You did not mention how old the trees are, how large when planted, your planting techniques, or how they were cared for. In general, many problems and declines of Leyland Cypress, begin to show up at the 15-20 year mark. They are not really well suited to our climate long term. Stresses such as winter injury, too much shade, planting too deeply, etc.)
can lead to disease and insect (bagworms) issues.

Here is more information, from our Maryland Grows blog recently written by our plant pathologist:
https://extension.umd.edu/hgic/topics/why-are-leyland-cypress-trees-turning-brown

and the diseases most prevalent: https://extension.umd.edu/hgic/topics/seiridium-and-botryosphaeria-canker-leylands-trees

It looks like the leyland cypress are a screen of trees across from a field and they are surrounded by weeds. We cannot tell how if they were mulched.
This does not look disease or insect related. This looks like the trees are not establishing themselves due to abiotic issues (not disease or insects). There could be many possible reasons for browning/dieback such as poor planting techniques, poor soils, poor drainage, drought, etc.
It can take a season or two for evergreens to start showing symptoms. The browning of the interior needles are old needles.
 Here is the planting process, our video, and post planting care. https://extension.umd.edu/hgic/topics/planting-tree-or-shrub 

Here are some reasons why plants fail to establish.
If the plants were balled and burlapped, were the cords removed and burlap cut loose.
If container plants - if rootbound within the container - were the roots teased apart so they could establish into surrounding soil.

If a lot of organic matter was added to the planting holes, the organic matter could hold a lot of water creating a bathtub effect and drown the roots. Plants often "drown" in these holes because organic matter holds water like a sponge, while the surrounding clayey soil is slow to drain.

Planting too deep -Planting holes should be wider than deeper. Over time root balls can settle even further into the ground or plants are overmulched.
This situation can contribute to trees and shrubs having too much soil piled up around their trunk causing failure to establish, trunk damage, poor growth, and decline. A properly planted and established tree flares at the base of the trunk at the soil line where it joins the root system. In some cases, soil is piled up around trunks at the plant nursery prior to digging up the trees for shipment. https://extension.umd.edu/hgic/topics/planted-too-deeply

Excess mulch - can cause bark deterioration at the soil line, rots can grow into the mulch, Light watering may only wet the mulch layer while the soil remains dry, etc. https://extension.umd.edu/hgic/topics/excess-mulch

Watering - If there is excess mulch, a light watering may only wet the mulch layer while the soil remains dry. Check the soil moisture about once a for new plants week especially during dry periods. Water deeply if needed. Move the mulch aside and check the soil moisture by probing with a screwdriver about 6 inches deep and feel with your finger. Soil should be damp to the touch. Let the soil dry before watering again. See watering guidelines https://extension.umd.edu/hgic/topics/watering-trees-and-shrubs

At this point, all you can do is check for the above.  Make sure the soil drains well, they are not planted too deeply, and water during dry periods.  Make sure mulch is no thicker than several inches and away from the base of the trunk.
If planted too deeply, Root collar excavation, which is the removal of excess soil and mulch around the root collar (base of the tree), can sometimes be helpful. Carefully remove the excess mulch or soil from the circumference of the trunk to the point where the trunk flares out into root growth.
Remove the weeds. If there is no mulch,  you can add no more than several inches out to the drip line of the tree to conserve moisture and prevent lawn mower damage. Keep away from the trunk.
Follow guidelines for watering and care of your shrubs. You will have to check this.

If the trees continue to decline,  you may want to plant a mix of different plants (a mixed privacy screen) that match the site conditions so you do not lose the stand to a cultural, disease, or insect issue. That way if some of the trees  dieback it will not look out of place.  https://extension.umd.edu/hgic/topics/plants-mixed-privacy-screens

Marian