Cotton / Soybean Rotations in Reniform Nematode Infested Fields

• Reniform nematode (Rotylenchulus reniformis) is widespread throughout the Southern United States and is a prevalent economic pest on cotton acres, potentially costing growers more than $60 per acre in management expense and yield loss.
• The southern root-knot nematode (Meloidogyne incognita) is also a major pest of cotton, as well as several other crops due to its wide host range.
• Even at moderate population levels, reniform nematode and root-knot nematode can reduce cotton yields enough for economic impact – sometimes without severe symptomology being apparent in the field.
• While seed treatments and other chemical control measures can provide short-term nematode suppression, the best management approach in cotton is to integrate nematode resistant varieties that reduce overall reniform nematode and root-knot nematode populations.
• In soybeans, the negative impacts of root-knot nematode and soybean cyst nematode are well known by producers, but reniform nematode is often overlooked as an economic threat.
• Many soybean varieties offer native resistance to root-knot nematode and soybean cyst nematode, but there are currently no soybeans that offer reniform nematode resistance.

  

• Two recent research studies led by Assistant Research Professor Dr. Tessie Wilkerson of Mississippi State University were conducted to study the value of reniform and root-knot nematode resistance traits in cotton varieties in a cotton / soybean rotation.
• The first study evaluated the efficacy of nematode resistance traits and seed treatments for protecting cotton yields under high reniform nematode pressure.
• The second study focused on the effect of nematode resistance traits on cotton yield, reniform nematode population levels and yield of soybeans grown the following season.

Experiment 1

• Research was conducted over three years (2020-2022) near Stoneville, MS on Bosket VFSL soil under continuous cotton production with high reniform nematode population levels.
• The experiment was conducted at two locations each year for a total of six site-years of data.
• Each experiment was set up as a two-way factorial with three different nematode trait packages and two different seed treatments.
• Nematode Traits
  • No nematode trait
  • Root-knot nematode resistance (RKN)
  • Root-knot + reniform nematode resistance (RKN + REN)
• Seed Treatments
  • Base seed treatment
  • PhytoGen TRiO™ seed treatment
• Soil samples were collected from each treatment at the end of the season and tested for reniform nematodes to assess population levels.

Experiment 2

• Research was conducted over three years (2022-2024) near Stoneville, MS on Bosket VFSL soil with high reniform nematode population levels.
• In the first year of the cotton / soybean rotation, large plots (12 row x 600 ft) were planted with four different cotton varieties:
  • Competitive variety – no nematode trait
  • PhytoGen variety – 1 gene RKN trait
  • PhytoGen variety – 2 gene RKN trait
  • PhytoGen variety – RKN (1 or 2 gene) + REN trait
• Soil samples were collected at planting and harvest and tested for reniform nematodes to measure changes in population levels over the course of the growing season.
• In the second year of the cotton / soybean rotation, each of the large plots from the prior season was subdivided into a small-plot trial with eight different soybean varieties (two of which had resistance to root-knot nematodes).

Experiment 1

• Seed treatment did not influence stand counts, early season vigor, cotton yield or reniform nematode populations.
• Yield was similar between cotton varieties with no nematode trait and varieties with a RKN trait (Figure 1).
• Cotton varieties with REN + RKN traits yielded an average of 175 lbs/A more than those with no nematode trait or RKN trait only (Figure 1).

  

  Figure 1. Average cotton yield (lbs/acre) over three years in two high reniform nematode locations as affected by seed treatment and resistance traits for root-knot (RKN) and reniform (REN) nematodes.

• End of season reniform nematode population levels averaged 30% lower in plots with REN + RKN trait varieties.

Experiment 2

• In the presence of moderate reniform nematode populations, REN + RKN traited cotton varieties yielded an average of 500 lbs/A more than cotton without a nematode trait (Figure 2).
• Cotton varieties with RKN traits outyielded cotton without a nematode trait by 100 lbs/A and 200 lbs/A; for single and dual gene RKN resistant varieties, respectively (Figure 2).

  

  Figure 2. Average cotton yields (lbs/A) of varieties with different root-knot (RKN) and reniform (REN) nematode resistance traits.

• Reniform nematode populations increased by 500% over one year when cotton without nematode traits was planted (Figure 3).

  

  Figure 3. Average reniform nematode population levels (number/pt of soil) at planting and harvest of cotton varieties with different root-knot (RKN) and reniform (REN) nematode resistance traits.

• Yields of soybean following cotton varieties with RKN traits (single or dual gene) increased by an average of 4 bu/A across varieties (Figure 4).
• Yields of soybean following cotton varieties with REN + RKN traits increased by an average of 8 bu/A across varieties (Figure 4).

  

  Figure 4. Average yield of eight soybean varieties planted following cotton with different root-knot (RKN) and reniform (REN) nematode resistance traits.

• The highest yield for each of the eight soybean varieties was achieved when planted following REN + RKN traited cotton.
• The two soybean varieties with root-knot nematode resistance did not have a yield advantage over non-RKN varieties in reniform nematode infested fields.

  

  Figure 5. Roots of cotton plants exposed to reniform nematode. Plants on the left are a variety with reniform nematode resistance and plants on the right are a variety without reniform nematode resistance.

• Reniform nematodes are an often-overlooked pest that can negatively impact yield in both cotton and soybeans.
• One reason reniform nematode populations can devastate cotton and soybean yields is because populations can increase dramatically in one season.
• In these trials, reniform nematode populations increased fivefold in one season with a non-resistant cotton variety.
• RKN-only varieties provided limited benefit against reniform nematode, and population levels were still able to double over the season.
• The only cotton variety that successfully managed reniform nematode populations was the PhytoGen brand variety with REN + RKN resistance.
• The yield benefits of planting a REN + RKN cotton variety carried over into soybeans planted the following season, demonstrating that successful management of reniform and root-knot nematodes in a cotton-soybean rotation begins with planting resistant cotton varieties.