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Updated : 21/9/2014

Leaf Disorders

A variation of leaves

Rose leaves may have from 3 to 15 leaflets. Three, five and seven leaflets on a stem is normal and indicates good cultivation.

A variation of leaves
Different leaf types

Black Spot

The number one fungus disease to cause defoliation. It is prevalent during rainy periods. Spray preventatively with RP, Cocktail 1 and/or 2. Retain infected leaves on bush

Black Spot infection on roses
Black Spot

Powdery Mildew

 A fungus disease that appears on the soft leaved tips causing curling of leaves and is unsightly. It appears at any season and climate mostly on plants that are dry, in windy positions, shade or varietal susceptibility. Spray with RP, Cocktail 1 and or 2.

Powdery Mildew infection
Powdery Mildew

Downey Mildew

A serious fungus disease that stops buds from opening and causes defoliation, bursting of the bark and is prevalent during high humidity and cool weather. Leaves should be hardened by foliar feeding Magical, liming the soil and by spraying cocktail 2 and or Propomacarb or Ridomil Gold.


Botrytis

A fungus disease that will only by that under extremely wet circumstance and standing water at root level. Remove plants of susceptible varieties. Spraying with Cocktail 2 prevents spreading.


Mosaic Virus

The markings on the leaves may vary and are a nuisance being more prevalent in cooler weather. It does not hinder or slow down growth, does not spread and cannot be treated. All plants of some varieties i.e. Climber ‘Cocktail’ are infected in South Africa.

Markings of the Mosaic Virus on rose leaves
Mosaic Virus

Aphid Soot

The black layer on leaves is a fungus that grows on the sweet sap secreted, milked out by ants from aphid. It is unsightly and prevents proper assimilation and should be washed off with a strong jet of water or sprayed with a dishwasher solution.

Aphid Soot on rose leaf
Aphid Soot

Spider Mite

They breed rapidly on the underside of water stressed leaves, with the concentrated sap being very nourishing. Conventional insecticides with the active ingredient of organo-phosphate does not kill these mites but rather induces hectic breeding. Regular wetting of the underside of the lower leaves, spraying with the oil based Insect Spray prevents outbreaks. With heavy infections use a combination of Ludwig’s Red Spider Spray and Efekto Spider Mite Spray, repeat after 5 days and again if movement is still noticed. Water more often or for longer periods especially when root competition from other plants might be the reason.

Signs of Spider Mite activity on underside of rose leaf

Spider Mite activity on underside of rose leaf

Signs of Spider Mite activity on underside of rose leaf Spider Mite activity on underside of rose leaf
 

Chafer Beetle

Also known as Christmas beetle they are active at night hiding in trees or mulch during the day. Lights, with a water/oil filled bucket underneath are effective, so are the blue light insect traps. Spraying the leaves weekly during invasion periods with insect spray and or Karbasol kills them off.

Rose leaf laced by chafer beetle
 

All types of Chlorosis

It is a deficiency of micronutrients arriving during the process of new leaf formation. Such deficiency does not mean these nutrients have disappeared from the soil but is rather an imbalance of the marco-elemts (i.e. brak water) It can also occur due to severe soil compaction & poor aeration at root level. Foliar feeding with chelated nutrients, mostly iron, will assist but not overcome the problem. A sprinkling of 50g LAN per bush may help, powdering with Flower of Sulpher for ‘brak’ situations & digging in coarse compost are possible remedies.

Chlorosis treated with LAN
Chlorosis treated with LAN
 

Fertiliser leaf burn

Fertilizer spread over wet leave even at the correct measure, instantly dissolves in the water on the leaves. Some leaves may be more burnt than others, however, the bush should re-sprout after a good watering application.


Fertiliser burn

The application of far too much fertilizer, especially on young plants leads to burning of the plants identifiable by black stems and brittle black-brown leaves. Replant in same hole after approximately three week.


Weedkiller damage

Rose leaves are incredibly sensitive in absorbing evaporation fumes from weed killer spray on pavements a few metres away. It does not cause burning, rather a miniaturisation of new leaves and blooms. Slight absorptions can be outgrown underneath. There is no remedy.

Slight Weedkiller damage Severe Weedkiller damage
Slight Weedkiller damage Damage by Roundup Severe Weedkiller damage
 

Frost Damage

The sap flow stoppage is severe in roses which have been affected by unexpected frost after sprouting. Overhead watering will slow down the iced sap melting. In accordance with severity, it may lead to the tips of the new sprouts to burn. No problem. Freezing of the sap in the main stems again leads to stem cancer.


Heat Stress

Superficial burning of leaves during periods of extreme heat in beds without a heat insulting mulch and or insufficient available water, should easily regrow if one or all three causes are addressed.

Signs of heat stress
 

Burnt edges due to drought

Due to drought during periods of very fast growth in extreme heat, the pipes are (xelym) are simply not large to allow sufficient transportation of water from roots to tip to make up for this loss due to evaporation. Short bursts of irrigation during the heat of the day.

Burnt leaf edges
 

Old leaves pushed off

 The first few leaves still sprouting during cold weather, with very harrow internodes are pushed off (sealed off) by mid September. This phenomenon of yellow leaves in the centre is natural, a varietal curiosity and cannot be avoided.

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