Plant Health Problems
Diseases caused by Bacteria:
Wilt, Pseudomonas solanacearum.
Infected plants yellow, wilt, and eventually die. Stems may develop black streaks and when cut, may ooze a bacterial slime from the cut ends. Roots often appear black and infected plants may die before flowering. The bacteria persist in plant debris in the soil and can infect nasturtiums through the roots.
Control strategies are aimed at prevention. However, removing and roguing of diseased plants is critical. It is also important to avoid overhead irrigation since these bacteria are easily spread in splashing water. Any equipment or tools that come in contact with diseased plants should be disinfested with 10% household bleach, 70% alcohol, or one of the commercially available compounds. Crop rotation is also effective since planting in clean soil gives best control. It is therefore helpful to avoid planting in areas used for other plants that are susceptible to the same disease, i.e., tomatoes, potatoes, eggplants, zinnias, dahlias, chrysanthemums, and marigolds.
Bacterial leaf spot, Pseudomonas sp.
Small brown to black spots appear on the leaves. These may have water-soaked margins.
This disease can be minimized by improving air circulation by thinning the plants and by avoiding overhead irrigation since these bacteria are easily spread in splashing water. Picking and destroying infected leaves and cleaning up all plant debris in the fall are also very helpful. Any equipment or tools that come in contact with diseased plants should be disinfested with 10% household bleach, 70% alcohol, or one of the commercially available compounds.
Bean aphid, Aphis fabae.
This aphid frequently infests nasturtium plants. Among the compounds registered for control of this pest in Connecticut are acephate or insecticidal soap, which can be sprayed on the insects. Imidacloprid, applied as a soil drench, will be taken up by the roots and provide season-long systemic control. Consult the label for dosage rates and safety precautions. Natural enemies, such as syrphid larvae, ladybeetles and lacewings can assist in keeping aphid populations in check.
Cabbage looper, Trichoplusia ni.
This caterpillar, which humps its back or loops when it crawls, feeds on leaves. It is light green and striped lengthwise with white and darker green. Its body is nearly smooth and is narrowest at the head. The adult is a grayish-brown moth with a small silvery spot resembling a figure 8, near the middle of each forewing. It flies at night when it deposits small round greenish-white eggs, singly, on the leaf surface. This species does not overwinter in Connecticut, but migrates up from the south in some years. Among the compounds registered for control of this pest in Connecticut are spinosad, Bacillus thuringiensis var. kurstaki (Bt), Bt var. aizawai, and carbaryl. A high rate of Bt may be needed and will be more effective when both the days and nights are warm. For either insecticide, consult the label for dosage rates and safety precautions.
Corn earworm, Helicoverpa zea.
The moths, with a wingspread of about 1.5", are tan with darker markings. They arrive in Connecticut each season from more southern areas after which they lay eggs singly on leaves. After hatching, the caterpillars feed, eventually reaching a length of up to 2". They vary greatly in color from brown, tan, green, or pink with light and dark longitudinal stripes. The head is golden brown and the body has small bumps and spines, giving it a rough texture. There can be two or three generations in a year, depending on when the adults arrive on winds from the south.
Spinosad and Bacillus thuringiensis var. kurstaki (Bt) are registered for control of this pest in Connecticut. Consult the label for dosage rates and safety precautions.
Serpentine leafminer, Liriomyza pusilla.
The larva of this fly makes a serpentine mine in the leaf of nasturtium. The turnip leafminer and the columbine leafminer (see Columbine) have been recorded as occasionally infesting nasturtium. Usually, no control is necessary. Among the compounds registered for control of this pest in Connecticut are acephate sprayed on the foliage or soil treatment with imidacloprid. Abamectin is an effective restricted use product. Consult the labels for dosage rates and safety precautions.
Western black flea beetle, Phyllotreta pusilla.
The small black beetles make small holes in the leaves, and jump readily when disturbed. Among the compounds registered for control of this pest in Connecticut are acephate or carbaryl used as foliar sprays. Consult the labels for dosage rates and safety precautions.