Edible Landscaping

July Q & A

Question: My onion plants are starting to turn yellow before the bulb forms. I pulled a few and noticed little white worms in the base, and those bulbs were soft.

Answer: It sounds like you have the onion maggot. The adult fly lays eggs at the base of onion plants in May or June. The eggs hatch and the white larvae burrow into the base of the onion plants, causing them to die prematurely. The larvae feed for a week or so and then pupate. There can be more than one generation a year, depending on where you garden. The maggots can also attack shallots, garlic, and leeks.

To control onion maggots, pull and destroy any infected plants in your garden now. Hopefully, it hasn't spread to all your onions. Next year, plant onions in a different location, one in which no Onion family members have grown for at least three years. Delay planting by a few weeks to avoid the first generation of pests. Hang yellow sticky traps over the newly set out transplants to catch the adult flies and prevent them from laying eggs. Cover plants with a floating row cover to block the adult from laying eggs. Clean up the onion bed well in fall so the pupae won't overwinter in your soil. You can also try sprinkling cayenne pepper, diatomaceous earth, sharp sand, or crushed sea shells around young plants to kill the developing larvae before they get into the plants.

Question: My elderberry bush is growing and blooming beautifully, but some of the stems have this black area, and above it the branch is dead. What's happening?

Answer: It may be a fungal canker is attacking your elderberry. Look for dead spots on healthy branches or branches that have died back completely and have the characteristic black girdling. This fungus attacks elderberry bushes that have been stressed due to drought, cold injury, insect attacks, or flooding. The fungus invades the branch tissue, cutting off the flow of water and nutrients from the trunk to the branch and causing it to die beyond where the infection started.

To control stem canker, prune off the infected branches to a main side shoot or all the way back to the ground. Remove the infected branch from the area and keep the bush healthy by adding compost each spring. Prune properly each winter, removing branches older than three years. Protect plants from drought, flooding, and insect attacks.

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