Need Help with Guidance for Spraying

We're looking for some sage advice, please.  We are a small operation in central TX. We have about 16 acres of coastal bermuda that we round bale. We spray the field ourselves with our 38HP Kubota tractor and a small sprayer with about a 13 foot boom. We spray mostly to control grass burs and johnson grass. We only got 1 cutting in 2015 but our neighbor who bales for us said it was the best hay he had seen all year. We kept some of the round bales for our horses and they are thriving. 

 

We are looking for advice on how to spray straight lines with minimal overlap and to avoid missing large swaths. 

 

Here are some things we've tried since I got my applicator license 2 years ago. Remember - we're tenderfoot beginners with limited resources. First year we tried a homemade foamer. My husband got the idea from youtube    He put tubing down the boom that was attached to a small air compressor. It was fantastic until the compressor burned out 3/4 way through "the spray." The next time we tried a better compressor and the same thing happened. We ended up missing an entire swath so I was out there with a wheel barrow cutting grass burs off a few weeks later before they matured. THAT was fun.  But - we are now ready to spray again in about a week. I have looked and looked for Apps on my phone to help with GPS spraying. The only one I've found is one called Farm Spryer for my iPhone which is way too small and is not very accurate. You have to stare at the phone, try to drive and the gps picture of your swath is behind you instead of guiding you. We've tried to figure a way to mount a tablet but ?? Do any of you have an App that works really well that you could recommend? Our neighbor says to follow your tractor tracks but that certainly hasn't worked. I've asked all around and looked on eBay, etc for for used foamers. Some locals sort of chuckle and keep their "secret spraying advice" to themselves. Or they have huge equipment and a big business. I would like some advice from others who may have faced the same challenge. Thanks in advance for anything that has worked for you..we love our hay and want to keep it that way

Need Help with Guidance for Spraying