Common Disease Problems
Damping Off: This is one of the most common problems when starting plants from seed. The seedling emerges and appears healthy; then it suddenly wilts and dies for no obvious reason. Damping off is caused by a fungus that is active when there is abundant moisture and soils and air temperatures are above 68 degrees F. Typically, this indicates that the soil is too wet or contains high amounts of nitrogen fertilizer. Burpee Recommends: Keep seedlings moist but do not overwater; avoid over-fertilizing your seedlings; thin out seedlings to avoid overcrowding; make sure the plants are getting good air circulation; if you plant in containers, thoroughly wash them in soapy water and rinse in a ten per cent bleach solution after use.
Downy Mildew: This fungus causes whitish gray patches on the undersides and eventually both sides of the leaves. Burpee Recommends: Rotate crops with plants in a different family. Avoid overhead watering. Provide adequate air circulation, do not overcrowd plants. Do not work around plants when they are wet.
Onion Smut: This fungus attacks mostly young seedlings as the new leaves emerge. It causes blister-like lesions near the base of the bulb and streaks on leaves, sheaths and bulbs. The streaks mature into black powdery spores. The fungus stunts the growth of the plants. More mature plants are not as susceptible. It is most prevalent in temperatures under 75 degrees F. The disease lives in the soil for several years. Burpee Recommends: Rotate crops and do not plant in the same area for at least three years. Encourage rapid growth with watering and fertilizer to get plants past the susceptible stage. Some fungicides are effective, Check with your Cooperative Extension Service for recommendations.
Pink Root Rot: A fungus that attacks scallion roots causing them to turn a light pink, then red and eventually purple-brown and causing them to shrivel. Infected plants show signs of nutrient deficiencies and drought because the roots cannot take up water and nutrients. Plants are stunted. The disease lives in the soil for several years and thrives in warm temperatures. Burpee Recommends: Plant as early as possible so the bulb of the plant growth will be in cooler temperatures. Rotate crops and plant resistant varieties.
Rust: A number of fungus diseases that rust colored spots on foliage and stalks. Burpee Recommends: Plant early as these diseases tend to be worse later in the season. Practice crop rotation. Remove infected plants.
Common Pest and Cultural Problems
Cutworms: These insects cut off the seedlings at the soil level. Burpee Recommends: Place a paper cup collar (use a coffee cut with the bottom cut out) around the base of the plant. They are usually mostly a problem with young seedlings. You can also control by handpicking and controlling weeds, where they lay their eggs.
Onion Maggots: These insects attack the bulb rather than the leaves of scallion plants, but this feeding habit can be a severe problem even for scallion growers, because the entire seedling eventually dies. If your plants begin to show weakened vigor, dig up a sample plant to see if the bulb looks like it is filled with tunnels. Burpee Recommends: If you see the symptoms, pull all the plants and use what greens you can. Destroy the rest of the plant parts because the flies that produce onion maggots can continue to lay eggs, causing problems for future crops. Practice crop rotation.
Onion Nematodes: Microscopic worms that live in the soil. They inject a toxin into root systems that cause scallion tops to turn yellow with blackened tips. The entire plant can become deformed. Burpee Recommends: Pull up affected plants, chop off any usable tops for kitchen use, and discard the rest of the plant. Crop rotation can reduce the amount of damage nematodes continue to wreak on future green onion crops.
Slugs: These pests leave large holes in the foliage or eat leaves entirely. They leave a slime trail, feed at night and are mostly a problem in damp weather. Burpee Recommends: Hand pick, at night if possible. You can try attracting the slugs to traps either using cornmeal or beer. For a beer trap, dig a hole in the ground and place a large cup or bowl into the hole; use something that has steep sides so that the slugs can’t crawl back out when they’re finished. Fill the bowl about ¾ of the way full with beer, and let it sit overnight. In the morning, the bowl should be full of drowned slugs that can be dumped out for the birds to eat. For a cornmeal trap, put a tablespoon or two of cornmeal in a jar and put it on its side near the plants. Slugs are attracted to the scent but they cannot digest it and it will kill them. You can also try placing a barrier around your plants of diatomaceous earth or even coffee grounds. They cannot crawl over these.
Thrips: These are tiny insects that are difficult to see. Plant tops develop silvery-white streaks or blotches and the plants can become deformed. Because the tops are the edible part of the scallion, this foliage disfiguration is more serious than it might be for other edible crops. Burpee Recommends: Blast the tops with a jet of water from your garden hose to get rid of the worst of the problem. It’s best to do this in late morning on a sunny day; wet leaves can lead to the fungal diseases to which scallions are prone. If the problem persists, coat leaves thoroughly with insecticidal soap.
Can I grow scallions over winter? Southern and frost free gardeners can grow scallions all winter.
Do scallions store well like onions? Scallions are used fresh and are not stored like mature onions. They may be kept for a week with their roots in water, or chopped up and frozen.
Can any onion be harvested as scallions? Yes, there are varieties that will only be grown as scallions, but any onion variety may be harvested early for scallions.
What parts of scallions are edible? All parts of scallions are edible, not just the bulb.
What’s the difference between scallions, green onions and spring onions? Nothing! These are all the same type of plant.