Mealybugs on Rex Begonia
Rex Begonia (Begonia rex)
Symptoms
- white cottony clusters at leaf stalks
- sticky honeydew residue on the patterned leaf surface
- black sooty mold developing on that residue
- new growth emerging stunted or misshapen
Causes
Mealybug infestation
This pest's soft body under a white waxy coating settles wherever foliage grows dense enough to hide it — on Rex Begonia that means where each leaf stalk joins the rhizome and in the shingled overlap of leaves this species is prone to when grown well. The honeydew it leaves behind while extracting sap coats the patterned leaf surface below in a sticky film that black sooty mold can then colonize.
Introduction from an unquarantined new plant
A newly purchased plant is the usual entry point for this pest, and Rex Begonia's dense, layered growth habit gives an early infestation plenty of hidden spots to build up in before it's ever noticed.
Humid, enclosed growing conditions
The terrariums and humidity domes commonly used to grow this species can also create a stable, sheltered environment favorable to mealybugs establishing and multiplying once introduced, since they are protected from some of the environmental fluctuation that might otherwise limit population growth.
How to Fix It
- 1
Isolate the plant immediately, especially critical if it is in a shared terrarium or enclosed space with other plants, since mealybugs spread readily in that environment.
- 2
Dab, don't wipe: a cotton swab wetted with 70% isopropyl alcohol should touch each cluster individually rather than pass broadly across the leaf, since this species' thin foliage bruises more easily than a tougher-leaved houseplant would tolerate.
- 3
Follow with a light application of insecticidal soap, diluted appropriately, since this species' thin leaves can be more sensitive to strong treatments than tougher-leaved houseplants; test on one leaf first if unsure.
- 4
Repeat treatment every five to seven days for at least three to four rounds, since mealybug eggs are protected and hatch on a staggered schedule.
- 5
Check the rhizome and base of leaf stalks closely, since this is where mealybugs cluster most on this species and where a treatment round can easily miss individuals hidden in the dense growth.
- 6
Continue checking weekly for at least a month after visible signs are gone, since a missed cluster can restart the infestation.
Prevention
- Give any newly acquired plant a two-week quarantine and inspection period before it joins a shared humid growing space
- Check leaf stalk bases and the rhizome regularly for early signs
- Avoid overcrowding within terrariums or humidity domes, which makes early detection harder
- Wipe down leaves periodically, gently given their delicate texture, to check for pests while cleaning
- Treat any infestation completely and promptly rather than partially
Quick Summary
| Plant | Rex Begonia (Begonia rex) |
|---|---|
| Category | Pests |
| Likely causes | Mealybug infestation, Introduction from an unquarantined new plant, Humid, enclosed growing conditions |
| Fix steps | 6 steps — see above |