iCowApp

(Rhyzopertha dominica)

(Trogoderma granarium)

Credits: Biovision-Infonet

Grains of pearl millet are attacked by major pests such as the lesser grain borer and the khapra beetle. For this reason, the popular concept that millets are hardly susceptible to damage by storage insect pests is erroneous, except for the very small-grained millets such as tef and fonio.

The lesser grain borer and the kapra beetle are relatively well adapted to extremely dry conditions and will cause serious damage to millet.

Other secondary storage pests do not thrive in semi-arid climates where millets are grown, where stored grain is typically very dry.

Other non-insect pests such as rats and birds may destroy a considerable part of the harvest.

What to do:

• Keep millet in sealed storage e.g. in drums or underground storage. Lower the temperature during drying of millet. The optimum reproduction temperature for these pests is 30-35degC, thus lowering the temperature to around 21 degC could check reproduction (Kajuna).
• Following are some farmer’s practices to manage millet storage pests in the Sahel (see reference: Sankung Sagnia):

1. Hang millet heads over kitchen fires to repel storage pests with the smoke.
2. Store millet on the head. This reduces damage by pests as opposed to storing it in the form of threshed grains because the glumes on the in-threshed head act as protective devices
3. Mix seeds with inert substances such as sand and wood ash. These substances fill the enclosed spaces and thus prevent movement and dispersal of insects inside the stored seeds. They also act abrasive to enhance water loss through the insect cuticle, thus killing the insect.
4. Mix seeds with plant materials such as leaves of Boscia senegalensis, and mint, Hyptis spp, and pulverised pepper. These materials show a repellent action against storage pests. 

Credits: Biovision-Infonet

Several species of grasshoppers attack millets. Short-horned grasshoppers include Zonocerus spp, Oedaleus senegalensis, Kraussaria angulifera, Hieroglyphus daganensis, Diabolocantatops axillaris among others.

The long horned edible grasshopper (Homorocoryphus niditulus) is a pest in East Africa.

Grasshoppers defoliate and eat the panicles. They are not of economic importance when present in low numbers. However, invasion by a swarm of grasshoppers may result in serious grain losses.

What to do:

• Conserve natural enemies. Important natural enemies include ants, larvae of blister beetles, parasitic flies, assassin bugs, predatory wasps, birds, lizards, snakes, frogs, and fungi. Robber flies are also major predator of grasshoppers.
• Domesticated poultry (e.g. chickens, turkeys, guinea fowl, geese, and ducks) and wild birds are good for keeping grasshopper populations in check. However, enclose the birds in wire fencing along the perimeter to avoid damage to the crop.
• Ensure the ground is covered with crops, grass or mulch. This is reported to reduce grasshopper numbers since they prefer laying eggs on bare soil.
• Dig or cultivate the land before planting to expose the eggs to predators and to the weather.
• Whenever necessary spray biopesticides. Neem extracts act as antifeedant (grasshoppers stop feeding when exposed to neem products) and affect development of grasshoppers.
• IITA (the International Institute of Tropical Agriculture) researchers and partners have developed an environmental friendly biopesticide “Green Muscle” for control of grasshoppers and locusts (www.iita.org).

(Atherigona soccata)

Credits: Biovision-Infonet

Sorghum shoot fly, (Atherigona soccata), is a particularly nasty pest of sorghum in Asia, Africa, and the Mediterranean area. Females lay single cigar-shaped eggs on the undersides of leaves at the 1- to 7-leaf stage.

The eggs hatch after only a day or two of incubation, and the larvae cut the growing point of the leaf, resulting in wilting and drying. These leaves, known as ‘deadhearts’, are easily plucked. When a “dead heart” is plucked, it releases an obnoxious odor.

Adult resemble small houseflies. They are about 0.5 cm long. The shoot fly has been reported as attacking pearl millet.

Damage occurs 1-4 weeks after seedling emergence. The damaged plants produce side tillers, which may also be attacked. The shoot fly’s entire life cycle is completed in 17-21 days.

