MOFGA Pest Report 2004 #1
May 10, 2004

(View List Of All Pest Reports)

APHIDS

Aphids are soft-bodied, pear-shaped insects that are about a quarter of inch long. They are sucking insects that weaken or kill plants by piercing them and sucking out the plant's juices. Dwarfed, weak looking plants with curled leaves should send a grower searching along the stem and under the leaves for aphids. Peppers are a particular favorite.

Under greenhouse conditions all aphids are usually females that give birth to live offspring. They probably have overwintered either as eggs or live adults on weeds in the greenhouse.

There are thousands of species of aphids of which only a few are real common on vegetable transplants, the green peach aphid and the melon aphid being most common. The green peach aphid is light green to rose colored and has an indentation in the head between the antennae. The melon aphid is similar but without the indentation. This spring potato aphids and foxglove aphids have also been found in greenhouses on flower transplants. It is important to know the species if you are going to turn to biological control because the control organisms are specific to species of aphids. It is very difficult to determine species and I suggest you have an entomologist do this. The University of Maine Pest Management office can do this for you if you get them a sample (491 College Ave, Orono, ME, 1800 287 0279). Or an insectory that sells beneficial insects may provide this service.

There are a number of biological controls including parasites (Aphidius colmani, Aphidius ervi and, Aphelinus abdominalis) and predators (Aphidoletes aphidimyza , lace wings and lady beetles). Two companies that have been good in Maine are IPM Laboratories (315 497 2063, or www.ipmlabs.com) and the Greenspot (603 942 8925, or www.GreenMethods.com)

Chemical controls that are approved for organic growers include pyrethrum (only use in worst case situations for a quick knockdown because this kills beneficials), insecticidal soaps and summer horticultural oils. Oils and soaps may be phytotoxic to some plants so I suggest testing on a small sample before a widespread spraying.

For next year, keep the greenhouse free of weeds during the winter. If you are overwintering plants, especially spinach, be sure that they are clean going into the winter.

HOW MUCH ORGANIC MATTER IS IN THAT RYE COVER CROP?

How much dry matter can you expect from a rye cover crop? In work conducted at Geneva in 2003, we found about 200 to 250 pounds of dry matter produced per acre for each inch of top growth. The variation in the amount of dry matter is due to the thickness of the stand. That means a rye crop five inches tall will yield over a thousand pounds of dry matter that may eventually add to the organic matter pool of the soil. During a three week period in 2003, rye grew from 5 to 7 inches tall on April 15, to 15 to 20 inches on May 5. The crop dry matter also increased, reaching 3,100 to 4,800 lbs/A. As the dry matter increases, the nitrogen content decreases. Starting off the season above 2% N, the percentage falls to 1.5 to 1.8% by the end of the period. This higher carbon to nitrogen ratio of the cover crop can lead to problems when it's incorporated. The cover crop will break down very slowly and microbes feeding on the organic matter will utilize soil N, making it unavailable for early crop growth. This immobilization of N can last several weeks and may adversely effect the growth of your crop.

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What to do? [Suggestions from Brian Caldwell:] Mowing the rye when it reaches 12" will tend to keep it in a higher-N state. You can also let the rye grow, then mow it and bale it up for mulch, removing the residue from the field. Or, add a moderate dressing of compost or manure when you till in the rye. Next year, add hairy vetch to the cover crop mix at a rate of about 2 parts rye to 1 part vetch. Then, because of the extra nitrogen from the vetch, N-immobilization will not be a problem.

From:
Brian Caldwell
Farm Education Coordinator
Northeast Organic Farming Association of New York

WINTER KILL

MUMMY BERRY IN BLUEBERRIES

Mummy berry is caused by the fungus Monilinia vaccinii-corymbosi. It overwinters within mummified fruit on the ground, becoming active in the early spring as the buds on the blueberries begin to swell. The fungus forms small, mushroom-like structures called apothecia that emerge from the mummies and produce spores that are carried by wind to infect young developing leaf shoots and flowers. This primary infection causes a shoot and blossom blight in the spring that is often mistaken for frost injury. The shoots wilt, turn brown and die. The fungus then produces more spores on this tissue, which infects developing blossoms. Fruit of infected blossoms may develop normally until they are nearly fully sized, then turn pink to tan in color and become lobed in shape, resembling a small pumpkin. The fruit eventually turn gray and hard, forming the "mummies" that will fall to the ground and provide the overwintering structures for the fungus.

Management of mummy berry by organic growers is really based on good sanitation practices. Removing and destroying the mummified fruit in the field can significantly reduce infections the following spring. Encourage your pickers to remove infected fruit when they are harvesting and give them separate containers to put it in. Offer discounts to pick-your-own customers who'll pitch-in and remove infested fruit when they are harvesting. In small plantings it may be practical to rake up mummies from under the plants in the fall or early spring. Where this is not practical, cultivating the soil under the plants early in the spring can disturb and bury the overwintering mummies and prevent them from disseminating spores. Covering the ground with at least two inches of soil or mulch before blueberries bloom will also bury the mummies and reduce infections.

Modified from report from
David T. Handley
Vegetable & Small Fruit Specialist

Mark G. Hutton
Vegetable Specialist

Highmoor Farm
P.O. Box 179
Monmouth, ME 04259
(207) 933-2100

(About the author: Eric is MOFGA’s Technical Services Director, essentially an organic "extension agent". He can be reached at the MOFGA office to answer your questions about farming and gardening. Link to MOFGA Contact Page, or email Eric directly.)