In 2022 a jassid the region had not seen before, Amrasca biguttula, native to South East Asia, established itself in Côte d’Ivoire and caused 30 percent yield loss on cotton, according to CIRAD, which now runs the DURAGOMBO project on this species in okra and African eggplant. For an okra grower the consequence is practical: the insect curling the leaves on your plot is no longer necessarily the one you were used to seeing. The working method does not change for all that. You read the damage, you name the pest, you count, and you treat only if the count justifies it.
Read the damage before choosing a product
On okra the visible symptom is almost always enough to point the diagnosis in the right direction, provided you look at the right part of the plant at the right time of day. The table below is the one our agronomists use on a field walk.
| What you see | Likely cause | Where to look |
|---|---|---|
| Leaves curling downwards, margins yellow then brick red, growth stalled | Jassids, including Amrasca biguttula | Underside of young leaves, in broad daylight |
| Small round regular holes, foliage riddled like a sieve | Flea beetles of the genus Podagrica | Leaves at the top of the plant, early morning |
| Yellow mosaic mottling, cleared veins, one stunted plant in the row | Okra mosaic virus, carried by the flea beetles | Young leaves, on a few plants at first |
| Sticky foliage, black sooty mould deposit, dense colonies on stems | Aphids and whitefly | Stem tips and leaf undersides |
| Bored pods, tunnels in the flesh, flower buds dropping | Pod borers | Buds and young pods, at picking |
| White powdery felt on the upper surface of the lower leaves | Powdery mildew | Base of the plant, after a dry spell |
Two traps come up again and again. The first is treating leaf curl as a disease when it is almost always a jassid feeding puncture. The second is treating a plant that has already turned, meaning one carrying okra mosaic virus: no product will cure it, and it serves as a reservoir for the flea beetles that come to feed on it. That plant has to leave the plot.
Jassids, the leading source of damage since 2022
The jassid pierces the vein and injects its saliva. The leaf responds by folding downwards, then losing colour from the margins inwards, from yellow to brick red. On a young plant, growth stops dead and flowering is delayed. CIRAD states that the invasive species Amrasca biguttula has replaced the native species on okra and eggplant, and that the DURAGOMBO project is assessing agroecological solutions: biopesticides based on neem, ginger and carapa vegetable oils, combined with insect netting. The insect causes both direct feeding damage and the transmission of viral diseases.
The practical consequence for crop management is this: protection against jassids is decided in the first three weeks after emergence. A plant pierced at that stage never catches up, however well it is fed afterwards. That is the window in which insect netting over the bed, or over the nursery before transplanting, pays best. The same reasoning applies under cover, where excluding insect vectors is one of the primary functions of the structure, as we set out in our article on agricultural greenhouses in tropical Africa.
Podagrica flea beetles carry the virus
Flea beetles of the genus Podagrica do two kinds of damage for the price of one. Riddling the leaves cuts the working leaf area, and the insect carries okra mosaic virus. The work of Givord and Den Boer, published in 1980 in Annals of Applied Biology and available in the IRD documentary collection, established the mechanism in Côte d’Ivoire: Podagrica decolorata is the most efficient vector, with up to 60 percent of test plants infected after a 24 hour acquisition period followed by 48 hours of inoculation, and the insect retains its ability to transmit for 6 days. The authors consider this flea beetle the main vector in the south of the country, because it is present in okra fields all year round. The variegated grasshopper Zonocerus variegatus transmitted the virus in only 2 cases out of 20 plants, which makes it an incidental vector.
That year round presence in the fields changes how a season should be planned. Okra sown next to an okra plot at the end of its cycle inherits its flea beetle population and its virus infected plants immediately. Separating sowings in space, pulling up crop residues as soon as the last picking is done and cleaning the field margins are protection measures, not housekeeping.
Count before you treat
Counting avoids the two expensive mistakes: treating too early, and treating too late. Pitan and Ekoja caged six densities of the flea beetle Podagrica uniforma, namely 0, 5, 10, 20, 30 and 40 pairs per cage, and published their results in Crop Protection in 2011. The lowest density producing a significant reduction in fresh fruit yield was 20 pairs, which the authors retain as the damage threshold at which control should be initiated. Above that level, fresh fruit yield loss exceeded 50 percent. Below it, at 5 and 10 pairs, the plant compensated for part of the damage on some of the variables measured. A cage trial does not transfer as it stands to an open field, but it says the essential thing: light riddling does not justify an intervention, and an established population makes it urgent.
The scouting round takes fifteen minutes on a market garden bed:
- Choose five counting points spread along a diagonal, away from the edges, and return to the same points every week.
- At each point, examine five plants: three young upper leaves turned over for jassids, and the top foliage for flea beetle holes.
- Go early in the morning, when the flea beetles are still slow and stay on the leaf.
- Record the number of affected plants separately from the intensity of damage on each, because the two do not progress at the same rate.
- Mark the plants showing mosaic symptoms, then pull them and take them out of the plot the same day.
- Write the counts in a dated notebook. Without a series of figures there is no way to tell whether a population is building or falling back on its own.
The protection response, in order
The order matters as much as the choice of products. The four levels stack, they do not replace one another.
- Sanitation. Sowings grouped in time, destruction of crop residues, weeding of margins that harbour relay hosts, and immediate removal of virus infected plants. This is the least visible level and the most profitable.
