Download Potatoes are basically easy and rewarding to grow. But it is also

Potatoes are basically easy and rewarding to grow.
But it is also easy to lose a crop, if you don't look after them!
Re-issued June 2015.
Potato Blackleg.
This disease was present in some potatoes on the NOAA allotment site in 2013, 2014 and is again present in 2015.
Potato blackleg is a common bacterial disease in potatoes. It causes black rotting at the stem base and rotten
(smelly) potatoes. Initial blackleg infections cause stunted growth and yellowing stems. Blackleg is nearly always
present on potato tuber prior to planting.
Blackleg is a disease caused by the bacterium Pectobacterium atrosepticum. It is one of the earliest potato diseases
to appear, you may see symptoms as early as June, especially in wet years that follow a cold planting season. This
disease only infects potatoes.
You may observe the following symptoms:
As early as June, the stems of potato plants appear stunted and pale green or yellow.
Leaves at the top of affected stems may be small, stiff and have margins curled inwards.
At ground level, the affected stems appear black and rotted.
If tubers form, the flesh may be grey or brown and rotten.
The following link included pictures and a detailed explanation of the bacteria.
http://www.rhs.org.uk/advice/profile?pid=223
Non-chemical control.
There are a number of control measures that do not require chemicals:
The most important control measure is the prompt removal and destruction of infected plants as soon as symptoms
are detected and before the disease has time to spread.
Commercially produced seed contain very low (but not zero) levels of infection. Gardeners who save their own seed
should be particularly careful that tubers are uninfected. Dry storage of seed or ware potatoes will minimise the risk
of spread in storage.
The disease thrives in warm, damp conditions so improve poorly drained sites.
Try to lift crops during dry weather.
Rotation is very important, since the bacteria may survive over winter in soil where potatoes were previously grown,
albeit at a low level. Rotation also reduces the risk of additional infection arising from infected volunteer potatoes.
Try to choose resistant cultivars.
The British Potato Council has produced an excellent British Potato Variety Database which lists resistant varieties
including ‘Charlotte’, ‘Pixie’, ‘Saxon’ and ‘Vales Sovereign’.
Follow either of the links below to obtain more detailed information on potatoes and of their disease resistance
qualities. The British Potato Council’s A to Z listing is extensive. Please go to The British Potato Variety Database for
more information. http://www.varieties.potato.org.uk/menu.php?
Chemical control.
There are no chemical control options available to gardeners for the control of potato blackleg.
Additional potato blackleg information.
Blackleg is caused by the bacterium Pectobacterium Atrosepticum (previously known as Erwinia Carotovora pv.
Atroseptica). It is one few important and potentially very serious plant diseases caused by bacteria in the UK.
This disease normally comes into allotments (or gardens) via infected seed potatoes. Care is taken to ensure that
infected plants are removed from commercial seed crops, but a small number of infected tubers escape detection.
Inevitably seed lots will usually contain a few infected tubers as they are impossible to fully detect.
If the infected plants that grow from tubers are not removed from the crop promptly, the disease will spread
through the soil to infect other plants. The bacteria can survive over winter principally in infected volunteer tubers
and potato plant debris. They also survive at low levels in the root zone of some weeds. The bacteria may also be
carried through the crop by insects, on contaminated soil or garden tools used to remove infected material. Consider
sterilising tools with a solution of Jeyes fluid after they have been used to remove diseased plants.
In allotments and gardens it is infected seed potatoes and poor crop rotation that is the most common source of
potato blackleg disease.
Potato Blight.
Blight can wipe out your potato harvest in a wet August; affected potatoes rot in store. Recent wet summers have
been ideal blight weather, seriously hitting commercial potato growers even with all the chemicals at their disposal.
Small allotment plots have little chance of escaping, since blight is carried by a wind-blown spore, which settles first
on the leaves before infecting the whole plant. If your potato leaves have yellow or brown patches in July or August,
look underneath the leaf - if you have blight, you will see a white mould fringe to each blight spot in damp weather.
How to deal with it.
When the weather is warm and humid, spray with Bordeaux mixture (it is currently approved for organic use) to kill
the spores before the rain washes them into and through the soil.
