Answer: Bamboos love hot and humid weather so the weather is most likely not to blame. It may be that they need to be watered more; bamboos are essentially grasses and do best in soil that is evenly moist (not sopping wet, not bone dry) and new plants will be especially sensitive to dry soil. To know when to water, use your finger to dig into the soil, if it is still damp do not water yet. When you do water, water slowly and very thoroughly so it soaks down to the deepest roots. After watering, wait a few hours and then dig down to see how far the water soaked in, sometimes it can be surprising. Using an organic mulch in a flat layer over the root area will help keep the soil evenly moist. It should be two to three inches deep, do not allow it to touch the canes.
Another possibility is that aphids are attacking the new growth tips. These are small soft bodied sucking insects, sometimes there will also be a sooty black mold around them. This can be treated with a commercially formulated insecticidal soap mixed and applied per the label directions. Be sure to contact all surfaces with the spray and repeat as indicatedon the label.
I hope this helps.
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