Is This Tomato Leaf Blight - Ask Extension
Hi, I've got some tomatoes that I planted a couple of weeks ago. Looks like they are now suffering from leaf blight. The soil is mixture of leaf compo...
Knowledgebase
Is This Tomato Leaf Blight #868313
Asked May 13, 2024, 10:00 PM EDT
Hi, I've got some tomatoes that I planted a couple of weeks ago. Looks like they are now suffering from leaf blight. The soil is mixture of leaf compost and mushroom compost. Can you confirm if this is leaf blight and if so can they be saved?
Howard County Maryland
Expert Response
"Blight" is a catch-all term for a variety of fast-killing or fast-spreading plant infections, so it's not a single disease that can be treated without narrowing-down which blight might be present. In this case, though, we do not see indications of any blight on the pictured plant. Instead, the small leaf lesions appear to be either caused by environmental stress or perhaps flea beetle chewing damage. You can explore our Key to Common Problems of Tomato web page to learn more about typical symptoms for the more serious infections, but so far they do not appear to be an issue in this planting.
Environmental conditions that can stress veggie transplants include a sudden change in light levels (if they were only recently moved outside, usually), cold snaps, heat waves, and changes in soil moisture (staying wetter or getting drier between waterings than they were accustomed to). Fortunately, as the plants acclimate, these symptoms abate and growth will pick up. While injured leaves cannot heal, as long as symptoms aren't spreading more dramatically, worsening, or manifesting in a different way, it's likely not of concern. Flea beetles can potentially cause heavy damage on some vegetable crop leaves, but usually they prefer eggplant and other species over tomato.
Have the plants been fertilized with something containing nitrogen? (The N in N-P-K fertilizer formulations.) While the organic nutrients present in compost will provide some gradual nutrition for the plants, usually a supplemental source of nitrogen can help transplants establish faster and support lusher growth. This plant looks a bit yellowed, which suggests it's a bit hungry for nitrogen. Using a liquid fertilizer (it doesn't have to be labeled specifically for tomatoes) will provide a faster-absorbed dose of N than a granular (dry-applied) fertilizer, but either would be fine. Information on our Fertilizing Vegetables page provides more detail, including how to best supplement tomatoes with nitrogen.
For the future, make sure any mushroom compost used is well-blended with the existing soil. This is because this type of compost can have potentially high salt levels. "Salt" in this context doesn't necessarily refer to sodium as much as it refers to any mineral content, and at high levels, these salts can injure or kill sensitive roots and stunt growth. While we don't see symptoms of root dieback in the pictured plant, it's something to keep in mind for future plantings so the mushroom compost doesn't hamper growth or cause leaf loss as the roots decline. Leaching those salts out of the soil with thorough watering can help, as will diluting it with regular leaf-based compost or plain good-quality topsoil, but unless you happen to test the mix with somewhat expensive meters designed to measure salt level, there's no way to know just how "salty" a given bag of mushroom compost might be. The levels might vary from brand to brand, but even from batch to batch within the same brand.
If you haven't already, it will also help the planting overall to be mulched, so any exposed soil is shielded from the hot sun, weed seeds, and rapid evaporation. The type of mulch is up to you as long as it allows moisture to seep into the soil below and isn't piled too close to the plant stems. Covering bare soil helps avoid some of the blight diseases whose spores can lie on the soil surface and splash up onto vulnerable foliage during heavy rain or irrigation.
This page has additional general tomato-growing tips, if useful: Growing Tomatoes in a Home Garden.
Miri
Environmental conditions that can stress veggie transplants include a sudden change in light levels (if they were only recently moved outside, usually), cold snaps, heat waves, and changes in soil moisture (staying wetter or getting drier between waterings than they were accustomed to). Fortunately, as the plants acclimate, these symptoms abate and growth will pick up. While injured leaves cannot heal, as long as symptoms aren't spreading more dramatically, worsening, or manifesting in a different way, it's likely not of concern. Flea beetles can potentially cause heavy damage on some vegetable crop leaves, but usually they prefer eggplant and other species over tomato.
Have the plants been fertilized with something containing nitrogen? (The N in N-P-K fertilizer formulations.) While the organic nutrients present in compost will provide some gradual nutrition for the plants, usually a supplemental source of nitrogen can help transplants establish faster and support lusher growth. This plant looks a bit yellowed, which suggests it's a bit hungry for nitrogen. Using a liquid fertilizer (it doesn't have to be labeled specifically for tomatoes) will provide a faster-absorbed dose of N than a granular (dry-applied) fertilizer, but either would be fine. Information on our Fertilizing Vegetables page provides more detail, including how to best supplement tomatoes with nitrogen.
For the future, make sure any mushroom compost used is well-blended with the existing soil. This is because this type of compost can have potentially high salt levels. "Salt" in this context doesn't necessarily refer to sodium as much as it refers to any mineral content, and at high levels, these salts can injure or kill sensitive roots and stunt growth. While we don't see symptoms of root dieback in the pictured plant, it's something to keep in mind for future plantings so the mushroom compost doesn't hamper growth or cause leaf loss as the roots decline. Leaching those salts out of the soil with thorough watering can help, as will diluting it with regular leaf-based compost or plain good-quality topsoil, but unless you happen to test the mix with somewhat expensive meters designed to measure salt level, there's no way to know just how "salty" a given bag of mushroom compost might be. The levels might vary from brand to brand, but even from batch to batch within the same brand.
