Common sukuma wiki pests (kales) and how to control them

Kales and other leafy vegetables are quite the hardy group of crops. However, sukuma wiki pests are a big problem because they eat leaves that are hard to recover from. Pests that affect leafy vegetables usually do not have such devastating overnight effects as you may have seen or heard in horticulture farming.

The common sukuma wiki pests are diamondback moths, aphids, and cabbage sawflies. These pests make it harder for the plants to grow bigger healthy leaves. In cases like the moth, they eat the entire leaf. Diseases include powdery mildew and ring spot which I talk about here. they are quite easy to control and usually involve incorporating hygienic practices into your farm routine. Occasionally spraying for fungal diseases and pests can be an added advantage.

Diamondback Moth (DBM)

The diamondback moth is easy to identify and is most dangerous at the larval stage. When they feed, they leave holes on the leaf surface. This is the easiest to see.

The larvae may eat an entire leaf if there are many of them on the leaf. You will find a leaf with only the veins left which I have seen once and hope to never see again.

Diamondback moth larvae infestations are normally serious when the climate gets drier. This weather favors their growth and reproduction causing their populations to multiply very quickly.

Symptoms of a diamondback moth infestation

You can find the larvae stage above or below the leaf surface when scouting.

Larvae are pale yellowish-green to green caterpillars covered with fine, scattered, erect hairs
When disturbed, the larvae will wriggle backward violently and may drop from the plant, suspended by a silken thread

Controlling Diamondback Moth

Biocontrol

Use of the bacteria Bacillus thuringiensis (Bt) based bioinsecticides, such as Delfin 6.4 W.G®, Lambda Cyhalothrin 17.5 g/L (DUDUTHRIN 1.75 EC ®) or Lufenuron (MATCH 50 EC®) works without harming the environment with chemicals. The bacteria infect the gut of the larvae causing their death after the hatch. You spray the mixture on the leaves and the larvae will get infected when they feed.
Diadegma spp. is a parasitic wasp that eats the diamondback moth. Introducing them to the farm can help reduce the population of the pest.

Cultural practices for control

The most common and first line of cultural control is to remove infected parts from the farm and burn them somewhere else.

When it comes to actual farm practice, intercropping with tomato or Indian Mustard reduces the destruction of Kale.

In addition to intercropping, you can alternate your crops from kales to some other crop like onions that discourages the moth. As a result, the next time you want to plant kales, you will not have a huge population of larvae waiting for you.

If that didn’t work, consider a chemical approach.

Chemical control of Diamondback moth

For chemical intervention, you can use an insecticide with emamectin benzoate as the active ingredient at a rate of 10ml in 20l of water.

In Kenya, you can get ‘Escort 19EC’ from Greenlife chemicals which contains emamectin benzoate at 15g per liter.

When dealing with the diamondback moth in cabbages and sukuma wiki (kales), one hectare requires 1000L liters of the mixture. That will be 400ml in 1000l and 0.4ml in one liter of water.

You can use that to calculate how much insecticide you will need for your plants.

Precautions for applying chemical control

When using chemicals on your plants, you should strictly adhere to the preharvest instructions and intervals which are written on the product labels.

For the diamondback moth intervention, such as Escort, you are recommended to spray at intervals of 7 days between each spray. The wait time before harvesting is 10 days from the last spray to give the chemicals time to degrade and leave the plants safe for consumption.

You might also like: 9 common tomato diseases to watch out for this season

Cabbage sawfly

The cabbage sawfly lays its eggs on cabbage and kale leaves. The eggs hatch into larvae or caterpillars that feed on the leaves of the crop leaving holes in the leaves. Cabbage sawfly is one of many key sukuma wiki pests which can lead to significant crop losses if not controlled.

Symptoms of a cabbage sawfly attack

You will see grayish-green larvae with a black head and more than six pairs of legs.

Windows on leaves from feeding by larvae
They feed on the blade of the leaves often leaving only the main veins and midrib

Control methods for the cabbage sawfly

Cultural control

Cultural control of the cabbage sawfly requires integrated pest management techniques. One way is to destroy the infected plant parts especially those in the same family as sukuma wiki (kales). This family consists of crops like cabbages, spinach, lettuce, and swiss chard among others.

