Tomato blight? - Ask Extension
Thank you for your assistance. Would you please let me know what you think might be afflicting my tomato plant? Is this blight? Do you have any rec...
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Tomato blight? #877708
Asked July 17, 2024, 8:05 PM EDT
Thank you for your assistance. Would you please let me know what you think might be afflicting my tomato plant? Is this blight? Do you have any recommendations on a treatment?
Montgomery County Maryland
Expert Response
Although Early Blight is a very common tomato disease, this is not a symptom of that fungus but rather looks like something abiotic (not caused by a pest or pathogen). Scorch or phytotoxicity would be the most likely match.
Is the plant being monitored for watering needs regularly, where the soil is felt a few inches deep? (Watering should be thorough once the soil begins to feel somewhat dry to the touch at that depth. In this kind of weather, and in a location right next to a wall that can trap heat, watering might need to occur every couple of days, depending on whether plants are in the ground or in a pot.) Scorch occurs when a leaf doesn't have enough moisture to keep itself cool with evaporation, or is exposed to a source of extra heat (like reflected heat from the wall, or the reduced air circulation it causes), and the tissues essentially sunburn. Scorch can affect ripening fruits as well. On very hot days, sometimes putting a temporary shade cloth (window screening mesh, for example) over vulnerable plants can reduce their stress, or potted plants can be moved into semi-shade. Return them to sun when extreme heat passes, though, so they can continue to bear a good harvest.
Was anything sprayed on or near the plant, like cleaning a window, power-washing a deck or siding, or a pesticide applied? If so, this would be phytotoxicity damage, which is tissue injury due to chemical exposure.
While there is no treatment because nothing can heal the damaged leaves, the injuries should not spread (unlike with infections) and can be left alone, or some of the worst-damaged individual leaves clipped off.
Miri
Is the plant being monitored for watering needs regularly, where the soil is felt a few inches deep? (Watering should be thorough once the soil begins to feel somewhat dry to the touch at that depth. In this kind of weather, and in a location right next to a wall that can trap heat, watering might need to occur every couple of days, depending on whether plants are in the ground or in a pot.) Scorch occurs when a leaf doesn't have enough moisture to keep itself cool with evaporation, or is exposed to a source of extra heat (like reflected heat from the wall, or the reduced air circulation it causes), and the tissues essentially sunburn. Scorch can affect ripening fruits as well. On very hot days, sometimes putting a temporary shade cloth (window screening mesh, for example) over vulnerable plants can reduce their stress, or potted plants can be moved into semi-shade. Return them to sun when extreme heat passes, though, so they can continue to bear a good harvest.
Was anything sprayed on or near the plant, like cleaning a window, power-washing a deck or siding, or a pesticide applied? If so, this would be phytotoxicity damage, which is tissue injury due to chemical exposure.
While there is no treatment because nothing can heal the damaged leaves, the injuries should not spread (unlike with infections) and can be left alone, or some of the worst-damaged individual leaves clipped off.
Miri
Thank you for your helpful response.
The plant is on a drip system where it receives 35 mins of water three times a week from a 1gph drip emitter. It sounds like this might be too little water, but maybe it's due to the below?
I have sprayed the plant a few times since planting in April with a mixture of cal-mag and fungicide. I used copper fungicide a couple of times earlier in the season and Garden Phos once about a week ago. Maybe it's the Garden Phos?
The Cal-Mag fertilizer spray or the fungicide might have caused the leaf damage, or contributed, if roots were under-watered. Any pesticide (which includes fungicides) applied while temperatures are above 85 degrees can risk phytotoxicity damage. Some pesticides are also incompatible with each other, though if used far enough apart and not specifically prohibited by product label directions, they might not interact.
It sounds like each drip emitter is only applying about a half-gallon per watering in this situation, which seems like too little. (That said, with a more thorough watering per session, if a plant is in the ground, it might not need watering as often as three times a week. If in a pot, though, it might.)
Miri
It sounds like each drip emitter is only applying about a half-gallon per watering in this situation, which seems like too little. (That said, with a more thorough watering per session, if a plant is in the ground, it might not need watering as often as three times a week. If in a pot, though, it might.)
Miri
The plant is in a raised bed but the soil seems to drain very easily because I'm using raised bed soil. This is why I'm watering the plant more frequently but for less time. Otherwise most of the water just seems to drain away. Should I maybe try adding another day into the watering schedule?
You can try, but you might just need to experiment to see how changing the watering affects moisture retention in the root zone. If mulch isn't used on top of the soil, it can help reduce evaporation. Adding organic matter like compost can also help soil retain moisture while maintaining drainage. Top-dressing with compost would need to be limited to only about an inch of added material, to avoid suffocating roots, but as preparation for the growing season next year, it could be mixed-in.
Miri
Miri
