Maine Organic Farmers and Gardeners Association

By Eric Sideman, Ph.D.

Sometimes it is better to be prepared for bad news then to be surprised by it. This chart prepares growers for some of the most common vegetable problems seen in Maine. It is based on the Bug Reporter, which used to be published by the University of Maine Extension Pest Management Office, and my own Pest Report, which is still published (http://www.mofga.org/Publications/PestReports/tabid/732/Default.aspx).

The recommended management practices and materials are quick and brief ideas. For more details growers should sign up to receive the Pest Report and get a copy of the new, 2nd edition of the Resource Guide to Organic Insect and Disease Management (http://web.pppmb.cals.cornell.edu/resourceguide/). The Resource Guide, which is available for a charge as a hard copy and free as a PDF, not only presents useful information about insect and diseases, cultural practices to avoid and manage problems, and recommendations of materials for control that meet organic standards, but it also has full chapters on each of the common insecticides and fungicides allowed by the standards. These chapters include efficacy data and health and environmental risks, such as risks to bees and buildup in soil, and guidelines for using these materials to reduce such risks.

If you are unlucky and an issue noted in the chart turns up in your fields, then read all about it in the Resource Guide.  


Maine Organic Farmers and Gardeners Association
Vegetable Pest and Disease Calendar
    May May June June June June July July July July Aug. Aug. Aug. Aug. Sept. Sept.  
Insect Pest Major Crops Affected 3rd wk 4th wk 1st wk 2nd wk 3rd wk 4th wk 1st wk 2nd wk 3rd wk 4th wk 1st wk 2nd wk 3rd wk 4th wk 1st wk 2nd wk Most Important Organic Solution
Seedcorn maggot Corn, spinach, beans ** ** * * *                       Wait for warm soil before planting; avoid fresh organic matter
Flea beetles Brassicas ** ** ** ** ** * * * *               Use floating row cover early in season
Cutworms Brassicas, onions, peppers, etc. ** ** ** ** * * * * *               Fall weed control; collars around transplants, beneficial nematodes
Cabbage root maggot Cabbage, brassicas   * ** ** * * *                   Use floating row cover early in season
Onion maggots Onion   * ** ** ** * * *                 Floating row covers; avoid fresh organic matter
Slugs Lettuce, greens   * * * * * * * * * * * *       Dry sand barrier; copper band; iron phosphate (Sluggo)
Common asparagus beetles Asparagus   * * * * * * * * * * * * * * * Clean harvest allowing no fronds to develop until done harvesting; If a big problem, spinosad (Entrust or Monterey Garden Spray)
Tarnished plant bug Strawberries, lettuce, peppers, eggplant, herbs   * * * * * * * * * * * * * * * Floating row cover; no other good organic control
Aphids Wide variety of vegetables and flowers   * * * * * * * * * * * * * * * Insecticidal soap; control ants if they are managing aphids; neem
Spotted asparagus beetles Asparagus     * * * * * * * * * * * *     Clean harvest allowing no fronds to develop until done harvesting; if a big problem, spinosad (Entrust or Monterey Garden Spray)
Striped cucumber beetles Cucumbers, squashes, melons     * ** ** ** * * * * * * *       Good sanitation in fall; floating row cover until flowering; kaolin clay (Surround) on transplants;  then pyrethrum if problem persists
Wireworms Potatoes, root crops     * * * * * * * * * * * *     Avoid new sod ground or garden edges with susceptible crops
Colorado potato beetle Potatoes     * * * * * * * * * * * *     Crop rotation; spinosad (Entrust or Monterey Garden Spray)
Imported cabbage worm Brassicas     * * * * * * * * * * * * * * Bt (Dipel)
Spinach leaf miner Spinach, beets, chard       * * * * * *               Control weed hosts (lambsquarters, chickweed); spinosad (Entrust or Monterey Garden Spray)
Mexican bean beetles Beans         * ** ** ** * * * *         Clean up crop debris in fall; biological control with Pediobiou foveolatus; spinosad (Entrust or Monterey Garden Spray)
European corn borer Corn, potatoes, peppers, beans         * * * * * * * * * * *   Destroy corn stalks in fall; Bt granules in whorl of young corn if damage is seen
Common stalk borer Corn, peppers, tomatoes         * * * * * *             Weed control in fields and gardens; mow weeds in fence rows
Japanese beetles Raspberries, roses, lawn           * * * * *             Beneficial nemotodes work if issue is with grubs
Common armyworm Corn           * * * * * * *         Very variable numbers from year to year; keep fields around corn mowed in fall; well-timed Bt (Dipel) spray
Corn earworm Corn           * * * * * * * * * * * Bt spray on fresh silk if moths are present; best results with Zealater
Potato stemborer Potatoes           * * *                 Rare in Maine
Potato leaf hopper Potato, beans, strawberry           * * * * * * * * *     Scouting for the insect is important because by the time there are symptoms, it is too late.  Pyrethrum (Pyganic 5.0)
Three-lined potato beetle Potatoes, others in tomato family           * * * * * *           Row covers; hand picking if small number; no highly effective organic spray
Blister beetle Wide variety of vegetables and flowers             * * * * *           Hand pick (wear gloves); pyrethrum
Diamondback moth Brassicas             * * * * ** ** ** ** ** ** Bt (Dipel)
Squash bug Squash             * * * * * * * * * * Clean up last year's squash debris; crop rotation; pyrethrum and/or neem on young nymphs
Grasshoppers Many vegetables and flowers             * * * * * * * * * * Nosema locustae; usually only a problem in drought
Hornworm Tomatoes             * * * * * * * * * * Bt (Dipel); handpick
Onion thrips Onions             * * * * * * * * * * Fall sanitation; spinosad (Entrust or Monterey Garden Spray); kaolin clay (Surround)
Carrot rust fly maggots Carrots             * * * * * * * * * * Row covers
Fall armyworm Corn               * * ** ** ** ** ** ** ** Well-timed Bt sprays
Sap beetles Many kinds of overripe fruit               * * * * * * * * * Destroy overripe fruit
Cabbage looper Cabbage, brassicas               * * * * * * * * * Control cruciferous weeds; till in crop debris; Bt (Dipel)
 