If you haven't already, it will also help the planting overall to be mulched, so any exposed soil is shielded from the hot sun, weed seeds, and rapid evaporation. The type of mulch is up to you as long as it allows moisture to seep into the soil below and isn't piled too close to the plant stems. Covering bare soil helps avoid some of the blight diseases whose spores can lie on the soil surface and splash up onto vulnerable foliage during heavy rain or irrigation.
This page has additional general tomato-growing tips, if useful: Growing Tomatoes in a Home Garden.
Miri
Ah ok. Thank you for the info and insight. I was thinking the plants were stressed bc of all of the rain. Good info about "salts" in mushroom compost and potential impact to young roots. Everyone at our community garden has this fever about mushroom compost. At others advice, I put it in all of my vegetables over apx 750 sf. The only think about compost though and this goes for leaf compost too is that it doesn't look like rich dirt. I'm looking for loamy soil. I've got clay soil and 3 yrs worth of adding pro-mix which is heavy peat, and leaf compost and now mushroom compost. I've had it soil tested last year at Univ of Delaware (your recommendation) and the results showed off the charts (excessive) for P, K, Mg and Ca. Organic matter was 12.0+. But, they don't test nitrogen levels. They advise to add it. So, maybe that's the problem. But they recommended a 34-0-0. I don't want to over do it with nitrogen bc it may impact fruiting plants i.e tomatoes. I'm also apprehensive on fertilizers bc I've killed my cucumbers and stunted watermelons and cantaloupe in the past. Also my pH last year was 6.7.
Yes, soil testing labs don't test nitrogen levels because it fluctuates much too often/quickly to be of much use for measurements. It's pretty standard to recommend adding nitrogen when planting veggies since they demand higher levels than "background" levels of N in the soil may provide, since other plants not grown for a harvest won't be deprived of nutrients since they aren't having leaves removed (like for leafy greens) or developing fruits to support, so their N demands are more moderate and able to be supplied by the soil's natural levels. Turfgrass, since it's mown regularly and therefore has to continually put out new growth to replace what is cut, also has above-average N demand levels, which is why it too is fertilized one or more times yearly while other plantings of trees, shrubs, and perennials generally don't need fertilization.
Some minerals, like the ones you listed, can commonly be "excessive" in soils without causing problems for plant growth; it's just the nature of that soil material itself and whatever kind of rock it eroded from over the eons, so that can be perfectly normal.
As long as fertilizer is applied either at the lab's recommended dosage or at the dosage listed on the package label, it shouldn't burn roots or cause damage. You can always lighten the dose if you are wary of heavy use, and just re-apply a bit sooner if needed based on how plants are growing. Since some forms of nitrogen are quite water-soluble, some levels can dip the more often soil is watered from either rain or irrigation. (This is why container-grown annuals and houseplants can be deprived of N faster when watered often compared to when they are watered less frequently.)
A 12% organic matter level is great, and shows that your years of amendment with compost and other materials is working well. Compost made from plant matter (like the Leafgro brand, which is commonly sold) should suffice as the only organic matter amendment needed, though other sources like the mushroom compost, composted manure, and other materials can still be useful. If mulch (bark, wood chips, pine needles, straw, etc.) is used atop bare soil around plants, that too will break down gradually into more organic matter as it composts in-place, further amending the soil. Clay has many advantages, including holding moisture for longer than loams or sandy soil types as the weather starts to dry, plus retaining nutrients better than sandier soil textures. Since compaction and the resulting poorer drainage is the main risk factor with clay, that's where amendments like organic matter come in, as they help to resist compaction and support the beneficial microbes in the soil that maintain a good soil structure that keeps drainage even.
Miri
Some minerals, like the ones you listed, can commonly be "excessive" in soils without causing problems for plant growth; it's just the nature of that soil material itself and whatever kind of rock it eroded from over the eons, so that can be perfectly normal.
As long as fertilizer is applied either at the lab's recommended dosage or at the dosage listed on the package label, it shouldn't burn roots or cause damage. You can always lighten the dose if you are wary of heavy use, and just re-apply a bit sooner if needed based on how plants are growing. Since some forms of nitrogen are quite water-soluble, some levels can dip the more often soil is watered from either rain or irrigation. (This is why container-grown annuals and houseplants can be deprived of N faster when watered often compared to when they are watered less frequently.)
A 12% organic matter level is great, and shows that your years of amendment with compost and other materials is working well. Compost made from plant matter (like the Leafgro brand, which is commonly sold) should suffice as the only organic matter amendment needed, though other sources like the mushroom compost, composted manure, and other materials can still be useful. If mulch (bark, wood chips, pine needles, straw, etc.) is used atop bare soil around plants, that too will break down gradually into more organic matter as it composts in-place, further amending the soil. Clay has many advantages, including holding moisture for longer than loams or sandy soil types as the weather starts to dry, plus retaining nutrients better than sandier soil textures. Since compaction and the resulting poorer drainage is the main risk factor with clay, that's where amendments like organic matter come in, as they help to resist compaction and support the beneficial microbes in the soil that maintain a good soil structure that keeps drainage even.
Miri
