Boneca,

I doubt it has to do with chemicals but more to do with soil compaction. Water will run off if the soil is too compact to absorb it.

What sort of watering maintenance does your friend practice? Did he/she water those trees last year? In watering, did he/she water behind those trees?

What kind of soil does your friend have? the entire yard looks quite compacted to me and not much organic in it.

Are there plenty of run offs from the neighbor's side? - which may explain the 'paths' I see.

So here are my thoughts:

Assuming there are plenty of run offs, as water run downs, that area affected will also be deprived of nutrients, hence the plants in their paths suffer. In clay soil, water pretty much drowns out everything. In compacted soil, the water rushes down with no time to be absorbed in the ground. Meaning, the ground remains quite dry under the surface.

To explain why the trees look this way - and they don't all look bad, it's just a few that look stressed. Trees don't show problems until the second year of their being planted in the ground. Often plants and shrubs will suffer from transplant shock. Meaning their roots won't be able to absorb water in the first couple of weeks and so they rely on their reserves in order to survive. During this first year, watering consistently but overly much is important. As the roots begin to recover, some of its branches will have suffered die backs but won't show until the following season - especiallly if these are evergreens like your friend's trees. It's also important during this time not to fertilize the roots - lest you burn the plant or cause the roots to rot. As the trees begin to recover, they will begin to take in a lot of water from it's surroundings. And so this too could be a reason why the area behind the trees have been affected.

However, let me guess that watering was limited to the trees themselves and not behind them. And when it was raining water runs off from your neighbor's yard and rushes down and out of the area with no time for absorption.

I suggestion for a solution: Improve the quality of soil behind the trees and the rest of the yard. Break up compaction, amend iwth organics. Create ways to slow down run offs - like a dry river bed. Add some slow release fertilizes to the healthy trees, add some organic compost to the trees that are suffering - like good composted manure.
in the future, those trees will take in more water and as they do, the surrounding grass will suffer and so in order to maintain that grass, add more good top soil and frequent watering. I do think that's a lot of trees - each will be huge at some point later and they will compete w/ each other. Some may eventually die in the process.

Looks like the neighbour has vegatables growing on his/her property. Looks like the lawn is in need of a good renovation. There are only weeds growing in it and full of roots. May be grub damage or fertilizer burn.

I'd take a rototiller and chew up the whole lawn. Rototill a bunch of good soil into the lawn and build the area up along the fence.

Drought and compacted clay soil are the main causes.
Amending soil,regular watering,lawn fertilizer and spreading some seeds would repair the lawn.
Hala.