Of Global Warming and Highbush Blueberries


When I was a kid, my dad planted about four hundred highbush blueberries in several varieties.  The plants have been there a good forty years now.  For most of that time, we raised organic berries and sold them to help pay the land taxes.  The plants needed little care beyond pruning and mowing. Between mid-July and early September was blueberry picking time.  I was a champion harvester, collecting by hand an average of twelve quarts per hour when the pickings were good.  That has all changed.b2b1

The year 2006 is the last date I have on blueberries in my freezer. Since then every crop has been ruined by the blueberry maggot.  The maggot is the larva of a very small fruit fly, (Rhagoletis mendax) slightly wider than 1/8″, with black-barred wings shaped a bit like a B2 Stealth Bomber when viewed from above.  And stealthy they are.  Just as the berries begin to ripen, the female flits around depositing one egg in each of an average of twenty to forty berries. With a horde of the flies working, that’s a lot of berries with eggs in them.  The egg quickly develops into a tiny white worm-like maggot that eats the inside of the berry.b3  When the berry shrivels and falls to the ground, the maggot burrows out and down into the soil where it winters over five to seven inches below the surface.  The next summer adults emerge to begin the cycle anew.

The maggot has several native plant hosts including wild blueberries and bunchberries.  Because Maine is full of these plants, it’s impossible to eradicate the fly.  For most of history, the fly has been limited in range by cold winter temperatures.  Blueberries along coastal Maine are sprayed heavily with pesticides like Malathion to control the maggots and produce a palatable crop.  The tolerance for maggots is 0%.  If someone finds a wiggly little white critter in their berry, they are unlikely to want any more.  The maggots are especially noticeable when berries are cooked, as the dead bodies float to the surface.  This ruins blueberry jam and pies.  For most of the years we had highbush berries, the cold winters with temperatures falling as low as forty below zero kept blueberry maggot infestations away.

Changes in climate due to the general warming of the Earth have made our winters too mild.  The maggot has spread its territory well inland, hitting our berry patch in 2007.  The coldest winter in recent memory occurred last year with temps to twenty below.  Still not enough to wipe out the maggots.  This year we have a bumper crop of beautiful, big berries.  Many are as wide across as a quarter, and so sweet.  Like eating little bites of the best blueberry pie.

Sadly, we can’t pick any for sale or even to put in the freezer because there is no way to reliably tell which berry is infested with maggot.  A ripe infested berry may feel slightly softer than a good berry. That’s a very subjective standard and not always accurate.  Upon opening a ripe berry, the maggot is usually obvious.  The thing is tiny and very active.  The inside of the berry where the maggot has been eating has a slight reddish cast where a clean berry is all white.b4  From the outside, good and bad berries look the same.

If I want some fresh berries to eat, or to bake, I have to open each berry and check for a bug.  The quickest way to open the berry is to use a thumbnail to make a slit in the bottom end and lay the berry open in half.  The reddish tint is the first indicator of infestation, then the tiny maggot becomes apparent as it squirms around.  In the photo at right, the top berry is clean, the bottom berry, infested.  I have been desperate enough for a blueberry pie to open a quart of berries.  Takes awhile, but worth the effort.  Most years I find one in twenty nice looking berries has a maggot inside.  That is the ratio this year as well.

Not all is lost, or we would have cut the plants and turned the berry patch back into pasture.  Highbush berries can be grown organically in maggot regions. The maggot requires high humidity at the time it drops from the plant so it can travel down into the soil. In dry years, maggots die.  The top few inches of soil must be easy for the insect to penetrate. The adult female fly does not lay too many eggs, usually between twenty and one hundred in her life span.  It is possible to catch the flies with sticky, baited traps before they can harm the crop. Commercial growers use such traps to determine when they need to spray.  When flies are caught, get out the spraying equipment.

To turn our blueberries into a cash crop again, we must invest time, money and effort.  When the plants were set out, they were spaced too closely.  As the crop matures, the branches droop, and each plant requires twelve feet of space.  Ours are set six feet apart.  They lie on each other, creating deep shade at the roots.  The close spacing makes them hard to mow so weeds grow up, providing even more shade–humidity for maggots.b7

Since the devastation by the maggots, we have sold about half the plants in the patch, the smaller ones that are easier to dig.  Easy is a matter of opinion.  Digging a mature highbush blueberry plant out of the ground would be good punishment for chain-gang criminals. The effort required to remove the mass of roots from the ground is back breaking.  We sold the plants we dug for $30 each, and didn’t feel justly compensated for the work involved.  The remaining plants are at the center of the patch:  huge, healthy, burgeoning specimens with giant root systems.  It is not feasible to dig them by hand.

I have developed a plan for returning the blueberries to a profitable crop that my husband is almost on board with.  It involves cutting every other of the remaining plants.  He has not quite wrapped his head around destroying nearly one hundred perfectly nice plants.  So we are at a stand-off.  Every other spring I prune the plants and cut away the young trees and vines that try to grow up.  Then the patch gets ignored as summer work adds up, mowing isn’t done on time,  weeds grow tall and the maggots have another feast.

I would like to thin the plants so there is adequate space around them, put down a mulch barrier to make it more difficult for the maggots to reach the ground, and buy enough sticky fly traps to control the adults.  The berries we could produce would soon pay for the mulch and traps.  We would not have to mow the patch, weeds would not grow well anymore.  This seems like a good plan to me.

My husband talks of getting a small machine that could be used in the rows to dig up the plants for sale.  Such a machine is expensive and not very practical since the rows are so tightly spaced, it would be hard to maneuver.  Finding the cash to buy or rent a tiny excavator has not been possible to date, so the crop continues to be lost.  I say bite the bullet, cut the plants and lets grow good blueberries again.  I almost have him convinced.b6



4 thoughts on “Of Global Warming and Highbush Blueberries

  1. What about string trimming the weeds and laying down plastic that the maggots can’t get through? Or laying it down at the start of the season before the weeds have a chance to grow?

    • Kinda what I want to do, except plastic doesn’t let air and water through properly. In the early spring, I want to cut out ever other plant, cut all weed trees and vines, lay down fabric mulch and cover it with 3”-4” of bark mulch. That would stop the weeds, stop maggot burrowing and bring light and air to the bases of all the plants. Half the plants have to go one way or another for the patch to produce usable organic berries.

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