How can I keep plants safe from rust?
QHow can I keep my hollyhocks safe from rust? I had real problems with it last year.
Ali Hutchings, Bristol
AThis rust is spread by windblown spores of Puccinia malvacearum and, as its name suggests, also affects members of the mallow family such as Hibiscus, Abutilon, Lavatera, Malvastrum and Sidalcea.
It presents as bright orange or yellow spots on upper leaf surfaces, with darker spore-producing pustules on the underside. It tends to start low and work up the plant, also contaminating stems. Badly affected plants lose their leaves and fail to thrive.
It is hard to control as the spores can travel long distances in the air. However it can be held at bay by monitoring new plants for symptoms, checking existing plants regularly and removing and destroying affected plant material.
Although hollyhocks are perennials, it is safest to treat them as biennials or, if you want them for more than one season, cutting them right back to the soil and removing all plant matter in the autumn.
Regrettably, there are no truly resistant varieties of hollyhock. The best way to keep yours from succumbing to this disease is to spray with Fungus
Fighter, a systemic control that protects for up to three weeks, or Scotts FungusClear Ultra, another ally that will guard your plants against attack for around three months.
Treat plants before the rusty red spots have appeared and to continue throughout the season.
In my experience, only basal leaves are badly damaged. Those higher up the stem usually escape.