I have grown from seed a rust-resistant hybrid antirrhinum ‘Liberty’. The leaves have dark red marks. Is it rust? Can I save the plants?
Antirrhinum rust is an American import from the last century. It is caused by a fungus that spreads by airborne spores, starting off as yellow spots that are brownish on the underside of the leaf (where they will spore). This rust is a biotroph, meaning that it feeds off the plant’s leaves, extracting nutrients slowly over its life cycle until it is ready to spore. Plants often look terrible, as the leaves slowly collapse. If the attack is heavy, pustules will appear on the stem as well.
You may be able to keep the rust at bay: start by removing infected leaves and disposing of them in the bin. Give the plants with seaweed feed to keep their strength up. If the rust continues to spread, you’d be better off binning them now than endlessly defoliating in the hope that the problem goes away.
Even if the plants do make it to the end of the season, it is important to dispose of them then. If they are left in the ground, they’ll spread spores next year.
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