Every symptom has a source. Symptomatic treatments never look for the origin of the problem — healthy soil biology does.
A 5–10% dilution with most waterings keeps your biology intact — provided your soil isn’t chemically contaminated and organisms like earthworms are present. If your soil is contaminated, use a 15–20% dilution for three months.
Focus on the roots/soil and the leaves. A 15% dilution on both leaves and soil, weekly, should resolve it. A 50% rate can be used on the roots.
For aphids, scale, phytophthora, pythium and the like, an 80–100% dilution sprayed on the affected area halts the breakout. Spray every two days — using the principles of competition, inhibition and predation.