    May May June June June June July July July July Aug. Aug. Aug. Aug. Sept. Sept.  
Plant Diseases Major Crops Affected 3rd wk 4th wk 1st wk 2nd wk 3rd wk 4th wk 1st wk 2nd wk 3rd wk 4th wk 1st wk 2nd wk 3rd wk 4th wk 1st wk 2nd wk Most Important Organic Solution
Damping off Seedlings of many vegetables * * *                           Wait for warm soil; use "sterile" starting mix
Seed rot Many crops, especially peas, spinach, corn * *                             Wait for appropriate soil temperature for particular crop
Sunscald Onion   * *                           Avoid transplanting onion seedlings on or just before hot, sunny days
Bacterial wilt Cucumbers     * * * * * * * * * * * * * * Control cucumber beetle
Botrytis (gray mold) Tomatoes, potatoes, beans     * * * * * * * * * * * * * * Maintain good aeration around plants; irrigate early in the morning rather than evening; good weed management
White mold Beans, carrots, lettuce       * * * * * * * * * * * * * Avoid waterlogged soil; promote good aeration; store carrots under cool conditions
Halo and common bacterial blight Beans       * * * * * * * * * * * * * Do not harvest from wet plants; crop rotation; plow under debris after harvest; buy seed produced in dry climate
Early blight Tomatoes, peppers       * * * * * * * * * * * * * Crop rotation; mulch at planting time; maintain healthy plants; copper based fungicide (Champ WG)
Anthracnose Tomatoes       * * * * * * * * * * * * * Crop rotation; mulch at planting time; destroy overripe fruit
Late blight Potatoes, tomatoes       * * * * * * * * * * * * * Destroy cull potatoes; promote quick drying of foliage; copper based fungicide (Champ WG)
Septoria leaf spot Tomatoes       * * * * * * * * * * * * * Use clean seed; sterilize flats; crop rotation; mulch at planting time; copper based fungicide (Champ WG)
Clubroot Broccoli, brassicas       * * * * * * * * * * * * * Raise soil pH above 7.0; plant no cole crops for 5-7 years
Scab Potatoes           * * * * * * * * * * * Maintain good soil moisture from potato set, on; resistant varieties; maintain soil pH of 5.2 or below
Purple blotch Onion           * * * * * * * * * * * Sanitation in fall, e.g.;  plow in debris; crop rotation; Bacillus subtilis (Serenade)
Corn smut Corn             * * * * * * * * * * Destroy infected ears; tolerant varieties
Verticillium Eggplant, tomatoes             * * * * * * * * * * Resistant varieties
Sunscald Tomatoes, peppers             * * * * * * * * * * Maintain foliage
Powdery mildew Summer squash, pumpkin               * * * * ** ** ** ** ** Resistant varieties; maintain fertility; tolerate if not present until late in season; potassium bicarbonate (Milstop); sulfur (Micro Sulf)
    * insect or disease is present  ** potentially a major problem  
For more information or help, contact MOFGA, PO Box 170, Unity, ME 04988; (207) 568-4142, esideman@mofga.org. See The Resource Guide to Organic Insect and Disease Management, http://web.pppmb.cals.cornell.edu/resourceguide/:  NOTE - Brand names of pesticide materials are mentioned as an example of a material with the noted active ingredient; it is not an endorsement of that brand.