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MOFGA's Pest Alert - July 17, 2012
Compiled by Eric Sideman, PhD - MOFGA's Organic Crop Specialist

Spotted Wing Drosophila. Photo by Martin Hauser, California Department of Food & Agriculture.

Spotted Wing Drosophila - The spotted wing drosophila (SWD) has been found in Maine. Only a few flies have been caught, but this may be just the beginning, and growers of soft fruits must be aware of the issue and make management decisions. See a detailed discussion, and a design of a trap that you can build to monitor the fly in your plantings.

This fruit fly is a new pest in our region. It is a very common pest in Asia. The tiny fly looks like a typical fruit fly, but the males have a spot on each wing that you can barely see with the naked eye. Common fruit flies that we see here only go after over ripe and rotting fruit. The SWD is a much greater problem because it can attack sound fruit and has been very damaging to raspberries, blueberries and many more fruits in areas south and west of us in recent years. Last year was the first year it was seen in large numbers in northern New England. It lays eggs in the fruit and in a few days, perhaps on your customer's counter, maggots will be wriggling.

The problem is that populations can explode quickly, and tolerance to maggots in the fruit is much less than let's say a corn earworm. I would say tolerance of maggots may be about zero.

At this time I do not have any tested recommendations other than common sense practices such as do not let ripe fruit sit on the vine or counter. Pesticides are quite effective if used timely. But the problem is timely is frequently. The generation time is so short that in order to control new arriving flies a grower may have to spray weekly or even more frequently. Alan Eaton, the entomologist at UNH, has put together some good fact sheets on potential efficacy of pesticides, including those used by organic growers. Check this out and look at the link to possible pesticides: http://extension.unh.edu/Agric/AGPMP/Spottedwingdrosphila.htm

Late Blight - Late blight has been found in a few more sites on potatoes in Maine. The newest one is Oxford County. It is still not widespread, a benefit of this hot, dry weather. Previous Pest Reports have had discussions of the problem, and for a detailed discussion see:


Above: Tarnished Plant Bug damage. Below: Tarnished Plant Bug. Photos by Eric Sideman.

Tarnished Plant Bug - Similar to the potato leafhopper, I often get calls from growers who believe they have a disease problem when actually it is feeding by the tarnished plant bug. This has been the worst year ever for us in Strafford, NH. But, I think it is local conditions that have led to that, not a regional problem. Our neighbor cut his hay field earlier than he usually does and that drove the bug out to find food. Our crops served well.

They are serious pests on strawberries (causing cat faced berries), lettuce (browning of midrib), flowers (destroying buds), eggplant and pepper (destroying buds and leaf tips), broccoli (brown beads in the head), and much more. But in potato they basically kill flowers (who cares?) and damage some of the leaflets (usually a minor problem). This year there are so many they are doing a lot of damage to potatoes.

The tarnished plant bug is a small (6 mm), bronze, brown and black bug that feeds on a very wide variety of plants, something like 300 species. They overwinter as adults under debris and become active in the spring. There are three or more generations per season. It is pretty easy to kill them with pyrethrum, but not worth it because their numbers are so great in all the fields of hay and weeds surrounding you that what you kill will be replaced in a day or two. Managing weeds and grassy fields so you keep the population low, e.g. mow short most of the time, but do not mow when you have sensitive crops, is about all you can do.

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