Pest and Disease Management
Pests and diseases are profoundly serious detrimental factors that hinder production and utilization of maize crop and produce. It is divided into pests and disease affecting maize crop during production stage and pests affecting stored maize.
Maize crop has numerous pests that attack maize right from time of planting all the way to harvesting. Below are some of the most destructive pests of maize and corresponding best practices of managing pests.
Common Maize Pests
Fall ArmyWorm (Spodoptera frugiperda)
This pest is native to South and North America and attacks more than 80 crop species. It causes severe damage on cereals especially maize and cereals. The pest was first reported in Trans Nzoia county in March 2017 and has since spread to all major maize production regions in the country. The fall army larvae can be green, brown or black, depending on maturity stage. When fully mature, the army worm develops four distinct black spots on the 8th segment towards the back end characteristic, inverted Y-shaped white lines between the eyes when placed in a position directly facing you. The first three instars damage on the crop usually pass unnoticed because they are usually very small to cause significant damage.
Damages
The larvae are the pest’s destructive stage and will rapidly destroy extensive fields of maize crop within a very short period. The larvae feed on the whorls of young plants and leaves resulting in short or long, rugged holes causing plants to exhibit stunted growth. Under severe pest infestation, the crop appears to have suffered hailstorm damage. The frass/fecal material of caterpillars (larvae) can be seen close to the whorl and upper leaves of the plant, usually resembling moist sawdust. The caterpillars also feed on the developing tassel and kernel, causing poor grain establishment and reduction in produce yield and quality. Under severe infestation, the pest can cause 100% crop loss.
Host Range
Fall armyworm is a major pest of maize but also attacks other cereals like sorghum, rice, millet, barley and wheat. Fodder crops like napier, bermuda and hay grasses also offer suitable survival sites to harbor the pest off season. Other alternate and susceptible hosts include tomatoes, bananas, cabbages, pulses/legumes, kales, capsicum, sugarcane, cotton, etc. In total, this pest attacks up to 80 crops.
Management
Fall armyworm is a difficult pest to manage, primarily because of the wide host range, first reproduction rate and the migratory habit. The first step to initiating management is early detection. For lack of visible symptoms in the early stages of infestation, the most appropriate detection technique is the installation of fall armyworm (FAW) specific pheromone traps. Frequent monitoring and scouting for the pest should be initiated as early as one week following seedling germination.
Mechanical management
Deep plough to expose the pupae to sun for death by desiccation.
Kill by hand or draw in hot water.
Select varieties with superior husk cover.
Cultural Management
Plant early as recommended by the regional calendar.
Do not plant new crops next to infested fields.
Clear the alternative host off season.
Avoid planting off-season.
Practice Good Agricultural Practices and apply fertilizers to help boost plant vigor.
Setting up 4 to 6 pheromones per hac. Helps suppress the pest population.
Plant Braccharia grass on the farm edge and intercrop with Greenleaf desmodium to act as push-pull technology.
Apply ash and chili powder. Sieve one tin (2 kg tin)/gorogoro of wood ash and thoroughly mix with five teaspoons of chili powder. Spray the mixture once into the plant funnel upon spotting.
Chemical control
Community blanket spraying for the pest is advisable to avoid re-infection.
Three sprays for the crop cycle should be enough to control the pest. The first spray should be done at two weeks after germination, at knee height and at two weeks just before tussling.
Using products with different modes of action is vital to help reduce potential for resistance development.
There are several products that are registered for management of fall armyworm in maize crop in Kenya. Some examples are below. For a more elaborate list, you can consult the PCPB website. https://www.pcpb.go.ke/crops/
BELT 480 SC
CORAGEN 20SC
ASATAF SP
DIMILIN 25 WP
DURSBAN 4 EC
XPAND MAX 92%
LEGACY EXTREME etc.
Maize Stalk Borer (Busseola fusca, Chilo patella and Sesamia species)
Maize stalk borers are pests of maize, sorghum and other crops throughout many countries in Africa. The caterpillars bore into the stem of maize, feed on the internal tissues and cause the plant to wither and die. The pest can be controlled through a combination of cultural practices (most notably intercropping and the ‘push-pull’ system) and chemical insecticides or neem powder (but only at the early stage, before the larvae have bored into the stem).
Damage
Maize stalk borers are common pests throughout sub-Saharan Africa. Older larvae feed inside the stems, weakening them and causing them to break. The caterpillars will cause dead heart in young plants. Larvae also burrow into the maize cobs in later stages of second generation attack. The stalk borers can cause between 20 to 40% yield loss if not controlled in time.
The top of the plant wilts, turns yellow, and eventually dries out and dies. If plants show symptoms, cut open the stem and look for larvae. A characteristic small dark caterpillar may be seen in the funnels. The stems of young plants show small holes resembling ‘window panes’.
Management
Cultural approaches
Planting plant resistant varieties
Improve soil fertility by incorporating manure or fertilizer to increase the plants resilience against the pest.
Implement a ‘push-pull’ system which involves intercropping maize with Desmodium, a repellent plant, and planting Napier grass on farm edges to act as a trap crop. The pest can then be easily sprayed on the Napier grass.
