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Gardening in the Rainy Zone.
Location: Outside the Maritime Pacific Northwest
Posted: Oct-19-2003 at 2:32pm
With that wind storm we been having, the row covers over the carrots and rutabagas are now at the neighors. Do you think it is okay to leave them off for the winter. Is the carrot maggot done doing its thing for the season?????
Location: Oregon, Greater Portland Metro
Posted: Oct-22-2003 at 9:15am
I referred to Steve Solomon's Growing Vegetables West of the Cascades for help. On page 193, there is information regarding Carrot rust fly, the adult of the maggot I think you are referring to. (He does say he's had little experience with this pest so he's referring to other literature.)
. . . the fly begins breeding rapidly in late summer and will go through a generation every month, often increasing to wildly high numbers by midwinter if the weather is not too severe. Carrots started in late May, after the spring hatch is through, may well finish their growth cycle relatively unharmed and be harvested by late summer. However, carrtos left in the ground become increasingly infested by rust fly maggots as the winter progresses.
He goes on to recommend Reemay as the deterrent of choice (nematodes aren't helpful, he says). He suggests the Reemay be carefully anchored with a sprinkling of soil all around a bed or row of plants. . . To deter the rust fly, thin the carrots when the tops are three or four inches tall, to about 150% of their normal spacing (to allow for the slight loss of light Reemay causes) and then cover the bed.
He unfortunately doesn't say when the danger has passed, other than "midwinter". Based on his recommendations, it sounds to me as if you need to cover them again. But as I said, I'm not a veggie expert. Perhaps you should contact your local county Extension service as well.
I hope your carrots grow well!
Location: Washington, Puget Sound Corridor
Posted: Oct-22-2003 at 10:45am
I found the following on a New Zealand website
Life cycle: Egg, Larvae, Pupae, Adult
Adults emerge from overwintering puparia in September, and are abundant until the following May. Eggs are laid from September to May and take 7-14 days to hatch.
Larval development takes 4-6 weeks, and the pupal stage lasts 2-4 weeks. A full generation may thus take 7-12 weeks to complete, which allows up to four generations a year to occur in some parts of the country.
Peak flights of carrot rust fly adults in the Auckland area have been recorded in mid October, late December, mid February, and mid April. The insect normally overwinters either as larvae in roots or as pupae in the soil, though a few adults may survive the winter too.
NZ is 180 degrees out of phase with us so the Peak flights of carrot rust fly adults in mid-April is mid-October for us so I think you should cover up again to be safe.
I should also say that Auckland is on the northern (warmer) island of NZ and the weather is near that of our Northern California coast with few frosts. But we haven't had any frost yet either.
For next season you might examine the research done 7-8 years ago by Dr. Carole Miles of the Lewis County WSU office. You can find it at:
Dr. Carole Miles research
Location: Washington, Puget Sound Corridor
Posted: Oct-22-2003 at 11:10am
This info below from Canada confirms my NZ inferences and Lisa's Solomon quote. Remeber that parsley and celery roots are also a target so do not plants carrots and parsnips over old beds of them and then tent in the emerging flies.
There are two generations of the pest each year in most areas, but a third occurs in southwestern British Columbia and sometimes in southwestern Ontario. The pupae, which are about 5 mm long, overwinter at a depth of 5-1 5 cm in the soil of old carrot, parsnip and celery beds. Adults emerge about the end of April in British Columbia and about a month later in Ontario.
Their emergence usually coincides with the blooming of lilacs. Soon after they appear, the green, yellow-headed flies deposit eggs in cracks in the soil around the plants or on the stems just below the soil surface.
A female may lay 100 eggs in 3 days. On hatching from the eggs 6-12 days later, the larvae enter the fine rootlets before tunneling into the main root and down to the tap root. In British Columbia, the second generation of flies appears in late July and in August, and the third generation in October and early November.