Plant Doctor Archive

Trouble with beans

I HAVE been growing scarlet runners for quite a few years, but about three years ago they started dying from the ground up. The leaves turn yellow then fall off. This happened rapidly over about two weeks and the beans were misshapen. Last year I planted them in a new garden and had a good result with no problems, but this year the problem has come back again.

Also, what conditions do radishes require? I have been growing them in a pot and I get a lot of foliage but just a long thin underdeveloped root.

THERE are several things that could be happening to your beans, including virus, bean fly, collar rot and root rot. Check the soil where you plant them is free-draining and make sure you don't have mulch or compost piled up against the stems.

Bean fly larvae can bore into the stems of young beans, causing them to become brittle and may eventually lead to the death of the plant. Spray every 7-10 days with a product such as Mavrik or pyrethrum when the plants are young, but stop once beans start forming.

If a plant does start to look yellow, cut into the stem - if the inside appears brown or discoloured, the problem may be the virus sometimes called "summer death" which can be spread by leaf hoppers who've fed on infected weeds nearby. Unfortunately, there's not much you can do to control the virus, apart from pulling the plant out immediately to reduce the chance of it spreading to the others.

Some gardeners claim scarlet runners grow best in areas with relatively cool summers, so how about next year you try growing the variety 'Shiny Fardenlosa' which is more tolerant of hot conditions - its beans are just as tasty.

It sounds like your radishes are putting everything into leaf growth and nothing into storage roots. They probably will eventually produce edible roots but may be bitter by then. Radishes grow best in garden soil, which is generally cooler than potting mix in a container and where the availability of nutrients is limited somewhat by the effect of clay. If you want to continue growing them in pots, try placing them in a relatively cool place and cut down on the fertiliser. You could do this by using old potting mix and only liquid feeding a little if the leaves look hungry or mixing some good topsoil in with the potting mix.

Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.