Intercrop with other host plants such as cowpeas or cassava. These plants will reduce the damage as the adult moth will lay eggs on the non-host plants, but the larvae will not be able to feed on them and die.
Dispose of crop residues after harvest to reduce stalk borer populations and limit the pest the following season. The crop residues can be burned, used as feed for livestock, or left on the ground exposed to the sun’s heat for one month to kill the larvae and pupae.
Rotate maize with a non-host plant, such as a legume (for example groundnut), to increase the nitrogen in the soil. This will make the next maize crop hardier and less susceptible to an attack and break the cycle of the stalk borer.
Spray with a mixture of wood ash and pepper.
Chemical approaches:
Chemical control can be used early in the season by applying appropriate insecticides, such as trichlorfon, as granules or dusts to the leaf funnel of young plants.
Neem powder can be effective and should be applied as a 1:1 mixture with dry clay or sawdust to the funnel of the plant: 1 kg of neem powder can treat 1500-2000 plants.
Once the larvae have bored into the stem of the plant, insecticides are no longer effective.
STORAGE PESTS
Larger Grain Borer (Prostephanus truncates)
The larger grain borer (LGB) is a major pest of stored crops, such as maize, dried cassava roots and yams. Although it is considered a post-harvest pest, the LGB attacks maize both before and after harvest. The adult beetles bore into maize cobs, husks and grains leaving tunnels and empty grain shells, and producing large quantities of grain dust. The adults prefer grain that is still attached to the cob rather than loose-hulled grain; damage is often greater on unshelled maize.
The pest often bore into the wood used to construct the stores in which the grains are kept.
Damage
LGB can cause significant losses in stored grain, ranging from 19-30% after 6 months’ storage. LGB causes a weight loss of the grain, as well as reduced quality and nutritional value, leading to economic losses for farmers and traders.
Management
Cultural approaches
Use maize varieties with a good husk cover that provide protection and are less likely to be attacked.
Sacks used to harvest or store grain should be immersed in boiling water to kill any remaining infestations.
Do not put crops that show signs of infestation inside the storage facility.
If using a wooden storage facility, inspect the wood for tunnels and remove infested boards.
Roofs should be constructed with iron sheets instead of grass-thatch to prevent the pest from harboring and breeding in the roof. If using grass-thatch, the roof should be thick and cone shaped.
Sell maize stock within three months after harvest when infestation of the LGB is lower.
Destroy crop residues after harvest and burn cob cores after shelling.
Harvest shortly after the maize has matured, before the LGB has an opportunity to enter the grain.
Mixing the stored grain with a dust, such as ash or clay, causes the beetles to desiccate and can help reduce populations.
Shell cobs should be dried before to a moisture point below 12% (or when it is too difficult to bite through the grain with your teeth).
Biological
At the regional or national level, releasing the predatory beetle Teretrius nigrescens can maintain the populations at a tolerable level.
Chemical
The following chemical pesticides can be used to manage the pest:
ACTELLIC GOLD DUST powder
K-OBIOL DP2 Dustable powder
PERMAL DUST
SUPER GRAIN DUST
SKANA SUPER GRAIN DUST
DISEASES
Maize Lethal Necrotic Disease
Maize lethal necrosis disease (MLND) is a new viral disease for Africa. It has caused great concern because plants are killed and little or no grain is produced. Promising resistance exists to maize chlorotic mottle virus (MCMV), the main virus associated with the disease, but further work is needed before recommendations backed by scientific evidence can be given on what varieties to grow.
Symptoms
The first symptoms are a scattering of small yellow areas (mottling) on leaves. These start to merge and the leaf becomes paler before the edges go brown and dry inwards. In some plants the young leaves die before they have expanded, producing a ‘dead heart’.
The first stages of mottling are similar to maize streak virus, but thereafter the two diseases are quite distinct: with maize streak virus the streaks do not merge and there is no marginal browning and drying up.
Maize lethal necrosis disease (MLND) kills plants. Plants become stunted and grain production, if it occurs at all, is poor: a consequence of distorted and shriveled ears. All stages of plant growth are affected and the earlier the plant becomes infected, the greater the damage.
Damage
MLND destroys whole fields of maize. The stunting and outright death of plants, together with little or no grain production, makes MLND a devastating disease whose long-term impact on maize production in other countries has been significant and poses a major threat to countries in East Africa and beyond.
MANAGEMENT
Cultural approaches
Using certified seed and varieties recommended by local extension services and national agricultural bodies.
Remove weeds and burning grasses around the field, both potential sources of the insect vectors.
Avoid walking through infested fields since the virus can be physically transmitted on clothes.
Rotate maize crops with non-cereals to reduce the virus inoculum of both MCMV and sugarcane mosaic virus (SCMV), the other virus needed for development of MLND.
NB: Maize planted less than 500 meters from an infected area is more likely to get the disease.
Chemical approaches
Reduction of vector populations through insecticide application is unlikely to have any impact on the disease unless applied consistently and over large areas. These conditions are difficult to achieve dense patchworks of smallholder plantings.
NB: It is important to note that use of non-chemical pests and disease management methods are encouraged before considering pesticide application.
