White Rust (fungus – Albugo occidentalis): White rust is the major disease of spinach in Texas. White, blister-like pustules form on the lower side of the leaf. In advanced stages, the white lesions form on the upper side of the leaf. Generally, the upper surface will only be chlorotic. Plants infected with the white rust fungus are weak and collapse quickly if environmental conditions are favorable for disease development. Initial outbreaks each season follow source event such as hard rains that deposit soil and oospores on the young plants. The fungus oversummers in soil as dormant thick-walled oospores and may spread within a field by windblown spores. Free moisture on the leaf surface must be present for spore germination and development. The optimum temperature for germination is 54oF. The disease develops most rapidly at 72oF or during periods of cool, humid nights and mild day temperatures. No variety is totally resistant to white rust but a few have very useful partial resistance, including Green Valley II, Ozarka II, Coho and Fall Green. A disease control program should combine the benefits of cultural practices, partial resistance, a systemic fungicide at planting (in Texas, Ridomil 5G) and protective fungicides sprays (beginning 40-50 days after planting). Cultural practices should include long rotations, planting on beds and furrow irrigation. The risk of developing tolerance to Ridomil fungicide is reduced if all of these disease control practices are used together.
Downy Mildew or Blue Mold (fungus – Peronospora effusa): The downy mildew fungus first causes yellowish areas on the upper side of the leaf. The underneath side of the leaf is marked by a gray to violet-gray fungal growth mat that bears sporangia. The entire leaf is killed on susceptible varieties under optimum environmental conditions. The fungus overwinters in living spinach plants and in the seed. The fungus spores require surface moisture for development. Optimum temperature is around 48oF for germination and 54oF to 60oF for development. This disease can be controlled by the use of varieties resistant to races 1, 2 and 3.
Anthracnose (fungus – Colletotrichum spinaciae): Anthracnose shows up as small, dark olive colored spots. As the spots enlarge, they become tan in color. As the lesions coalesce, they kill the entire leaf. During periods of favorable disease development, the foliage appears as if the crop will be lost. With a change in weather, the diseased foliage drops off and the healthy foliage goes on to produce a crop. The fungus overwinters in seed and in crop refuse. Fungicides used in a white rust control will also control anthracnose.
Leaf Spots (fungi – Cercospora beticola, Heterosporium variable): These are minor diseases of spinach which may cause damage in some years. Cercospora leaf spots are white and, usually, small in size. Extended periods of precipitation and high humidity may allow spots to become large and even coalesce. Protective type fungicides offer some control. Ridomil does not control Cercospora.
Heterosporium leaf spots are larger and have a greenish black fungal growth on both sides of the leaf as the disease develops. Control measures are not generally recommended.
Fusarium Decline (fungus – Fusarium oxysporum f. sp. spinaciae): Plants are subject to infection at any stage of development. Infected plants turn yellow and wilt. The lower, older foliage is affected first. Plants which are infected are either stunted or killed. Infected plants lose their feeder roots and the vascular system of the taproot is darkened. The fungus is seed borne and can live in the soil indefinitely. Fortunately, white rust resistant varieties also have Fusarium resistance.
Blight (virus): Cucumber mosaic virus attacks spinach causing plants to become faintly chlorotic. Chlorosis increases until the entire plant becomes yellow. Crown leaves are narrow, wrinkled and develop an inward rolling of the margins. Plants are stunted. Death may occur in some severely infected plants. The virus is aphid transmitted. Most commercial varieties are resistant [see table].
Reaction of Spinach Varieties to White Rust and Blue Mold
|Variety||White Rust Reaction*||Blue Mold Race 3 Reaction*||Plant Type|
|Green Valley II||MR||S||semi- to full-savoy|
|Ozarka II||MR||S||semi- to full-savoy|
|Chinook II||S||R||semi- to full-savoy|
R = Resistant MR = Moderately Resistant MS = Moderately Susceptible S = Susceptible
Seedling Disease (fungi – Fusarium spp., Rhizoctonia spp., Pythium spp., Others): Preemergence and postemergence damping off can seriously reduce stands. Rotate with corn, plant after soils have cooled down in the late summer or fall, use a fungicide seed treatment and buy fresh, high quality seed.
Tobacco Ringspot (virus): First symptoms are small, indistinct, chlorotic spots which appear on the young foliage. These may coalesce to form large yellow areas. In advanced stages, leaves take on a copper bronze chlorosis. There is no malformation of the foliage. Affected plants rarely die but remain yellow and stunted. No control measures are known.
Beet Curly-Top (virus): Infected plants are marked by a rosette of tightly curled, small leaves in the center of the plant. As the disease develops, the growing point is killed and the plant dies. The virus is transmitted by beet leafhoppers.
Aster Yellows (mycoplasma-like organism): See Page on Aster Yellows.
False Root Knot (nematode – Naccobbus crucifera): Plants are stunted; in cases of severe early infection, death will occur. The root system of infected plants is characterized by large galls covered with numerous rootlets. This nematode is particularly damaging on spinach plants in the fall. This nematode does little damage in hot soils.
Root Knot (nematode – Meloidogyne sp.): See Page on Root Knot.
Stress (abiotic – heat and/or saturated soils): The quality of spinach can decrease quickly following stress. Yellowing occurs within a few days after high temperatures and/or flooding. Choose planting dates carefully for your areas and provide good drainage.