Nematodes on grain sorghum

Charles Overstreet, Xavier-Mis, Deborah  |  4/27/2016 3:44:03 PM

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Galling by the Southern root-knot nematode evident on lateral roots. The galls are still very small.

There are several nematodes that can cause problems on grain sorghum. These nematodes damage the root system causing stunting and delay blooming,consequently suppressing yield. Grain sorghum can be an effective rotation crop against the reniform nematode since it is considered to be a nonhost for this pest. Grain sorghum is often grown on heavier soils where there is little danger from nematodes. When planted in coarse-textured soils such as sandy loams or some silt loams, nematodes are more likely to cause problems.

Nematodes

The Southern root-knot nematode is widely distributed throughout Louisiana attacking a number of crops including cotton, soybean, corn, sweetpotato, and grain sorghum. Although the Southern root-knot nematode may cause fairly large galls or swellings of the root around the nematode on most plants, both grain sorghum and corn usually have very small galls that may be difficult to identify. Galling tends to be on the small lateral roots and not on the brace roots. There apparently are considerable differences in susceptibility among varieties of grain sorghum to this nematode as well as nematode populations from different areas in our state or other states. The reaction to this nematode ranges from very susceptible to fairly resistant. However, most varieties appear to support fairly high levels of the root-knot nematode and may not be suitable as a good rotation crop when this nematode is present.

The lesion nematode is another problem pest on grain sorghum that may cause stunting and yield loss. The damage from this nematode shows up as dark, discolored lesions on the root system. Unfortunately, these symptoms are not very distinctive and may not be readily identified as being caused by nematodes. A soil sample may be required to identify problems with this nematode. Problems with this nematode usually have not occurred unless crops like corn or grain sorghum are planted in the same location for multiple years.

Stunt nematodes are the third type of nematode associated with some damage to grain sorghum. These nematodes may cause some browning or discoloration of the root system and stunting of the above-ground foliage. Symptoms from this type of nematode are not very distinctive and may also be difficult to recognize as being caused by nematodes.

Management

Although the Southern root-knot nematode can occur on grain sorghum, we don’t have a good idea of the level of damage this pest can cause. Yield losses of 15-30% have been reported in the past from this nematode from other states. Since varieties may be important in the amount of reproduction or damage by this nematode, variety selection may become important. The following Table I identifies the variety reaction against an isolate of Southern root-knot nematode in Louisiana. Current research is being conducted to evaluate damage by this nematode and the impact of varieties on population development of this nematode for the following crop.

Table 1. Grain sorghum varieties and reproduction by an isolate of the Southern root-knot nematode from Louisiana.

Very susceptible

Moderate susceptible

Moderately resistant

Dekalb DKS 53-67

Dyna-Gro M72GW14

REV RV9782

Pioneer 83P17

Sorghum Partners X715

Pioneer 83P99

Dyna-Gro M77GR61

Pioneer 84P80

Sorghum Partners NK7829

Sorghum Partners X446

Sorghum Partners K73-J6

S. Partners SP6929

Sorghum Partners SPX3675


Grain sorghum is often rotated with other crops such as cotton, corn, or soybeans. Rotation can help reduce nematode pressure from other nematodes such as lesion or stunt. As mentioned earlier, rotation may not be ideal when southern root-knot nematode is involved.

There are a few nematicides labeled for use with grain sorghum including Counter 15G and 20G and Poncho/Votivo. These nematicides would be applied at the time of planting or on the seed (Poncho/Votivo).
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Galls from the Southern root-knot nematode may be small. The developing females are actually protruding from the gall.

Multiple root-knot females (stained red) can be seen inside slightly larger galls.

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