THE NEW WORST BLUEBERRY PEST - Rhagoletis mendax

In May, we posted an old Root Concerns article about blueberries' preference for acidic soils;  and, in case you are still just thinking about blueberries or  have more questions now after planting them, I  recommend  your checking out this very readable  guide from the University of Maine's Cooperative Extension.

But,  now it's July and blueberries are starting to ripen throughout the Capital District.  If you've grown blueberries for a while, you probably already have them under some kind of a bird netting arrangement.  If not, the birds say thanks.  My mother-in-law, who lived in Maine,  used to just drape netting over her high bushes (6+ feet) and then crawl under the netting to pick. She always  got a lot of berries and didn't mind sharing those berries located just under the netting with the birds...  However, if you are planning to build a frame for netting, make sure that your netting is securely fixed to the ground in order to stymie both the more clever birds and  the pernicious squirrels from finding easy low level access. 

Blueberry maggot flu lavae devastate berries. Photo: sercadia.wordpress.com

Unfortunately, more than just birds like blueberries.  Many insects look at some part of blueberry bushes for a meal, but there are three  pests that  focus on consuming the fruit -- the blueberry maggot fly, the cherry fruitworm and the cranberry fruitworm.

Of these three, the newest pest that has only recently  established itself in the Capital District including Rensselaer County is the blueberry maggot fly (Rhagoletis mendax). This villain is very, very  small --   the maggots that live inside of a berry only measure 5 - 8 millimeters in length.   Given their  tiny size, you  probably might not notice either the eggs or  the newly hatched maggots in the berries. This means that  occasionally you may be ingesting a little extra protein along with your berries and cream.  Anyway, after about  three weeks of feasting those maggots  emerge from the berries (whose pulp has  now turned into a  noticeable brown mush), drop to the ground to pupate, and turn into the flies that are eager to start the next generation.  The adult flies are about 3/16" in length; and if your eyes are sharp enough to spot one, look for the black stripes on its wings to confirm your misfortune. Because the last generation of the season buries itself 1 - 6 inches into the soil to overwinter, just cleaning up under the bushes doesn't help. I don't know if covering the ground under your bushes with  landscaping cloth would serve as  an effective prophylaxis. It seems that it might.  [Are there any berry experts who can comment about this idea?]

Adult blueberry maggot fly. Source: Jerry A. Payne USDA/ARS

As for the two other insect pests affecting the blueberries, the cherry and cranberry fruitworms are present in the area and can cause serious damage.   The telltale clue of cranberry fruitworms is a web that the worms spin linking the berries in a cluster a little more securely together. The  lavae also drop to the ground to pupate and turn into moths. In this case,  keeping the ground clear under the bushes will reduce their population, and Bacillus thuringiensis (B. t.) can be used on the berries as a control.  

The cherry fruitworm, also a moth, produces just a single generation a year.  Eggs are laid on the surfaces of unripe fruit, and upon hatching the lavae bore into the fruit to feast.  Cherry fruitworms can be controlled by pyrethrin and Bacillus thuringiensis. Because cherry fruitworms overwinter by seeking out protected spots on stems, regular pruning to remove older stems can help control their numbers.

For gardeners trying to follow organic principles, controlling the blueberry maggot is especially challenging.  Traps may be able to control  the cherry and cranberry fruitworms in backyard berry patches, but are  unlikely to  be effective against the prolific maggot fly. Farmers  only use   the traps to indicate if they  have infestations and not for control purposes.  I did stumble upon one note that suggested regularly spraying the fruit with a cayenne solution, but I found no confirming research  about using this elixir for this purpose.  

If you have an infestation of maggot flies, multiple applications of an insecticide appear to be the recommended solution (probably, the only solution).  Organic insecticides, e.g. Neem oil or pyrethrin, can reduce maggot populations, but they  will also collaterally kill beneficial insects. Because the maggot's life cycle is just a few weeks, multiple applications of an insecticide are required throughout the berry season.  The bottom line for the backyard gardener may be simply to look a little more carefully before you pick and maybe not so much before  you  bite into the muffin...

FWIW:  Blueberries are native to North America. 

And remember...

"The darker the berry, the sweeter the juice." - Thomas Jefferson