Pests Diseases on spinach tend to be those that develop under cool, moist conditions. One symptom characteristic of downy mildew is light-yellow areas on the leaves. Infected young plants may be pale green, stunted, with leaves heavily savoyed. During periods of high relative humidity or rainfall, sporulation will occur, appearing as a white mass, eventually turning purple. Most modern varieties are resistant to downy mildew.
White rust is a serious problem in spinach production in the southern Great Plains and Texas.
White, blister-like pustules appear, usually only on the lower side of the leaf. Surrounding tissue browns and dies. A few fungicides are available for use in spinach produced on a commercial scale. There are no fungicides registered for use by home gardeners on spinach. Insect pests include the green peach aphid, seed corn maggot, cabbage looper, cucumber beetles and the spinach leaf miner.