Nematodes are microscopic unsegmented roundworms. Many nematode species may be found in association with millet, including stubby root (Paratrichodorus minor), cyst (Heterodera gambiensis), dagger (Xiphinema americanum), lance (Hoplolaimus indicus), root knot (Meloidogyne spp.), root lesion (Pratylenchus spp.), and stunt (Tylenchorhynchus spp.) nematodes among others. The life cycles of different nematodes vary, but generally females lay eggs that hatch in response to root exudates and feed on or infect roots. Eggs generally can overwinter, but some nematodes can survive years in cysts or in dormant states.
Injury from nematodes in the High Plains is generally not considered important, although nematode injury to millet can be significant in some environments. Symptoms are often subtle and may include stunting and unthrifty growth. Nematode injury often appears very similar to drought stress or nutrient deficiency. Plants can be predisposed to root rots and other soil-borne diseases when nematode injury is significant. When feeding or infection does occur, damaged plants are generally found in patches in the field.
Incorporation of green manure crops such as oat, sudangrass, sesame, rapeseed, white mustard, or perennial ryegrass the season before millet is planted can reduce some nematode populations.
Control of lesion nematodes is based on practices that prevent populations from increasing to damaging levels. Crop rotation may be of some benefit, but likely is not effective for root lesion nematodes because of their broad host range. For example, very high populations of root lesion nematodes are often found in roots of field corn. Many weed species support high populations of nematodes and should be controlled throughout the crop rotation. Millet varieties resistant to root knot nematodes have been developed.
Chemical nematicides are not available and probably are not necessary in most fields. Nematicides used on a previous crop in the rotation, i.e., sugar beet or potato, may exhibit some beneficial carry-over effects on a following millet crop.
Categories: Millet, Disease, Nematodes
Date: 03/22/2005