Timing Is Important When Addressing Iron Chlorosis In Perennial Plants
High-pH calcareous soils comprise a large amount of the acreage where perennial crops are grown in California. As a result, chlorotic leaf symptoms from reduced availability of iron is fairly common. In the most severe cases, the problem begins to show early in the growing season. Under these conditions it is important to begin addressing the problem shortly after leaves start emerging.
Iron has very low mobility within the plant. If the source of available iron for the plant becomes limited, the plant does not have the ability to scavenge iron from older leaves and tissues and remobilize it to support new growth. Nutrients with a high mobility within the plant, such as nitrogen, can be readily acquired from older leaves and moved to areas that are actively growing. For this reason, low-mobility nutrients like iron will show deficiency symptoms first in the most recent growth, while nitrogen deficiency shows first in the older growth.
Take Corrective Steps Early
In an attempt to correct iron chlorosis symptoms, it is important to address the problem early in the growth cycle since trying to eliminate chlorosis in older leaves of perennial crops is more difficult than supplying the correct iron to the new growth as it is emerging. Iron is necessary for the formation of chlorophyll in the plant, and this directly affects the photosynthetic capability of the plant to produce carbohydrates. If chlorophyll is limited during the growing season, it will reduce the overall growth and vigor of the plant.
Not only will this have negative impacts on yield, it will also make the plant more susceptible to stresses such as cold or heat injury, dry soil conditions, and even insects and diseases.
Amending the soil pH is the long-term fix for iron chlorosis, because plants grown in soils with high pH will have chronic iron deficiency symptoms. However, in the short term there are cultural practices that can reduce the severity of these symptoms.
The quickest response can be achieved with an application of the proper soil chelate. There are many different chelates available on the market, but most become quickly insoluble and unavailable to the roots shortly after application.
The chelate that is the most stable across the widest pH ranges is Fe-EDDHA. This chelate can be effective in soils with a high pH and has even shown benefits in soils with pH up to 9 (highly alkaline). Another major attribute of Fe-EDDHA is that not only does it stay available in calcareous soils, it has the ability to resist being fixed on the clay fraction of the soil.
The Causes Of Iron Chlorisis
Addressing iron chlorotic symptoms after they appear is beneficial, but it is also important to ensure that other external conditions are not contributing to the problem. In addition to calcareous soils, the second-most-common reason for iron chlorosis symptoms is waterlogged soils. Often times, this actually occurs in dry-winter/spring years.
Following a dry winter, many orchards are irrigated early and often, with the assumption that the rootzone is dry. Since significant transpiration does not start until leaf emergence, the soil moisture present at the lower rooting depths may be sufficient to start the season, and too much added water may actually create a saturated rootzone which could lead to other problems such as lower limb dieback. If this is the case, a gradual greening of the foliage can be seen as the soils dry out and more oxygen becomes available to the roots.