28 May 2013

Root Diseases and Other Root-related Injuries

Chilling injury sometimes occurs on seedling cotton, just as it emerges. Symptoms might be confused with disease, soil-applied herbicide injury, or soil salinity.

Root rots, caused by a number of pathogens, are usually characterized by discoloration and necrosis of seedling roots. Some of the more common root diseases include Rhizoctonia, black root rot, and common root rot. More detailed root disorder symptoms and descriptions can be found in the Cotton Incorporated publication
titled Cotton Root Disorders.

It is available on-line at >http://cipm.ncsu.edu/cottonpickin/disorders/<.

Nematode injury can result in reduced root growth and function, and reduced yields. Root-knot nematode symptoms include swelling and formation of galls.

The first indication of nematode presence may be chlorotic or stunted plants in localized areas in fields. Proper diagnosis of the presence of root-knot and other root-damaging nematodes ... such as reniform, lance, and sting nematodes ... requires representative and timely soil and root sample collection, handling, and laboratory assays. Well-developed taproots may be observed infrequently in nematode-infested areas.

Soil compaction injury symptoms may depend on the depth at which roots become restricted. When compaction is directly under the seed at planting, the young root either dies or grows horizontally before turning downward. Compaction in the rootzone can restrict rooting and lead to problems such as drought stress, saturated surface soil layers during wet periods, and nutrient deficiencies.

Soil pH level can have significant effects on relative root growth. At pH below 5.0, roots may appear stubby and yellowish, with a few blackened root tips. With a more desirable pH level up to the range of 6.5, roots will be longer and exhibit more branching. The illustration shows the effects of lower soil pH (greater soil acidity) on root length and growth.

Drought-affected cotton will often have drooping leaves, with a dusky, grayish-green color, and an overall limp appearance. Poorly developed
root systems, associated with diseases, nematodes, and inadequate nutrition (especially P and K), can cause plants to be more susceptible to drought. Symptoms of drought will be most evident mid-day. If observed, yields will be reduced.

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