Duration of Cover Crop for Enhancing Nematophagous Fungi in Fields

Under field conditions, sunn hemp is recommended to be planted for 2 to 3 months and then plowed under for maximum nitrogen (N) input into the soil. In a pineapple field in Hawaii, sunn hemp was grown for 3 months and incorporated into the soil. One month after incorporation, pineapple crowns were planted. Repeated measure analysis of the population densities of nematode-trapping fungi (NTF) revealed that NTF were higher in sunn hemp treated plots than weed fallow or plots treated with 1,3-dichloropropene (Fig. 6-1). Population densities of NTF remained high in sunn hemp treated plot 4 months after pineapple planting or 5 months after cover crop incorporation. Although this effect is not sufficient to manage reniform nematode infection on pineapple throughout the pineapple cycle (usually 18 months to fruiting), it suppressed the initial population densities of reniform nematodes. Further studies need to be conducted to search for post-plant treatment for reniform nematode management in pineapple. Continuous increase of NTF population densities for 5 months after sunn hemp incorporation is encouraging for short-term crop production.

Fungal density

Fig 6-1. Nematode-trapping fungal population densities in a pineapple field. Plots were planted with sunn hemp (Cj), rapeseed (Bn), or marigold (Te), or left fallow with weeds (W) or treated with 1,3-dichloropropene (1,3-D). Values in the table are means of 4 replications according to repeated measure analysis over time from cover crop planting to 9 months after pineapple planting. Means followed by the same letters were not different according to Waller-Duncan k-ratio t-test (P < 0.05) (Wang et al., 2002).