Plant Doctor Archive

Pests on beans

MY Scarlet Runner beans haven't done well this year. They grew and flowered well, but produced very few beans and the ones that did grow were misshapen and small. I fed them with compost, lime and Nitrophoska. There were a lot of passion vine hoppers around earlier, so I sprayed the beans with Neem oil a couple of times. Can you offer any help?

IT sounds as if the passion vine hoppers are part of the problem. Both the fluffy nymphs and the adults are sap suckers, feeding on leaves, stems and fruits. The damage they cause feeding on immature beans could result them being small and deformed.

You'd need to spray quite often with Neem to control them, making sure you actually hit the passion vine hoppers with the spray for best effect, which can be difficult as they hop off the plant when disturbed.

Less common, but sometimes a tricky problem, is the damage caused by some bumble bees. Being too large to enter the flower through the opening in the front, they cheat by chewing a hole at the rear of the flower to get to the nectar. With the nectar gone, smaller bees and other insects aren't interested, so the flower misses out on pollination and no bean forms.

Also, at the height of summer, very high temperatures and humidity can have a negative effect on bean formation, but once the weather cools down, it comes right again. Make sure you keep them well watered.

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