- Physical exclusion. Insect netting over the nursery, then over the bed for the first three weeks. CIRAD pairs these nets precisely with biopesticides in the system it is assessing on okra.
- Biopesticides. The neem, ginger and carapa vegetable oils cited by CIRAD act by contact and by repellence. They call for careful coverage of the leaf undersides and closely spaced passes, because they do not persist.
- Conventional treatment. It is triggered on a count, never on a calendar. Respect the rate on the label and the pre harvest interval, and alternate modes of action between two passes so that a resistant population is not selected. On a crop picked every two to three days like okra, the pre harvest interval is the first criterion for choosing a product, ahead of any other consideration.
The reasoning is the same one we apply to other major pests, for instance in our integrated control plan against fall armyworm in maize, or in our note on tomato late blight in tropical climates: observation, threshold, then a targeted intervention.
The sprayer does half the work
A good product badly applied gives the result of a bad product. The FAO guideline on agricultural pesticide sprayers, published in 1998, sets the quality requirements a knapsack unit has to meet: at the maximum recommended pressure and flow rate, variation in flow rate at the nozzles must not exceed 10 percent either way; the sprayer must have a minimum capacity of 5 litres and a total weight when full of no more than 25 kg; nozzles must be interchangeable and not adjustable, manufactured to international standards; load bearing straps must be at least 50 mm wide. The same guideline requires the manufacturer to supply a method for determining when a nozzle is worn and should be replaced.
Setting up in the field takes three measurements, to be repeated at every nozzle change:
- Measure the actual output of one nozzle over one minute, at the working pressure you genuinely hold at the pump, and repeat on every nozzle on the boom. A marked gap between two nozzles signals wear or a blockage.
- Measure your walking speed over a distance marked out with a line, carrying the loaded unit, then record the width you actually treat in one pass.
- Work out the volume applied per hectare from those three numbers, and adjust the concentration of the spray mix accordingly, never the other way round.
Three safety rules close the chapter, because they condition the right to spray at all: prepare the mix outdoors and never indoors, wear the protection stated on the product label, and store products locked away, in their original packaging, away from seed and foodstuffs. Tank rinsing is done in the field, away from a well or any water abstraction point.
The next six weeks
- Weeks 1 and 2. Weekly scouting on sowings in place. Nets kept on the nurseries. Removal of last season’s residues still standing.
- Weeks 3 and 4. First treatment decision based on counts. Picking begins and the pre harvest interval becomes binding: favour short interval solutions.
- Weeks 5 and 6. Watch for powdery mildew on the lower leaves if a dry spell sets in, and check nozzle wear, which drifts quietly after some twenty hours of work.
Where JOGOO comes in
JOGOO Agriculture supplies crop protection products, knapsack sprayers and their wearing parts, insect netting and seed, and supports diagnosis in the field. If you are torn between two responses on your okra, an agronomist visit and a count settle it faster than a blind trial. For the basics of growing the crop, our article on growing okra covers sowing, fertilisation and harvest. For protection equipment and inputs, see our Crop Protection offer, and go through the Contact page for a quote matched to your area.
Frequently asked questions
How do I tell a jassid attack from a nutrient deficiency?
A deficiency colours the leaves evenly across the whole plant and often along the whole row. A jassid puncture produces downward curling of the leaf blade and discolouration starting at the margins, with neighbouring plants very unevenly affected. Turn over three young leaves and you will see the insects moving sideways.
Should an okra plant with mosaic be pulled up?
Yes, and taken out of the plot. No treatment cures a virus infected plant, and it acts as a source for the flea beetles that visit it, of which Podagrica decolorata retains its ability to transmit for 6 days according to Givord and Den Boer.
At what level of leaf riddling should flea beetles be treated?
Light riddling does not justify an intervention. In the cage trial by Pitan and Ekoja, the significant yield reduction begins at 20 pairs per cage, and the plant compensates partly at 5 and 10 pairs. In the field that translates into regular counting rather than calendar treatment.
Is neem oil enough on an okra plot?
It is part of the agroecological system CIRAD is assessing, in combination with insect netting, and not a replacement for everything else. These oils do not persist, so they call for closely spaced passes and good coverage of the leaf undersides.
How often should a sprayer be checked?
At every nozzle change and at least once a month in full season. FAO requires that variation in flow rate between nozzles stay within 10 percent either way at the maximum recommended pressure, which is verified in one minute per nozzle, with a stopwatch and a graduated container in hand.
Can okra be treated the day before picking?
Only the pre harvest interval stated on the product label answers that question, and it has to be respected without exception. On a crop picked every two to three days, that interval rules out part of the available products from the start, which makes it the first criterion of choice.
Sources
- CIRAD, DURAGOMBO project: sustainable management of a new jassid species responsible for emerging okra virosis
- Givord L. and Den Boer L., 1980, Insect transmission of okra mosaic virus in the Ivory Coast, Annals of Applied Biology, IRD documentary collection
- Pitan O. O. R. and Ekoja E. E., 2011, Yield response of okra to leaf damage by the flea beetle Podagrica uniforma, Crop Protection 30(10), Federal University of Agriculture Abeokuta
- FAO, 1998, Agricultural Pesticide Sprayers Volume 1: FAO Guidelines on Equipment Quality Control and Use
