Yellow spots on potato leaves can be alarming for any gardener While your first instinct may be to panic, try to stay calm. Not all yellow spots mean disaster for your crop The key is identifying the cause accurately so you can take appropriate action.
In this article we’ll explore the most common reasons for yellow speckles and blotches on potato foliage. We’ll also provide tips to remedy nutrient deficiencies pest issues, diseases, and environmental stresses leading to symptoms. Armed with the right info, you can properly treat and stop leaf spotting issues in their tracks.
Common Causes of Yellow Spots on Leaves
There are a handful of usual suspects behind yellow potato leaf discoloration:
- Nutrient deficiencies
- Pest damage
- Fungal, bacterial and viral diseases
- Environmental stresses
- Herbicide injury
- Age/maturity
The distribution, shape, and progression of yellowing can provide clues to pinpoint the exact problem Here’s an overview of specific causes and distinguishing symptoms
Nutrient Deficiencies
Lack of key nutrients like nitrogen, iron, magnesium, and manganese can induce yellowing. Nitrogen deficiency typically starts on lower, older leaves. Iron and magnesium deficiency manifests as interveinal chlorosis – yellowing between leaf veins starting on lower leaves.
With manganese deficiency, young leaves show interveinal chlorosis, necrotic spots, and upward cupping. Ensure proper soil pH and supplement with foliar sprays or granular fertilizer to correct.
Pests
Sap-sucking insects like aphids, leafhoppers, and psyllids can feed on plant juices and leave yellow stipples or mottling behind. Leaf miners and spider mites also cause yellow streaking. Caterpillars, beetles, and other chewing bugs make holes and ragged edges that later turn yellow.
Closely inspect leaves to spot culprits, then apply appropriate treatments. Keep populations low through maintenance like row covers and regular scouting.
Diseases
- Early blight fungus produces dark brown spots with yellow halos that can take over entire leaves.
- Late blight begins as pale green spots that develop fuzzy white undersides then turn brown or black.
- Viral infections like potato leafroll virus (PLRV) and potato virus Y (PVY) lead to yellow mottling, curling, and crinkling.
- Bacterial diseases like bacterial wilt and blackleg first yellow lower leaves.
Prevent diseases through crop rotation, certified seed, and fungicides/bactericides where applicable. Rogue infected plants immediately but do not compost.
Environmental Stresses
Too much or too little moisture, extreme temperatures, herbicide drift, and nutrient imbalances can stress plants. Stressed plants respond by dropping lower leaves which turn yellow before falling off. Reduce stress through proper planting times, watering, fertilization, and pest control.
Herbicide Injury
Drift or overspray from broadleaf herbicides like 2,4-D can twist and yellow new potato growth. Avoid use of these weedkillers nearby and always spray on calm days.
Maturity
As potatoes near full maturity, yellowing lower leaves is natural and signals tubers are ready for harvest. Upper leaves follow suit and will fully brown and die back.
Solutions for Yellow Potato Leaves
If you spot yellow leaves on your spuds, take these steps:
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Note the pattern (interveinal, spots, etc) and distribution (lower, upper, or all over) of discoloration. This helps identify causes.
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Check under leaves for pests like aphids. Look for signs of chewing damage.
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Review recent weather data and soil conditions for stresses.
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Test soil nutrients and pH to catch deficiencies early.
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Send leaf samples to a diagnostic lab for disease testing.
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Increase irrigation, mulch, or provide shade if leaves are heat/drought stressed.
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Apply fungicides labeled for edibles to protect from blights.
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Remove and destroy severely infected/damaged plants immediately.
Preventing Future Outbreaks
An ounce of prevention is truly worth a pound of cure when it comes to problematic potato leaf spots. Here are some important tips to avoid issues proactively:
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Choose disease-resistant potato varieties when possible.
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Rotate potatoes to different beds/rows each year to disrupt disease cycles.
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Control insects like aphids that can transmit viruses.
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Space plants appropriately to encourage airflow and dry leaves faster.
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Use drip irrigation instead of sprinklers to reduce leaf moisture.
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Weed consistently to remove alternate hosts for diseases.
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Scout often and treat pests/diseases at first signs of trouble.
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Test and amend soil nutrients before each growing season.
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Apply preventative copper fungicide sprays every 7-14 days.
Remaining vigilant and addressing issues early provides the best odds of overcoming leaf spotting challenges. Don’t delay taking action at the first signs of yellowing to protect your potato crop. With quick identification and treatment, you can get back to growing vigorous, green, productive plants.
Corky Ring Spot Tobacco Rattle Virus
- Leaves may have no symptoms or have yellow rings, spots and arcs
- Stems may be mottled green and yellow
- Brown rings and arcs form on the skin and in the flesh of tubers
- Potato tubers can be cracked and malformed if infections comes in early
- More information on Corky Ring Spot
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Verticillium Wilt Verticillium spp.
- Leaves turn yellow then brown and wilted, stems remain erect
- Symptoms are often seen on one or a few stems but not the entire plant
- Often only random plants scattered in the field are affected
- If the stem is cut near the soil line, brown streaks or rings can be seen just under the skin
- Dark brown to black streaks or rings can be seen in the tuber flesh if cut on the stem end
- More information on managing plant diseases in the home garden
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Blight: 5 Ways to Control Potato Blight (Late Blight)
FAQ
What are the yellow spots on potato leaves?
Alfalfa mosaic virus (AMV) symptoms can look like PMTV. This virus can also produce yellow spots and blotches on potato leaves. The disease is also called ‘calico. ‘ The symptoms we see in potatoes are the result of current season spread.
How to fix yellow potato leaves?
If you’re still not sure what the issue is, prune all the yellowed leaves and push some compost around the base of your plants. Stop giving your plants extra water until you’re sure the soil has dried out a bit. If the problem persists, then you may need to harvest your plants early.
What do overwatered potatoes look like?
Signs of overwatering include yellow leaves and dieback – which can be challenging to recover from. Potatoes need 1-2 inches of water weekly from rainfall and irrigation. Take care not to over-saturate the ground, and use your finger to check the moisture levels around 6 inches deep.