Potato diseases & common pests: detect, prevent and control

Potato diseases - and there are a multitude of pests. However, problems can very often be avoided with a varied crop rotation.

The potato (Solanum tumberosum) can be attacked by many different pathogens. In particular, the reproduction of the nutritious tubers on the same area favors the infestation and the spread of the pathogens via the soil or the tubers remaining in the bed. Before and after Planting potatoes Therefore, a cultivation break of 4 - 5 years should always be observed. In this article we provide an overview of the most important potato diseases and pests, as well as prevention and control strategies.

Overview of potato diseases 

Below you will find the most important potato diseases, their pathogens, symptoms and measures to combat them. We only give a brief overview of diseases that occur rarely, as they are of little importance in hobby cultivation.

Potato bacterial diseases

Bacteria mainly cause weeping, rotting spots on potatoes. This often makes the tubers completely inedible. The main vector for bacterial diseases is an infected plant tuber, so the best avoidance strategy is to buy certified, healthy plant material.

• Wet stem and tuber rot(Pectobacterium carotovorum and Dickeya): The bacterial wilt is also known as black-leggedness. From mid-June, infested potato plants wither and roll up their leaves. The bacterium blocks the water channels and leads to a wet rot on the blackened stalk, which means that the shoots can be easily pulled out of the earth. The inside of the stem is mushy and slimy. Tubers damaged during harvest develop wet rot in the warehouse. They become mushy and soft and are separated from the healthy tissue by a black line. Direct control is not possible. As a preventive measure, only use designated seed potatoes, do not plant the tubers too early or too late and remove the infected plants and their tubers. Let it dry off after the gentle harvest and check it regularly in the warehouse.

Other bacteriosis in potatoes are:

• Ring rot (Clavibacter michiganensis subsp. sepedonicus): Nonspecific symptoms such as wilting, chlorosis or the curling of leaves develop on the potato plant. The bacterial ring rot can only be clearly identified by looking at the cut tubers. A brown discoloration of the conduction pathways can be seen here a few millimeters below the shell. Often such tubers are attacked by other pathogens and rot. Bulge rot is a quarantine disease that must be reported!
• Mucus disease (Ralstonia solanacearum): Here, too, unspecific symptoms of the disease appear on the plant, whereas in the tuber a whitish bacterial slime emerges from also browned pathways. The mucus disease is a quarantine disease with mandatory notification!

Fungal diseases on potatoes

Fungi cause many different diseases in potatoes. The best way to combat it is to prevent it. In the case of some diseases, however, crop protection measures no longer help when the symptoms appear.

Prevent fungal diseases on potatoes:

• Choose less susceptible varieties
• Remove stubborn potatoes from the previous year at an early stage
• Pre-germination of the tubers for an earlier harvest before infestation
• Choose wide row and plant spacing for good drying
• Apply a balanced fertilization
• Harvest only ripened tubers that are firm on the skin
• Against soil-borne fungi: wide crop rotation; Use of healthy seedlings
• In the event of an acute infestation: Dispose of the infected plant tissue in the household waste; Approved sprays

The following fungal diseases are important in hobby cultivation:

• Colletotrichum wilt(Colletotrichum coccodes): Soil-borne mushroom, which causes entire shoots to die off, especially in hot and dry years. The leaves wither, soon turn brown and dry up on the often still green stem. At the base of the stem there are small black dots, the roots are brittle and rotten. The tubers can also be affected.
• Potato scab(Streptomyces scabies): The ray fungus occurs naturally in the soil and infects the potato tuber from June to July, preferably on dry, calcareous soils. When infected, the tubers show a corky-pock-like surface with partially reticulated cracks, but no spore formation. The potato scab is only visually significant, as it does not affect the taste or the yield. One can easily prevent potato scab by planting resistant varieties. In addition, the soil life can be promoted as competition for the pests. Liming the soil before laying the potatoes should be avoided.

• Late blight and tuber blight(Phytophthora infestans): The disease, also known as potato brown rot, is transmitted by an egg fungus (oomycete) that overwinters in infected tubers in the field. The first symptoms appear from the end of June, depending on the weather. On the potato leaves yellowish, soon dark colored spots form, on the underside of the leaf there is a gray-white fungal lawn. Over time, the entire plant is attacked and dies. The tubers show sunken, gray-blue, hard spots; under the skin the tissue is hard and discolored dark brown.

• Powder scab(Spongospora subterranea): Fungal disease especially in damp and cool weather and at higher altitudes. Dark, wart-like lumps and bumps appear on the tubers, which later tear open and release black spores. In the home garden, the powder scab spreads over potato peels on the compost or any tubers left in the ground from the previous year. Infested tubers and their remains should therefore be disposed of with household waste. A wide crop rotation, less susceptible varieties and healthy seedlings are the best control methods.
• Dry rot or White rot (Fusarium): Storage disease, with white fungal mycelium forming on the tubers and deep, dry rot spots underneath. The pathogens penetrate the potatoes through injuries during harvest or from sticking earth residues.

• Root killer disease Beet rot(Rhizoctonia solani): Potato disease that causes dark, superficial spots on the tubers and sunken, brown spots on the stem. The plants grow poorly and develop only a few shoots. At the base of the stem, a whitish fungal coating ("white hatred") can form, sometimes the leaves of the shoot tip curl up ("top roll"). The pathogen is native to the soil, only a change of area and a wide crop rotation prevent renewed infestation.

