Castor shoot & capsule borer
One caterpillar, two stages of damage — first it kills the growing tip, then it moves into the capsules and eats the seed from inside a silk-webbed cluster.
- Pest type
- Caterpillar (shoot & capsule borer)
- Attacks
- Growing shoot tip, then capsules
- Worst in
- Humid weather, dense canopy
- Main risk
- Dead shoot tip; hollowed, webbed capsules
Overview
Castor shoot and capsule borer is a caterpillar that attacks the plant in two phases. Early on, it bores into the tender growing shoot near the tip, and that part of the plant wilts and dies, forcing the plant to push out side branches instead of growing straight up.
Later, once capsules (the seed pods) start forming, the same pest bores into them, webbing several capsules together with silk and dark droppings (frass) and feeding on the developing seed inside. This second phase is the more costly one, since it damages the part of the plant that is actually harvested, and it often overlaps with damage from castor semilooper in bad outbreak years.
How to identify it
- On young plants, the growing shoot tip wilts and dries up while the rest of the plant looks healthy — a sign the caterpillar has bored inside and killed it.
- On older plants, look for capsules bound together in a cluster by silk threads, with dark, crumbly droppings (frass) caught in the webbing.
- Breaking open a webbed capsule cluster or a wilted shoot usually reveals the caterpillar itself, or at least a clean tunnel where it has been feeding.
The damage it does
- Early shoot boring kills the main growing tip, so the plant loses that spike and has to regrow side branches, delaying and reducing that part of the harvest.
- Later capsule boring eats the seed directly, which is the part of the plant that is actually sold — this is a straight loss of yield, not just a growth setback.
- Webbed, damp capsule clusters can rot in humid weather, adding further loss on top of what the caterpillar itself eats.
- In bad outbreak years this pest often overlaps with castor semilooper, and combined losses from the two pests together can be severe.
When to act
- Check the growing tips of young plants regularly — a wilted tip on an otherwise healthy plant is the first warning sign, and acting early limits how many shoots are lost.
- Once capsules start forming, watch for webbed clusters, since capsule damage is harder to reverse and costs more in yield than early shoot damage.
- Remove and destroy wilted shoots and webbed capsule clusters as soon as you find them, rather than waiting to see how far the damage spreads.
Organic & cultural control
- Clip off and destroy wilted shoot tips and webbed capsule clusters promptly — this physically removes the caterpillars before they can spread or complete their life cycle.
- Set up light traps to catch the adult moths at night, which helps cut down the next generation of caterpillars before they lay eggs.
- Avoid unnecessary early-season sprays so natural predators and parasites can keep caterpillar numbers in check on their own.
- Sow at the recommended time for your area so flowering and capsule formation do not stretch out over an unusually long window, which only gives the pest more opportunities to attack.
Chemical control
- Spray a recommended insecticide such as quinalphos or chlorantraniliprole as soon as shoot wilting or capsule webbing is seen, since the caterpillar is protected once it is inside the shoot or capsule cluster.
- A second, well-timed spray at capsule formation often helps, since this is the stage where the pest does its most costly damage.
- Confirm the current recommended product and dose for castor with your local KVK.
Crops most at risk
Where this problem is called out in our crop guides — open a crop for the full package of practices.
Frequently asked questions
The growing tip of my young castor plant has wilted and died. What caused this?
This is a common sign of castor shoot borer — a caterpillar that tunnels into the tender growing tip and kills it from inside. The plant usually survives and pushes out side branches, but that spike’s growth and yield are lost. Clip off and destroy the wilted tip to remove the caterpillar.
Some of my castor capsules are stuck together with a web and have dark specks on them. Is this a disease?
No — this is capsule borer damage. The caterpillar spins silk to bind several capsules together and feeds on the seed inside, leaving droppings (frass) caught in the web. Remove and destroy the webbed cluster to stop it from spreading further.
Is this the same pest as castor semilooper?
No, they are different pests, even though both can attack a castor field in the same season and sometimes overlap in bad years. Semilooper is a leaf-eating caterpillar that strips foliage, while shoot & capsule borer specifically tunnels into the shoot tip and capsules. Both need to be checked for separately.
Symptoms and control measures follow ICAR, KVK and state agricultural-university package-of-practices; any named chemical is a registered use. Always read the product label and confirm the dose for your crop and zone. editorial policy.