Can diagnose my tomato problem?

Question: For the past 3 years, I've had a leaf spot/yellowing/wilting issue with my tomato plants (see photos). It affects all the plants, in both raised beds and containers, and has been starting earlier every year. I amend the bed soil every year with compost and old chicken straw, and put fresh potting mix mixed with compost in the containers. I sterilize the tomato cages between seasons and rinse out the buckets I use for growing, but that doesn't seem to help. It happens to tomatoes even when they're on opposite sides of the garden. It does not affect the fruit. It also does not affect the peppers or any other plants. I tried spraying copper fungicide as soon as it appeared this season but this year there's been so much rain that it washed right off. So my only recourse right now is to prune the worst leaves and hope for the best. Is this just bad luck with leaf spot? Would love any info/advice you can give. Thank you!

responder: An Ask Extension Expert Replied July 28, 2023, 2:31 PM EDT
response: Good Afternoon -  Thanks for writing in! From the photos presented, I would say that your tomatoes are suffering from Septoria Leaf Spot - a common fungal infection of the tomato plant which affects the leaves mainly, as well as the stem and outer parts of the flowers. This fungal affliction can overwinter in soil, which is one reason why you are seeing it yearly. First, I would suggest as I mention below, removing as many of the affected leaves/branches as possible. Details are below.  As far as management and preventative practices you can take to reduce your chances of seeing it:  - Since the fungus spores can overwinter in soil, crop rotation is a good practice if it is practical in your garden, meaning planting your tomatoes in different spots every year, not returning to the same soil for 3-5 years if possible. Obviously for smaller home gardens this is not always practical, and regarding your situation it sounds like the potted tomates receive fresh new soil yearly, so this may not be the primary solution for those. In beds however, rotation could give you a head start against this disease - Moisture is a big factor in the proliferation of this disease, so it makes sense that you are seeing more of it this year with the higher than average rainfalls. The fungus begins at the ground level, as the spores are typically in the soil - this means that the disease will start at the branches/leaves that are touching or close to the soil first and move rapidly upwards. A strong adult tomato plant can lose up to 1/3 of their foliage through good pruning, so I would recommend that, in the future,(and on your current plants) to keep up with pruning. As a preventative measure, trimming the lower branches will leave a good amount of space for airflow as the tomatoes grow, and as your tomatoes stand now, I'd aim to remove as much of the diseased branches as you can without stripping them bare (again, up to about 1/3 of the leafing branches can be removed). To make the plants less dense overall, suckers can be removed if you are growing indeterminate varieties - these are the growths that begin at the "armpit" of a main branch and if you are checking your tomatoes frequently, small ones can usually be spotted if you know where to look and can be quickly pinched off. This also helps the tomato to focus on its main fruiting stems. Another moisture related suggestion is to water only the soil at the base of the plant - avoiding splashes of soil and water to reach the lower branches, and don't water from above if avoidable. With all this rain lately, some of the leaf moisture obviously cannot be avoided... - Thirdly, for future plantings, avoid throwing diseased leaves or fragments of the diseased plants anywhere near the growing site. The spores that have infected the plants will likely end up in the same soil you intend to plant next year - And lastly, a good practice to avoid any diseases in the garden is to sterilize tools and containers where possible to avoid spreading anything  And plant pathology expert Ann Hazelrigg's guidance on copper fungicide is to apply it every 5-7 days depending on rainfall to maintain effectiveness. It is the recomendation for organic control assuming all the cultural practices mentioned above are being performed first and foremost - and a clarifying note:  applying it to already diseased leaves will not be effective.  About Septoria Leaf Spot of Tomato: Septoria Leaf Spot of Tomato (ct.gov) Beneficial Pruning Practices for Tomato plants: Pruning for Healthier, More Productive Tomatoes | Extension Marketing and Communications (ncsu.edu) Hopefully this is helpful - happy planting! Kristin

responder: The Question Asker Replied July 28, 2023, 4:15 PM EDT
response: Thank you so much for your response, Kristin! I suspected it was septoria leaf spot and have been doing most of what you recommended, but I did not sterilize my grow bags or buckets (just rinsed them) and my garden is too small to allow me more than a year off for any given bed when doing crop rotation. It's good to know it's okay to prune up to a third of the branches--I'd been wondering if maybe I was overpruning--and will be more aggressive on that end. And next year, I'll use new grow bags and allow my beds to be tomato-less for more than just a season. Again, thank you so much!SuOn Fri, Jul 28, 2023 at 2:31 PM Ask Extension <<personal data hidden>> wrote: