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 MOFGA's 2009 Pest Reports - Compiled by Eric Sideman, PhD Minimize

Late Blight Recap | September 3 | August 12 | July 22 | July 13 | June 25 | June 19 | June 14 | June 1 | May 19
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July 13, 2009

LATE BLIGHT: No questions now. Late blight is showing up around the state in potatoes and tomatoes and we should all be on the look out and responsibly handle it. Remember, late blight is a community problem because if it is in your field then you become a source of spores effecting your neighbor.

Spores are reported to be blowing in the wind now, but that does not take you off the hook. We all have to be responsible and keep the number of spores in the air to a minimum.

Look at the previous Pest Report for a description of the disease symptoms and biology of the pathogen. For really good pictures see:


If you positively ID late blight in areas of your field, then pull those plants, bag them (DO NOT JUST PULL AND THROW ON THE GROUND!), and dispose of them so they are not a source of spores. Do this for an area about 5-10 feet in diameter around the plants showing symptoms. Then, spray the field with an approved formulation of copper fungicide. Some growers are doing both an Oxidate spray, and then a copper fungicide spray.

There are lots of diseases of potatoes and tomatoes showing up now after all that rainy and damp weather. Mostly what I am seeing is Botrytis and early blight. If you are not sure that your diseased plants have late blight feel free to email me a picture, or contact your Extension office.

ONION THRIPS: Thrips are one of those problems that you rarely spot the insect but see the symptoms of their feeding first and then start searching. I have had reports of them being out this year in onions in central Maine. These insects feed on lots of different kinds of plants and often are there but in small numbers so can be ignored. Sometimes the populations get large and can really take down an onion field or at least greatly reduce your yield.

The onion thrips feed on onion leaves by rasping the tissue and sucking juices. The feeding leaves white streaks that get larger if feeding continues, and white patches on the leaves develop. I am surprised to hear that this pest is a problem this year because it tends to be a problem in dry years, and heavy rains often wash the pest away.

If you see what you think is the damage, then look for thrips in the tiny spaces between the leaves. Thrips are very small, about 1mm.

Crop rotation can help as can sanitation and weed control. The pest overwinters as an adult in crop refuse. Infestation often begins on field borders if the pest overwintered in weeds or nearby fields and then migrated to the new onion field. Mowing fields of alfalfa can drive the pest into the onion field. Heavy irrigation may wash the thrips off. If you have them bad and need to spray, Entrust should work.

ROSE CHAFER: The rose chafer is in the same family of beetles as the Japanese beetle and has a similar life history. The adult is out now and voraciously feeding on many different crops such as rose, raspberries, apples, grapes and some vegetables too. They skeletonize the leaves and are feeding on blossoms and young fruit too.

The adult is a half inch long, gray-tan beetle with a reddish-brown head. The adults are mating now and will lay white, shiny eggs in the soil soon. The larvae are white grubs that live in sod feeding on roots, especially on sandy ground. The life span of the adult is only about three weeks so you may just want to wait them out. But if your population is large you may loose your crop while you wait.

Crop rotation will not help because they are good fliers. You may be able to control grubs with beneficial nematodes, but that is likely to help little with controlling adults because your neighbor's sod ground will be a source even if yours is not.

Hand picking or knocking the critter off the leaf into a jar of water works well for small plantings.

Pyganic and Surround seem to do little to deter adults. Rotenone may work, but there are no formulations permitted in organic production and its EPA registration as an insecticide has been dropped.

I have heard from a grower that neem oil works well, especially a neem and diatomaceous earth combo. Has anyone else tried that with success? Are there any other suggestions?

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