check your fertilizer for all the micronutrients (aka: Trace minerals) ...especially - Boron
There are 7 essential plant nutrient elements defined as micronutrients: boron (B), zinc (Zn), manganese (Mn), iron (Fe), copper (Cu), molybdenum (Mo), chlorine (Cl)
Boron is believed to be involved in carbohydrate transport in plants; it also assists in metabolic regulation. Boron deficiency will often result in bud dieback.
Chlorine is necessary for osmosis and ionic balance; it also plays a role in photosynthesis.
Copper is a component of some enzymes. Symptoms of copper deficiency include browning of leaf tips and chlorosis.
Iron is essential for chlorophyll synthesis, which is why an iron deficiency results in chlorosis.
Manganese activates some important enzymes involved in chlorophyll formation. Manganese deficient plants will develop chlorosis between the veins of its leaves. The availability of manganese is partially dependent on soil pH.
Molybdenum is essential to plant health. Molybdenum is used by plants to reduce nitrates into usable forms. Some plants use it for nitrogen fixation, thus it may need to be added to some soils before seeding legumes.
Zinc participates in chlorophyll formation, and also activates many enzymes. Symptoms of zinc deficiency include chlorosis and stunted growth.
Use any fertilizer that also provides these trace elements ....
