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 MOFGA's 2006 Pest Reports - Compiled by Eric Sideman, PhD Minimize

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This is the first Report Report for the 2006 growing season. Again I want to thank the Cooperative Extension folks in New England for sharing their great reports with me and allowing me to modify them for my report. If I do not say where it comes from then the report is my own.

If you are a MOFGA certified grower then you will only receive the next Pest Report if you reapplied for certification for the 2006 season. If you did not reapply and would like to receive the Pest Report anyway, contact me.

Eric Sideman
Organic Crop Specialist for MOFGA

PYTHIUM ROOT ROT: Pythium is one of the most common fungi found in roots of greenhouse crops. It is a natural inhabitant of the soil and can survive there indefinitely as well as in debris in the greenhouse. Stunted growth and wilted plants are common above-ground symptoms caused by Pythium root rot. To examine plants, remove plants from pots and examine roots. Healthy roots are white and firm; decayed roots may be dark colored and the rotted outer covering of the root slips from the central core.
 
Growers having re-occurring problems with Pythium, should review their overall production practices including fertilizing, watering and media handling. Over-watering and excessive fertilizer levels promote Pythium. Good sanitation is crucial for prevention. Keep hose ends off the floor, wash hands before handling plants and avoid contaminating growing medium.
 
Since symptoms can be confused with other causes such as high soluble salts or other diseases, suspicious plants should be diagnosed through your University diagnostic lab. There are several materials registered for Pythium including potassium salts of phosphorous acid (Alude), which works by stimulating the plant‚s natural defenses, and the more traditional fungicides Aliette, Banol, Banrot, Subdue, etc. Apply treatments as a drench, following label directions. After application, irrigate with additional water to move the fungicide into the root system. Note that about half of most isolates received at the UMass diagnostic lab over the past few years have been resistant to Subdue. Some growers have reported some success using a rescue treatment of hydrogen dioxide (ZeroTol) drench, followed by a fungicide treatment, the theory being that ZeroTol will knock down the pathogen in the soil and the fungicide will act as a protectant. A study is currently being conducted to determine whether growing media affects the activity of hydrogen dioxide. -Adapted from article by Tina Smith, UMass Extension


CUTWORMS: This is the time of year to start thinking about cutworms which often become a real challenge especially for transplants, carrots, onions. 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 makes a good barrier. I have received good reports about making a bait from bran, a Bt solution and molasses and then sprinkling it or making patties and putting them 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).

Another method for managing cutworms may work in some systems that can delay planting. The cutworm is the caterpillar of a moth. Some species fly in the fall and lay eggs and other fly in the spring. In any case, the caterpillars are feeding early in the spring and if there is no food they will starve. Keeping a field completely free of weeds and crops for a few weeks in the spring may work.


CABBAGE ROOT MAGGOT: Watch for cabbage root maggot eggs, especially on transplants. Flies spend the winter as small brown pupae in the soil. Adults emerge in spring (around the time forsythia flowers) and seek out crucifer plants to lay eggs at the base of the stem. Adults can travel considerable distance in search of host plants (1/2 to  1 mile). (Onion growers should also watch for onion root maggot activity at this time. See below)

Hot dry soils are not a favorable environment for maggot egg survival. Eggs are killed when temperatures exceed 100 o F, and are also subject to desiccation under dry conditions.

Recent research by Tony Shelton at Cornell University produced a degree day model for cabbage maggot emergence in New York State. According to the model, the first emergence of cabbage maggot occurs at 160 degree days +/- 8 degree days (DD). 25% emergence occurs at 203 DD +/- 3 DD, 50% emergence occurs at 251 DD +/- 8 DD, 75% emergence occurs at 304 DD +/- 37 DD and 95 % emergence occurs at 387 DD +/- 8 DD. We do not know if this model fits for New England maggot flies, as there can be regional variations, but it gives an estimate. For growing degree day information in Maine go to http://pronewengland.org/AllModels/MEmodel/RADARME-Monmouth.htm

Growing Degree Days are calculated by taking the average of the maximum and minimum temperatures for the day (Max + Min /2) and subtracting the base temperature (either 50 or 55 oF for most plants and insects). Below the base temperature, growth and development are minimal.

Cabbage root maggot flies are smaller and more delicate than a housefly, and can often be seen moving from plant to plant in early crucifers. To monitor for adult flies, use a flat water-pan trap painted bright yellow (Federal Safety Yellow), placed on the ground in the field. These can be made from any sturdy plastic dish, or purchased. Add a drop of soap to break the surface tension. Flies are attracted to the yellow color and to the moisture. Yellow sticky traps can also be used - these are placed vertically on stakes, near the soil. Check traps twice weekly. This will tell you when the flight peaks, and when it declines. Flights in Maine decline after late-May and many June and later plantings do not need protection.

Floating row covers provide an effective barrier against this pest. Use in a rotated field only, as flies overwinter in fields of late season crucifers, including crucifer weeds. Remove and replace in order to weed. If covers are not a practical option, and eggs are found by scouting, cultivation that brings soil up around the stem may help encourage formation of adventitious roots from the stem., which can help compensate for root loss. This assumes some soil moisture is present in the upper layers of soil. --Modified from an old report by Ruth Hazzard, UMASS


ONION MAGGOT: The onion maggot is in the same genus as the cabbage maggot and has very similar habits. It is one of the most serious pests of onions and can wipe out an entire crop (it wiped out my entire crop in my garden 2 years ago). Onion is the preferred host and related crops such as scallions, garlic, leeks and shallots are only occasionally infested. Wild onion is not an important host either.

The greatest damage is caused by the first-generation larvae that attacks young seedlings in the early spring. They move up rows to new plants as they devour the young seedlings quite quickly and need more food. The first symptom seen in very young seedlings is a slight wilting of the plant. Later they will simply disappear. Plants attacked at later seedling stages will turn a grayish yellow and wilt and will later detach at the ground level as the maggot consumes everything below ground. Onion plants attacked later are rarely killed and fewer plants are attacked as the maggot does not move to new bulbs. However, plants attacked at the later stage are likely to have misshapen bulbs and usually are attacked by fungi and rot.

The onion maggot overwinters as a pupa in the top five or so inches of soil. When spring soil temperature rises above about 40 degrees the overwintering pupae begin to develop and, depending on the weather, in a number of weeks the adult onion maggot flies will emerge and fly around and mate. Later they will search for onions to lay eggs around. Eggs are laid around the base of onion plants and the resulting larvae crawl down to start feeding on the roots. There can be three generations in a season.

Adults of later generations disperse very little from onion fields so crop rotation is a very important tool for avoiding infestations. Good sanitation is very important because cull onions will attract flies that will lay eggs that result in overwintering pupa. Damaged onions are the preferred site for egg laying so avoid mechanical damage to onions and dispose of any damaged onions rather than leaving them laying around the field. Discing onion fields in the early fall when the flies are still active actually makes things worse because it makes many pieces of onions and so increases the number of sites for egg laying. Ash and diatomaceous earth around the base of onion seedlings may deter egg laying and maggot survival.


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