Just Look at Those Beans!

Plant Pathology Infobytes

April 28, 1999

If you were a gardener whose green beans just wouldn't come up to a good stand last season, the problem could have been due to fungus seedling disease. Seedling diseases often make their appearance following a period of rainy weather and cool soil temperature. These conditions encourage the growth of fungi which live in the soil and cause seedling disease in green beans and other vegetable crops.

One of the most common forms of green bean seedling disease is seed rot. Soil fungi, such as Rhizoctinia and Pythium, attack seed after planting and cause seed rot and poor stands. Occasionally the entire stand may be lost to seed rot seedling disease.

Rhizoctonia and Pythium fungi also attack young bean seedlings as they emerge, causing root and stem rot. Bean seedlings affected by root and stem rots are usually stunted, show top dieback, and produce poor yields.

While gardeners can't control the weather which favors seedling disease, gardening practices can be adopted which will help reduce losses from this problem. Gardeners who want to avoid stand loss from seedling disease and get those extra-early green bean pickings will improve their chances by following these production tips.

Use high quality disease-free seed that will germinate and produce seedlings quickly. If you saved part of last season's harvest for planting the 1999 crop, inspect the seed closely to make sure they are free from surface defects (discolored seed coats, insect puncture wounds, and similar conditions). Avoid planting seeds of poor quality because this often leads to slow germination, seedling emergence, and greater chances of attack by seedling disease fungi. If you have doubts about your seed, consider purchasing a new supply for this season's crop. It could be a wise investment. Also, new seeds are less likely to carry viruses and other disease-causing microorganisms.
Plant seeds which have been treated with a fungicide. Seed purchased from a dealer are generally treated with a fungicide such as captan or thiram, both of which protect seeds from seed rot and provide some disease protection for young plants a week or so after seedling emergence. Seeds treated with a fungicide can be recognized by a red or green color. If you aren't sure whether a treatment is present on seeds, find out when you buy your seed.
In addition to fungicide seed treatment, some gardeners use in-furrow treatments with a fungicide such as Terraclor 75 Wettable Powder (available at many farm and garden supply stores under several trade names). This fungicide provides additional protection from Rhizoctinia seedling disease. Terraclor wettable powder is mixed into a liquid solution, and when used according to label directions, will help obtain a healthier stand of green bean seedlings.
Avoid planting beans where they were grown last season (use crop rotation), and choose a planting site that does not have a history of seedling disease problems.
Use the "raised row" planting approach. Soils in raised rows drain and warm up faster following rains. Warmer, well-drained soils lead to faster seed germination and emergence of vigorous seedlings which tend to resist seedling disease infection.
If nitrogen fertilizers are applied, use care to avoid over-fertilization, since excessive nitrogen can favor seedling diseases caused by Rhizoctinia.
Control insects and nematodes, since these organisms weaken seedlings, making them more vulnerable to seedling disease attack.
When cultivating, avoid throwing soil onto stems. This soil is often infested with disease-causing fungi and may contribute to seedling disease problems.

Need more assistance on disease control in the garden? Check with us at your county Extension office.

Infobytes newsletter was written by the late Dr. Frank Killebrew, Extension Specialist.