Root diseases of cotton can occur during all phases of the growing season.Once a seed begins to germinate,fungi and nematodes will move to infect the roots.During the first two weeks after planting,most plant pathogens are already colonizing roots.Seedling disease, which can include root discoloration (necrosis) and sunken lesions on the root and hypocotyl, is usually the first root disease problem observed.Later in the season other symptoms can be found such as galling from root-knot nematodes or complete root death from the fungus causing Texas root rot.Once the plant is dead,it is difficult to determine what caused the root problem.However,if roots are examined when plants first begin to show above ground symptoms of stress,it is often possible to diagnose a root disease problem.

Rhizoctonia solani
This fungus causes cotton seed rot, lesions on the hypocotyl and root rot in cotton s e e d l i n g s. Rhizoctonia solani can cause disease under a range of environmental conditions, but is most damaging in cool,wet soil. Hypocotyl lesions are generally reddish brown in color and sunken. Root lesions can be wet areas where the root appears as a string (the surrounding tissue has rotted away) or darker colored lesions. When more than one seedling disease pathogen is present, such as R.solani and Thielaviopsis basicola, then root lesions are brown in color. As the plant matures, the hypocotyl area hardens and is not susceptible to damage. Management of R.solani i n v o l v es planting high quality seed, using a fungicide seed treatment with activity on R.solani, planting when soil conditions are warm and rain is not imminent and, in severe cases, using an in-furrow fungicide at planting.

Black Root Rot
Thielaviopsis basicola
This fungus causes a disease known as black root rot. The root system turns black, particularly in young plants,but the root tissue remains firm. It does not rot. However,if there is a disease complex involving several different fungi,then the black color (necrosis)can be combined with actual root rot (softening of the tissue)and root death.This disease can be severe when soil temperatures are cool. Generally,soil moisture is not necessary to have serious black root rot,though disease symptoms may be more severe when cool temperatures are combined with wet soil. Once the soil temperatures warm, the black root systems will be sloughed off and the roots will appear white and healthy colored. An unusual exception is seen when soils are heavily infested with this fungus,or when root- knot nematode is present with T.basicola.Then, root symptoms may persist all season. Plants with black root rot can recover and produce high yields. However,if cool spring weather is prolonged,plants may be sufficiently delayed in their maturity and growth to the point that they will remain stunted all season. Management of this disease involves planting when soil temperatures are warmer. Generally crop rotation of 1-2 years is not sufficient to significantly reduce disease pressure.Seed applied fungicides like triademenol can provide limited protection, but only under low disease pressure.

Cotton Root Rot
Phymatotrichum omnivorum
This lethal disease of roots is caused by the fungus Phymatotrichum omnivorum.The fungus lives deep in the soil and grows as mycelia strands (threadlike structures)upwards towards the taproot.Once it infects a root it can move down and across rows killing additional plants.The symptoms of wilt start usually in midsummer.The plant dies soon after wilt symptoms start.The leaves of the plant generally remain attached to the plant.The roots are darkened with a reddish stain and mycelia strands (called rhizomorphs),which are tan in color,can be seen on the roots.Under very moist conditions,mats of white to tan mycelia can be found on the soil around the dead plants.This disease is worse in summers when there is good rainfall.Dead areas of the field can run from several feet to acres.It is possible to lose more than 50%of the cotton in a field to this disease. The dead stalks also create a problem with harvest since they get stuck in cotton strippers. Management of cotton root rot is nearly impossible when weather is conducive for the disease.The most effective control is to deep plow the field and plant varieties which mature early.This fungus produces a long-term survival structure called a sclerotia,which can survive for years deep in the soil.The depth that this fungus survives is one of the main reasons that control is so problematic.

Rhizoctonia solani


Rhizoctonia solani


Rhizoctonia solani


Black Root Rot


Black Root Rot


Cotton Root Rot