Growing Magazine - September, 2012


Keep It Clean

End-of-season field maintenance for healthy future crops
By Kathleen Hatt

Now that the growing season is about over, it's time to start thinking about next year's crops. What can you do to improve them? What can you do to limit the pests and diseases you saw this year?

As the harvest season wraps up, it's important to clean up to ensure this year's issues don't become next year's issues.
"In a word, sanitation," says Dr. Cheryl Smith, extension professor and plant health specialist with the University of New Hampshire Cooperative Extension. "One of the simplest and most obvious ways to help prevent the start of diseases is through good cultural practices and sanitation, such as removing the prior season's infected crop debris," she says.

What's effective

While sanitation is always part of the solution to controlling pests and diseases, it is more effective in limiting organisms that do not reside in the soil than those that do. Diseases that do not live in the soil include bacterial canker on tomatoes. Pests and diseases residing in the soil include root rots and nematodes.

Unless organisms such as Phytophthora root rots and vascular wilts are diagnosed early and plants are removed from the field early in the season, sanitation is usually not effective. "Planting resistant varieties and rotating crops are the most effective ways to limit these diseases," says Smith.

Crop rotation must go hand in hand with sanitation. Septoria leaf spot and early blight on tomatoes, for example, can be controlled if infected plant material is removed as soon as it is identified. These diseases can come from bits of plant material left in the field. Diseased material should not be left lying on the surface. To be effective, plowing needs to be deep - 4 to 6 inches or more, depending on soil type.

Some diseases, such as bacterial canker on tomatoes, can be seed transmitted or transmitted on the stakes or clips used in greenhouses and high tunnels. Here year-end maintenance should include soaking these items in bleach or a hydrogen dioxide product followed by air-drying. The alternative is to use new stakes and clips for each crop every growing season. Be sure the seeds for next year's crop are certified disease free or have been treated in hot water.

"Remove as much diseased material during the growing season as possible to prevent greater problems later," says Smith. The alternative is treating with fungicides to prevent disease build-up. It is especially important to remove plants infected with soilborne pathogens with wide host ranges, such as fusarium or verticillium.

Equipment used in sanitizing should also be cleaned to lessen the chance that it will transmit diseases to other fields. A tractor used in a pumpkin field with, for example, Phytophthora blight could carry the infection to other fields. Try to plow infected fields last. Then, at a minimum, hose down the tractor and any other equipment to get the soil off.

Orchards also need year-end attention. Since leaves are the source of infection for apple scab, chopping them in the fall is effective in controlling the disease.

Row cover removal

Pull up-do not plow under-plastic mulch at the end of the growing season.
Row covers can be big and bulky and a nuisance to wrestle, but a heap of them in a corner of a field or barn may be an invitation to insects to stay the winter and return next year. Row covers that protected healthy crops can be reused if they have been dried and rolled or folded before winter storage. Others should be destroyed.

Biodegradable row covers are available, but whether or not they make economic sense is still open to discussion. Although they are initially more expensive, the cost of using biodegradable row covers may be offset by the fact that you don't have to pay to dispose of them. Also keep in mind that even though there is no labor involved to remove them, the buried edges must be exposed to sunlight in order for them to degrade in place, which entails some labor.

To keep nonbiodegradable row covers, as well as any other useable items, out of landfills, consider posting on Freecycle ( Items such as row covers and plastic mulches may be useful to home gardeners who can use undamaged pieces as covers or mulches or cut pieces for use as plant ties. As the name suggests, the service is free and no money is ever exchanged either with the organization itself or among members.

Pulling mulch

Plastic mulches have been beneficial to many growers, enhancing early growth and yield of a number of crops. Like conventional row covers, plastic mulches should be removed from fields at the end of the season. However, plastic mulch removal can be costly: Removing 1 acre of plastic mulch can take up to eight hours of labor, but leaving plastic mulch on fields after the growing season should not be considered an option. Plastic mulch invites slugs and other hungry critters to continue residence.

In areas where plastic mulch is widely used, such as parts of Florida, recycling is available. Recycled plastic mulch can be used to make new mulch or other products. Where recycling is not available, growers often rototill or disk plastic mulch at the end of the season. This may not be the best practice. When replanting these fields with cover crops, rototillers or seeders can become entangled with pieces of the plastic. More important, say soil scientists, is that plowed-in plastic mulch can degrade soil quality by altering subsurface movement of water and nutrients and by disturbing microorganisms in the soil.

Biodegradable mulches are being used more widely, in part to control the cost of labor to pick up plastic mulch and dispose of it. Cost of disposal at a landfill, together with the labor involved to pull up the mulch and transport it, can exceed $25 to $100 per acre.

A significant issue with biodegradable mulches made of paper, plant starch or wheat is that degradation can occur at unpredictable rates. In short, biodegradable mulches can disappear before the end of the growing season. This feature of biodegradable mulches may contribute to reducing year-end field maintenance, but it also means growing crops may not be protected as long as they need to be. The rate at which biodegradable mulches break down is affected by temperature, sunlight and moisture. Ideal growing conditions (warm temperatures, plentiful rainfall and bright sunlight) speed degradation. The type of soil, crop cover, and weed pressure are also factors in the rate of degradation.

Clear it out and break it down

Year-end (or earlier) field maintenance can go a long way toward controlling plant diseases. Remove diseased material, and then break it down. Limit the time any one crop is grown in a given field and consider adding a nitrogen-fixing green manure crop to help mitigate field weed populations. As a bonus, cuttings of the green manure crop can help support farm operations.

Kathleen Hatt is a freelance writer and editor and a frequent contributor to Growing. She lives in Henniker, N.H.

For Further Information

National Plant Diagnostic Network ( Help with diagnosing and treating plant pests and diseases and links to individual states' plant diagnostic labs.