This does not look like an insect or disease issue. This looks like winterburn or winter damage on the holly leaves. There is no need to treat. The leaves will drop and the shrubs will put out new foliage in the spring. 

Winterburn is caused by soil moisture becoming temporarily unavailable for root absorption during periods of freezing weather. Meanwhile, dry winter air and winds are still evaporating moisture from evergreen foliage. Since the plant can't replace what's being lost, the leaf tissue dries too much and dies, becoming bleached-looking or brown and brittle. You can think of it a bit like freezer burn. Injured leaves can't heal, but they will gradually be replaced as the plant resumes growth, at which point the damaged leaves will fall off.

If you are looking for trees/shrubs that will survive in containers over the winter, it is recommended to look for ones that are cold hardy to two zones lower than your local growing zone. In other words, if you are in USDA zone 7, look for trees/shrubs that are cold hardy down to zone 5.

The key to overwintering plants in containers is to prevent the soil mass from freezing and to maintain moisture in the soil throughout the winter. It is good the plants are in large containers. The larger the pot size the better because size will minimize the stress of fluctuating soil temperature and moisture. However, the containers have to be monitored throughout the seasons for moisture. They also need holes for good drainage. If the  planters are on hard paving they should be elevated for effective drainage.
Check the soil moisture about once a week especially during dry periods and also if under an overhang. Water deeply if needed.  Check the soil moisture by probing with a screwdriver about 4-6 inches deep and feel with your finger. Soil should be damp to the touch. Let the soil dry before watering again.
https://web.extension.illinois.edu/containergardening/overwintering.cfm

Marian



You are welcome.

Marian