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 MOFGA's 2010 Pest Reports - Compiled by Eric Sideman, PhD Minimize

September 22 | August 23 | August 9 | July 26 | July 20 - Late Blight Update | July 19 - Late Blight Is Here | July 7 | June 24 | June 19 - Late Blight Update | June 18 | June 8 | May 25 | May 20 | May 3 | April 22
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This is the first Pest Report for the 2010 growing season. The Pest Report is sent out every week or two during the heart of the season and highlights problems happening then or likely to show up soon. I hear about problems from growers all around the region so please help out and let me know if something big or unusual is happening so I can share the information.

I write much of the Pest Report, and much of the writing is reprinted from newsletters by crop advisors around the region. The ones I use the most are from the University of Vermont (Vern Grubinger), University of Massachusetts (Ruth Hazzard), and the University of New Hampshire (Becky Sideman). As you can guess, using material from there often gives us here in Maine a bit of time to prepare because many pests move into Maine from the south and west during the season, i.e., do not spend the winter here. Also, this year I will be picking out some pieces from previous Pest Reports because usually the warning is the same year after year.

The Pest Report pieces include a description of the pest, the biology of the pest, a description of the damage, and some suggested management practices allowed under organic standards.

This Pest Report is being sent to everyone on my list in 2009. If you were a MOFGA certified grower in 2009 and did not renew in 2010 you will NOT automatically receive the Pest Report. You will have to write to me and request to be added to the list of non-certified growers receiving the report.

PEA WEEVIL Bruchus pisorum: You may not even know that pea weevil is a problem for you. You may be wondering why germination of your seed is low but never make the connection. Of course, there are many other reasons why pea seed germination is low, so don't make assumptions. The problem is not common or big here in the Northeast.

Adult pea weevils are short, chunky beetles with brown, white, black and gray flecks. They are not true weevils and so do not have the typical snout. Adults hibernate though the later part of the summer, fall, and winter under bark, crevices of fence posts, sides of buildings, crop debris, etc. In the late spring when the peas are flowering the awake adults are flying and smelling the flowers. After feeding on pollen for a while the females lay eggs on the newly forming pea pods. They lay eggs, which look like little cigars singly, but there may be more than one egg on each pod. When the eggs hatch in 2-4 weeks, the white grubs with a small brown heads borrow through the pod into the young peas. They grow inside the pea for about 5-6 weeks consuming the contents. Then they chew an escape hole and pupate. In as little as 1-3 weeks after pupation the new adult may come out using that escape hole and fly off to hibernate. But many adults just stay in the pea and hang out until things seem good, or they are disturbed by jostling or planting or something. There is no tolerance in the market for peas with grubs in them, and people selling and buying seed are not happy when a good portion of them are truly shells of what they should be.

There are no silver bullets for organic pea growers. Management practices are aimed at reducing the population. Conventional growers will spray when the flowers begin to wilt but before pods are sizing. But first they scout the field to see if the pea weevil is a problem. Scouting is done with a sweep net around the edge of the crop starting when flowering begins. The critter is only active when it is warmer than about 65 during the day. Sprays have to catch the adult because once the eggs are laid and larvae bore into the pod there is no way to catch them. I have been unable to find studies of efficacy of organic insecticides for pea weevil, yet.

Cultural practices are the most important means of reducing numbers for organic growers. Harvest peas when they are ready and do not leave crops hanging around after harvesting season, which would allow adults to leave the peas and move to hibernating sites. Clean up spilled peas and destroy crop debris right after harvest for the same reason. The important thing is that it does not seem to be a big problem here in the Northeast and your most important practice is to not plant infested seed.

SEEDCORN MAGGOTS Hylemya platura [Reprinted and modified a bit from New Hampshire Vegetable, Berry and Tree Fruit Newsletter by Becky Sideman]. Last spring, I heard a couple of reports of seedcorn maggots causing damage for vegetable growers. Now is the time to be aware of the problem. Seedcorn maggot larvae feed on seeds and young seedlings of many crops (corn, beans, beets, peas, cole crops, etc.). The first symptoms are usually poor germination (or failure of seedlings to emerge). Symptoms can be difficult to distinguish from other problems, like damping off due to Pythium or other soilborne fungi, or wireworm feeding. If seedcorn maggots are the culprit, maggots can usually be found in the soil around and inside seedlings and seeds. The seedcorn maggot is yellow-white, 1/4 inch long, legless, with a wedge-shaped head. The adults look like small houseflies. Seedcorn maggots overwinter in the soil as pupae. In early spring, the adults emerge and lay eggs, which hatch within 2-4 days at soil temperatures of 50F. In Minnesota, research has shown that peak emergence of the first three generations occur when 200, 600 and 1000 degree days have accumulated. Degree days are calculated on a daily basis by using the formula: (Max temp – Min temp)/2 – 39F. You can also refer to a handy calculator at http://www.weather.com/outlook/agriculture/growing-degree-days. This calculator tells me that we already reached 200 DD using a base temperature of 40F by April 12, which is much earlier than normal. The first generation usually causes the most damage. Will seedcorn maggots be a problem this year? It depends. The adults prefer to lay eggs in wet soil that is rich in organic matter. Crop seeds that germinate slowly are more vulnerable to attack. The adults are likely to be active ahead of schedule this year, and crops that are planted in wet soil when the soil is too cool for them to germinate quickly may be especially susceptible to damage.

Management strategies:
By the time you see damage, it is too late to control the problem using either cultural or chemical methods. Prevention is the key.
  • Avoid seeding fields (especially wet fields) too early. Seeds germinate more quickly and are less vulnerable in warmer soils.
  • Disk and incorporate organic matter (such as a cover crop) at least 4 weeks before seeding to give it time to break down and make it less attractive to the flies
  • Avoid applying manure in late fall or early spring to heavy soils that you might want to plant early. Lighter, well-drained, sandy soils are less likely to have problems (because they warm up faster than others).
  • Rowcovers can help – but only if the maggot flies are coming from elsewhere. Damage can occur if the flies have overwintered in the soil underneath the rowcovers.
  • If you need to replant, wait at least 5 days if maggots that you find are a quarter inch long; if they are smaller than that, wait at least 10 days to make sure they have pupated and will not damage the new seeds.

LATE BLIGHT: I bet you are all tired of hearing about late blight and mostly hope that there is not a lot of talk about it this year. I want to make sure that everyone understands that late blight does not overwinter in New England EXCEPT in potato tubers. The very important message to get out is to make sure your potato seed is not diseased, and to look for any volunteer sprouts from potatoes left in the field, garden or piles. If diseased potatoes sprout they will then start spreading spores. Late blight does not live in tomato debris, or tomato seed. The only way to get it to New England on tomatoes is to carry the tomatoes here from the south already infected, as was not so kindly done for us last year. Do not support any store buying tomatoes that were grown for any time down south.

May 3 | Page 15 of 15 | April 22


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