The Geometric Mean. In this video, I show how to find the geometric mean of two numbers and show what that number means in relation to the numbers that you started with.1  Education. 2  Standard YouTube License.he Geometric Mean. In this video, I show how to find the geometric mean of two numbers and show what that number means in relation to the numbers that you started with. 1  Education.
Symptoms often appear first on older leaves. If weather conditions are moist and temperatures are low, masses of gray to violet fungal spores envelop infected leaves, which become girdled, collapse, and die. The dead leaf tissue is rapidly colonized by purple blotch, which is dark in color and obscures downy mildew. Downy mildew seldom kills onion plants, but bulb growth may be reduced. Bulb tissue, especially the neck, may become spongy and the bulb may lack keeping quality.
Remove and destroy spinach plants affected by downy mildew. Apply a fungicide to plants not yet showing symptoms of disease. Spray spinach with a fungicide containing an active ingredient such as mefenoxam for effective control of mildew. Examine plants for white rust disease, a common problem on spinach.Search first for the presence of tiny yellow specks on leaf surfaces. Look for chalk-white, cheesy, raised spore masses (sori) which occur mostly on the underleaf surfaces, according to the University of Illinois Extension.. Search spinach leaves for symptoms of downy mildew disease. Look for yellow spots on leaves that grow and fade to a light brown hue. Search the undersides of leaves for a fuzzy growth in a purple hue.