There is an old saying that states "an ounce of prevention is worth a pound of cure". While these words have a practical application for many aspects of life, they are especially true for vegetable growers. Insects and diseases arguably rank as two of the biggest problems growers face each season. While fall cleanup cannot eliminate them from our plantings next year, it can help to make control a bit easier.
The structures that overwinter and give rise to plant diseases the following growing season is referred to as inoculum. While they vary in nature from pathogen to pathogen, in most cases they are referred to as "spores". Spores are part of the natural reproductive cycle of many fungal diseases such as grey mold of tomato. Many spores have the ability to survive very harsh conditions during the winter and yet “spring to life” when the environment is more favorable the following growing season. The greater the population of spores in the immediate area to begin with the more difficult pest management becomes.
We have long advocated an integrated approach to pest management in horticulture crops production. IPM, as it is known, involves a series of measures designed to give optimum pest control with minimal chemical input. One of the tenets of IPM is exculsion. The latter attempts to eliminate disease inoculum (and insects or their eggs) that might overwinter in the field by practicing good sanitation. Without practicing sanitation, a population of pests is present and waiting for crops to emerge or be planted in the spring, and the job of pest management becomes much more difficult.
Using tomato as an example, the spores that cause the leaf disease early blight overwinter in the soil. If there is an abundant supply of these spores from plant refuse from last year’s crop the job of controlling the disease becomes even more challenging. The same can be said for insects whose eggs might overwinter on tomato leaves or other plant debris allowed to remain after a crop is finished.
Best management practices dictate that strict sanitation be observed in all stages of plant production, ending with a thorough cleanup of the production field. This means that all plant material should be removed each fall from the previous year’s crop as carefully as possible and disposed of properly. Any leaf that is allowed to remain in the field is a possible source of disease infestation for next year. Therefore after removing plants from the field go back and do a thorough sweep of the area to collect as much remaining debris as possible. This is especially important in greenhouses and high tunnels where environmental conditions for pest infestation are more favorable than out-of-door.
Proper disposal involved taking the material to a safe place and discarding it. Burning the debris is very effective but must be done with great care especially during the fall when humidity is low and conditions often windy. Avoid placing discarded plant debris in a compost pile. The temperature reached inside the pile may not be hot enough to kill disease and insect inoculums. Spreading this compost back on the production field will inoculate the soil with pests—the exact opposite of what was intended by removing the old plants.
Unfortunately, sanitation by itself is not enough to prevent diseases and insect pests in the greenhouse or production field next year. However, it can go a long way to reducing infestation and make control of that infestation less expensive.
REVISED: December 3, 2015