| [Image: Stunted plants from reniform damage.] |
| [Image: Root-knot produces galls that are visible on the root.] |
| [Image: Stunted cotton from high levels of root-knot nematode.] |
Plant-parasitic nematodes continue to be a major pest problem to cotton production in Louisiana in 2005. Reniform and root-knot nematodes are the two types that cause the most problems to cotton and infest many of the soils where cotton is produced. Reniform nematode has been found in about 50% of the acreage and root-knot in 15% to20%. Either can damage yield seriously.
Reniform nematode has rapidly spread in the past 20 years, surpassing root-knot nematode in importance as the worst nematode pest in Louisiana. Reniform nematode is basically a tropical or subtropical nematode that seems to thrive in our soils and weather conditions. Hard freezes and frozen soil to depth of several inches could reduce populations of this pest, but they are basically nonexistent in our state.
Root-knot nematode is a widespread pest that is considered indigenous to our state. This pest has been bothering cotton farmers since the earliest cotton production in our state; however, it wasn’t even recognized as a pest until the 1890s. Crop rotations were some of the earliest methods of managing it although, in many cases, farmers weren’t even aware of the problem but could recognize the benefits.
Many producers have chosen to rotate out of cotton this year into either corn or soybeans. Corn has strong resistance against reniform nematode but is a good host for root-knot nematode. There are only a few soybeans varieties available with resistance against either or both nematodes. Stoneville 5599BR variety of cotton does have a fairly good level of resistance against root-knot nematode. Unfortunately, there are no commercial varieties with resistance against the reniform nematode.
Nematicides continue to be one of the most important management options for cotton producers. Use lower rates for light to moderate infestations and increased rates for the higher levels. Most producers who had fields with extremely high levels of nematodes have, it's hoped, already decided to plant either corn or milo. Although soybean varieties may be resistant, extremely high levels of nematodes may still cause some damage to this crop.