Infested Scarlet Runner Beans

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Q: For years I have grown successfully Scarlet Runner Beans in a half barrel, teepee-style. This season I am experiencing an infestation problem where all the leaves are being destroyed. Last night, I went with a torch after dark and I noticed maggots at soil level and tiny insects under the leaves. I have tried a soap solution to no avail. The soil has come from my composter in case that is a clue.

Without getting more details on the “maggots” or the “tiny insects” you saw that night, I can’t say for sure if they are the ones damaging your scarlet runner bean.

The insects might be scavengers found in your compost pile, e.g. sow bug or pill bug. Generally these are not true insects but are rather more related to crustaceans such as lobsters, which like moist, shady soils where they feed on dead matters. Sow bug or pill bug looks like a gray armadillo in appearance and may roll up in a tight ball. You may also encounter sow bug or pill bug indoors but they do not live very long since they die when exposed to dry air. Because of cooler than normal spring weather, plants will have a slower time getting established so the sow bug or pill bug may have turned their appetite to bean plants. Scarlet runner beans generally require warm soils to grow the best.

You may also be seeing “climbing cutworms” which is a nondescript caterpillar usually grayish to brown in colour. When you pick cutworms they tend to curl up in a letter “C.” Cutworms eventually turn into those brown fluttering moths you see flying into the light bulb in the evening. Cutworms are also known for their voracious appetites during the evenings, often consuming entire leaves and stems.

Without a positive identification of the insect in question, I would not suggest any spray at this point.

If it’s cutworms I would usually suggest handpicking (not everyone likes this idea but is very effective). For sowbugs or pillbugs try replanting, avoid unnecessary evening watering (unless of course it rains). You could also try better spacing of plants to increase air circulation and praying for some warmer weather to encourage better plant establishment. There is a stronger chemical which is more effective than soap but I am hesitant to recommend since we do not know the actual insect(s) doing the damage – plus we are applying onto an edible crop.