No, potato leafroll is not a starchy new snack.
Potato leafroll, also known as potato leaf curl virus (PLCV), is a viral disease spread by aphids. This disease predominantly affects the vascular tissue of potato plants. The potato leafroll virus (Rhizoctonia solani) is responsible for up to 50% of potato crop losses worldwide. That works out to about 20 million tons of lost potatoes each year. There is also a sweet potato leaf curl virus, but we’ll leave that one for another day.
Potato leafroll symptoms
Potato leafroll affects plants in two waves of infection. The first wave is recognized by leaves curling upwards, yellowing, and brown leaf edges. These symptoms are most often seen first on lower leaves of plants infected the previous season. Plants infected during the current season are just the opposite, with symptoms occurring first on younger leaves.
The second wave is more severe. Entire leaves can become chlorotic and may develop purplish or reddish margins. Eventually, infected leaves dry out completely, plants become severely stunted, and smaller tubers are produced. Symptoms may also be seen in the phloem of the haulm, or stems. You might also see something called net necrosis. Net necrosis appears as small brown strands or speckles of discolored tissue that start at the tuber’s stem end and move through the tuber. Net necrosis may be confused with zebra chip.
Potato leafroll infects other plants, too, with slightly different symptoms. You might see interveinal necrosis [dying veins] and curled, leathery leaves in infected golden pearls (Solanum villosum), moonflowers (Ipomoea alba), and thorn apples (Datura stramonium). Groundcherries and tomatillos infected with PLRV exhibit chlorosis, leafroll, and stunting. Weeds in the nightshade family can also contract and harbor this disease.
Potato leafroll looks a lot like stem end discoloration (SED), but SED is a physiological disorder believed to be caused by too much heat, cold, or frost. PLRV may also be confused with early signs of Rhizoctonia stem canker and black scurf.
Potato leafroll virus is spread by several types of aphids, with green peach aphids (Myzus persicae) being the most destructive. When an aphid feeds on an infected plant, the virus enters the aphid’s gut and starts reproducing. From there, the virus floats around in the aphid’s circulatory system until it reaches the salivary glands. Then, when the aphid pierces the leaf of a healthy plant to feed, the virus is spread through the saliva into the phloem of the new host. Once an aphid has become a carrier, it stays that way, potentially infecting dozens of plants.
How to prevent PLCV
Aphid control is the first line of defense against potato leafroll. As any gardener knows, controlling aphids is a battle of epic proportions that never ends. Insecticidal soap is probably your best aphid treatment. [Do not use dish soap or other types of detergent, no matter how many people say otherwise.]
In some cases, infected seed potatoes (and grocery store potatoes) can carry this disease, so always plant certified disease-free seed potatoes. Sadly, seed potatoes sold at many garden centers have been found to carry both the potato leafroll virus and aphid eggs, so be picky when it comes to shopping for seed potatoes.
Also, keep weeds from the nightshade family away from your potato crop. This group includes bull nettle, horse nettle, and creeping wolfberry. Mustard and shepherd’s purse can also harbor this disease.
If you find an infected plant, remove it and three other plants in each direction, and throw them in the trash. Just to be sure.
You can grow a surprising amount of food in your own yard. Ask me how!
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