You would be wasting your money on a back sprayer, or any sprayer, for the materials you plan to spray. Those materials need to be applied by the pound, not by the fraction of an ounce that a sprayer applies.

Frankly, I've never used any of those materials, because preemergents rely on critical timing (I'm too lazy to care about that), humic acid is much better produced by a healthy biosphere (use only organic fertilizers), and iron really goes on by the pound IF your soil has a low enough pH and calcium content to allow it to work.

Based on what you want to apply, I'm guessing you have weeds and chlorotic looking grass. Tell us where you live and what kind of grass you have and how frequently you are watering, and we can get you turned the right direction.

you are too lazy to care for timing to apply pre emergents??? what the heck are you doing in a lawn forum :-) I am a believer in Humic acid combined with kelp. Also I am forced to apply liquid aeration as my soil in spots is very compacted ... even though I also do a regular cork pull aeration. For weed spraying I mostly utilize my hand pump 1 gal sprayer. I am in North NJ.

If you do a lot of spraying, get yourself a 3 nozzle spray boom to attach to the end of your spray wand. I have brass fan nozzles but I wouldn't say they are any better than plastic, just more durable. Also, get yourself a nozzle brush and velcro it to your boom for easy access. I personally find such things as humic acid, compost teas, phosphites, and other adjuncts to be a waste of time. But whatever makes you happy. I use my backpack sprayers for Tenacity and prodiamine applications and that's pretty much it. Iron definitely does make a difference but the effect is transient and to me, not worth the effort.

As for electric backpack sprayers, I am a big fan. They've come a long way and work extremely well. Much more uniform pressure and less prone to leaks than the manual type IMHO.

you are too lazy to care for timing to apply pre emergents??? what the heck are you doing in a lawn forum :-)

I know, right? My St Augustine grass is very dense, so most weeds can't get a start. The only weed that becomes a problem is horse herb, and that goes away easily with post emergent control.

But okay, don't say I didn't I tried to dissuade you.

Plastic nozzles are more prone to damage than brass, but brass can erode under water pressure. I ruined the female fitting on an expensive hose in less than 30 minutes, because I didn't tighten the fitting enough. With male end fittings you can file away the brass, but not the females. Plastic does not erode. Beyond that, not having used a fancy sprayer, I'll leave it to the pros.

I use a hose-end for most of my kelp and pre-emergents, which are designed to be watered in anyway so I just do it with the app. :-) Same with my soil conditioner.

Iron...I use my backpack for spray applications. The nozzle they sent me works fine, and I keep a variety of pins attached to my spray shirt so I can clean the nozzle when it clogs from the crud.

Soil applications of iron go through my broadcast spreader, usually via Milorganite, by the literal pound.

I tend to keep it simple. Fractionated milliwhatnots are not generally required, and when I spray herbicides, I use a one-gallon to spot spray. I only get a weed or two per year anyway and rather than "triangle approach" I have Round Up and Tenacity handy.

@ dchall some.people like me benefit from spraying because I live on a hill/slope where we get hard rains. Seems like everytime I applied granulars would get a heavy rain which I am assuming alot of that washed away. So starting last year I have been doing more spraying than spreading and have been seeing good results. But your pounds does make a lot of sense using granular. And that's why I will never go totally away from granulars. With spraying you can get products alot cheaper but it's a lot harder work mixing it all up, doing it more frequently., Get it all over you, etc

@ igor. I use a red nozzle fine mist and the air induction tip. the first one is great for foliar applications and the second one is great for applications that need to go to the ground pre-emergent, humic acid etc. You can buy them off sprayer depot. .com for $5 a piece minus shipping. I think standard shipping is $5 so 15 for all three ship to your front door. I did have problems with the fan tip it was started shooting out weird offline sprays but they replaced it free of charge

Check out this video, these are the same tips I use

https://youtu.be/mgKK1j2QCUM