Infestations are especially high when sorghum planting is staggered due to erratic rainfall. Temperatures above 35degC  and below 18degC  reduce shoot fly survival, as does continuous rainfall.

What to do:

• Conserve natural enemies. Parasitic wasps and several species of spiders are important predators on eggs.
• Collect and destroy crop residues after harvest to reduce carry-over from one season to the other.
• Use shoot-fly resistant varieties, if available

(Heliocheilus albipunctella)

Credits: Biovision-Infonet

It is the most important insect pest of pearl millet in the Sahel. Moths deposit their eggs on the heads of millet, preferring half-emerged and fully-emerged flowering heads.

The caterpillars mine into the seeds of the millet head, damaging the millet panicle (i.e. the flower head, where the grain is formed). It has been reported to cause complete crop loss. Pupation takes place in the soil.

What to do:

• Plough deeply to expose residual larval populations and pupae to natural enemies and desiccation.
• Conserve natural enemies. Efforts in artificial augmentation (rearing and releases) of an effective parasitic wasp (Habrobracon hebetor), and identification of other useful, complementary natural enemies, are going on in West Africa. (IITA, The McKnight Foundation). A two-week delay in planting of short cycle millet varieties (75 days to maturity) to desynchronise the peak flight period of the susceptible phenological stage of the crop has been reported to be effective against this pest (DFPV, Niger).

Credits: Biovision-Infonet

Several species of stemborers attack millet including the millet stemborer (Coniesta ignefusalis), the maize stalkborer (Busseola fusca), the spotted stalkborer (Chilo partellus), and the pink stalkborer (Sesamia calamitis).

Stemborer caterpillars bore into stems of millets disrupting the flow of nutrient from the roots to the upper parts of plants.

Attack on young millet plants causes damage known as “dead hearts”. In older plants the top part of the stem dies as a result of tunnelling by the borers.

The millet stemborer (Coniesta ignefusalis)

It is the dominant stemborer of millet in the Sahelian zone of Africa, and also attacks sorghum, maize, and wild grasses. Major damage has been reported in West Africa. It has also been found causing considerable damage to millet in Western Eritrea, being considered as the major pest of millets in Eritrea (B. Le Ru, icipe, personal communication).

The moths have golden brown forewings. They are active throughout the night and during the day rest on the lower surface of leaves or along stems. Caterpillars are cream-coloured with black spots along the body.

However in the dry season, when caterpillars enter in diapause (a resting period) they change colour to pale yellow or uniform cream white. They stay in this resting period from 6 to 7 months, but occasionally for more than a year.

Moths lay eggs between the leaf sheet and the stem in batches of 20 to 50 eggs. Caterpillars tunnel in the leaf sheets and in the underlying stem. They normally pupate within the stem.

Small plants on which eggs are laid may be thoroughly riddle with caterpillars and soon collapse, but in larger plants external symptoms show two to three weeks after stems have been infested.

Economic damage results from early plant death ( “dead-heart”) stem tunnelling, disruption of nutrient flow, steam breakage, poor or no grain formation and empty heads. Crop losses have been estimated at $91 million a year.

What to do:

• Sow early, soon after first rains. Delayed planting tends to increase the incidence of diapause, resulting in significantly higher numbers of diapausing larvae in millet stalks at the end of the growing season. Burn all crop residue left in the field after harvest. When using millet stalks for construction, burn them partially immediately after harvest.
• Use resistant varieties if available
• Monitor the millet stemborer. In West Africa, pheromone technology has proved to be highly effective in monitoring this stem borer. These pheromones can also be used to reduce stemborer populations.Mass trapping using pheromones has been tried in farmers’ fields in Niger. These traps were particularly effective along fences and granaries, areas that harbour borers. Results indicate that inexpensive, locally made pheromone-baited traps are efficient and well adapted to local conditions (ICRISAT).