The fungus causes both seed and seedling rot and drastically reduces plant stand. In moist soil, seeds may be attacked and killed due to rotting. Seeds removed from soil show black sooty cover.
The infected areas of seedlings are covered with black fungal spores. Mature plants are also attacked.
Symptoms include permanent wilt of branches, and or wilting of entire plant.
The dead and dried branches are easily detached from the collar region. Infected pods reveal patches of black sooty spores.
Related species (Aspergillus flavus) causes deterioration of seeds.
It also produces the toxin (aflatoxin) in infected seeds that can cause death or other symptoms of toxicity when eaten by animals or humans.
A. flavus as a mould contaminant and toxin producer is much less serious during growth of the crop than during subsequent storage of kernels. Minimising moisture stress during growth can reduce invasion and toxin production by A. flavus.
What to do:
Rapid drying to moisture content of about 10% is the only means of preventing infection by A. flavus.
Minimise damage to the nuts during harvesting because the fungus can easily enter a broken shell.
Remove diseased crop debris from the field to reduce source of infection.
Rust on lower leaf surface of French beans. Symptoms are similar on green grams. (c) A. M. Varela, icipe
Pustules (spots or blisters) can form on all aerial plant parts except flowers. Orange coloured pustules first appear on the lower surface of leaflets.
Later, pustules may appear on the upper surface of the leaflets.
The pustules on the stem are elongate and elevated.
The pustules when mature rupture to release masses of reddish-brown spores, which blown by wind, spread the disease from plant to plant and far away to other groundnut fields.
What to do:
Plant resistant varieties if available.
Remove volunteer groundnut plants from the field to check build-up of rust infection.
Adopt cereal-cereal-groundnut crop rotation.
Adjust
the sowing time to avoid the most conducive environmental conditions
for rust development i.e., high humidity, cloudy weather.
Symptoms of early leaf spot (Mycosphaerella arachidis, Cercospora arachidicola) consist of sub-circular dark brown spots produced on the upper leaflet surface.
The spots are of lighter shade of brown on the lower side of the leaflets.
Yellow halo is seen around the brown spots. Oval to elongate spots are also seen on stems, petioles, and pegs.
Late leaf spot can be distinguished from those of early leaf spot.
Late leaf spots (M. berkeleyi, Cercosporidium personatum) are darker with no or light yellow halo.
The late leaf spots on the lower leaflet surface are rough in appearance. They exhibit circular rings of fungus fruiting structures on the lower leaflet surface.
Severe disease attack leads to shedding of leaflets resulting in premature ageing of the crop. Oval to elongate spots similar to early leaf spot are also formed on stems and pegs.
Late leaf spot attack is usually seen along with rust disease.
What to do:
Plant tolerant / resistant varieties, if available.
Damping-off on groundnut (c) Clemson University – USDA Cooperative Extension Slide Series, www.insectimages.org (Courtesy of EcoPort, www.ecoport.org)
Damping-off diseases affect the initial establishment of a crop. Their main features include poor emergence and death of seedlings leading to poor stands in seedbeds and fields. Seeds may rot before germination.
Affected seedlings that have emerged from the soil show water-soaking, browning and shrivelling of the stem at the soil level.
They eventually fall over and die.
Damping-off diseases are favoured by excessive wetness of the soil and low soil temperatures.
What to do:
Use certified disease-free seeds
Avoid over-irrigation and excessive fertilisation with nitrogen fertilisers.
Avoid fields previously planted with cotton or other related crops.
Chafer grub( Schyzonycha spp.) (c) A. M. Varela, icipe
Termites
Termites(Coptotermes formosanus) (c) A. M. Varela, icipe
Millipedes
Millipedes are brown to blackish in colour and curl-up when disturbed. (c) Courtesy EcoPort (http://www.ecoport.org) : Agricultural Research Council of South Africa
Aphids
Groundnut aphid colony on cowpea. Apterae are 1.4-2.2 mm long. Alatae (winged form) 1.4-2.1 mm. (c) James Litsinger. Reproduced from the Crop Protection Compendium, 2004 Edition. (c) CAB International, Wallingford, UK, 2004
Groundnut Hopper
Groundnut hopper Hilda patruelis. Size is about 5 mm in length (c) ICRISAT
Thrips
Thrips damage on groundnut (c) Steve L. Brown, University of Georgia, Bugwood.org
Groundnut Leafminer
Damage caused by Groundnut leafminer (Aproaerema modicella). Leaflets became deep brown, rolled, and dried up prematurely due to enlarged leaf mines (c) ICRISAT
Storage Pests: Moths and Beetles
Dried currant moth (Cadra cautella) – The larvae range from 1.5 mm to 1.5 cm (15 mm) in length and are light brown in colour with dark brown spots on the skin (cuticle). (c) Clemson University – USDA Cooperative Extension Slide Series, Bugwood.org
Root-knot Nematodes
Root-knot nematodes(Meloidogyne incognita / M. javanica) Roots of severely attacked (left) and healthy plant (right). Affected plants are normally stunted and eventually wilt and die. The most characteristic symptom is formation of root galls (knots) and these can be seen with the naked eye. Affected roots rot. (c) A. M. Varela, icipe
Spider Mites
A related Spider mites species on cotton leaf. They are very tiny (they rarely exceed a size of 0.5 mm) (c) O.P. Sharma, NCIPM, New Delhi. India, Bugwood.org
Dried currant moth (Cadra cautella) – The larvae range from 1.5 mm to 1.5 cm (15 mm) in length and are light brown in colour with dark brown spots on the skin (cuticle). (c) Clemson University – USDA Cooperative Extension Slide Series, Bugwood.org
Stored groundnuts are attacked by moths (Ephestia cautella, Plodia interpunctella, Cadra cautella), and beetles (Caryedon serratus, Tribolium castaneum, Trogoderma granarium).
