|I've created what should be the perfect low light garden in a patch of yard next the house where a pine tree used to grow. The area grows hostas very well. The soil is well drained and not sandy. Bulbs that were planted there do quite well. The first year I initially applied liberal amounts of lime and manure. I planted impatiens and coleus, they performed excellently until about July, when the impatiens leaves turned spotted and yellow and dropped from the stem. The coleus however grew insatiably and never showed any problems. The second year I planted the same combination and neither the coleus nor the inpatiens ever proliferated as observed the previous season. I sprayed them diligently with insecticde and an all purpose fungicide to no avail. What is the problem?|
|It sounds like your impatiens may have been suffering from Leaf-Spot. A number of different fungi can cause this affliction. Some will kill the plant while others merely make it a bit unsightly. Leaf-spot fungi are spread by the wind, insects, splashing water and even tools that have come in contact with it on other plants. This organism is most active in humid areas where the temperature ranges from about 50<SUP>o</SUP>F to 85<SUP>o</SUP>F.
My suggestion would be to become a fastidious "housekeeper" in this part of the garden. Rake up those leaves, clean your tools (a little bleach goes a long way -- use a solution made from 9 parts water and 1 part bleach to disinfect your tools) and perhaps add some clean mulch under them to prevent splashing raindrops!
Is the insecticide and fungicide you sprayed labeled for these plants? It is possible that repeated applications could be causing the leaf damage, rather than an insect or disease. I recommend holding off on any spraying until you have a better idea of what exactly is causing the problem.