You can also plant volunteers by repelling plants that are not hosts for the cabbage sawfly. This will help reduce the population because sukuma wiki pests will be starved and die.

Chemical control of cabbage sawfly

The same active ingredient called emamectin benzoate is used to kill the larvae, as is used on the diamondback moth above because it is killed the same way.

Aphids

Aphids are pale green and are usually covered with a light dust of mealy powder. There are some aphids that are red, brown, black, or blue.

Aphids cause damage to plants through their feeding. They suck plant sap from the central part of the plant and near the base of the leaves. As a result, the leaves curl and shrink in size which might result in leave distortion.

Symptoms of aphid attack on kales (sukuma wiki)

Powdery substance on the leaf

Because they grow rapidly, aphids shed their exoskeleton which is usually white. The exoskeletons are deposited under the leaf and form a powdery substance that will drop to the ground when you pass your fingers on the bottom of the affected leaf.

Leaf curls

During the early stages, you might not notice any symptoms until the advanced stages when some leaf curling may be detected.

Honeydew

When the aphids feed, they secrete honeydew as a waste product. Honeydew is a sticky-sugary substance that attracts ants and provides food for fungus to grow on the leaf. I should mention that honeydew has no direct effect on the health of the vegetable plant.

You can easily wash off aphids from your plants with soapy water.

Virus vectors

Aphids also play the role of a virus vector which means that they carry around plant viruses in their body. When they pierce the stem, the viruses get into the plant where they cause disease.

Control for aphids

Field hygiene can work through the removal and destruction of crop residue in conjunction with close monitoring of the crops.

Weeding to reduce habitats that can act as alternative hosts is recommended. Clear the space between the crops regularly to prevent the buildup of an aphid population.
Use of insecticides with active ingredients like deltamethrin and lambdacyhalothrin. The use of pesticides should be a last resort and instructions printed on the label should be strictly followed.
In conclusion, when it comes to aphids, quick intervention is advised because waiting for the problem to go away on its own will not work.

You Might also like to read: How To Get Rid Of Aphids On Tomatoes

Cutworms

Cutworms are grayish-black larvae that curl up to form a c-shape when disturbed. These sukuma wiki pests like to hide under the soil during the day to avoid heat and other predators.

The name comes from the damage they cause when they feed on the stems of plants which get cut as a result. They usually feed on the stem because it is closer to the ground where they hide.

The best time for scouting cutworms is early in the morning before the sun comes out and late in the afternoon to evening when it’s not too hot to feed. They cut the stems from young vegetables and drag them to their holes where they can feed on them during the day.

They are notorious for feeding on crops such as tomatoes, cabbages, beans, and kale beans soon after transplanting.

In the morning, you can pass your hand in the soil and overturn the soil particles to see if any might show themselves. They will curl up to form a ‘C’ at any sign of danger.

Symptoms of cutworm attacks

Cutworms usually do not hide too far from where they feed and come out in the evenings. You will know you have a cutworm problem when you see cut stems on the ground or on the soil in pots where you planted them.

In some cases, you will see some young seedling leaves drooped because the feeding of the cutworms did not cut the entire stem so a portion is left keeping the plant upright. Read my article about sukuma wiki seedling care.

Young plants are at a higher risk of getting killed by cutworms because their stems are still soft and thin. They are therefore severely affected by the small bites from the worm.

Controlling cutworms in the garden…

Is quite simple.

You can begin by removing any plant remains from the garden to cut down on egg-laying sites. This can be followed by some manual weeding to expose the lower soil to the sun which will kill the cutworms.
When preparing your soil for growing kales, you should plow early and leave the soil exposed to the sun.

If you want to add manure, the best option will be composting because green manure will provide sites for the moth to lay eggs.
Any pesticides used should follow the instructions printed on the label based on the crop and insect target. You can look for one with cypermethrin as the active ingredient at your local agro vet supplier.

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Common sukuma wiki pests (kales) and how to control them

Diamondback Moth (DBM)