Post category: Leaf spots
Leaf spot diseases are caused by fungi that invade the leaf tissue causing it to turn brown or purplish, often with a concentric ring and perhaps a tiny centre spot. Mostly, leaf spot diseases are not very virulent, causing only spotting but not much tissue loss. Plants often respond to leaf spot diseases by shedding leaves, and this can be debilitating
Tar spot on sycamore
Almost every kind of plant has its own particular leaf spot disease. Most are not very damaging, being no more than curiosities like sycamore tar spot, but blackcurrant, celery, iris, beans, hellebore, honeysuckle, poplar and cineraria are among the plants that suffer serious leaf spot diseases.
White blister disease affects the Cabbage family, including weeds. It causes raised yellow bumps about a centimetre across on the upper surface of the leaves, and white spots on the underside. It spoils the foliage but does not greatly weaken the plant. Since it usually affects old leaves, the crops are generally edible. Remove old crops.
The major source of infective material for leaf spot diseases is the fallen leaves and a good measure of control can be achieved by raking these up and destroying them. In the case of repeated severe attacks, a spray of Bordeaux Mixture or Liquid Copper in late spring and early summer might give some control. There are so many different species of leaf spot fungi involved that precise recommendations are not possible.