- A number of soil-borne, fungal and bacterial root rots affect a wide range of vegetable crops.
- Three pathogens - Phytophthora, Pythium, and Rhizoctonia- are collectively referred to as "damping off". These pathogens are water molds - they must have free water to grow and reproduce.
- Damping-off can affect seeds in the ground prior to germination as well as young seedlings.
- Seedlings grown inside homes under fluorescent lights and in greenhouses succumb to damping-off if the media is poorly drained and kept too wet.
- In the garden, the disease can be a problem on poorly drained soils during cool, wet, and cloudy spring weather. Symptoms are more likely to be observed on slow-growing, weak plants. Above-ground symptoms include leaf yellowing and browning, stem cankers, and stunted and wilted plants.
- Rhizoctonia girdles or constricts lower stems (known as "wirestem") and pythium causes stunting, browning, and malformation of the root system. Damping-off is more likely to infect large seeds (corn, bean, pea).
Management of damping-off
TRANSPLANTS AND SEEDLINGS
Use soilless potting media for growing transplants. Don't overwater seedlings grown indoors or in a greenhouse or cold frame. Allow the top of the growing mix to dry slightly before watering. Plant seeds and transplants in loose, well-drained soil. Infected plants should be pulled up immediately, indoors or out in the garden, and composted.
IN THE GARDEN
Avoid planting seeds or transplants in low-lying, poorly drained areas. Plant on raised beds if your garden soil stays wet for days following rainfall. Plant at the proper depth and spacing. If you've had a problem with damping-off, mix in aged compost but avoid incorporating un-decomposed organic materials prior to planting (straw, leaves, fresh manure, etc.).
Seeds can also be pre-sprouted to give them a head start. Place seeds on a moistened paper towel. Roll up the paper towel, place it in a plastic bag with some holes and set it on top of the refrigerator. Check the germination rate after 5-7 days. When the radicle (new root) begins to develop, remove seeds and plant in garden soil. However, do not pre-soak bean and corn seeds in water. This treatment will make them more susceptible to soil pathogens.
Infected plants should be pulled up immediately, indoors or out in the garden, and composted.
Low seed vigor
- Low seed vigor is a function of the age and storage conditions of the planted seed as well as the health and maturity of the plant from which the seed was harvested. Always purchase seed from reputable seed companies.
- Only buy what you will use in one or two seasons.
- Onion, corn, leek, and parsley seed, in particular, are short-lived (1-2 years).
- Leftover seeds from other crops should be stored in the refrigerator or freezer if possible in small glass containers. Otherwise, place seed in sealed glass containers and store in the coolest and driest location in the home.
- You can test the germination rate of questionable seeds by placing 20 seeds on a moistened paper towel. Roll up the paper towel, place it in a plastic bag with some holes and set it on top of the refrigerator. Check the germination rate after 7-10 days. Throw the seed out if it less than 50% germinates.
- Learn about the details of seed saving if you intend to save seeds from your vegetable plants.
Poor soil conditions
- Cloddy and compacted soils that are high in clay will inhibit seed germination and emergence. Soils with a lot of plant residue in the top four inches and soils that form a crust when dry may also prevent effective germination and emergence. Seeds need air and moisture to germinate. This can be achieved by sowing seeds in soils that are loose and have a fine crumb structure. Soil structure can be improved over time through consistent applications of compost. Covering seeds with vermiculite or screened compost and pulling up the soil into raised beds can also hasten germination.
- Never till, turn over, or cultivate wet soil. Here's a test to determine if the soil is suitable to work: Gather a handful of soil and gently squeeze it into a ball. Bounce the ball up and down in your hand. If the ball falls apart easily you can work the soil.
Plant genetics/Slow germination
- Lima bean, parsley, watermelon, and okra are examples of vegetable crops that germinate relatively slowly (10-21 days) at typical spring soil temperatures.
Seeds planted incorrectly
- Seeds planted too deep may not germinate or emerge and those planted too shallow may wash away, fail to germinate or be eaten by wildlife.
- The rule of thumb is to plant seeds at a depth that is 2-3 times their diameter. It is easy to plant seeds too deeply, especially when covering the seed with soil.
- On light, sandy soils, seed can be planted more deeply. On heavy, clay soils, seed should be planted shallower.
- The seed of celery and lettuce should be left uncovered. Their seed germinates best in light.
- The spatial orientation of planted seed does not have much influence on seeds. Beans, especially limas, are an exception. They should be planted with the "eye" (the hilum) facing down. The young root will emerge from the "eye" and thus will be heading in the right direction. Seeds sown "eye" down will produce a more uniform and productive stand.
- The seeds of most warm-season vegetable crops (beans, squash, cucumbers, etc.) will not germinate if soil temperatures are below 50° F.
- Lettuce, pea, radish, carrot, beet, spinach, and other cool-season crops will germinate if soil temperature is above 40° F. (High soil temperatures- over 85° F. are usually only a problem for spinach and lettuce seed.)
- Seed germination in low-temperature soil is spotty and slow. Determine germination requirements of the crops you grow. Use a soil thermometer or online soil temperature map to check soil temperatures prior to planting.
- Corn and bean seed, in particular, will rot in cold, wet soil. Large seeds contain large amounts of sugars that attract soil pathogens. Pre-sprout vegetable seeds indoors where appropriate, for planting in cool soil. To pre-sprout seed: place seeds on a moistened paper towel. Roll up the paper towel, place it in a plastic bag with some holes and set it on top of the refrigerator. Check the germination rate after 5-7 days. When the radicle (new root) begins to develop, remove seeds and plant in garden soil.
- Heavy rains can dislodge and wash away seeds, especially small seed.
- Avoid planting on slopes and consider using row covers, cloches, and cold frames to get seedlings up quickly in the spring.
- A lack of rainfall and warm winds can dry out a seedbed and prevent germination. Seedbeds should be kept uniformly moist.
Wild animals like voles, chipmunks, birds, and squirrels may feed on vegetable seeds. Starlings, finches, crows, pigeons, and sparrows will dig out and consume seeds before or after they have germinated.
Below are some tips for minimizing wildlife problems:
- A 3-foot high fence of chicken wire or other closely woven wire is very effective at excluding rabbits, groundhogs, cats, and dogs. Be sure that the fencing extends 4-6 inches below the soil line. Groundhogs are excellent diggers.
- A two-strand electric fence can be very effective against a wide range of animals. The wires are strung 6-8 inches and 3 feet from the ground.
- Cover seedbeds and young plants with a floating row cover. This works very well for all types of wildlife.
- Rabbits and voles can be repelled by sprinkling blood meal, human hair, or crushed hot pepper around the garden. Repellents lose their effectiveness over time and after rainfall.
- Seeds can also be pre-sprouted to give them a head start. Place seeds on a moistened paper towel. Roll up the paper towel, place it in a plastic bag with some holes and set it on top of the refrigerator. Check the germination rate after 5-7 days. When the radicle (new root) begins to develop, remove seeds and plant in garden soil. However, do not pre-soak bean and corn seeds in water. This treatment will make them more susceptible to soil pathogens.
- Wireworms are a common pest of shallots, onion, and garlic.