potato plant leaves curling

Potato Leaves Curling: virus, herbicide, or drought?

After months of careful planning and preparing seed, soil, and nutrients to plant your potato crop, the last thing you want to see are the leaves on the plants looking curled up, stunted, and knarly. There are many things that can cause your potato plants to have curled leaves. In this article, I will discuss the possible causes and help to identify what has happened to your potato plants with the help of images and descriptions. Then you can start to remedy the unfortunate problem this season or help prevent it from occurring again.

Reasons why your potato plants have curled leaves

There are a few reasons why your potato plants will have curled leaves – they are:

Potato Virus

A potato plant infected with one of the many viruses will cause its leaves to curl. Aphids are usually responsible for carrying the virus to the plant but viruses can be transferred via seed also. The main viruses affecting potato plants are Potato Virus Y (PVY) and Potato Leafroll Virus (PLRV) both will transfer the virus through their seed and via aphids.

Leaf roll symptoms of virus infection

Potato plants infected with potato viruses will have the leaves curled up from the outside edge in towards the center of the leaf – almost forming a cylinder. The leaves will be small and the plant will have stunted growth. If allowed to grow it may produce potatoes but they will be small and there will be many rotten, unusable potatoes.

potato leaf roll virus
Viruses like Potato Leaf Roll Virus cause the leaves to roll along the sides forming a cylinder

Combatting potato virus

  • Plant only certified/virus-tested potatoes.
  • Remove infected potato plants from the crop if possible – depending on how widespread the infestation has been.
  • Apply neonicotinoid insecticides early in the development of the plant to control/prevent aphid arrival.

Herbicides

Potato plants can be affected by chemical residues from herbicides. These residues can be transferred from treated land used to grow hay, silage, and straw and transferred into the potato plot soil through farmyard manure, or slurry. One of the chemicals known to cause leaf roll in vegetable and potato plants is aminopyralid found in commercial herbicides which go by the names of Milestone and Forefront. This spray is very effective a controlling persistent weeds such as thistles, docks, and nettles, so are well known and used.

Leaf roll symptoms of herbicides

If your potato plants are being affected by herbicides, the leaves will curl up into a ball, this looks completely different from a virus infection which makes identifying it much easier. The plant will remain small and the leaves may never unfold fully. There is a strong chance the plant will not produce a usable potato. It is advised not to eat the potatoes.

herbicide contamination on a potato plant
Herbicide contamination will cause the leaves to roll into a ball

Combatting herbicide infection

If you do not know the origin of the manure then it is safer not to use it. If it must be used it is important that the manure has been well rotted and should be used in small amounts. It should be mixed well into the soil months in advance of planting preferably with a rototiller.

The long rotting, sparse use and good mixing with soil all help to lower the available concentration of the chemical residue in the soil. If green manure has been added to the soil in large amounts and is not well mixed through the soil the potato plants have a high chance of being badly affected.

A good crop rotation is also advised – potatoes should not be grown in the same plot each year.

Potato Leafhopper

These small winged bugs (Empoasca fabae) use their mouths to pierce and suck on the leaves of the potato plant causing it to die, if the attack is widespread it could result in the plant losing all its leaves. The leaf will begin to die from the outside edges inwards. As it dies the leaves will change colour from green to yellow to brown. Potato Leafhoppers are native to North America and stay in this region.

Leaf roll symptoms of Potato Leafhopper

The leaves will roll inward similar to the virus attack although not as much as the virus or herbicide. The other difference is the leaves will turn yellow and brown with Potato Leafhopper attack whereas they will remain green with a virus or herbicide attack.

Potato Leafhopper attack will cause the leaves to die from the outside edges inwards, changing the colour of the leaves.

Combatting Potato Leafhopper

Avoid planting potato crops near alfalfa fields as this provides a host to the leafhopper- an attack on the potatoes is more likely after the alfalfa has been harvested. Ensure enough water is available to potato plants to provide more resistance to attack.

Drought

Potatoes need a lot of water when their plants begin to get big. I wrote an article that is a good guide for how often you should water potatoes.

Leaf roll symptoms of drought

If potatoes are experiencing a shortage of water their leaves will begin to lose their shine and start to wilt and curl inwards. The whole plant will begin to droop and this will be the same for all the plants. The leaves will not curl tightly or harshly like the other problems above. It should be quite evident that it is a lack of water.

Combatting drought

You should be aware of the rainfall in your region, if it has been dry for a week or more you need to water your potatoes. Soon after deep watering the plants will recover and they will be back on track to produce a bounty of beautiful potatoes.

healthy potato plants growing in a field
Healthy potato plants

Summary

If your potato plant leaves are curling up and the plants growth is affected check which way the leaves are curled – into a cylinder – it will most likely be a virus – into a ball it will most likely be herbicide contamination. Either way, the potato plants and their seed should be destroyed and no potatoes planted in that soil for at least a year.