The larvae of moths and the grubs and adult beetles bore into and damage seeds.
Moths cause extensive webbing.
The bruchid beetle Caryedon serratus is the major pest of groundnut in pod shell in West Africa.
A good post harvest pest management programme based on good storage practices is very important.
What to do:
As
most post-harvest groundnut pests except bruchids are unable to
penetrate intact pods, leaving the crop in the shell for as long as
possible during storage is an effective method of limiting damage.
Research into low cost technology to protect stored groundnut showed that Samadaka (Swartzia madagascariensis),
2 kg of powdered fruits to treat 100 kg groundnuts, was very effective
against bruchids and moths for the groundnuts stored in granaries.
Addition of sand as an abrasive material at the farm level was very effective (INPhO Compendium)
Damage caused by Groundnut leafminer (Aproaerema modicella). Leaflets became deep brown, rolled, and dried up prematurely due to enlarged leaf mines (c) ICRISAT
It is a common pest of groundnuts in South and South-East Asia and a major pest in India, and it has recently invaded Africa.
It was first found in Uganda in 1998 and is now recorded in Mozambique, Malawi, Democratic Republic of Congo and South Africa.
In all African countries where this leafminer has been found, the pest has reached epidemic densities and severe yield losses have been observed on groundnut (The New Vision. 2004; Kenis and Cugala, 2006).
The adult is a mottled moth, with a full wing span of up to 18mm. The moth lays eggs on the underside of the groundnut leaf and petioles. Yellowish green caterpillars hatch, tunnel into the leaves and feed between the upper and lower epidermis of the leaf.
Mined leaves become distorted within a few days. Caterpillars are grey-green with a shiny black head. There are five larval instars. The first instar has an average length of 0.56 mm. At pupation, they rarely exceed 8 mm in length.
Three or four mines per groundnut leaflet can cause so much distortion that a leaf exposes as little as 30% of the potential photosynthetic area to the sun.
Later, when the caterpillar becomes too large to occupy the mine, they emerge to the leaf surface and either fold over a single leaf and hold it down with silk, or web together two or more leaflets.
They live and feed in the shelter they have constructed.
Pupation takes place inside the webbed leaflets.
Damaged leaves become brownish, rolled and dry, which results in early defoliation and affects the growth and yield of the plants.
What to do:
Use tolerant/resistant varieties. In Uganda, it has been reported that the variety “Egola-1” had shown signs of relative resistance.
Plant during the first short rains when normally the miner population is low.
Avoid drought stress by irrigating or early sowing so as to avoid periods when drought is likely. Plants that are drought stressed are much more susceptible to leafminer attack than irrigated plants.
(Megalurothrips sjostedti and Frankliniella schultzei)
Credits: Biovision-Infonet
Thrips damage on groundnut (c) Steve L. Brown, University of Georgia, Bugwood.org
Several species of thrips attack groundnuts. They have been reported as important pests of groundnuts in Uganda.
The flower thrips (Frankliniella schultzei and Megalurothrips sjostedti) infest mainly buds and flowers.
Attacked flowers are discoloured and scarred; terminal leaf buds are blackened and distorted after unfolding.
Other species of thrips (e.g. Scirtothrips dorsalis and Caliothrips indicus) infest foliage.
Thrips feeding causes yellowish-green patches on the upper leaf surface and brown necrotic areas and silvery sheen on the lower surface of the leaf; leaves become thickened and some curling occurs.
In severe infestations, young leaves are severely deformed, plants are stunted and leaves are blighted.
What to do:
Conserve natural enemies. Thrips are attacked by predatory thrips, lacewings and predatory bugs.
Whenever necessary spray the crop with botanicals, such as plant extracts (e.g. garlic, rotenone, neem, pyrethrum, etc.). A mixture of garlic and pepper has been recommended for organic growers in USA.
Plough and harrow before transplanting. This can be useful in reducing thrips attacks by killing pupae in the soil.
