You can fight leaf yel­low­ing from rains

Winnipeg Free Press - Section G - - A LOOK AT RECENTLY SOLD HOMES IN AND AROUND WINNIP - By Michael Allen

LAST year, at around this time, I wrote about prob­lems with south­ern Man­i­toba fruit trees caused by heavy rain­falls.

This year, it’s no dif­fer­ent. In fact, it’s worse. Here’s what I wrote last year: “In in­fer­tile soils that are cer­tainly typ­i­cal of most ur­ban ar­eas, fre­quent rain causes leach­ing of highly sol­u­ble valu­able plants nu­tri­ents such as ni­trates and phos­phates. Also, pro­longed wa­ter­logged soils are de­fi­cient in avail­able nu­tri­ents.

“Here is the prob­lem. The first set of leaves pro­duced dur­ing the early part of spring de­velop a good green colour; how­ever, as the spring turns into early sum­mer, the new leaves be­come yel­low­ish-green in colour. Some trees and woody shrubs are more sus­cep­ti­ble to this colour change than other plants.”

Typ­i­cally, the yel­low-green leaves will have no­tice­able green veins. With our al­ka­line soils, much of the avail­able ni­tro­gen for plants is tied up in soil com­pounds dom­i­nated by cal­cium and mag­ne­sium that plants can­not use.

This leaf yel­low­ing prob­lem is a nutri­ent dis­ease called chloro­sis. In south­ern Man­i­toba it’s usu­ally a re­sult of iron de­fi­ciency in the soil. When freely avail­able, iron in the form of an ox­ide “un­locks” the grip that cal­cium and mag­ne­sium com­pounds have on ni­tro­gen.

Set­tlers many years ago knew that adding iron fil­ings or iron nails to veg­etable gar­dens would pro­duce health­ier plant growth. In the pres­ence of wa­ter and air, iron from the black­smith shop would turn to rust. As the rust broke down into very small flakes, mol­e­cules of iron ox­ide were re­leased into the soil. The plants read­ily ab­sorbed these mol­e­cules to stim­u­late the process of pho­to­syn­the­sis.

Sus­cep­ti­ble woody shrub species are more prone to chloro­sis than trees. Vir­tu­ally all yel­low and gold-leaved shrub va­ri­eties are typ­i­cally chlorotic af­ter pe­ri­ods of pro­longed rain. The hard­esthit of these are Gold Flame and Gold Mound pink flow­er­ing spireas. Other shrubs that can suf­fer this prob­lem are co­toneaster, cara­gana, some va­ri­eties of rose (es­pe­cially ru­gosa ones), el­der­berry, Dart’s Gold ninebark, Sum­mer Wine ninebark, Ja­panese bar­berry va­ri­eties such as Rose Glow, rasp­berry and cur­rant.

In ad­di­tion to fruit trees, Sil­ver maple, Amur maple, white birch, Tower po­plar, Swedish aspen, and Euro­pean moun­tain ash also sus­cep­ti­ble to the chloro­sis prob­lem.

The so­lu­tion to chloro­sis con­sists of the fol­low­ing treat­ment pro­gram:

1. Prop­erly fer­til­ize the trees this fall with a suit­able tree fer­til­izer (21-7-7 or 20-20-20, for ex­am­ple) with added iron chelate. For larger trees this is best done by a li­censed spray­ing/fer­til­izer ap­pli­ca­tor, but not in sum­mer.

If you are do­ing this your­self, dig one-inch di­am­e­ter holes six inches deep (clay loam soils only) in con­cen­tric rings un­der the tree’s crown. Space the holes 15 inches apart, start­ing three feet from the trunk, and go out to half the tree’s height from the trunk. The se­ries of con­cen­tric rings can be spaced at 15 inches apart.

Add two ta­ble­spoons of gran­u­lar tree fer­til­izer and one tea­spoon of iron chelate pow­der to each hole. Cover with soil or com­post, and wa­ter, Iron chelate is used to sup­ple­ment the de­fi­cient iron in the soil. Re­peat fer­til­iza­tion in spring 2011.

2. Woody shrubs can be fer­til­ized in the fol­low­ing man­ner. Fill a stan­dard house­hold pail (mine is 15-litre ca­pac­ity) with wa­ter and mix in two ta­ble­spoons of sol­u­ble tree/shrub fer­til­izer along with one ta­ble­spoon of iron chelate pow­der. Use one pail for each one to two square feet of bed un­der the branches of the shrub. Do this in May and then again four to six weeks later.

Make a note for next year to start the fer­til­iza­tion pro­gram in May. Shrubs just start­ing to leaf out can also be treated with a fo­liar iron chelate spray, but be sure to fer­til­ize the soil area un­der the shrub branches.

Sus­cep­ti­ble woody shrub species are more prone to chloro­sis than trees.

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