Blueberry Fruit Scale Infestation
In my community, there has been much talk recently about significant incidence of scale insects discovered on supermarket blueberries. I have been trying to read up about this online, and I found only one mention of it in a Rutgers Extension manual, and it seems to me that they say that it is quite controllable. So why should it be so common to find this scale in NJ supermarkets? Is it just a fluke, or is it really not a scale insect (although it does look like Rutgers' picture of Putnam Scale on the berries), or did I misunderstand what I read?
And if there really is a significant incidence of this, what could a consumer do to rid the berries of this scale, short of inspecting each and every berry?
I have attached images taken of this scale, or whatever it is, on bluberries recently purchased fresh in a NJ supermarket.
Outside United States
Nice pictures of Putnum scale. Can I use them in my talks about unintended consequences? We are seeing more scale in blueberries and we think it is due to changes in grower pest management practices. I am sorry for this long winded answer to a simple question of why is there scale on these blueberries, but I think you need to understand why new pests can cause problems and old pests can reappear. Integrated Pest Management (IPM) is the pest management strategy that farmers use to control pests and diseases in their crops. They use cultural practices and field scouting for pests and diseases to reduce pesticide use to a minimum. This reduces costs, pesticide use and exposure to the grower and the consumer. It also allows natural predators to keep minor pests at low levels. Scale and other unusual blueberry pests have become more common because berry growers are forced to apply more insecticides more often to control a new invasive fruit pest called the Spotted Wing Drosophila (SWD, which I call the Spotted Weapon of Destruction). SWD appeared in the United States in 2008 and by 2010 was a pest in all berry growing regions of the country and it is also destroying berry crops in many other countries. The SWD is a small fruit fly, which attacks all thin skinned fruit. The fly moves from host to host as berries ripen throughout the year. The fly lives for about a month and lays about 600 eggs. The eggs hatches and develops into a fly in about 2 weeks. SWD can infest a field of blueberries in less than a week and force a grower to abandon their fields because the berries are infested and unsalable. Growers have lost tens of thousands of dollars because they had to walk away from their planting due to SWD. The insecticides that growers can use are strictly regulated by the government as to amounts and the days between sprays and harvest so that any pesticide residues are below safe levels in the marketplace. Because of this focus on SWD, scale and other insect pests which were only a curiosity can flare up and become a serious problem before the grower realizes it is even in the field.
To answer your question on how to remove the scale from the berries, There is no easy way other than picking them off. Nor is there any easy way to sort these berries out in the packing process. There are electronic sorters which remove many berries for defects color or softness and they catch the bad ones. Humans do inspect the fruit after these sorters before they are packed and they catch more. These sorters will remove all the scale they see, but they will miss some.There is no risk to you if the scale are eaten. Fresh blueberries are not washed during the packing process as this would result in a loss of quality to the fruit, so you can wash them.
Yes, scale is relatively easy to control with a dormant oil spray in the early spring, but it is almost impossible to control during the growing season. Sprays during the growing season can be targeted on the crawler stage, but this requires careful scouting to determine when that stage is present. This specific scouting is not usually done because scale insects have not been a problem in the past. Scale is such an unusual pest in that its appearance is usually a surprise to the grower after the crawler has passed. There is no control of the adult scale with the materials registered on blueberries for insect control around harvest. Until the SWD appeared scale was not a pest of concern.
I am sure that next year many blueberry growers will be applying oils early in the season to reduce the overwintering adult scale is their plantings so scale numbers should be down. Scouts will also focus on looking for the crawlers early in the season.
There is an extensive effort to do research into controlling SWD around the world and especially here in the US wherever berries are important crops. We are still adapting to how to effectively control SWD in blueberries and other fruit crops. Flare ups of unusual pests are common whenever growers make significant changes to their pest management practices. Growers are really struggling to control SWD and protect their fruit and livelihoods to remain in business and provide a safe product to consumers.
Here is a link to more information about SWD.
Thank you very much
Your information and explanation were quite helpful.
I have secured permission for you to use the lovely pictures of scale
May I just please confirm a couple points?
1) do you think that all farms have the scale problem right now, or is it grower by grower? If the latter, would you have any guess as to the percentage of growers that might be struggling with this?
2) if a grower has a problem with scale, would it be all over his fruit or just on some canes?
3) is there always a bug under that scale on the berry, or does it crawl out from under it?
Thank you again,
Scale are immobile as adults. eggs hatch under the scale and the crawlers emerge and move about the plant looking for a place to settle. Males can fly and will find and mate with female. All the scales are female and live the rest of their lives under the scale laying eggs and dying. The scale on the berries this late are overwintering scale. The scale moves from plant to plant by the crawler hitching a ride with a large animal. Occurrence is spotty depending which plants are colonized. starts out on a few plants and spreads through the field. I assume the pattern is the same in New Jersey as in Michigan. Starts as spots in the field and then some fields are really bad and others don't have a problem.