Wednesday, April 23, 2014
By Tom Atwell
People attending a Maine Organic Farmers and Gardeners lecture at the Maine Agriculture Show earlier this month learned about a few new pests that may threaten vegetable gardens in the coming growing season.
The biggest concern still remains the spotted wing drosophila, which first showed up in the state in 2011.
“It was pretty bad last year,” Eric Sideman, a crop specialist with MOFGA, told the group, “and we expect it will be worse this year.”
The spotted wing drosophila is closely related to the fruit fly you find in your house if you let some bananas get overripe. The difference is that the spotted-wing drosophila has a serrated appendage, so that it can cut through skin on ripening fruit to deposit its eggs.
The result will be maggots in the fresh fruit eating it from the inside.
Spotted wing drosophila can over-winter in Maine, but only a tiny percentage of them make it to spring, Sideman said.
Each female drosophila can lay about 600 eggs, and with each generation lasting only seven days, the fruit fly can have five to seven generations each summer.
“Up until Aug. 20 we don’t see them in any great numbers,” Sideman said.
What all of this means is that strawberries are safe from the pest. Other crops that are harvested in July and early August should suffer only minimal damage.
Gary Fish of the Maine Board of Pesticide Control, with whom I spoke after Sideman’s lecture, said that commercial blueberry growers combatted the drosophila by harvesting their crop earlier than they have in the past. It meant that they got more green and unusable berries, but the berries were less likely to contain drosophila eggs or maggots.
Sideman said that the insecticide Entrust, which is approved for use by organic growers, works well on the spotted-wing drosophila, but label instructions for Entrust dictate that it be used only three times per year on a particular crop. Because the fruit fly reproduces so quickly, Entrust would have to be used about every five days.
With a crop like blueberries, that means farmers could use Entrust late in the blueberries’ growing cycle to get a couple more weeks of ripening.
Sideman also said the David Handley and other University of Maine Extension crop specialists at Highmoor Farm are working to improve traps for the spotted-wing drosophila. To date, traps have been used only to determine when the pests appear so that spraying can be scheduled. The goal now is to create traps that would kill a significant number of the flies, thus reducing damage to crops.
Many of the other pests Sideman discussed target the allium family.
Garlic bloat nematode is a tiny worm that attacks onion and leek bulbs in addition to garlic. If you see some yellow plants in an otherwise healthy planting of garlic, Sideman advises that you pull it and send it to a testing lab to see if you have the bloat nematode.
The best ways to fight the nematode are to use clean seed, good compost and to practice good sanitation. The nematode does not survive in the soil, but only in the plant debris.
Bulb mite is another pest that damages garlic, and this will survive in the soil, although Entrust will kill it, but you should also check the bulbs before planting.
White rot also attacks onions, and can live in the soil for up to 25 years.
Sideman noted that the wet season last year caused a lot of disease problems. He said that he wasn’t able to successfully plant any potatoes until the third week of July last year, but that he got a good crop out of that planting.
A lot of growers had problems with downy mildew on basil last year, according to Sideman. This is a disease that is similar to late blight on potatoes, and is spread by the wind. It attacks all sweet basil but will not affect lemon basil and purple basil.
Some growers suggested growing basil under row covers to keep the leaves dry.
Sideman also told the growers that the second edition of the Resource Guide for Organic Pest and Disease Management has been published. Sideman was one of the writers of the book.
The first edition was published in 2005; the second has been in the works for about five years. The new edition is available for sale at calsbookstore-lamp.cit.cornell.edu/catalog, and you can get it free as a pdf at web.pppmb.cals.cornell.edu/resourceguide/.
Tom Atwell has been writing the Maine Gardener column since 2004. He is a freelance writer gardening in Cape Elizabeth and can be contacted at (207) 767-2297 or at: