Yellow Spots and Streaks in St Augustine Turf Grass Lawn are Caused By Lack of Iron


By Rick Orr
St Augustine lawn with iron chlorosis
St Augustine lawn with iron chlorosis

Lack of Iron Causes Yellowing

The yellow streaks and spots are caused by a lack of iron in the leaf. It is called iron chlorosis. Iron chlorosis turns a St Augustine lawn into a patchwork of unsightly yellow spots and streaks. Iron chlorosis is common during the summer months when rapid growth exceeds the plant's ability to extract Iron from the soil. There is no permanent fix for iron chlorosis. The only solution is to apply supplemental iron in a form that the St Augustine grass can absorb.

Foliar Applied Liquid Iron

The best fix for the iron chlorosis is foliar applied liquid iron. The best and most expensive supplement is chelated iron. A good alternative is iron sulfate - which not only is absorbed by the St Augustine grass plant but also promotes iron to be released from the soil (acid-forming)

I also use acid-forming fertilizers to create micro releases of iron. Most of the soils in Pinellas are alkaline (high pH). Iron is readily available in neutral to slightly acid soils (low pH). Acid-forming fertilizers will lower the soil pH – if only for a brief time – and release iron to be used by the plant.

Iron Absorption is Slow

Iron absorption is slow and playing “catch-up” takes time – there is no “spray today – lawn looks great tomorrow” scenario. For best effect, small amounts of preventative foliar applied liquid iron should be applied year-round to iron-deficient lawns - not just when yellow spots and streaks appear. Applying small amounts throughout the year helps build up iron in the plant and enables the St Augustine grass plant to "coast" through the rapid growth of summer without going "yellow".

DIY Solutions

For the homeowner, this is a difficult problem to solve. The best solution is to apply acid-forming fertilizers with high iron content every 2 – 3 months. The iron content can be found in the analysis on the container. Millorganite is a good (but expensive) source and a very good product to keep the yellow out. With Millorganite be prepared to use 50 - 100 lbs. per thousand square feet or about 5 – 10 bags for an average lawn. Millorganite has a noticeable musty smell when applied to lawns during the rainy season.

Professional Solutions – Custom Formulations for Pinellas County

Throughout the year, I use a water-soluble blend of acid-forming fertilizers plus a chelated iron. This foliar-applied liquid application used throughout the year will prevent yellow spots and streaks in even the most difficult lawns. During the nitrogen blackout periods, I rely on the more expensive chelates to keep the grass green and to mask the effects of low nitrogen.

Rick Orr Owner-Staff Agronomist Barefoot Grassl/Creator of ILOVETURF.COM
Staff Agronomist at Barefoot Grass

Since 1995, Rick Orr has worked in Pinellas County providing turf management and pest control. Rick Orr is a graduate of VA Tech in Agronomy (Turf Ecology) and the creator of 

Since graduating from VA Tech in 1979, Rick worked in the green industry, mostly with golf courses, resorts, and large communities. Rick has obtained certifications in arboriculture, landscape, irrigation, and taught Environmental Horticulture at St Petersburg College. 

Currently, Rick is the Staff Agronomist at Barefoot Grass in Largo, FL. To learn more about Barefoot Grass Free Price Quote from Barefoot Grass for Home Pest Control and/or Lawn Care 

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