Are Your Plants Suffering From This Common Summer Problem?

You're watering your plants more because it's hot outside. 

It seems like the logical thing to do in the summer, but your plants are responding by turning yellow!

What gives???

Your plants could be suffering from Chlorosis.

What is Iron Chlorosis? Iron chlorosis is a yellowing of newer plant growth caused by a lack of plant-available iron. Iron chlorosis gives the plant a light green to yellow appearance. Closer inspection of the plant reveals that the yellowing occurs between the veins of the leaf the veins remain green. This is called interveinal chlorosis and in Southern Nevada is a fairly reliable indication of an iron deficiency. As this condition worsens, leaves turn completely yellow, scorch on the edges and drop from the tree. If no action is taken, branches begin to die back and death can result.

Other nutrient deficiencies can cause chlorosis, but they do not respond to iron sprays. The following simple test will determine if iron chlorosis is the problem: fill a trigger spray bottle with iron sulfate (at one teaspoon per gallon) or iron chelate solutions and spray the plant. Leaves sprayed with iron will turn green in 24-48 hours. For reference, mark the sprayed branches with tape then, in several days, compare them to the unsprayed branches. 

Controlling Iron Chlorosis With Fertilizers. 

Soil-Applied Fertilizers. 

Soil applications of iron fertilizers should be made between late fall and early spring, a few weeks before new growth starts. Soil treatments can last two to three years. Iron fertilizers include iron sulfate or iron chelates. Iron chelate is a substance which holds available iron and prevents it from being locked up in the soil and unavailable to the plant. Not all chelates are equally effective. In Southern Nevada’s alkaline soils (pH above 7.6), Sequestrene 138® (packaged for the homeowner as Ke Rex® ) has been the most effective iron compound for soil applications. Application rates are listed on the label.

 Table 1. Dosage for treating trees & shrubs by soil application of a equal parts of iron (ferrous) sulfate & sulfur

Tree Diameter	Total amt. of iron sulfate & sulfur per tree	Number of holes in ground around tree	Total amt. of iron sulfate & sulfur (1:1) in hole
(inches)	(pounds)	(number)	(pounds)
1	1	4	0.25
2	2	4	0.5
4	6	8	0.75
6	12	12	1.0
8	16-23	16-23	1.0-1.25
10	20-30	20-30	1.0-1.25
15	30-45	30-45	1.0-1.25
20	40-60	40-60	1.0-1.25

Foliar-Applied Fertilizers 

Iron solution sprayed on leaves gives the fastest response,

 but affects only sprayed foliage. Repeat spraying will be 

needed for some plants as new growth appears throughout 

the season. Iron sulfate is an inexpensive foliar spray. Two

 and one-half ounces per three gallons or five pounds per 

100 gallons of finished spray should be used. Iron sulfate 

sprays will stain cement, so they should be kept away from

 sidewalks, driveways, stucco and light-colored walls. Iron 

sulfate sprays should not be used during the heat they will 

burn foliage. Iron chelate sprays work and do not burn 

foliage, but are more expensive to use.

Trunk Injection of Fertilizers. 

Trunk injections of iron fertilizers are effective for 

controlling iron chlorosis up to three years. 

 Most often injection is done by trained commercial arborists.

 Whenever holes are drilled into living plant tissue, plant 

damage occurs. Holes should be few and as small as 

possible. Injection should be done only when trees can’t be

 sprayed or receive soil applications. 

 For more information on Iron Deficiency in plants and what to do to prevent and treat it, check out Star Note #615.

*This is an excerpt from a reprint of “Controlling Iron Chlorosis In Urban Mojave Desert Landscapes” by Bob Morris, Area Extension Specialist (Horticulture) Southern Nevada. The original is undated.