Potato diseases like potato scab and potato blight

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Potato diseases are also a problem for many hobby gardeners

Are you one of the gourmets who want to see even simple foods on your table in high quality? So grow their own potatoes in the garden, maybe the savory, nutty Cilena and as an ideal complement to the creamy and mild Bintje - the Potato of the Year 2012? These potato diseases could make life difficult for you as a hobby potato farmer:

Potato scab - a problem that can be solved for hobby farming

Potato scab is caused by a bacterial species, this one Streptomyces scabies There are in all growing areas, especially when growing on light sandy soil, they can infect your potatoes. The pathogen enters the adolescent tuber via wounds and breathing holes, but also through the uninjured shell. In the first two weeks of the tuber approach, the potato is most susceptible to infestation.

It is unfavorable if there are still high temperatures and dryness during this time. The pathogens need a lot of oxygen, which is why the fastest potatoes are infested in well-ventilated soil. If the soil has a pH below 5.5, scab attacks rarely occur, as the bacteria prefer higher pH levels. Then there are scabs that do not affect the taste of the potatoes, and the yield is not noticeably affected. Due to the scabs, however, other parasites can gain better access. In addition, the potato loses more moisture during storage and shriveled faster.

Recognize potato scab - and fight?

  • Potato scab shows only on the tubers, not on the aboveground parts of the plant.
  • On the potato itself develop brown cracked spots, which flow together in large infestations to larger verschorften areas.
  • The scab may remain on the surface, crater-like penetrate into the tuber or form new tissue under the scurf (flat or net scab, Tiefschorf, Buckoschorf) - the formation of various forms is influenced by the weather.

Potato scab can not be fought directly, there are no plant protection products for the cultivation of this disease. So it's all about cultivating resistant varieties. The variety list of the Bundessortenamt lists which potatoes are susceptible to scurf. In addition, a well-orchestrated crop rotation reduces the risk of infestation if you fertilize with alfalfa, rye, or vetches, promoting your soil-borne antagonists, such as the B. the Bacillus subtilis, You should avoid subsequent cultivation of other plants that are also part of the host's pathogen, eg. B. turnips.

  • Because the bacteria are so oxygen-dependent, you can combat the scab infestation very effectively, especially in the most vulnerable well-ventilated locations, if you deliberately rinse the potatoes during the period of tubers.
  • During this time, you should also slow down any zeal in the mechanical care, if it would result in aeration of the soil.
  • If you know that you grow at a problem site, you should also skip the liming the year before the potato cultivation.

Potato scab is therefore for the hobby growers rather not a very serious problem, because the professional cultivation with the mentioned treatments can counteract well here. In addition, the infested potatoes can certainly be consumed. Only commercial growers, who are allowed to produce exclusively flawless specimens in the trade, have to accept losses as the shredded tubers have a lower market value.

Moisture and damage to the potato skin favor the infestation

Potato blight - a serious threat

Potato blight is caused by a fungus that also attacks tomatoes (tomato cabbage and brown rot). In potato blight, there are potato herb rot and potato blight, serious diseases that have already caused famine and in Berlin 1847 led to the potato revolution. Even today, the potato blight can cost the hobby gardener more than 20% of the harvest. Among other things, this is due to the fact that in the mid-1980s a novel type of fungus from Mexico was introduced to Europe, which is more unpleasant than the potato blight known in Germany until now: it is more aggressive, and it does not only multiply by spreading through spores but also sexually.

The pathogen finds optimal conditions for propagation when spring and / or summer are particularly humid. The fungus enters the potatoes through wounds, breathing holes and germination systems either during growth or harvest.

Recognize and combat potato blight

  • The first symptoms of the disease are usually on the leaves and stems: from the leaf margins spread out dark brown spots that grow rapidly in wet weather and dew formation until they form on the underside of leaves a mushy lawn that looks like mold.
  • In the wet spores spread from the above-ground spore containers, which can actively penetrate into the tissue through their germinal tube. If tubers are affected, gray-blue discolored spots appear on the surface, the tuber meat turns brown and inedible.

The fight against potato blight is not easy: Since the beginning of this year, the recreational gardener has been obliged under our Crop Protection Act to give priority to the idea of ​​integrated pest management. The legally binding obligation begins on January 1, 2014. After that only pesticides may be used, if all non-chemical means did not bring success.

  • Non-chemical agents are first of all the selection of a resistant variety (note that there is leaf resistance and tuber resistance with respect to potato blight).
  • The probability of infestation can also be reduced by pre-germination of the seed potatoes.
  • If potato herb rot is detected, the spread of the pathogen to the tubers must be prevented and therefore the herb is completely removed a few weeks before harvest.

Then only the use of fungicides is conceivable - in the home garden, however, only of funds that have an explicit approval for the home and allotment and for the pest in relation to the affected plant! For the use of these funds then the creation of a prognosis model is prescribed so that the minimum amount is applied, otherwise the resistance formation of the pathogen is promoted against the control agents. This is anyway a problem with potato blight, especially if the same active ingredient is always used. If a plan for the application of different funds in certain minimum quantities created, these funds are applied repeatedly until harvest.

Prevent potato rot

Especially important next year is to ban as much old soil as possible and any old tuber from the garden, as the mushroom overwinters in both. The newly applied soil can be treated prophylactically with garlic-onion-slurry. If, under these precautions, you alternately grow the existing semi-resistant varieties, piling up the potatoes well and immediately cutting off and stinging infected stalks with a very sharp knife, this helps the next-generation potatoes. Incidentally, you should still leave infected potatoes in the ground for several weeks after burning the infested herb, so there is a chance that they will not come into contact with spores.

There are new approaches to combat the potato blight, z. B. the EU project Blight-MOP, which has set itself the goal of developing new ways to control late blight in organic farming. The fight against the genome is also being researched.

Other potato diseases

Even more annoying than an infestation with the potato diseases treated here would be an infestation with potato cancer or with bacterial ring rot (potato cyst nematodes), which would lead to total loss of crop and is notifiable. Currently, however, these two potato diseases are kept well in check by horticultural hygiene and cultivation of resistant varieties.
(from Halina)

Video Board: Blight: 5 Ways to Control Potato Blight (Late Blight).

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