If there is any more than a touch of blight, cut the haulms off at least three weeks before harvesting your potatoes.
Any blight spores which have fallen on the soil will die BEFORE they get to your potato crop.
Prevention.
Burn potato waste (potatoes and foliage) - do not compost it or leave infected material lying around, as you will
simply be building up a stock of blight for successive seasons.
Consider planting your earlies and second earlies as soon as the soil begins to warm up - so they are out of the
ground before the blight season starts. Again, it cannot be stressed often enough that crop rotation is essential.
Choose resistant varieties.
Worth noting, though, that there's a whole variety of other viral infections which may look similar to blight. They are
more or less endemic on most allotment sites, simply because potatoes are such a popular crop - and can only really
be controlled or avoided by being very careful about removing and burning potato haulms, and volunteer potatoes.
The British Potato Variety Database is an excellent reference site when making your choices as to which potatoes to
grow.
Potato eelworms.
These are nematodes, tiny vegetarian worms, also endemic in many allotment plots. Your plants will die back early,
and with a severe infestation you may get a very poor yield. If you want to confirm whether you have eelworm,
carefully expose the roots of a plant, and look for pinhead sized white, yellow or brown cysts on the roots (a
magnifying glass may assist in the process). Control is not easy as these little pests can live for up to 20 years.
Rotation will reduce the population. Rotation would need to be longer than 4 years if you have a serious problem.
Kestrel and Sante have some resistance to both white and golden eelworms; other varieties are resistant only to the
golden eelworm.
If you have a serious eelworm infestation, your potato rotation should be longer than four years. Tagetes (French
Marigolds) are said to discourage and kill vegetarian nematodes, such as eelworm. You would have to plant the
whole potato bed the year before you grow your potatoes.
Common Scab.
An unsightly but superficial bacterial infection, which does not affect the eating or storing qualities of the potato.
You just don't feel like baking them in their jackets! The infection is impossible to treat, but it is avoidable.
The condition is aggravated by lime in the soil. It is recommended that you only lime beds the year after potatoes
have been grown. By the time of the next rotation, the soil should be acid enough to grow the following crop scab
free.
Water regularly during the summer.
When you plant the potatoes, put a layer of grass cuttings in the bottom of your trench. This can help mitigate the
effects of common scab.
Black Scurf.
Another unsightly, but cosmetic, problem. When you lift your potatoes, does soil stick? Are there black raised
spots (not warts), under the soil, on top of the skin? Are they hard to wash or scrub off? Could be Black Scurf,
caused by a soil-borne fungus.
In some cases Black Scurf appears to come on infected seed potatoes.
A warning/suggestion is to only use reputable sources for your seed potatoes.
The importance of strict crop rotation cannot be overemphasised. If you risk the occasional short-cut by using a bed
that you think is healthy it is likely to be the one occasion you have major problems. Potato planting should always
be on a strict four-year cycle to guarantee a reasonable chance of a disease free crop.
In the case of Black Scurf it is only cosmetic - it can be scraped off easily, and doesn't affect the eating or storage
qualities.
Wireworm.
A pest which likes grassland. It is the grub form of the Click Beetle. They frequently attack potatoes sown in new or
renovated plots. The year prior to clearance, the beetles will have laid their eggs. These will hatch into hungry grubs
in the spring - and finding nothing to eat, target the newly planted potatoes.
Once wireworm grubs have metamorphosed into beetles, they leave the cultivated area and promptly fly off to a
more wireworm friendly grass patch nearby to lay the next generation of their eggs.
Wireworm eggs can lay dormant in the soil and remain viable for up to four or five years. Again the importance of
rotation cannot be stressed enough, especially if there has been a bad infestation in the first instance.
It is suggested that when you first clear your allotment/garden, move the grass turves off the bed (along with most
of the eelworm eggs), and put them on the compost heap. This single step will substantially reduce, but not fully
eradicate the population.
Grow potatoes which can be harvested before September in the year after clearing the bed, you will then avoid the
main damage season.
Nature’s solution - digging exposes many insect to insect eating birds and helps to control insect pest levels
of many species.