Germinating bean seeds are under attack
We have had a very low germination rate outdoors in June/July this year with Blue Lake bush bean seeds. To eliminate some of the outdoor growing factors, we experimented with the indoor germination of 8 beans in moist 'MiracleGro' compost. This was taken from the manufacturer's bag and microwaved for 20 seconds, and then cooled before planting the seeds. The 8 beans were in individual 2 inch pots, set in a container, with perforated cover, set indoors under lights, with bottom heat. We misted the soil daily. Within 4 days we had two shoots with healthy leaf buds opening and green cotyledons. One shoot came up with cotyledons but no leaf bud. We examined one bean in the soil. It was was sending out a root, but the green bud developing inside the bean was crawling with tiny transparent mites. The cotyledon was brownish at its base. We could only see the mites under a 10 times loupe lens. At first they looked like tiny water droplets but they have legs and appear to have frontal mouth parts. The unsuccessful beans either had mites or went soft and molded. Next, we set another 8 bean seeds to germinate in a glass jar. We put crumpled moist paper towel inside the jar to support the beans against the side of the jar. In 3 days under lights with bottom heat and loosely covered, 7 of these beans are sending out roots and we can see healthy green leaf buds opening. The 8th seed has mold growing on it. Do you have any idea what the soil mites are and how we can combat them?
Thank you for your question. I suspect all of these problems can bectraced back to the initial seed growing medium. The method you used to sterilize the compost failed to kill both insects and pathogens. Alternatively, the containers might not have been clean. The following is the beginning page of a comprehensive guide to seed starting that might help: https://extension.umd.edu/hgic/containers-and-growing-medium-seed-starting In terms of insect control, we would need an accurate ID of the insect, and mites (related to spiders) are not common in commercial soils. If you could take a photo and return it, we can help with a solution. The mold you’re finding indicates it was already present in the soil, or arose through airborne fungal spores, often assisted by too much water. Lift it off and reduce watering. Thank you!