Is your soil sandy? Clay? Over watering can cause the N to leach out of the soil or overwatering especially when mulched can cause root issues. I doubt it is the drippers themselves causing the problem. Can you post a picture of the plants?

My soil is clay. The rest of the plant seems ok, it's just the bottom couple of leaves. The raspberries seem to take it the worst. Assuming the nitrogen leached away, what's the best way to replace it and reduce the problem from occurring in the future?

Please do the math: How much water is supplied in 20 minutes by a half-gallon per hour dripper?
(Answer: Not much.I.E.: Far too little for a raspberry plant.)

A question: How can you determine how much soil has been moistened by one dripper in 20 minutes?
The answer: Put a trowel in the soil and look.

Bottom line: You'll need to add more drippers and will need to run the system longer than 20 minutes.

My mother has clay soils and mine is sand/loam. I transplanted Arapaho and heritage from her house and the difference is remarkable in vigor, overall health and size of berries. Berries like sand, however I've seen wild BlackB's in clay.

This post was edited by Noogy on Sat, Jul 20, 13 at 9:02

JT,

It is just hard to say..if it is too much water especially in clay it could be root issues from being waterlogged......or it could be too dry.or it could need more nitrogen. You will have to investigate a bit.

I hate drippers but that is just me. Perhaps try giving a couple plants more nitrogen and see if you notice a change in them compared to the others.

For an instant answer about moisture content and watering efficacy, check the soil.

I'm going to throw in with jean001a. Stick your finger in the dirt and follow up with a moisture meter. Once soil crusts over, a slow drip will not penetrate deep enough to reach plant roots. I use a wand at full blast jammed into the soil to deep water my beds. To do otherwise in my locale is to watch plants fail. Don't trust, test.

...the bottom couple of leaves out of how many leaves? It is common once a berry cane has reached shoulder high or taller for the oldest, bottom leaves to yellow or dry up. Once the plants mature and shade each other, the lower leaves can be affected also.

The probe the soil for moisture content is good advice. Minutes and rates can have varying effects in different soils or weather spells. If you have small, recent berry starts, your water may be fine; for an established planting in mid-summer, perhaps not enough water.

What is the dripper spacing versus the plant spacing?