The tunnel environment differs from the field, so the type and timing of insects and diseases also differs. For example, spider mites and aphids are more frequent pest in tunnels than outdoors, and foliar diseases in tunnels are typically due to humidity levels. The use of biological insect controls is more practical in tunnels than outdoors due to the (at least partly) enclosed space, high crop value, and extensive information developed for many crops. See the University of Vermont’s high tunnel pest management web site for more information. Maintaining the area around the perimeter of the tunnel with mowing and trimming is a passive way of minimizing mammalian pests by reducing cover.
Pesticides. Outdoors, pesticide residues break down after application by exposure to ultraviolet radiation and rainfall. Inside tunnels, plastic coverings reduce U/V and rain, and as a result, pesticides break down differently. Each state’s pesticide regulatory agencies may have different interpretations of whether high tunnels are considered open fields or greenhouses, however it is safest to consider a high tunnel a greenhouse from the perspective of pesticide labels. The label may 1) specifically state that the product may be used in greenhouses and may provide different guidelines for greenhouse and outdoor use, 2) specifically state that the product may not be used in greenhouses, or 3) may not mention greenhouse use at all. The Environmental Protection Agency’s current position is that a label does not have to specify greenhouse as a site, provided the crop is on the label, in order to use the product in a greenhouse. If the label has multiple sections, and one of those sections is for greenhouse application, then the label must be followed explicitly for greenhouses with no exceptions. The rate for outdoor applications on those crops is for outdoor use ONLY and CANNOT be used for those crops in the greenhouse, since those crops were not included in the greenhouse section of the label. Using a pesticide inside a greenhouse where the label does not mention greenhouse use can increase risks to workers or plants. Also, when using a fumigant or smoke generator for an entire greenhouse, every crop in the greenhouse must be listed on the product label. We advise against applying a product in high tunnels unless the label specifically allows its use in greenhouses.