Bacterial Leaf Spot disease has developed on certain varieties of Verbena. DonÃ¢â‚¬â„¢t confuse this disease with powdery mildew or with fungal leaf spot diseases .
Thielaviopsis basicola has been seen on a number of crops this year including Calabrachoa, pansy, vinca (Catharanthus) and snapdragon. Plants in a tray will often be uneven in height and stunted plants tend to be lighter in color. Roots may be shriveled, brown to black and under-developed. The fungus thrives in cool weather and pH above 5.6. As temperatures warm up injury to the root system may slow down and plants may or may not recover. However, infected plants should be discarded.
Edema (oedema) is a physiological problem occurring primarily on ivy geraniums. It also occurs on sweet potato vine, begonias, and cole crop vegetables like cabbage and cauliflower. Edema is not a disease or virus and it is not transmittable from one plant to another.
Edge burn is beginning to appear on geraniums and marigolds where growth medium pH is low (below 6.0). As pH decreases, iron and manganese become more soluble. Some plants are very efficient at taking up iron (Fe)/ manganese (Mn) in the tissue causing toxicity symptoms. See photos, "Iron Toxicity" Crops such as zonal and seed geraniums, marigolds, lisianthus and all types of impatiens are susceptible. This disorder is sometimes called "bronze speckle" due to the appearance of numerous small brown spots on the leaves.
A common problem often diagnosed this time of year with spring crops is excess soluble salts. Generally, this is a result of too much fertilizer in relation to the plants needs. Inadequate watering or leaching, or poor drainage can also result in high soluble salts.
Sometimes high soluble salts levels occur when root function is impaired by disease or physical damage. Always check the condition of the root system when trying to diagnosis a problem.