If it wasn't enough for the plants, they sure grew fine on it for the first month.

They were smaller the first month, and if your temps have been anything like the massive heat wave in NorCal, the soil moisture is evaporating faster than ever now. Hard to tell but if you don't have mulch down I'd add a layer. Also, you want to encourage the plants to grow deep roots (how tall are those raised bed & do they connect to the topsoil below or do you have some sort of weed barrier at the bottom?) and 1/2 gallon at a time might not be enough to infiltrate deep and encourage deep root growth.

Keep pruning off those yellow/dying lower leaves. You can try spraying a copper fungicide to slow it down.

One thing to watch out for on your "new" soil is that it may not have active enough microbes to digest and break down the organic fertilizer very fast. So keep an eye on the newer plants in case you need to use a faster-acting liquid fertilizer.

Must always determine cause before spraying bcause then you can select the correct spray.

Fungicide not needed.

Yellow older leaves may be due to nitrogen shortage. Or may be due to water shortage. Or old age -- leaves die.

Agree with aniaja that while you may need some fungicide for what appears to be early alternaria the primary issue is far too little water and far too frequently. Deep. less frequent watering is always far better for tomato plants than shallow - and 1/2 gallon is very shallow - frequent watering.

The needs of the plants increase greatly throughout the season as the grow and set fruit and you have to adjust for that.

My soil may be very different from yours but my drip lines deliver 1.5-2 gallons once a week and as the weather warms and the plants grow it is the amount that is increased, NOT the frequency.

Strip off all the damaged foliage to reduce stress on the plant.

Dave

I planted two determinants in "new" soil in late April. One set two
fruit within 3 weeks (!) but has barely grown in the 4+ weeks since.
Those, although small, are still looking very healthy.

***************

Determinants don't grow too fast and too tall. Then if the soil is not rich and not fertilized enough they will stay small.

Sey

Thanks, all. I've removed the worst of the leaves, and left some that were only slightly browning along the edges. Probably took off <10% of the total leaves. I turned the water to every 4 days, and .75 gallons each.

As for the weather, no, it hasn't been at all like Nor Cal. It's been hugely disappointing down here, barely any full sun days in May, few cracked 70F. "May gray" as they call it. Has me questioning why we left Marin County!

Regarding the soil that the determinants are planted in, it's a very high-end and expensive organic soil that the local nursery says is awesome. I have fed every two weeks with Tomato Tone. Should be fairly rich soil. Makes me wonder if the lack of sun has been the major factor.