Comprehensive disease management is vital to successful potato production. Unfortunately for growers, potato plants are vulnerable to numerous bacteria, fungi, viruses and parasites that consistently cause yield losses. Here, we’ll review some of the most common diseases seen in U.S. potato crops, focusing on foliar symptoms.
Early blight
Caused by Alternaria solani, a disease-causing fungus, early blight occurs mainly on plant leaves, and can be found in all potato-growing areas. Early blight first appears as small, dark brown to black spots on older leaflets on the lower parts of plants. The spots expand, forming concentric rings that are characteristic of the disease.
Early blight symptoms can be easily confused with those produced by brown leaf spot. However, early blight lesions tend to be larger and have alternating rings of raised and depressed tissues that form a target pattern. Unlike brown leaf spot lesions, those of early blight are limited by leaf veins. Potato plants infected with A. solani may also have brown or black elongated lesions on petioles (leafstalks) and stems.
Late blight
Late blight, caused by the water mold Phytophthora infestans, can rapidly destroy a potato crop. All parts of the potato plant are susceptible to late blight.
Early symptoms of late blight are small, light to dark green, circular to irregular-shaped, water-soaked spots. The lower leaves are usually the first to show symptoms. Left untreated, late blight lesions grow into circular patches of dying leaf tissue in just a few days. Stem lesions are typically dark brown to black with collapsed, water-soaked centers.
Under cool, damp conditions, a white downy mildew can be seen on affected leaves.
Alternaria brown spot
Alternaria brown spot, also known as brown leaf spot, is a common disease that can be found in many potato growing areas. Caused by the fungus Alternaria alternata, brown leaf spot is closely related to early blight and the similarity of their foliar lesions can be a source of confusion — and frustration.
Initially, leaf lesions associated with A. alternata infections are dark, round and necrotic, and range in size from pinpoint to about one-eighth inch in diameter. As the infection progresses, small lesions may merge together, forming sizable lesions that are unrestricted by large leaf veins. Entire leaves may be affected, developing an abnormal yellow color (chlorosis) and drying up, yet remaining attached to the plant stem. Lesions can also crumble and disintegrate, causing leaf edges to curl.
White mold
White mold, also known as Sclerotinia stem rot after its causative fungus Sclerotinia sclerotiorum, is prevalent in some potato-growing regions such as Idaho and the Pacific Northwest. The fungus can infect more than 400 plant species and is now becoming a greater issue for potato growers in areas where it wasn’t previously.
Symptoms of white mold first appear as water-soaked lesions in the intersections between the potato plant’s stem and branches or on branches or stems in contact with soil. These lesions are quickly covered by a cottony white growth that can spread to nearby stems and leaves if moisture is present for several hours. As white mold lesions grow, they can girdle stems causing foliage to wilt.
Once field conditions dry out, the lesions dry as well and change in color (beige, tan, white) and texture. As the infected plant tissue decomposes, irregularly shaped, hard resting structures called sclerotia are formed. Sclerotia eventually fall to the ground as infected stems dry out and the potato plant dies.
The right fungicide package provides protection options
Potato growers need disease management solutions that not only provide options but offer a return on their investment. UPL offers a number of fungicide solutions to help growers keep diseases in check, including ELIXIR® Fungicide, MANZATE® PRO-STICK™ Fungicide, ORANIL® Fungicide, PENNCOZEB® 75DF Fungicide and SUPER TIN® Fungicide.
- Created specifically for potato growers, ELIXIR is a dual-mode, multi-site protectant fungicide that effectively controls early and late blight.
- MANZATE PRO-STICK is the preferred option for early and late blight control. Its multi-site action reduces the risk of disease resistance, and an advanced formulation provides better coverage and adherence to leaves.
- When fighting early and late blight in potatoes, ORANIL 6L works well in rotation with MANZATE PRO-STICK or PENNCOZEB 75DF. Chlorotalonil, the active ingredient in ORANIL, has no known cross-resistance to any other fungicide active.
- PENNCOZEB 75DF, the foundation of many growers’ early and late blight control programs, also offers multi-site activity against disease pathogens.
- A versatile stand-alone product or tank-mix partner, SUPER TIN is yet another option for early and late blight control. Plus, it’s labeled for Colorado potato beetle suppression.
You can read more about the other products in UPL’s potato portfolio here. To learn more about how to incorporate UPL fungicides into your integrated disease management program, contact your local UPL sales representative.
