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 MOFGA's 2007 Pest Reports - Compiled by Eric Sideman, PhD Minimize

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NOTE: This is the first Pest Report for the growing season of 2007. I am sending it to the list I used last year. If you are a MOFGA certified grower, then you will automatically receive the rest of them this season. If you are not a certified grower and want to receive future reports, then please email me and let me know. The next report will be sent to the 2007 MOFGA Certified Grower list, and those others who make the request.

I want to remind you all and again thank my sources for much of the information in these reports. Extension educators from across New England are kind enough to allow me to use their material that they post in various places. Whenever I use a piece from someone else, I always cite the source and you may want to contact them after reading something and request to get on their direct mailing list. I modify the reports from Extension and tailor them to fit organic farmer needs.


Potato seed tubers are often the source of infection for a crop and inspection before planting is well worth the time. Some problem seed pieces are not going to spread a disease and can be planted. Here are some common issues:

Ring Rot - This is one of the worst diseases you can get on your farm because once you get it, it is very hard to get the farm clean again, and it spreads very easily by the bacteria clinging to boots, crates, and equipment. Check your seed carefully and discard the whole load if any ring rot is found. In the tuber you will see the disease as a break down of the ring of vascular tissue when you cut the potato. Squeezing the tuber will expel creamy, odorless ooze of bacteria. Planting these tubers will introduce the bacteria to your soil.

Scab - Lesions on the tuber are usually circular and seldom larger than a half inch, but in very bad infections they coalesce. They may be a cork like layer or pitted. The layer under the lesion is straw colored. Planting these tubers will introduce the bacteria to your soil.

Black Scurf - If you have little black, irregular lumps on the skin of your potatoes that resemble soil but will not wash off, and then you have black scurf. This is a disease that is caused by a fungus called Rhizoctonia solani. The black specks are one of the ways the fungus reproduces. They are called sclerotia, which are tight, dry masses of fungal tissue (mycelium) in a resting phase. In the spring the sclerotia germinate and infection of the new potatoes begins. Most commonly, infection of potatoes is from planting potato seed pieces with sclerotia on them. Crop rotation is not very effective because sclerotia can survive for many years without a host crop. So, avoid ever planting seed with the disease.

Hollow Heart - Just as the name implies, the center of the potato is hollow. It appears as splitting within the tuber and the inner walls may be white, tan or even may be rarely infected with a secondary disease. Hollow heart is not caused by a pathogen but rather by rapid tuber enlargement especially after a period of moisture stress. Potato seed with hollow heart will not spread the disease.

Knobby potatoes - Potatoes with knobs are usually the result of high field temperature and drought or other conditions that cause irregular rates of tuber development. Planting knobby potato seed will not spread the problem.

(adapted from UMass Extension)

A key to suppressing foliar disease in the greenhouse is to keep the plant canopy dry, especially from dusk to dawn. This is accomplished through proper watering and adequate plant spacing, having well-drained floors, warming plants, moving air and venting moisture. The least expensive method is to keep the greenhouse dry, especially going into the night, when the temperature drops. Puddles on the floor and water on leaf and media surfaces evaporate and add moisture to the greenhouse, which creates humidity, and that takes away energy that is intended to keep a house warm. Water your plants just enough to prevent excess water on the floor, and water early enough in the day so plant surfaces can dry before evening. The highest relative humidity in a greenhouse is in the plant canopies, where moisture from transpiration gets trapped due to insufficient air movement. Adequate plant spacing and mesh benches will help to improve air circulation at the plant level. Remove weeds as they also contribute to high humidity.

Bottom heat will improve air circulation inside plant canopies and helps prevent condensation on leaf surfaces. As warm air rises it creates air movement around the plants, and it keeps plant surfaces warm, preventing condensation on them. Combining heating with ventilation is important for reducing humidity. Ventilation exchanges moist greenhouse air with drier outside air. Heating brings the outside air up to optimum growing temperature, and it increases the capacity of the air to carry moisture, avoiding condensation. Neither practice alone is as efficient as both combined.

To vent humid air in greenhouses with vents, the heat should be turned on and the vents cracked open an inch or so. When doing this the warmed air will hold more moisture (RH), escape from the greenhouse through the vents, and be replaced with outside air of lower RH. This natural rising of the air will result in a greenhouse of lower relative humidity. In houses with fans, they should be activated and operated for a few minutes and than the heater turned on to bring the air temperature up. The fans should then be shut off. A clock could be set to activate the fans. A relay may be needed to lock out the furnace or boiler until the fans shut off so that both the fans and heating system do not operate at the same time and flue gases are not drawn into the greenhouse.

The venting and heating cycle should be done two or three times per hour during the evening after the sun goes down and early in the morning at sunrise. The time it takes to exchange one volume of air depends on whether or not fans are used and the size of the fans and vents. For some greenhouses it may take only 2 to 3 minutes for air exchange. If using natural ventilation, it may take 30 minutes or longer. Heating and venting can be effective even if it is cool and raining outside. Air at 50 degrees F and 100% RH (raining) contains only half as much moisture as the greenhouse air at 70 degrees F and 95% RH. (Reprinted from Vermont Vegetable and Berry News, compiled by Vern Grubinger)


This is the time of year to start thinking about cutworms, which often become a real challenge especially for transplants and carrots and onions. Cutworms are the caterpillars of a few different species of night flying moths. Some of the species fly in very early in the spring and others in the fall. They lay eggs at the base of plants (weeds and cover crops in the fall). The eggs hatch into tiny, dark gray, greasy caterpillars that feed at night. Some species just simply cut off your plants just about at ground level. Other species climb up and cut off leaves. The caterpillars can be found in the soil by digging around. They curl up into a "c" shape when you handle them.

The big problem is you never know whether it will be a problem or not. On a small scale, Dixie cups with the bottoms cut out placed around a transplant make a good barrier.

One method that works on a large scale but is usually not practical is to starve them out. If you can keep a field completely free of any growing plants (weeds or crops) for a few weeks after they hatch then they will die.

I have received good reports about making bait from bran, a Bt solution and molasses and then sprinkling it or making patties and putting the patties along the row of effected crops.

I have also heard very good reports from folks who have used parasitic nematodes. The best results for cutworms is achieved when a combination of two types of nematodes are applied in a mixture because the different species work different levels in the soil and attack the cutworms both while they hide deeper in the soil during the day and when they move up at night. A mixture of Heterorhabditis bacteriophorea (Hb) and Steinernema carpocapsae (Sc) has essentially eliminated cutworm problems for some of our growers. The nematodes are usually shipped on a sponge ready to mix with water and apply to the soil. It is important not to let the soil surface dry out shortly after application. A few suppliers of these insect-attacking nematodes are The Green Spot (www.greenmethods.com), IPM Laboratories (www.ipmlabs.com), and ARBICO (www.arbico.com).

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