Can sodium selenate kill plants as well as insects?

Yes, a strong solution can harm or even kill plants. What is known as the Standard Solution (1 gram to 1 gallon of water) is generally considered dangerous for such tender plants as African violets and is not recommended for them unless the plants have got to a ” kill-or-cure” condition. The Extra Dilute Solution (1/4, gram to 1 gallon of water) is much safer and effective if four doses are given at weekly intervals.