My Debian testing laptop running gnome has two interfaces - eth0 and wlan0.
When I switch to wlan0, the routing table has an entry for eth0, so I
cannot access my local network.

root@orca:/home/mark# route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use
Iface
default         gateway         0.0.0.0         UG    0      0        0
wlan0
link-local      *               255.255.0.0     U     1000   0        0
wlan0
192.168.25.0    *               255.255.255.0   U     0      0        0 eth0
192.168.25.0    *               255.255.255.0   U     0      0        0
wlan0

if I remove the eth0 line, I can connect to my local lan.

How do I permanently remove this route? I can do it manually with route del
-net....., but that does not survive reboot. I have no idea where this
setting is created.

When I switch to eth0 (ie plug in a cable), I get this routing table, which
is correct.

root@orca:/etc/network# route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use
Iface
default         gateway         0.0.0.0         UG    0      0        0 eth0
link-local      *               255.255.0.0     U     1000   0        0 eth0
192.168.25.0    *               255.255.255.0   U     0      0        0 eth0

Thanks,

Mark