Weeds are a major obstacle in increasing the productivity of finger millet crops in Uganda especially during rainy season. Several weed species including grasses (especially wild relatives of finger millet like Eleusine indica and E. africana (Fig. 17 (a)) which are hard to distinguish from finger millet in vegetative stages), Sedges (e g Cyperus rotundus (Fig. 17 (b) and Nutsedge Cyperus (Fig. 17(c)), Johnson grass (Fig. 17 (d)), broad leaved weeds (e.g. poison ivy (Fig 17(e) and wandering jew ( Fig 17 (f)), do affect millet production in the following ways:
- Competition for soil moisture – water is one of the limiting factors in finger millet production. Weeds often require more water than crops and are more efficient at capturing available soil moisture by developing deeper roots that spread wider than the crop roots.
- Competition for nutrients – Weeds are better competitors for nutrients than crops because of their more efficient root system and fast growth. Weeds compete for limited supplies of nitrogen, phosphorus and potassium in the soil thus depriving the crop plants of essential nutrients resulting in weak plants and poor yield.
- Competition for light – most weeds tends to grow faster than finger millet thus developing large canopies that easily intercept light at the expense of the crop.
- Some weeds are allelopathic in nature i.e. they produce certain chemicals or hormones that interfere with the growth of finger millet. For example, the nut sedges (Fig. 17 (c)) and Johnson grass (Fig. 17 (d)) are known to produce allelopathic chemicals that inhibit growth of finger millet
- Some weeds are parasitic in nature e.g. striga weed
- Weeds serves as alternate hosts for crop pests and diseases e.g.
- Weeds also affect the crop quality by producing a large number of seeds, which contaminate finger millet grain.
- Some weeds are poisonous to humans e.g. Poisonivy (Toxicodendron radicans) (Fig. 17 (e)) causes severe skin irritation (dermatitis) in humans.