of blueberry harvest, fruit being picked for processing is at higher risk for spotted wing drosophila (SWD) infestation for several reasons: It is often softer than fruit picked for the fresh market, and SWD prefer soft fruit; Processing fruit may be harvested less frequently than fresh market fruit, increasing the time ripe berries are exposed to SWD; Finally, because processing fruit is often machine harvested, all the fruit in the field (good and bad) may be picked.

There are some strategies that growers can employ post harvest to decrease the likelihood that SWD infested fruit will be send off for processing:
1. Hold fruit at cool temperatures. Work in our lab suggests that SWD eggs and larvae cease development at temperatures less than 41F.  They will not necessarily die at cool temperatures, but they likely will not cause further damage to the fruit. The longer fruit are held and the cooler the temperature they are held at, the more likely that small SWD larvae will die.  Holding fruit at cooler temperatures also give growers the added benefit of determining how significant any infestation is, as large larvae will exit fruit as it cools.

2. Sort out soft fruit. Soft fruit are the most likely to be infested with SWD for two reasons--egg laying SWD are more attracted to soft fruit, and because blueberries become softer as SWD feed. If growers can remove soft fruit before sending fruit off for processing, this will further decrease risk of infestation being present.  I suspect our aggressive soft sorting standards for fresh market blueberries are one of the reasons that SWD has been a less significant issue in this crop than some other hosts.

3. Sample collection timing. When receiving fruit, processors can either collect samples before or after fruit are sorted/de-stemmed.  Samples collected before fruit has been soft sorted are not necessarily representative of the status of the fruit that will be processed.  Samples of fruit after chilling and sorting, prior to processing/freezing are likely more 

Post harvest leafhopper treatments

Treatments to manage sharpnosed leafhopper vectors of blueberry stunt disease typically begin post harvest.  Blueberry stunt disease is caused by a phytoplasma, and symptoms include "bushy" growth due to short, stunted branches and yellowed leaving during the growing season which may prematurely turn red and fall off in late summer.  Most importantly, plants infested with stunt-causing phytoplasma do not produce 

Aerial applications of ULV (ultra low volume) malathion been used in the past for leafhoppers, due to effectiveness and ease of application.  However, many growers have also used this material for SWD management during the season, and careful attention must be paid to label restrictions on the number of applications that can be made of materials when selecting tools to manage sharpnosed leafhopper.  Application limits apply to the entire growing season, not just harvest season, so label limits on the number of applications also apply to leafhopper treatments.  Application limits apply the amount of active ingredient, not the trade names of those active ingredients.  Sources for updated labels with current use restrictions include CDMS and Agrian.

Alternatives to malathion that are effective against sharpnosed leafhopper include Assail (acetamiprid) and Asana (esfenvalurate).  Imidaclorprid and thiamethoxam are also options for sharpnosed leafhopper.  The NC Agricultural Chemicals Manual has recommendations for the use of these materials. It's important to note, however, that all these materials pose some risks to pollinators. While blueberries are not in bloom, some of our most efficient blueberry pollinators are ground nesting bees that may remain near fields after bloom.  Therefore, any insecticide treatments should be timed to leafhopper flights, ideally determined through trapping, to provide maximum efficacy against target pests and limit unnecessary applications.  See here for information on trapping and here for images to aid in sharpnosed leafhopper identification.

More information
How should growers manage spotted wing drosophila in rainy conditions - Strawberry Growers Information Portal
Study offers new insights on invasive fly threatening U.S. fruit crops - NC State University Newsroom
Implementing IPM at the Ideal Track - NC Small Fruit & Specialty Crop IPM
Crop Data Management Systems
Label Look Up - Agrian