End gun troubleshooting: signs it's not reaching the corner
An end gun earns its keep in the last twenty or thirty feet of travel, the stretch where the span can't reach and the corner would otherwise go dry. When it's working, the corner gets roughly the same depth as the rest of the circle. When it's not, you get a crescent of stressed crop at the field edge that shows up on every pass and never seems to get better no matter how many times you adjust the timer.
The trouble is that from the cab or from the end of the driveway, a weak end gun often looks the same as a dry spot caused by something else: a bad nozzle package, a low spot in the ground, a sprinkler that's clogged. You end up driving to the corner, checking the gun, finding nothing obviously wrong, and moving on until the next time the crop in that wedge looks worse than the rest of the pivot.
Signs the end gun isn't reaching the corner
A few patterns point specifically at the end gun rather than at the main system.
- The dry area is shaped like a pie slice at the corner of the field, not a streak down one span or a round spot in the middle of the circle. End gun problems have a geometry to them, because the gun only fires in the sectors the control panel tells it to.
- The stress shows up at the same corners every pass, on the same side of the field. A nozzle problem on a span usually drags a line across several sectors as the pivot rotates. An end gun problem stays put at the corner, because the gun only ever covers that one arc.
- Pressure at the tower nearest the end gun reads low compared to what you'd expect, especially if there's a booster pump that's supposed to kick on and isn't.
- The gun fires but the throw looks short, water landing well inside the fence line instead of reaching it. That's usually a worn nozzle, a stuck valve, or a pressure regulator that's not holding.
- The corner looked fine in spring and started showing stress by mid-season. That timing points at something in the end gun's plumbing degrading rather than failing outright: a gasket wearing down, a filter screen partially clogging, a solenoid sticking on hot days.
None of these prove it on their own. Together, especially the pie-slice shape repeating at the same corners pass after pass, they're a strong enough pattern to go check the gun before you check anything else.
What causes it to fall short
Most end gun failures trace back to one of three things. The booster pump isn't building enough pressure to push water past the normal throw radius, so the gun undershoots. The control that tells the gun when to fire is set wrong or has drifted, so it cuts in and out at the wrong point in the rotation and shorts the corner by a few degrees every pass. Or the gun itself, the nozzle, the valve, the swivel, has worn or clogged to the point where it's not putting out what it used to, even with normal pressure behind it.
A field check usually sorts these out fast: pressure gauge at the tower, a look at the gun while it's firing, a comparison against the controller's sector settings. The hard part is catching the problem early, before the corner has been running dry for three or four weeks and the yield hit is already locked in.
Catching it before the corner tells you first
Most districts catch end gun trouble the same way: someone drives the circuit, eyeballs the corners, and if nothing looks obviously wrong, moves on to the next pivot. That works until the week you're covering six circuits and the corner problem that started two passes ago hasn't turned into visible crop stress yet.
Irrigation Monitor checks each pivot's sectors weekly against its own geometry, corners included, and flags a dry sector before it's the kind of damage you can spot from the truck.
If a corner's been running thin without you knowing it, it's worth putting a weekly check on it instead of waiting for the crop to tell you.