Pest and Weed Control

Root Knot Nematodes

root-knot (Meloidogyne ssp.), lesion(Pratylenchus spp), sting(Belonolaimus spp.), stubby-root( Trichodorus spp.) and cyst (Heterodera spp.). Roo-knot is probably the most common nematode and causes the most damage.

Symptoms.
These attack roots causing lesions, root galls or swellings, plant stunting and wilting of severely infected plants.  The     Lesions also serve as entry points for Bacteria and fungi. Affected plants are dwarfed and have distorted leaves.

Control

  • Crop rotation with non-susceptible crops such as maize and grasses.
  • Good weed control to remove weeds which are also hosts to the Nematodes.
  • Leaving fallow infested fields during dry  weather.
  • Soil application of 5 gm/m² Mocap at planting, or 6-10 gm/m2 Ethoprophos, 2-3 times a year.

Bean Fly

(Ophiomyia spp, Phorbia spp)

a. Symptoms
The adult is a small 2 winged insect which can be seen resting on leaves where it lays the eggs.  The damage is caused by the larvae which mine the stem. The larvae also feed on the cotyledons of seedlings before or after emergence.    Affected plants are yellow, stunted, and stems are cracked at the soil level
b. Control
Spray with chemicals such as:

  • Cypermethrine at 100ml/20lt at 7 days intervals,
  • Fenvalerate at 100ml/20lts at 7 days interval.
  • Karate and decis could be applied in the stages that follow through the harvesting period, at weekly intervals.

Treat soils with chemicals such as:

  • Triazopho, at 30-60 ml/100lt, at 10-14 days intervals, or
  • Chlopyrifos at 150ml/100lts. At 7 days intervals.
  • For Triazophos and chlopyrifos, allow 21 and 7 days pre- harvest interval respectively.

Seed treatment with chemicals such as: –

  • Imidacloprid at 570gm/100kg of seeds.
  • Cypermethrin at 100 ml/20L At 2 weeks intervals
  • Fenvalerate at 100ml/20lts at 7 days intervals.

Bean Thrips

(Megalothrips Spp)

a. Symptoms.
The damage is caused by the nymphs  and adults which feed and puncture flower structures.
b. Control

  • Foliar spray before crop flowering
  • Apply Karate Decis or Ambush CY during flowering

Aphids

(Aphids fabae)

a. Symptoms
Aphids cluster on plant stems, leaves, and bean pods. They suck plant sap and cause the plants to stunt.
b. Control

  • Chemical sprays as for bean fly above.

Red Spider Mites

(Tetranychus Telarius)

a. Symptoms
These are tiny organisms also known as red     spider mites, since they are in the same group as spiders.  Their main damage is on the leaves    which turn silvery and brownish in colour. Infested leaves have cobwebs on the lower leaf surface.
b. Control

  • Weed control to remove alternate hosts.
  • In severe infestation, burn the bean straw.
  • Spray with chemicals such as Kelthane (or Dicofol), Cabaryl, Dimethoate, Tedion (or Tetradifon 18% E.C). The safety period for Kalthane is 7 days, while. for the others it is 14 Days.

Cutworms, Beetles and Caterpillars

(Agrotis Spp, Astylus spp Rutelinae spp)

a. Symptoms.
These are active at night and hide during the day. They cut stems of young plants above or below soil level. They also feed on plant foliage.

b. Control.
Treat soil with chemicals such as:

  • Chlorpyrifos,, at 150150ml/100lts, at 7 days intervals. Observe 7 days pre-harvesting interval.

Foliar spray using chemicals such as: –

  • Deltamethrin, at 30-50 ml/20lts, at 7-10 days interval and 7 days pre-harvest interval.
  • Cabarl, at 50gm /20lts, at 15 to 21 days intervals and 14 days pre-harvest Interval..
  • Malathion at 30-35ml/20lts and 14 days pre-harvest interval.
  • Fenitrothion at 40 ml/20lts. (14 days intervals, 7 days pre-harvest interval).

American ballworm

(Heliothus armigera)

a. Symptoms
The larvae bores holes in flower buds and young maturing pods. Pods either fails to form or don’t develop to maturity.
b. Control

  • Foliar sprays with Bestox, Thuricide, Desis.
  • Physical removal

Weed control

Timely and thorough weeding is absolutely essential.  The first weeding should be done 2-3 weeks after emergence. Second weeding should follow 2-3 weeks later. Care should be taken to avoid damaging the shallow roots especially during the first weeding. Crops should not be weeded at flowering time and when the field is wet to avoid flower shedding, spread of diseases and soil compaction. Use of herbicides could be economical for the commercial French beans grower.  The following pre-emergence herbicides can be used: -.

  • Lasso 4 EC (Alachlor) at 3 Litres in 400 litres of water per hectare
  • Stomp (Pendimethalin) at 2.5 Litres in 400 litres of water per hectare
  • Basagran (Bentazon)     can be applied post-emergent at 2.5-3lts/ Ha for control on broad-leaved weeds.