Aphids are the biggest problem on nasturtiums. The black bean aphid is the most serious pest but other aphids also attack the plant. Severe infestations turn the leaves pale yellowish green and the plant begins to wilt. Aphids can be controlled with sprays of Sevin, or rotenone.
Cabbage looper feeds on the leaves and may strip the plant of foliage. No chemical control is listed.
Thrips cause circular or irregular white spots, up to an eighth inch in diameter on the upper leaf surface. Larger and more irregular spots are on the undersides of the leaves. These will be marked by the dark, greenish black excreta of the thrips. Sprays of rotenone or Sevin will control these pests.
Mites cause leaves to lose their green coloration. If the infestation is heavy fine webbing may be seen.