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Causes of Yellow Leaves on Roses: Heat, Water and Salt Stress and Chemical or Soil Toxicity - Page 2

Page 2

Jul 30, 1999

Reduced plant growth.
Scorched leaf margins.

Treatments:

Irrigate deeply (where drainage is good) to leach accumulated salts from the root zone.
If drainage is unsatisfactory, consider addng gypsum before leaching.
If using synthetic fertilizers with a high "salt index," apply per label directions, or use smaller amounts on a more frequent basis.
If using organic soil amendments (like manure), watch for high salt concentrations.
Perform regular soil tests to determine toxic levels of accumulated aluminum, ammonium nitrates and chlorides.
For containered roses, flush potting soils frequently. Change out the soil every three to four years.

Phytotoxicity

Yellowing leaves can be due to "suffocation" caused by spraying. When chemicals or their surfactants clog leaf pores, plant tissues cannot transpire moisture and essential gasses. They cease producing chlorophyll, and the leaves yellow and eventually fall. This symptom will be readily apparent, usually within a few days of the chemical's application.

Some roses are less tolerant of spraying than others. Roses with textured leaf surfaces seem to be the most affected. Phytotoxicity can alscaused by drift from nearby herbicide applications. Other symptoms:

Brown or scorched leaf margins.
If caused by herbicide drift, dead growth tips on apical stems.
Leaves will fall from the plant within a few days.

Treatments:

Avoid spraying chemicals with high viscosity ingredients (such as oils) or surfactants during the heat of summer.
If spraying is necessary, do so very early in the morning.
When working with a chemical new to you, always test a small, out of sight area of the plant first to determine if phytotoxicity will occur.
If applying herbicides nearby, do so per label directions and on days when air movement is at its lowest. Use application techniques that permit direct contact with the pest weed.
Select roses that do not require excessive chemical treatments.

Damaged Roots

Cultivate roses too close to roots can damage them. This can happen without our knowing about it, especially if the roots are brought to the surface but are not quite exposed. Damaging roots and destroying their associated micorrhizal fungi induces a water and/or nutrient stress situation to the rose, thereby causing yellow leaves. Check for roots coming out of the soil below mulch layers.

Treatments:

Use caution cultivating in and around root zones.
If roots are exposed, trim away broken sections and replant immediately.
Irrigate deeply so roots will penetrate below normal cultivation zones.

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