Foliar Chlorosis?

[ahosey01]

First post.

I am fairly new to raising citrus, have some experience with other trees.  I live in Wickenburg, AZ, in a 9a climate.  The soil in my yard is, for the most part, really good.  This area is in a floodplain that was a cottonwood and mesquite forest for who knows how long, then - about a hundred years ago - was converted to crop farmland.  Afterwards, it was turned into a subdivision, and the house that formerly sat where mine is now had a lawn for 50 years or something.  The soil is, largely, a nice, dark loam that holds moisture well and is generally full of earthworms.

Unfortunately, however, there is one place where my soil isn't great.  This is underneath my lawn, where my grass is.  I had to buy a fair amount of screened fill dirt to build up the lawn area in order to elevate the lawn to a flat plane.  The area is flood irrigated, currently 3x per week (it's a small area, about 35ft x 10ft).

I have two citrus planted in this lawn.  One is a Nagami Kumquat - rootstock unknown but a presumed to be a product of Sunset Nurseries in Yuma - and an Owari Satsuma.  I have noticed that the Kumquat took on a fairly yellow color over the winter, and the new leaves are a bright, neon green.  The Satsuma has remained mostly dark green, but the new growth is - similarly - vibrant.  Photos are attached.

Anyways, I'm thinking this is foliar chlorosis.  I applied some 10-10-10 fertilizer earlier this month, and today added some Kerex as well.  If it is foliar chlorosis, I don't know if it's because I'm water the area too much, or if it's just because the soil is poor.

Can anyone offer some insight?  Does this appear to be foliar chlorosis, or just normal colors of new citrus growth?  Is there anything I should be doing beyond applying Kerex and 10-10-10?  Should I apply a liquid iron fertilizer to the leaves, or cut back on watering?

Let me know, thanks!

Adam

[poncirsguy]

Your trees need at least a 3 foot radius free of grass/weeds.

[ahosey01]

Your trees need at least a 3 foot radius free of grass/weeds.

Healthy, highly productive citrus trees exist all over the low desert in flood irrigated lawns, and grass is commonly understood to condition the soil over time, due to the lack of other decomposing organic matter we have.  The soil in flood irrigated commercial groves here are also commonly covered in grass and weeds, as it's generally not cost effective to remove them and the alluvial floodplains in which citrus are grown are typically weedy with the addition of water.

I presume the reason you make this claim is that the grass will compete with the tree for nutrients.  I struggle with this idea, however.  Can you elaborate and we can discuss?  I have never heard of planting a tree in a mesic setting in the low desert producing foliar chlorosis because of the surrounding vegetation except in cases of desert-native trees (or ones with otherwise low nutrient requirements or seasonally wet-dry soil needs, like Eucalyptus camaldulensis) planted in chronically wet soil conditions.

[Millet]

First, your tree is still small, and has a corresponding small root system.  The roots most likely extends out about the same distance and the above leaves Poncirus guy recommendation to remove the grass from under the tree is one thing that NEEDS to be done., as it is surely robbing most of the available nutrients from the tree.  I would remove the grass to match the trees drip line. Further, what has been the tree's nutrient plan.  A young tree such as your needs should to be fertilized 4 times equally spaced out during the growing season (March through September)  You can use 6-6-6 or 10-10-10.

[brian]

You could try a low dose foliar fertilizer spray as a band-aid and see if it becomes yellow again or eventually adapts to its current planting.

I have no grass in my greenhouse so I can't offer any advice on the competition aspect. 

[Vlad]

I am not convinced that the grass is a significant competitor for nutrients. Are there any scientific papers about this?

[ahosey01]

I am not convinced that the grass is a significant competitor for nutrients. Are there any scientific papers about this?

I'm in the same boat here.  If anything, I think the low-nutrient soil that is watered as heavily as it is would have more to do with the yellowing of the leaves, in my own opinion.

Still thinking it through and trying a few things, though.

[poncirsguy]

Grass also poisons the soil to defend its space and is not good for a small citrus tree.  Citrus tree with grass growing up to the trunk are more likely to loose bark to string trimmers than those free of grass or weeds.  The grass also uses up the oxygen the tree needs.  LOSE THE GRASS!  Pappers?  I didn't keep records but just absorbed the information.

[mar3]

I like how mulching lowers the risk of mower and weed eater damage. The guidelines I've followed are:

• An area of weedless soil around the root collar. This prevents the mulch from keeping the root collar and trunk wet. In areas where frosts can happen, it allows the ground to absorb more warmth during the day.
• An area of mulch to around the drip line.

From the University of Minnesota:

When trees and shrubs are planted into turf, competition for nutrients, water, and space occurs below ground between turf roots and woody plant roots. Turf wins because its dense fibrous root system prevents woody plants from producing water- and nutrient-absorbing roots in the top few inches of soil. As a result, woody plant establishment and growth is slower in turf areas than in mulched or bare soil areas.

The paper "Orchard soil management trials. 1. Effect of a weed-free or straw mulched strip on the growth and yield of young fruit trees" found evidence in support for mulching young fruit trees. Although they only tested it against herbicide controlled weedless soil, not grass.