We can only give general advice here, as conditions vary significantly between regions.
Powdery (erysiphe necator) and downy (peronospora) mildew fungi infections are offered some control when using a shelter due to the increased temperature. These fungi to not generally survive above 37°C so most (European and North American) climatic conditions would produce these temperatures fairly early on in the season.
Where temperatures are lower, fungal attack is still a risk. Well managed sites should be able to prevent downy mildew infection (which does not travel well), but powdery mildew might still be a risk so the normal treatment (e.g. copper spray) might be required. Either way the shelter should not affect this situation.
Botrytis survives in the soil and as such is not controlled by the vineshelter temperature. However, we have no evidence to suggest that the shelter affects the level of any infection. Normal control measures apply.
Generally we experience fewer pests within a shelter, particularly where temperatures within the shelter exceed 40°C for a period. Temperatures at this level will kill pupal stages of most insects.
Soil borne pests might sometimes migrate to the shelter, but this is prevented if the normal insecticide procedures are in place.
Adult pests are often prevented from accessing the vine by the physical barrier presented by the shelter.
Shoot burn is evidenced by desiccation of the leaves followed by progressive death of the shoot. A vine can re-grow but will often produce numerous laterals. It can occur at excessive temperatures (>50°C), but will be prevented by good root formation and soil conditions.
This condition can be experienced in very hot areas, and is usually experienced when a hot spell follows a long cool one.
If shoot burn is a concern it can be avoided by combining careful irrigation with a shelter that will give lower temperature rise (e.g. smaller diameter shelters).
Some users recommend that the shelter is installed after at least 2 fully expanded leaves have appeared – to humidify the shelter. However, others do not follow this technique and insist on plant newly grafted (dormant) vines.
Shoot burn can also occur where low melting point waxes (cheese wax) has been relied upon to protect the union. We recommend that vines with higher melting point waxes are used – ask your nursery.