Many of the strategies required to manage various in-season pests (insects and diseases) are preventative in nature. These are best applied prior to the development of any disease or insect pest population, either during the off-season or at the end of the growing season.
Many of the strategies are general and tend to be cultural in nature. These will provide some general benefits in the management of an assortment of pests, with enhanced impact for specific pests.
Culls
Culls are anything that is damaged, off-grade (size, shape, quality) or otherwise unmarketable in some way, and are therefore discarded from the marketing system. Depending on the crop, the percentage of culls (and volume of product) can vary significantly. On the surface, culls are might seem harmless, however infested, or infected cull material can represent a heavy amount of inoculum or insect life stages. Culls represent a consolidated quantity of host plant material that some pests might take advantage of to continue their life cycle, either being drawn to them, or being already present. From an inappropriately dealt with cull pile, a pest can make the leap into a healthy crop and could potentially be able to bridge growing seasons. So, in this way, they are high risk, and should be dealt with carefully.
The key concept with culls is to do whatever is necessary to accelerate their breakdown, typically through exposure to killing cold and/or heavy microbial activity. Culls should be spread out far away from crop production areas, buried or incorporated into the soil, or disposed of in a landfill. Some cull crops are suitable for feeding to livestock or might be used as an ingredient in some sort of secondary processing or biproduct system.
For serious diseases like late blight of potatoes and tomatoes, which require a living host on the Canadian Prairies to survive, cull piles represent a major opportunity (for the pathogen) and a major risk (for the crop and the producer). Big cull piles can resist freezing and living material can survive. Cull piles can draw in migratory pests to production areas or can shelter an insect pest long enough for it to complete its life cycle. Cull piles outside of greenhouses can produce significant spore loads that can be drawn into the new crop, or produce a flush of insects that can make their way into the greenhouse.
The bottom line is this. Do not have cull piles. Spread them or bury them. Period.
Debris Management (a.k.a. sanitation)
In any horticultural crop, there can be a lot of leftover or remnant material during or after a growing season. Like the cull pile management philosophy, the focus is on taking that debris out of the pest equation.
While it can be challenging to address the debris left from a finished or previous planting during the heat and busy-ness of the peak growing season, this debris represents a big, wide open door for pests to gain a foothold and jump to your younger crops. The plant parts are old, weak, and likely somewhat damaged, and will certainly have some level of infestation and infection. Whenever possible, incorporate that material into the soil as quickly as possible, or get it off the field. Incorporation helps to get the debris off the surface and into the soil profile where the microorganisms can get to work on breaking them down.
Tops and old plant material can continue to spread problems even after they are done producing and even after they are removed from the field. Depending on the types of pests that you have been facing in recent years, or threats that have been identified, consider avoiding dumping tops and debris into open compost piles. For diseases such as Late blight, or any sort of disease that will continue to sporulate as the removed tops die down, piles should be covered until plant material is frozen, or material should be bagged, buried and disposed of in another location.
Sanitation can also include cleaning up weed patches, to cut down on alternative hosts, or to remove areas with higher humidity and poor air flow.
In a closed environment, such as a greenhouse or a storage structure, sanitation will have to move to another level. Debris will be removed, but surfaces must be washed and sterilized to keep any lingering pathogens at bay and to keep them from infecting a new crop coming into storage.
Pruned material represents a potential inoculum source, which should be removed, burned, or buried, again depending on the types of pathogens or pests that might be present. Chipping and spreading of the mulch can be acceptable if there are not any pathogens that will continue to survive on the smaller debris. An example of a disease that should not be put into the mulch, it is generally NOT advisable for black knot-infected branches to be chipped and spread, as there is some potential for the galls to remain viable for a time, if the pieces are large enough. Other material is probably okay to spread.
Other practices
There are other late- or end-of-season practices that can have a positive impact on disease and pest population management. The post-harvest curing of bulb, tuber and winter squash vegetable crops will improve skin set and tighten up outer protective tissue layers. Top killing potatoes at least two weeks prior to harvest will improve potato tuber skin set, reducing skinning and bruising, as well as any subsequent disease infection levels.
Post-harvest treatments may be appropriate for managing some diseases in some crops, such as seed potatoes. This might include treatment with a fungicide, or the use of a surface disinfectant like hydrogen peroxide. Some vegetables will also benefit from washing, but this varies between crops.
If insect pests have a soilborne overwintering stage, a late season shallow tillage operation can disrupt soil conditions enough to reduce the survival of pupae or other overwintering stages.
While extremely indirect, giving perennial plants a bit of late season TLC can be an important part of the long-term pest management toolbox. Ensuring that plants are fully hydrated, adequately fertilized, have good air and water drainage, as well as being liberated from any dead, diseased or dying plant parts will go a long way to ensuring they are capable of resisting attack from outside threats.
Conclusions
Much of the focus of end-of-season pest management practices is focused on trying to knock pest populations back down to a manageable or acceptable level for the next season. In some ways, it is an attempt to bring things back into balance, as well as augment the health of a crops.