Other fungal diseases of potatoes are:

• Spot disease (Alternaria solani): Fungal disease in particular Late potatoes. From June onwards, sharply demarcated, round, brown spots appear on the older leaves that can break out. On the tuber, there are demarcated, sunken, brownish areas with firm tissue.
• Gray mold (Botrytis cinerea): This fungal disease causes grayish spots on dead tissue of the leaves, especially after a dry period in damp and cool weather. It does not need to be treated with potatoes as it disappears on its own in drier weather.
• Potato crab (Synchytrium endobioticum): Quarantine disease with mandatory reporting, which is triggered by a soil-borne fungus. There are knobbly, cauliflower-like growths on the tubers and partly on the stems, which later rot and disintegrate.
• Stem rot (Sclerotinia sclerotiorum): Disease that is more widespread in northern Germany, in which the mycelium of the fungus covers parts of the stem. In addition, there are dark, round protrusions, the sclerotia. The infected stalks break easily in wind or thunderstorms.

Viral diseases

Viruses on potatoes are mainly caused by sucking pests, above all aphids (Aphidoideae) and some nematodes which are harmful to plants (Trichodorus and Paratrichodorus) transfer. They cause stunted growth, often also leaf symptoms and yield losses between 10 - 80%. Resistant varieties, certified seedlings and a wide crop rotation are helpful measures before planting. Also about mechanical injuries, when piling up, chopping, etc. viruses can be transmitted. Infested plants should be carefully removed, but their tubers can be consumed without hesitation.

• Leaf roll disease(Potato Leaf Roll Virus PLRV): Viral disease with typically rolled up leaflets and yellow coloration. The plants are much smaller and have a steep leaf position, the foliage is rigid and rustling. Yield losses of up to 80% are possible.
• Iron stain(Tobacco rattle virus TRV): The potato disease iron stain is transmitted by free-living nematodes that have previously been infected with infected wild herbs Chickweed (Stellaria media) or shepherd's purse (Capsella bursa–pastoris) have sucked. The often compressed shoots rarely show symptoms on the leaves and the yield hardly suffers. However, black-gray spots and sunken rings are visible in cut tubers.
• Tobacco rib tan(Potato Y Virus): The world's most important potato virus causes dark brown, necrotic speckles on the underside of the leaf, as well as a slight mosaic chlorosis. The leaves can die off completely, the tubers are sometimes attacked and show dark spots, which, however, do not penetrate particularly deeply compared to the iron spots.

Soil-borne pathogens can make potato cultivation in an area unprofitable for years. A real alternative is cultivation in pots, because most pests do not get access here. Our Plantura organic tomato and vegetable soil is also suitable for potato cultivation. It has a high compost content, is also pre-fertilized and provides important nutrients for the first few weeks after planting.

Common potato pests

Various pests cause feeding marks on potatoes, sometimes only on the plant, but often also on the tasty tubers. We present the most common potato pests and give tips on how to prevent and control them.

• Aphids (Aphidoideae): The small, sucking insects can deform the leaves of potatoes. In the wild, however, the small insects quickly become infected with beneficial organisms such as Ladybug (Coccinellidae), Lacewing larva (Chrysoperla carnea) and Co. decimated and thus kept in check.
• Wireworms (Agriotes): The deep yellow, a few millimeters long beetle larvae eat deep tunnels in the nutritious tubers. An infestation of wireworms on potatoes can be prevented with tillage, an early harvest (early Variety and pre-germination) as well as a balanced crop rotation with a break in cultivation of 4 - 5 years strong to reduce.

• Groundworms (Agrotis): The caterpillars of moths prefer to live in light, warm soils and can cause severe damage to the potato tubers. The gray-brown, up to 5 cm long, shiny caterpillars curl up when touched. Moths also lay eggs on weeds, so chopping the rows of potatoes is an important preventive measure. An acute infestation by earthworms on potatoes can be with nematodes of the genus Steinernema capsicae be combated, which are simply stirred in water and distributed with the watering can. For example ours Plantura SC nematodes you can use for this.
• Colorado potato beetle (Leptinotarsa ​​decemlineata): The beetle overwinters in the ground and lays its eggs on the underside of the leaf shortly after the first potato shoots appear. The Colorado potato beetle larvae eat whole potato plants within two to three weeks. The oil of the Neem tree (Azadirachta indica), for example in the form of ours Plantura pest free neem, can be injected against the Colorado beetle larvae in the young larval stages L1 - L3. A daily check of the plants is therefore particularly important in order not to miss the sensitive stages. Colorado beetles and their larvae can be harvested if they are already too large to be treated with neem.

• Cyst-forming potato nematodes(Globodera): If potatoes are planted too few years apart, they can harmful nematodes settle and repeatedly attack the roots of the plants. A strong infestation is indicated by growth disorders and yellowing of the leaves. Small, brownish cysts appear on the roots that can persist in the soil for up to 15 years. The potato plant produces up to 50% less yield. A wide crop rotation without additional host plants and resistant varieties prevent nematode infestation.
• Voles(Arvicolinae): Different types of Arvicolinae, especially the field mouse (Microtus arvalis) gnaw at the potato tubers and can cause great damage. Above ground, individual shoots can wither and die because their roots have been cut. In our special article you can read everything about rodents and how they are Drive voles away can.

Many potato diseases can be prevented or limited by good crop rotation and mixed culture instead of monoculture. We give tips on what to do with the Mixed culture of potatoes should pay attention to and which neighboring plants are suitable.